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Many organisms engage in metabolic tradeoffs to manage costs associated with reproductive output which often leads to these costs carrying over into the future. Compensatory mechanisms vary across life history strategies and are expected to result in near-optimal fitness gains for the investor. Here we investigated whether environmental differences associated with increasing montane elevation and variation in reproductive output of a resident passerine songbird, the Mountain Chickadee (Poecile gambeli), were related to physiological conditions during annual molt. Higher elevations are associated with harsher environmental conditions during the winter, which results in later and shorter breeding seasons than at lower elevations. We sampled the outermost tail feathers from adult birds in the fall after their prebasic molt, which initiates closely after reproduction (e.g. after parental care has ceased, ~1–3 weeks). We measured the hormone corticosterone deposited in feathers (fCORT) and feather growth rates for evidence of physiological effort predicted to be driven by several units of reproductive output (e.g. breeding timing, clutch and brood size, and offspring mass). There were no relationships between any measure of reproductive output and feather characteristics between elevations or across years, despite substantial variation in reproductive output in the wider population across this same time. However, birds at the high-elevation site grew their tail feathers significantly faster and had higher fCORT deposition compared to low-elevation birds. These results suggest that although differences in reproductive output and any related signals of associated physiological effort (e.g. fCORT and feather growth rate) may not extend into individual conditions during annual molt, shorter breeding seasons associated with harsher environmental conditions may favor faster feather growth as required by earlier onset of winter. [ABSTRACT FROM AUTHOR]

Passerines are the most successfully diversified bird order (around 60% of all avian species). They have developed complicated songs to defend their territories and to attract females for mating that can evolve quickly due to cultural transmission. Complex singing as well as plumage coloration of male birds are honest signals for potential partners and provide information about the males' quality. To function as honest signals, both traits must be costly for the males. Of course, not all passerine species are equally clever or beautiful. Even within a single family of 50 to 70 species, relevant traits may vary considerably. Tits and chickadees (Paridae) comprise species of similar size, varying a lot in coloration and plumage pattern. The territorial songs are relatively short and simple. We investigated the relationship between song complexity and plumage coloration, taking phylogenetic relationships into account. We studied 55 out of the 64 species with 1084 song recordings retrieved from an online database. In the best model, besides colorfulness, body size had a negative impact on song complexity. Large colorful species were found to sing less complex songs. This result supports the hypothesis of a trade-off between costly traits and their likely intense signal function. This study contributes to a better understanding of how sexual selection influences the diversification of traits. In addition, we found that despite the relatively uniform size, the general negative correlation between body size and song frequency can be recovered. Some song traits are further influenced by distribution and thus by interspecific differences in climate niche. [ABSTRACT FROM AUTHOR]

Passeriformes populations have experienced a marked decline in number during the last decades. Several infectious agents have been described as key factors for this population’s decrease, as they can cause mortal diseases like the recently reported Suttonella ornithocola. S. ornithocola is a bacterium from the Cardiobacteriaceae family that has been linked to several outbreaks. This systematic review aims to collect all the scientific information available about S. ornithocola to better understand its epidemiology and pathogenesis and to assess the potential hazard that it can pose to garden songbirds. Although it has been considered a respiratory pathogen, S. ornithocola has been isolated from several organs, suggesting a systemic pathogenesis. However, it has also been described as a normal taxon from the microbiota of some bird species. Therefore, further studies in healthy birds are necessary to establish if S. ornithocola is a primary pathogen or an opportunistic bacterium in songbirds. [ABSTRACT FROM AUTHOR]

Abstract : As an important determinant of reproductive success, avian nest building is under strong selection and requires behavioral plasticity to optimize conditions in which offspring develop. Learning is a one form of plasticity that allows adaptation to the local environment. Birds may refine nest-building behavior with personal experience or use social information to guide their choices. While there is mounting evidence for an effect of experience-based learning on nest building and social information use when selecting nesting material in the laboratory, experimental evidence for social information use in wild birds is lacking. Here, we provided sources of two differently colored wool as nest lining material in a wild mixed-species community of tits (Paridae sp.) to investigate experimentally (i) whether females use social information to locate lining materials and (ii) whether preferences for specific materials (here color) are socially influenced. We investigated pathways of social transmission through a foraging association and a spatial breeding network using the time of arrival at the wool in a network-based diffusion analysis. Our results gave evidence that birds learned about the location of lining resources from foraging associates. Furthermore, we found significant non-random clustering of wool colors in nest boxes across the study area, suggestive of a social influence on selecting lining materials. Taken together, we provide quantitative evidence for a role of social information use in both finding and selecting lining material in wild tits and demonstrate that social information use constitutes an important factor towards behavioral plasticity in nest building in wild birds. Significance statement: As vessels of reproduction, avian nests are under strong selection to provide optimized conditions for developing offspring. Learning is one mechanism that allows individuals to adapt to local environmental conditions. Previous work has shown that nest-building birds use both social information and personal experience to refine their nests. Yet, evidence for social information use for nest construction in the wild has been purely anecdotal and experimental evidence lacking. Here, we demonstrate for the first time experimentally that in wild tits (Paridae sp.), females rely on social information from their foraging associates to locate and choose material to line their nests. This research highlights the importance of social information use as a potential mechanism of behavioral plasticity in wild nest-building birds.

Passerines are the most successfully diversified bird order (around 60% of all avian species). They have developed complicated songs to defend their territories and to attract females for mating that can evolve quickly due to cultural transmission. Complex singing as well as plumage coloration of male birds are honest signals for potential partners and provide information about the males’ quality. To function as honest signals, both traits must be costly for the males. Of course, not all passerine species are equally clever or beautiful. Even within a single family of 50 to 70 species, relevant traits may vary considerably. Tits and chickadees (Paridae) comprise species of similar size, varying a lot in coloration and plumage pattern. The territorial songs are relatively short and simple. We investigated the relationship between song complexity and plumage coloration, taking phylogenetic relationships into account. We studied 55 out of the 64 species with 1084 song recordings retrieved from an online database. In the best model, besides colorfulness, body size had a negative impact on song complexity. Large colorful species were found to sing less complex songs. This result supports the hypothesis of a trade-off between costly traits and their likely intense signal function. This study contributes to a better understanding of how sexual selection influences the diversification of traits. In addition, we found that despite the relatively uniform size, the general negative correlation between body size and song frequency can be recovered. Some song traits are further influenced by distribution and thus by interspecific differences in climate niche.

The efficient analyses of sound recordings obtained through passive acoustic monitoring (PAM) might be challenging owing to the vast amount of data collected using such technique. The development of species-specific acoustic recognizers (e.g., through deep learning) may alleviate the time required for sound recordings but are often difficult to create. Here, we evaluate the effectiveness of BirdNET, a new machine learning tool freely available for automated recognition and acoustic data processing, for correctly identifying and detecting two cryptic forest bird species. BirdNET precision was high for both the Coal Tit (Peripatus ater) and the Short-toed Treecreeper (Certhia brachydactyla), with mean values of 92.6% and 87.8%, respectively. Using the default values, BirdNET successfully detected the Coal Tit and the Short-toed Treecreeper in 90.5% and 98.4% of the annotated recordings, respectively. We also tested the impact of variable confidence scores on BirdNET performance and estimated the optimal confidence score for each species. Vocal activity patterns of both species, obtained using PAM and BirdNET, reached their peak during the first two hours after sunrise. We hope that our study may encourage researchers and managers to utilize this user-friendly and ready-to-use software, thus contributing to advancements in acoustic sensing and environmental monitoring. [ABSTRACT FROM AUTHOR]

Supplemental feeding of wild animal populations is popular across many areas of the world and has long been considered beneficial, especially to avian taxa. Over 4 billion dollars are spent by hobby bird feeders in the United States each year alone. However, there is mixed evidence whether wildlife feeding is beneficial, including when it is implemented as a conservation management tool, a targeted experimental design, or an avocation. Much of the current evidence suggests that providing supplemental food is advantageous to the reproductive output and general survival of focal taxa. However, many of these studies are limited in scope and duration, leaving possible negative impacts unaddressed. This is particularly true regarding passive backyard feeding, which describes the majority of supplemental feeding, including the immense effort of millions of public enthusiasts. Here we show that winter supplemental feeding prior to reproduction had no significant impact on a range of reproductive parameters in a resident, montane passerine species, the Mountain Chickadee (Poecile gambeli). This population resides in an intact natural environment with no exposure to supplemental food beyond our experimental treatments, and individual birds were tracked across six years using radio frequency identification technology. Our results add to the growing evidence that supplemental feeding alone, isolated from the effects of urban environments, may have little to no impact on the population dynamics of some avian taxa. [ABSTRACT FROM AUTHOR]

Beak deformities are rare, although they have been documented in different parts of the world, mainly in North America and Europe. I present records of three individuals of Black-crested Titmouse (Baeolophus atricristatus) with beak deformities, registered on 26 May 2018, in the Ranchito de Juárez locality, municipality of Zaragoza, San Luis Potosí, Mexico. The birds were observed when they attended a rustic feeder. The upper mandible of their beaks (maxilla or rhinotheca) had an abnormal prolongation, crossing the lower mandible of the beak. These records are novel and represent the first known cases of avian keratin disorder in the species. [ABSTRACT FROM AUTHOR]

A new feather mite species Proctophyllodes gracilitussp. nov. is described from the mountain bulbul Ixos mcclellandii (Horsfield) (Passeriformes: Pycnonotidae) in China. The new species belongs to the mecistocaulus species-group and differs from the most similar species, P. stenophyllusGaud & Mouchet, 1957, by having the following characters: in males of P. gracilitus, the terminal lamellae are thinner and longer (45–49×4–5) and the posterior part of the hysteronotal shield has circular lacunae; and in females setae h1 are situated at the level of posterior margin of supranal concavity, setae h2 are longer than terminal appendages, do not have enlargement in base, and setae h3 are about 2/3rds the length of terminal appendages. In addition, Proctophyllodes weigoldiVitzthum, 1922 has been collected from the willow tit Poecile montanus (Baldenstein) (Passeriformes: Paridae) that is a new host record for this species. This species is redescribed, because it was found that specimens from Po. montanus have some minor morphological differences from specimens of the common blackbird Turdus merula Linnaeus (Passeriformes: Turdidae) (a type host) and eyebrowed thrush Turdus obscurus Gmelin (Passeriformes: Turdidae). [ABSTRACT FROM AUTHOR]

Las deformidades en picos de aves son raras, aunque sí se han registrado en diferentes partes del mundo, principalmente en Norteamérica y en Europa. Se presenta el registro de tres individuos de carbonero cresta negra (Baeolophus atricristatus) con pico anormal, registrados el 26 de mayo de 2018, en la localidad Ranchito de Juárez, municipio de Zaragoza, San Luis Potosí, México. Las aves fueron observadas al acudir a un comedero rústico de forma frecuente. La mandíbula superior del pico (rinoteca) de los individuos presentó una prolongación anormal cruzada a la mandíbula inferior del pico. Los registros son novedosos y representan los primeros casos conocidos del trastorno de queratina aviar en la especie.

Motor inhibition refers to the ability to inhibit immediate responses in favour of adaptive actions that are mediated by executive functions. This ability may be an indication of general cognitive ability in animals and is important for advanced cognitive functions. In this study, our aim was to compare motor inhibition ability of two closely related passerines that share the same habitat. To do this, we tested motor inhibition ability using a transparent cylinder task in blue tits in the same way as we previously tested great tits. To test whether the experience of transparent objects would affect the performance of these species differently, both in the present experiment using blue tits and our previous one on great tits, we divided 33 wild-caught individuals into three different treatment groups with 11 birds each. Before the test we allowed one group to experience a transparent cylindrical object, one group to experience a transparent wall and a third group was kept naive. In general, blue tits performed worse than great tits, and unlike the great tits, they did not improve their performance after experience with a transparent cylinder-like object. The performance difference may stem from difference in foraging behaviour between these species.

Mediterranean woodland environments are characterised by high spatial and temporal heterogeneity, which means the inhabiting species face a wide variety of selective pressures. Species may respond differently to habitat heterogeneity and so distinct eco-evolutionary scenarios may be responsible for the inter-habitat variability in reproductive strategies observed in certain species. The inter-forest variability of some reproductive traits in passerines has been examined by comparing forest patches or separated fragments. However, there is still little information regarding how such highly mobile animals adjust their breeding performance across continuous and heterogeneous woodlands. Here we studied the reproductive performance of a population of Blue Tits (Cyanistes caeruleus) in an area of continuous Mediterranean woodland that included two mountain slopes and four different types of forest, ranging from deciduous oak forests to perennial non-oak forests. We studied the habitat heterogeneity and inter-forest phenotypic variation in terms of reproductive performance and adult and nestling biometry, besides also exploring the effects of ectoparasites on Blue Tit reproduction. Eggs were laid earliest in deciduous Pyrenean Oak (Quercus pyrenaica) forests, while clutch size and the number of fledglings were highest in the humid Pyrenean Oak forest, which had the greatest tree coverage and most humid climate, and lowest in the coniferous Scots Pine (Pinus sylvestris) forest. There were no inter-forest differences in hatching (percentage of nests with at least one egg hatched) and fledging (percentage of nests in which at least one nestling fledged) success. Similarly, there were no inter-forest differences in adult and nestling biometry, but adults that raised more fledglings had a lower body mass, while males whose females laid larger clutches had smaller tarsi. Most ectoparasites did not affect Blue Tit reproduction, although Culicoides had a negative impact on nestling body mass. These results suggest that Blue Tits can adjust their reproductive effort to the forest where they breed even across a very small spatial scale. Different eco-evolutionary scenarios, such as phenotypic plasticity or genetic structuring and local adaptation, might explain the phenotypic differentiation in the reproductive strategies observed over small areas in woodlands.

Studies of natural hybrid zones can provide documentation of range shifts in response to climate change and identify loci important to reproductive isolation. Using a temporal (36–38 years) comparison of the black‐capped (Poecile atricapillus) and Carolina (P. carolinensis) chickadee hybrid zone, we investigated movement of the western portion of the zone (western Missouri) and assessed whether loci and pathways underpinning reproductive isolation were similar to those in the eastern portion of the hybrid zone. Using 92 birds sampled along the hybrid zone transect in 2016 and 68 birds sampled between 1978 and 1980, we generated 11,669 SNPs via ddRADseq. These SNPs were used to assess movement of the hybrid zone through time and to evaluate variation in introgression among loci. We demonstrate that the interface has moved ~5 km to the northwest over the last 36–38 years, that is, at only one‐fifth the rate at which the eastern portion (e.g., Pennsylvania, Ohio) of the hybrid zone has moved. Temperature trends over the last 38 years reveal that eastern areas have warmed 50% more than western areas in terms of annual mean temperature, possibly providing an explanation for the slower movement of the hybrid zone in Missouri. Our results suggest hybrid zone movement in broadly distributed species, such as chickadees, will vary between areas in response to local differences in the impacts of climate change. [ABSTRACT FROM AUTHOR]

Laboratory studies show that increased physiological burden during development results in cognitive impairment. In the wild, animals experience a wide range of developmental conditions, and it is critical to understand how variation in such conditions affects cognitive abilities later in life, especially in species that strongly depend on such abilities for survival. We tested whether variation in developmental condition is associated with differences in spatial cognitive abilities in wild food-caching mountain chickadees. Using tail feathers grown during development in juvenile birds, we measured feather corticosterone (Cortf) levels and growth rates and tested these birds during their first winter on two spatial learning tasks. In only 1 of the 3 years, higher feather Cortf was negatively associated with memory acquisition. No significant associations between feather Cortf and any other measurement of spatial cognition were detected in the other 2 years of the study or between feather growth rate and any measurement of cognition during the entire study. Our results suggest that in the wild, naturally existing variation in developmental condition has only a limited effect on spatial cognitive abilities, at least in a food-caching species. This suggests that there may be compensatory mechanisms to buffer specialized cognitive abilities against developmental perturbations. [ABSTRACT FROM AUTHOR]

Mixed-species broods appear to be an uncommon phenomenon in altricial birds. In secondary hole-nesting birds, such as tits (Paridae), mixed-species clutches occur as a consequence of facultative interspecific brood parasitism or as a byproduct of nest takeover. Here, we report a case of a mixed-species brood composed of one Coal Tit Periparus ater and three Blue Tit Cyanistes caeruleus nestlings that was successfully raised by a Blue Tit pair. The foreign Coal Tit nestling received more food than its Blue Tit nestmates, possibly resulting in a larger tarsus length compared to other Coal Tit nestlings from a regular single-species brood in the same forest. [ABSTRACT FROM AUTHOR]

The efficient analyses of sound recordings obtained through passive acoustic monitoring (PAM) might be challenging owing to the vast amount of data collected using such technique. The development of species-specific acoustic recognizers (e.g., through deep learning) may alleviate the time required for sound recordings but are often difficult to create. Here, we evaluate the effectiveness of BirdNET, a new machine learning tool freely available for automated recognition and acoustic data processing, for correctly identifying and detecting two cryptic forest bird species. BirdNET precision was high for both the Coal Tit (Peripatus ater) and the Short-toed Treecreeper (Certhia brachydactyla), with mean values of 92.6% and 87.8%, respectively. Using the default values, BirdNET successfully detected the Coal Tit and the Short-toed Treecreeper in 90.5% and 98.4% of the annotated recordings, respectively. We also tested the impact of variable confidence scores on BirdNET performance and estimated the optimal confidence score for each species. Vocal activity patterns of both species, obtained using PAM and BirdNET, reached their peak during the first two hours after sunrise. We hope that our study may encourage researchers and managers to utilize this user-friendly and ready-to-use software, thus contributing to advancements in acoustic sensing and environmental monitoring.

Many animals respond to heterospecific signals that indicate the presence of food or predators. Although the benefits of responding are clear, the behavioral and cognitive mechanisms underlying responses are not. Whether responses are learned, innate, or an epiphenomenon created by following other species as they respond to signals remains unknown because most studies have involved respondents that are sympatric with their heterospecific signalers and that have therefore had opportunities to learn their signals. In this study, we tested the mechanisms underlying avian responses to heterospecific chick-a-dee calls. All North American parids produce chick-a-dee calls in response to arousing stimuli, such as food and predators, and diverse species respond by approaching the caller and consuming the food or mobbing the predator. We broadcast chick-a-dee calls plus two control stimuli in Costa Rica, Colombia, and Brazil, where no parids ever occur. We conducted our trials in the winter, when Neotropical migrants that might be familiar with chick-a-dee calls were present, and in the temperate breeding season, when migrants were absent. Across 138 trials, 38 resident species from 14 families and four orders responded to chick-a-dee calls by approaching to within 5 m of the playback speaker. A phylogenetic logistic regression showed that whether a species responded was not significantly associated with the species' mean body mass or the structural similarity between its calls and chick-a-dee calls. Residents were significantly more likely to approach chick-a-dee calls than either control stimulus. This pattern was unaffected by the presence of migrants, thus demonstrating that the observed responses are innate. Our study shows that learning cannot fully explain responses to heterospecific chick-a-dee calls and that structural features distinguishing these calls from other vocalizations are important. [ABSTRACT FROM AUTHOR]

Many species of birds emit mobbing calls to recruit prey to join mobbing events. This anti-predator strategy often involves several species and, therefore, implies heterospecific communication. Some species of tit exhibit a sensitivity to allopatric mobbing calls, suggesting that heterospecific recognition is based on an innate component. To date, however, we have no information on whether the perception of allopatric calls varies with season, despite seasonality playing an important role in the perception of heterospecific call in some species. In this study, I investigate the responses of European great tits (Parus major) to the calls of a North American bird species, the black-capped chickadee (Poecile atricapillus), during two seasons: spring and in autumn (breeding and non-breeding seasons, respectively). Great tits approached the sound source during both seasons, with no significant difference in response between seasons. These findings indicate that season does not influence the response of birds to allopatric calls, and will help to shed light on the evolution of interspecific communication. [ABSTRACT FROM AUTHOR]

Abstract Territorial aggression in birds is widely observed and is commonly linked to sex, age, body size, physiology, seasonal cues, food resource, urbanization, and a variety of social contexts including conspecific audience effects. However, little is known about the heterospecific audience effects on territorial aggression. Here, we address an emerging idea that heterospecific audience effects may be pervasive influences in the social lives of free‐living birds. We tested the hypothesis that the composition, number, and relative body size of heterospecific audiences observing an aggressive contest will influence the response probability and intensity of aggression displayed. We subjected two Paridae species, tufted titmouse (TUTI, Baeolophus bicolor) and Carolina chickadee (CACH, Poecile carolinensis), to playbacks of aggressive calls during a breeding season in north‐central Florida. At widely spaced playback sites (N = 134) in woodland habitats, we characterized the makeup of heterospecific audiences, aggression type (intra vs. interspecific territoriality), local population density, and various environmental factors (tree density, wind speed, and noise level) that are likely to influence territorial aggression. We found that the presence of heterospecific audiences increased TUTI aggression levels and that both parids were more likely to respond to playback stimuli when their audiences had higher heterospecific diversity (more heterospecific individuals and species). We also found TUTI were more likely to respond when CACH were present but not vice versa. In conclusion, we found evidence that heterospecific audiences significantly influenced the metrics of territorial aggression of free‐living animals and we suggest that the definition of audience effects on the behavior of free‐living animals be expanded to incorporate heterospecific audiences.

The hippocampal formation (HF) processes spatial memories for cache locations in food-hoarding birds. Hoarding is a seasonal behavior, and seasonal changes in the HF have been described in some studies, but not in others. One potential reason is that birds may have been sampled during the seasonal hoarding peak in some studies, but not in others. In this study, we investigate the seasonal changes in hoarding and HF in willow tits (Poecile montanus). We compare this to seasonal changes in HF in a closely related non-hoarding bird, the great tit (Parus major). Willow tits near Oulu, Finland, show a seasonal hoarding peak in September and both HF volume and neuron number show a similar peak. HF neuronal density also increases in September, but then remains the same throughout winter. Unexpectedly, the great tit HF also changes seasonally, although in a different pattern: the great tit telencephalon increases in volume from July to August and decreases again in November. Great tit HF volume follows suit, but with a delay. Great tit HF neuron number and density also increase from August to September and stay high throughout winter. We hypothesize that seasonal changes in hoarding birds' HF are driven by food-hoarding experience (e.g., the formation of thousands of memories). The seasonal changes in great tit brains may also be due to experience-dependent plasticity, responding to changes in the social and spatial environment. Large-scale experience-dependent neural plasticity is therefore probably not an adaptation of food-hoarding birds, but a general property of the avian HF and telencephalon. [ABSTRACT FROM AUTHOR]

Behavioural flexibility allows animals to adjust to changes in their environment. Although the cognitive processes that explain flexibility have been relatively well studied in psychology, this is less true for animals in the wild. Here we use data collected automatically during self-administered discrimination-learning trials for two passerine species, and during four phases (habituation, initial learning, first reversal and second reversal) in order to decompose sources of consistent among-individual differences in reversal learning, a commonly used measure for cognitive flexibility. First, we found that, as expected, proactive interference was significantly repeatable and had a negative effect on reversal learning, confirming that individuals with poor ability to inhibit returning to a previously rewarded feeder were also slower to reversal learn. Second, to our knowledge for the first time in a natural population, we examined how sampling of non-rewarding options post-learning affected reversal-learning performance. Sampling quantity was moderately repeatable in blue tits but not great tits; sampling bias, the variance in the proportion of visits to each non-rewarded feeder, was not repeatable for either species. Sampling behaviour did not predict variation in reversal-learning speed to any significant extent. Finally, the repeatability of reversal learning was explained almost entirely by proactive interference for blue tits; in great tits, the effects of proactive interference and sampling bias on the repeatability of reversal learning were indistinguishable. Our results highlight the value of proactive interference as a more direct measurement of cognitive flexibility and shed light on how animals respond to changes in their environment. [ABSTRACT FROM AUTHOR]

The estimation of abundance and distribution and factors governing patterns in these parameters is central to the field of ecology. The continued development of hierarchical models that best utilize available information to inform these processes is a key goal of quantitative ecologists. However, much remains to be learned about simultaneously modeling true abundance, presence, and trajectories of ecological communities.Simultaneous modeling of the population dynamics of multiple species provides an interesting mechanism to examine patterns in community processes and, as we emphasize herein, to improve species‐specific estimates by leveraging detection information among species. Here, we demonstrate a simple but effective approach to share information about observation parameters among species in hierarchical community abundance and occupancy models, where we use shared random effects among species to account for spatiotemporal heterogeneity in detection probability.We demonstrate the efficacy of our modeling approach using simulated abundance data, where we recover well our simulated parameters using N‐mixture models. Our approach substantially increases precision in estimates of abundance compared with models that do not share detection information among species. We then expand this model and apply it to repeated detection/non‐detection data collected on six species of tits (Paridae) breeding at 119 1 km2 sampling sites across a P. montanus hybrid zone in northern Switzerland (2004–2020). We find strong impacts of forest cover and elevation on population persistence and colonization in all species. We also demonstrate evidence for interspecific competition on population persistence and colonization probabilities, where the presence of marsh tits reduces population persistence and colonization probability of sympatric willow tits, potentially decreasing gene flow among willow tit subspecies.While conceptually simple, our results have important implications for the future modeling of population abundance, colonization, persistence, and trajectories in community frameworks. We suggest potential extensions of our modeling in this paper and discuss how leveraging data from multiple species can improve model performance and sharpen ecological inference. [ABSTRACT FROM AUTHOR]

Ecology and epidemiology of murine gammaherpesvirus 68 (MHV-68) have been intensively studied since the isolation of the virus from murid rodents in 1976. This virus was detected in various mammalian species that share the biotope with rodent reservoirs of MHV-68. However, a survey of MHV-68 in birds has not so far been performed. Therefore, the aim of this study was to investigate the presence of MHV-68 in blood samples from two bird species captured at four localities in Slovakia. Using the nested PCR targeting ORF50 gene of MHV-68, we confirmed the presence of MHV-68 DNA in 9 out of 57 blood samples from Great tits (Parus major) (prevalence 15.8%, confidence interval [95% CI]: 8.5–27.4) and in 3 out of 43 blood samples from Eurasian blue tits (Cyanistes caeruleus) (prevalence 7.0%, 95% CI: 2.4–18.6). Our results suggest that not only mammals but also birds may serve as reservoirs for MHV-68, providing further evidence that MHV-68 is capable of frequent cross-species transmission. [ABSTRACT FROM AUTHOR]

Mobbing is an anti-predator behavior where multiple species collectively harass a predator while vocalizing. These flocks are made up of species whose vocalizations contain information about predator threat (information sources), and those that eavesdrop on this information (scroungers). To be a community informant (a key information source), a species needs to meet two criteria: (1) the detailed predator threat information they produce must be consistently reliable across mobbing events, and (2) this information must be used by eavesdropping species. As tits (Paridae) have traditionally been assumed to be community informants, we tested whether they meet these criteria. Specifically, we used field experiments with predator mounts to: (1) test the reliability of the encoded information across mobbing events with different community compositions (different species present), and (2) examine the vocal response of previously assumed scrounger species to predators. We found that only blue, great, and coal tits, produced reliable predator threat information regardless of community composition, and each scrounger species acted on the information that tits provided to a different degree. Additionally, we found that both ‘scrounger’ species produced their own information about predators by varying their own mobbing vocalizations in response to the presence of predators. These results suggest that not all species that produce predator threat information are community informants, not all species that appear to eavesdrop on this information do so to the same degree, and some species that initially appear to be scroungers will actually produce their own information about predator encounters.

Abstract Vertebrates obtain social information about predation risk by eavesdropping on the alarm calls of sympatric species. In the Holarctic, birds in the family Paridae function as sentinel species; however, factors shaping eavesdroppers' reliance on their alarm calls are unknown. We compared three hypothesized drivers of eavesdropper reliance: (a) foraging ecology, (b) degree of sociality, and (c) call relevance (caller‐to‐eavesdropper body‐size difference). In a rigorous causal‐comparative design, we presented Tufted Titmouse (Baeolophus bicolor) alarm calls to 242 individuals of 31 ecologically diverse bird species in Florida forests and recorded presence/absence and type (diving for cover or freezing in place) of response. Playback response was near universal, as individuals responded to 87% of presentations (N = 211). As an exception to this trend, the sit‐and‐wait flycatcher Eastern Phoebe (Sayornis phoebe) represented 48% of the nonresponses. We tested 12 predictor variables representing measures relevant to the three hypothesized drivers, distance to playback speaker, and vulnerability at time of playback (eavesdropper's microhabitat when alarm call is detected). Using model‐averaged generalized linear models, we determined that foraging ecology best predicted playback response, with aerial foragers responding less often. Foraging ecology (distance from trunk) and microhabitat occupied during playback (distance to escape cover) best predicted escape behavior type. We encountered a sparsity of sit‐and‐wait flycatchers (3 spp.), yet their contrasting responses relative to other foraging behaviors clearly identified foraging ecology as a driver of species‐specific antipredator escape behavior. Our findings align well with known links between the exceptional visual acuity and other phenotypic traits of flycatchers that allow them to rely more heavily on personal rather than social information while foraging. Our results suggest that foraging ecology drives species‐specific antipredator behavior based on the availability and type of escape cover.

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Currently, there is considerable debate surrounding the presence of some human language‐specific characteristics in non‐human animals, such as the use of compositional syntax (i.e. meaning of a sequence determined both by meaning of its individual parts and in the way they are combined). Compositional syntax has been investigated in mobbing calls of two closely related tit species, the Japanese Tit Parus minor and the Great Tit Parus major, but with one contrasting result: hearing calls in the reversed order diminished the behavioural responses of Japanese Tits but only partially those of Great Tits. This difference may have been due to an external factor such as the season in which the experiment was undertaken, as the Japanese Tits were tested in winter and Great Tits in spring. Here, we studied the responses of Great Tits towards natural and reversed mobbing sequences during spring and winter by investigating two behaviours: approaching and vigilance behaviours. We found that sensitivity to syntax reversal was impacted by the season. The birds were vigilant but less likely to approach reversed calls in winter. However, the opposite occurred in spring, with the birds scanning less but still approaching. This study suggests that the perception of combinatorial calls in Great Tits is influenced by the season, emphasizing the importance of context in studies investigating complex cognitive processing in animals. [ABSTRACT FROM AUTHOR]

Las cajas-nido constituyen una herramienta muy útil para el desarrollo de diversos estudios en aves, pues permiten el diseño experimental y la comparación de muestras sometidas a distintos tratamientos o localizaciones. Igualmente, son útiles para la conservación de aves en hábitats con muy poco arbolado maduro, como ocurre en muchos parques urbanos. Con el fin de impulsar la biodiversidad en el ámbito urbano, la Sociedad de Ciencias Aranzadi inició en 2018 el proyecto Hirilife, entre cuyas acciones estaba la colocación de cajas nido para aves paseriformes insectívoras en arbolado en calles, paseos y parques urbanos de la ciudad de San Sebastián. Este artículo se presenta con el fin de (1) determinar la tasa de ocupación de estas cajas-nido; y (2) explorar los factores que condicionan esta ocupación, con el fin de establecer, a futuro, una guía de buenas prácticas orientada a optimizar su colocación. A lo largo de la primavera de 2020 se revisaron 202 cajas en total, de las 220 que se habían colocado. Se ocuparon un total de 91 (45%). La tasa de ocupación, no obstante, varió significativamente entre zonas. Las cajas en las que se pudo determinar la especie fueron ocupadas por dos especies de páridos: el herrerillo común Cyanistes caeruleus y el carbonero común Parus major. Se observa una dominancia del carbonero común (31 versus 10 cajas; el resto se corresponde con las que no se pudo determinar la especie). Según los modelos las cajas son ocupadas con más probabilidad cuando se sitúan en entornos con una gran cantidad de hábitat natural. Abstract: Nest-boxes constitute a very useful tool in ornithological studies, since they allow the development of experimental designs and permit comparisons to be made between samples subjected to different treatments and locations. Moreover, they are also useful for bird conservation in habitats with low amounts of mature trees, as occurs in many urban parks. The ‘Hirilife’ project, developed by the Aranzadi Sciences Society, was launched in 2018 with the aim of promoting biodiversity in urban areas. This project included actions oriented to install and monitor nest-boxes for insectivorous passerine birds in the streets, promenades and parks of the city of San Sebastian. As a result, in this article we (1) describe the nest-box occupation rate, and (2) examine those factors that determine this rate, with the aim of drawing up a good practice guide to optimize the installation of new nestboxes in the future. During the spring of 2020, 202 nest-boxes were surveyed. Overall, 91 were occupied (45%). The occupation rate, however, varied substantially between zones. The nest-boxes were occupied by two species: the blue tit Cyanistes caeruleus and the great tit Parus major. The latter species was dominant (31 versus 10 nest-boxes). According to the model of nest-box, these were more likely to be occupied when they were situated in areas close to/surrounded by a high amount of natural habitat.

Territorial aggression in birds is widely observed and is commonly linked to sex, age, body size, physiology, seasonal cues, food resource, urbanization, and a variety of social contexts including conspecific audience effects. However, little is known about the heterospecific audience effects on territorial aggression.Here, we address an emerging idea that heterospecific audience effects may be pervasive influences in the social lives of free‐living birds. We tested the hypothesis that the composition, number, and relative body size of heterospecific audiences observing an aggressive contest will influence the response probability and intensity of aggression displayed.We subjected two Paridae species, tufted titmouse (TUTI, Baeolophus bicolor) and Carolina chickadee (CACH, Poecile carolinensis), to playbacks of aggressive calls during a breeding season in north‐central Florida. At widely spaced playback sites (N = 134) in woodland habitats, we characterized the makeup of heterospecific audiences, aggression type (intra vs. interspecific territoriality), local population density, and various environmental factors (tree density, wind speed, and noise level) that are likely to influence territorial aggression.We found that the presence of heterospecific audiences increased TUTI aggression levels and that both parids were more likely to respond to playback stimuli when their audiences had higher heterospecific diversity (more heterospecific individuals and species). We also found TUTI were more likely to respond when CACH were present but not vice versa.In conclusion, we found evidence that heterospecific audiences significantly influenced the metrics of territorial aggression of free‐living animals and we suggest that the definition of audience effects on the behavior of free‐living animals be expanded to incorporate heterospecific audiences. [ABSTRACT FROM AUTHOR]

Hybridization is an important aspect of speciation, yet questions remain about the ecological and environmental factors that influence hybridization among wild populations. We used microsatellite genotyping data and collected land cover and environmental data for four North American chickadee species: black‐capped Poecile atricapillus, mountain P. gambeli, chestnut‐backed P. rufescens and boreal P. hudsonicus chickadees. Combining these datasets, we sought to examine whether there is evidence of admixture between four widely distributed North American chickadee species; whether admixture takes place more often between more closely related species pairs or between species pairs with more similar ecological preferences; and whether certain habitat types have higher rates of admixture than others. We detected admixture for five of the six species pairs analyzed (chestnut‐backed–mountain chickadee pair showed no evidence of admixture), and found rates of admixture varied geographically, and within taxa pairs. Admixture was higher among less closely related species than more closely related species, although habitat similarity was not a significant predictor. Finally, rates of admixture were higher in urban parkland habitats than deciduous, mixed or coniferous forest habitats. Our work indicates admixture occurs frequently among North American parids, and habitat and environmental variation may play an important role in the frequency and geographic distribution of hybridization. [ABSTRACT FROM AUTHOR]

Abstract The optimum body mass of passerine birds typically represents a trade‐off between starvation risk, which promotes fat gain, and predation pressure, which promotes fat loss to maintain maneuvrability. Changes in ecological factors that affect either of these variables will therefore change the optimum body masses of populations of passerine birds. This study sought to identify and quantify the effects of changing temperatures and predation pressures on the body masses and wing lengths of populations of passerine birds throughout Britain and Ireland over the last 50 years. We analyzed over 900,000 individual measurements of body mass and wing length of blue tits Cyanistes caeruleus, coal tits Periparus ater, and great tits Parus major collected by licenced bird ringers throughout Britain and Ireland from 1965 to 2017 and correlated these with publicly available temperature data and published, UK‐wide data on the abundance of a key predator, the sparrowhawk Accipiter nisus. We found highly significant, long‐term, UK‐wide decreases in winter body masses of adults and juveniles of all three species. We also found highly significant negative correlations between winter body mass and winter temperature, and between winter body mass and sparrowhawk abundance. Independent of these effects, body mass further correlated negatively with calendar year, suggesting that less well understood dynamic factors, such as supplementary feeding levels, may play a major role in determining population optimum body masses. Wing lengths of these birds also decreased, suggesting a hitherto unobserved large‐scale evolutionary adjustment of wing loading to the lower body mass. These findings provide crucial evidence of the ways in which species are adapting to climate change and other anthropogenic factors throughout Britain and Ireland. Such processes are likely to have widespread implications as the equilibria controlling evolutionary optima in species worldwide are upset by rapid, anthropogenic ecological changes.

We explored interspecific and intraspecific aggressive contacts of three species of Paridae birds: Great Tit (Parus major), Blue Tit (P. caeruleus) and Marsh Tit (P. palustris) at the local watering place during breeding season by ethological methods of total observation and continuous logging. We recorded for which of 27 bird species present at the local watering place tits show aggression, and for which not. We considered the relationship of interspecific and intraspecific contacts among which non-aggressive and interspecific contacts are dominant. The percentage of interspecific contacts was slightly higher than intraspecific among all aggressive interactions in P. caeruleus, but the apparently opposite was found in P. palustris. In P. major it differed among study sites. The frequency of aggressive interactions in the studied species is rather small, but its index is always higher in intraspecific conflicts than in interspecific. We checked the statistical significance of differences of displaying interspecific and intraspecific aggression in different territories, and actually between these types of aggression at each location. The interspecific and intraspecific ratio of aggression for P. caeruleus and P. major is the same in most areas, but is always different in P. palustris. We calculated the success of the aggression reaction in defense and attack for the tits to all other species and estimated its aspects for the study sites.

When mobbing a predator, birds often produce specific mobbing calls that are efficient in recruiting both conspecifics and heterospecifics. Recent studies on Parids have demonstrated that these mobbing calls are in fact a combination of two distinct calls—first, introductory notes eliciting vigilance in the receiver, then broadband frequency notes (D notes) triggering approach. Debates on a parallel between human syntax and this form of combination have emerged. The degree to which this combinatoriality is perceived in heterospecific communication may shed light onto the relative complexity of such combinatoriality. In this study, our aim was to determine whether European great tits (Parus major) appropriately responded to mobbing calls (and their isolated parts) of an allopatric species, the black‐capped chickadee (Poecile atricapillus), a North‐American species which produces similar combinatorial mobbing calls. In addition, we tested whether the behavioural response to complete mobbing sequences was different than the simple sum of its two constituents. As we hypothesized, great tits behaved differently when hearing the two isolated calls or the complete mobbing sequence: they produced calls and displayed excitement signs only towards the complete mobbing sequence. Moreover, great tits responded to the introductory and D notes by respectively scanning and approaching, and to the complete sequence by mobbing. Our results altogether support the emerging hypothesis of semantic compositionality in Parids, although the present study does not definitively demonstrate the existence of this cognitive process in the great tit. [ABSTRACT FROM AUTHOR]

Numerical competence—the ability to represent, discriminate, and process numerical quantity information—is a widespread cognitive ability in animals that influences survival and reproductive success. Little is known about the role of numerical competence during predator mobbing—when a prey moves toward and harasses a predator. Since being in a larger group dilutes the risk of injury or death during a mobbing event and large groups are more efficient than small groups at repelling predators, the capacity to evaluate the number of mobbers before joining the mobbing flock may be highly beneficial for individuals. We tested whether the strength of the mobbing response of great tits (Parus major), a songbird that frequently mobs predators, is related to the number of callers. The minimum distance to the loudspeaker tended to be lower, and the number of calls produced by great tits was higher during playbacks simulating several callers than during the playbacks of one caller. These results suggest that numerical competence plays a central role during mobbing and that great tits reduce uncertainty of information by collating information from several individuals. We suggest further studies testing whether birds use individual vocal discrimination to assess the number of heterospecifics during mobbing. Significance statement: Can animals count? Although historically the ability to count has distinguished humans apart from the rest of the animal kingdom, studies in the last decades have shown that numerical competence, the ability to represent, discriminate, and process numerical quantity information, is a widespread cognitive ability in animals. While this competence influences an individual's survival success, little is known about the role of numerical competence during predator mobbing. Using a field-based playback experiment on a population of wild great tits (Parus major), we demonstrate that great tit responses to mobbing calls were affected by the number of individuals calling. The minimum distance to the loudspeaker tended to be lower and the number of calls produced by great tits tended to be higher during playbacks simulating multiple callers than during the playbacks of one caller. Thus, numerical assessments are used to decide whether or not to participate in mobbing responses. [ABSTRACT FROM AUTHOR]

The article focuses on egg recognition abilities of tit species in the Paridae family and Indomalayan tits exhibit higher recognition than Palearctic tits. It mentions reproductive output but also expend considerable time and energy raising unrelated chicks. It also mentions selective pressure causes hosts to evolve defensive measures to resist cuckoo parasitism, including nest defense and egg recognition.

Animals use behavioural cues from others to make decisions in a variety of contexts. There is growing evidence, from a range of taxa, that information about the locations of food patches can spread through a population via social connections. However, it is not known whether information about their quality transmits similarly. We studied foraging behaviour in a population of wild songbirds with known social associations and tested whether flock members use social information about the profitability of patches to inform their foraging decisions. We provided artificial patches (ephemeral bird feeders) that appeared identical but were either profitable (contained food) or unprofitable (contained no food). If information about patch profitability spreads via social associations, we predicted that empty feeders would only be sampled by individuals that are less connected to each other than expected by chance. In contrast, we found that individuals recorded at empty feeders were more closely associated with each other than predicted by a null model simulating random arrival of individuals, mirroring a pattern of increased connectedness among individuals recorded at full feeders. We then simulated arrival under network-based diffusion of information and found that the observed pattern at both full and empty feeders matched predictions derived from this post hoc model. Our results suggest that foraging songbirds use social cues only about the location of potential food sources, but not their profitability. These findings agree with the hypothesis that individuals balance the relative economic costs of using different information, where the costs of personally sampling a patch upon arrival is low relative to the cost of searching for patches. This study extends previous work on information spread through animal social networks, by suggesting important links between how individuals use information at different stages of the acquisition process and the emerging patterns of patch use at the level of the population. • Songbirds used social information to find food. • Social connections predicted patch discovery, i.e. order of arrival of individuals. • Upon discovery, individuals gathered personal information about patch quality. • Social and personal information is used at different phases while foraging. • The relative costs of social and personal information predict information use. [ABSTRACT FROM AUTHOR]

Many species of birds produce distinct calls when mobbing predators. These calls often recruit nearby conspecifics and heterospecifics to help drive the predators away. In some species, such as members of the family Paridae, mobbing calls are composed of multiple elements that seem to follow a characteristic order. Previous work in parids demonstrated that note ordering influences both the responses of conspecifics and some other co-occurring Paridae species. Cross-species sensitivity to note ordering could result from individuals' learning to associate individual heterospecific calls with threats or, rather, because the typical note orderings are shared across species. Here, we test these hypotheses by assessing the responses of European great tits (Parus major) to the naturally and artificially ordered calls of black-capped chickadees (Poecile atricapillus), a North American species. In response to the naturally ordered mobbing calls of chickadees, we found that great tits exhibit vigilance and rapidly approach the sound source, behaviors that were indistinguishable to those expressed in response to conspecific calls. If learned associations are necessary for sensitivity to note ordering, then a key prediction is that great tit responses to naturally ordered and artificially reversed chickadee calls should be similar (and weak). In contrast to this prediction, we found that great tits were less vigilant, but approach the sound source in response to artificially reversed chickadee calls. These findings suggest that perception of note ordering patterns is conserved. However, they are also in agreement with a "perception bias" hypothesis: that the first notes of the call mask the notes that follow them, preventing the receiver from perceiving the second part of the call. Although we provide evidence against perception bias, further research is needed to convincingly disentangle these two hypotheses. Significance statement: How do animals decode other species' vocal sequences? Great tit responses to chickadee sequences depend on the ordering of their notes. Great tits and chickadees never encounter one another in the wild, but their alarm call sequences have similar note orderings. Using a series of playback experiments, we demonstrate that great tits respond strongest to chickadee calls whose order matches their own. Thus, response to unfamiliar calls does not depend on learning, but, rather, shared call ordering across species. [ABSTRACT FROM AUTHOR]

When animals vocalize under the threat of predation, variation in the structure of calls can play a vital role in survival. The chick-a-dee calls of chickadees and titmice provide a model system for studying communication in such contexts. In previous studies, birds' responses to chick-a-dee calls covaried with call structure, but also with unmeasured and correlated parameters of the calling sequence, including duty cycle (the proportion of the calling sequence when a signal was present). In this study, we exposed flocks of Black-capped Chickadees (Poecile atricapillus) and heterospecific birds to playback of chick-a-dee calls and taxidermic models of predators. We quantified birds' responses to variation in number of D notes and duty cycle of the signalling sequence. Chickadees and heterospecific birds responded more intensely to high-duty-cycle treatments, and equally to treatments where duty cycle was held constant and the number of D notes varied. Although our study does not disentangle the effects of call rate and duty cycle, it is the first to investigate independently the behavioural responses of birds to variation in structural and sequence-level parameters of the chick-a-dee call during a predator confrontation. Critically, our results confirm that the pattern previously observed in a feeding context holds true in a mobbing context: variation in calling sequences, not in call structure, is the salient acoustic feature of chick-a-dee calls. These results call into question the idea that chick-a-dee call structure carries allometric information about predator size, suggesting instead that sequence-level parameters play a central role in communication in a mobbing context. [ABSTRACT FROM AUTHOR]

Vertebrates obtain social information about predation risk by eavesdropping on the alarm calls of sympatric species. In the Holarctic, birds in the family Paridae function as sentinel species; however, factors shaping eavesdroppers' reliance on their alarm calls are unknown. We compared three hypothesized drivers of eavesdropper reliance: (a) foraging ecology, (b) degree of sociality, and (c) call relevance (caller‐to‐eavesdropper body‐size difference). In a rigorous causal‐comparative design, we presented Tufted Titmouse (Baeolophus bicolor) alarm calls to 242 individuals of 31 ecologically diverse bird species in Florida forests and recorded presence/absence and type (diving for cover or freezing in place) of response. Playback response was near universal, as individuals responded to 87% of presentations (N = 211). As an exception to this trend, the sit‐and‐wait flycatcher Eastern Phoebe (Sayornis phoebe) represented 48% of the nonresponses. We tested 12 predictor variables representing measures relevant to the three hypothesized drivers, distance to playback speaker, and vulnerability at time of playback (eavesdropper's microhabitat when alarm call is detected). Using model‐averaged generalized linear models, we determined that foraging ecology best predicted playback response, with aerial foragers responding less often. Foraging ecology (distance from trunk) and microhabitat occupied during playback (distance to escape cover) best predicted escape behavior type. We encountered a sparsity of sit‐and‐wait flycatchers (3 spp.), yet their contrasting responses relative to other foraging behaviors clearly identified foraging ecology as a driver of species‐specific antipredator escape behavior. Our findings align well with known links between the exceptional visual acuity and other phenotypic traits of flycatchers that allow them to rely more heavily on personal rather than social information while foraging. Our results suggest that foraging ecology drives species‐specific antipredator behavior based on the availability and type of escape cover. [ABSTRACT FROM AUTHOR]

Using information acquired from other individuals (social information use) is ubiquitous in animals and not restricted to within-species context. Some of the textbook examples of interspecific information use in the wild has been provided using apparent novel niche experiment approach, with migratory flycatcher species (Ficedula spp.) cueing on apparent nest site preferences (geometric symbols) and clutch sizes of resident great tits (Parus major) and blue tits (Cyanistes caeruleus) to choose their own nest site. However, the interpretation of these results has recently been challenged. It has been argued that there is no evidence that flycatchers visit tit nests to collect information about clutch size or that flycatchers are capable of "counting" tit eggs. Instead, it has been proposed that the decision-making patterns of flycatchers found in earlier studies resulted from aggressive interactions, not information use, between tits and flycatchers (termed owner aggression hypothesis). Here, I contribute to the debate around both hypotheses and specifically explore the remaining points of disagreement, related to the timing of flycatchers prospecting and the cognitive abilities needed to assess tit clutch size. I argue how interannual variation in phenology can explain the apparent discrepancy between the observed and predicted timing of flycatchers prospecting. I also argue why assessing tit clutch size neither requires "counting" eggs nor any sophisticated cognitive capacities. Finally, I propose experimental designs to test the hypotheses on the underlying mechanisms explaining the observed patterns, which will allow taking further leaps in resolving the selective interspecific information use vs. owner aggression hypothesis dilemma. [ABSTRACT FROM AUTHOR]

Studies investigating tool use in animals that are not known tool users in the wild are important in helping to understand how and under what circumstances this ability might arise. Tool use appears to be uncommon in great tits (Parus major), with only a single documented observation in which a wild great tit used conifer needles to extract larvae from crevices in trees. In a laboratory‐based experiment, we examined whether wild‐caught great tits could learn to use tools in a similar manner. We presented the birds with two different tool use tasks in which they would need to use either a stick or a hook to extract an otherwise inaccessible meal worm from a transparent plastic tube. First, the birds passed a simpler training criterion (pulling a tool with an attached food reward) that aimed to reduce the difficulty of the task. Nevertheless, none of the individuals learnt to use tools in either of the two tasks. This result stands in stark contrast to the abilities of some corvids and parrots, which can learn to use tools in captivity, even though some of them are not tool users in the wild. We believe that tool use might be difficult for some birds to learn since the skills required for this ability seem not to be part of their natural foraging behaviour. [ABSTRACT FROM AUTHOR]

When they detect a predator, many birds exhibit mobbing behaviour and produce mobbing calls that quickly draw other prey against the predator. This anti-predator strategy often involves several species and, therefore, implies heterospecific communication. As fledging and nestling stages could be particularly targeted by predators, a high mobbing intensity is to be expected during the breeding season. While recognizing other species' mobbing calls is critical to setting up this behaviour, to date, we have no information about the perception of these calls with regard to the season. Here, we used playbacks of mobbing calls to study the variation in response of the Great Tit (Parus major) and the Blue Tit (Cyanistes caeruleus) exposed to the mobbing calls of two heterospecific species, the Eurasian Nuthatch (Sitta europaea), and the Eurasian Wren (Troglodytes troglodytes). To investigate mobbing response seasonality, we conducted playback experiments during spring (breeding season) and autumn (non-breeding season). Contrary to most previous studies, we found that mobbing intensity was greater in autumn than in spring. Additionally, although neither Nuthatch nor Wren is related to the Tit family, we found that both Tit species responded more to the former than the latter species. At the heterospecific communication level, this study demonstrates a previously unsuspected level of complexity in the use of mobbing calls. [ABSTRACT FROM AUTHOR]

Summary: Laying data and clutch size of Great Tits were studied in four different habitats in eastern Spain: two holm oak(Quercus ilex) forests, at 500 and 900–950 m a.s.l., a zeen oak(Quercus faginea) forest, at 900–1100 m a.s.l., a pine(Pinus sylvestris) forest, at 1000–1050 m a.s.l., and orange(Citrus aurantium) plantations, at 30 m a.s.l. All sites were placed at about the same latitude (39–41°N), and all were studied during the same years (1992–95). Our results show that (1) laying date did not differ between the natural habitats at the same altitude (range of the means of yearly means 4–8 May); (2) within the same habitat type (holm oak forest) laying date was earlier at low altitude (30 Aprilvs. 8 May); (3) laying date was earlier in the orange plantations (21 April) than in natural habitats; (4) among natural habitats at the same altitude, clutch size decreased from zeen oak (mean of yearly means 7.3 eggs) to holm oak (7.0 eggs) to pine forests (6.4 eggs), though only the difference between zeen oak and pine forests was significant; (5) within the same habitat type (holm oak forest), the clutch size tended to be larger at high altitude (7.0vs. 5.9 eggs); and (6) clutch size in orange plantations (7.7 eggs) did not differ significantly from that of the zeen oak forest, but was larger than in the holm oak and pine forests. We discuss the effect of the habitat type on laying date and clutch size of Great Tits. [ABSTRACT FROM AUTHOR]

The optimum body mass of passerine birds typically represents a trade‐off between starvation risk, which promotes fat gain, and predation pressure, which promotes fat loss to maintain maneuvrability. Changes in ecological factors that affect either of these variables will therefore change the optimum body masses of populations of passerine birds. This study sought to identify and quantify the effects of changing temperatures and predation pressures on the body masses and wing lengths of populations of passerine birds throughout Britain and Ireland over the last 50 years. We analyzed over 900,000 individual measurements of body mass and wing length of blue tits Cyanistes caeruleus, coal tits Periparus ater, and great tits Parus major collected by licenced bird ringers throughout Britain and Ireland from 1965 to 2017 and correlated these with publicly available temperature data and published, UK‐wide data on the abundance of a key predator, the sparrowhawk Accipiter nisus. We found highly significant, long‐term, UK‐wide decreases in winter body masses of adults and juveniles of all three species. We also found highly significant negative correlations between winter body mass and winter temperature, and between winter body mass and sparrowhawk abundance. Independent of these effects, body mass further correlated negatively with calendar year, suggesting that less well understood dynamic factors, such as supplementary feeding levels, may play a major role in determining population optimum body masses. Wing lengths of these birds also decreased, suggesting a hitherto unobserved large‐scale evolutionary adjustment of wing loading to the lower body mass. These findings provide crucial evidence of the ways in which species are adapting to climate change and other anthropogenic factors throughout Britain and Ireland. Such processes are likely to have widespread implications as the equilibria controlling evolutionary optima in species worldwide are upset by rapid, anthropogenic ecological changes. We used passerine bird biometric data from the British Trust for Ornithology database to investigate the effects of climate change and predation pressure on body mass and wing length of three garden bird species. We find that increased temperatures over the last fifty years have resulted in significant decreases in winter body mass of all three species, and that this is correlated with a decrease in wing lengths. [ABSTRACT FROM AUTHOR]

Aposematism is the combination of a primary signal with a secondary defence that predators must learn to associate with one another. However, variation in the level of defence, both within and between species, is very common. As secondary defences influence individual fitness, this variation in quality and quantity requires an evolutionary explanation, particularly as it may or may not correlate with variation in primary signals. The costs of defence production are expected to play a considerable role in generating this variation, yet studies of the cost of chemical defence have focused on species that sequester their defences, while studies in species that produce them de novo are scarce. Here we examine effects of resource availability on the production of chemical defences in female wood tiger moths Arctia plantaginis. This species produces defensive fluids when attacked, and advertises this protection with bright colours on its hindwings. Furthermore, the chemicals in these fluids are produced de novo. In order to establish if the production of this chemical protection is costly, and thus resource‐limited, we manipulated resource availability (i.e. food) during larval development and measured its subsequent effects on adult chemical defence. We presented defensive fluids from female moths to wild blue tits, in the absence of any visual cues, to determine their effectiveness against avian predators. Our results demonstrate that the defensive fluids produced by female moths repel birds, and that these defences require resource investment to produce. We found that moths that were resource‐limited during development had less effective chemical defences, despite producing the same volume of defensive fluids as the control moths. As a reduction in available resources negatively influences the effectiveness of the chemical defence, resource availability may explain the variation seen among individuals. [ABSTRACT FROM AUTHOR]

Urbanization results in novel ecosystems with unique challenges. These may lead to problems during song learning or development and could result in the singing of atypical songs. During studies of Mountain Chickadees (Poecile gambeli) and urbanization in British Columbia, Canada, we observed males singing atypical songs along an urbanization gradient. We found that eight of 78 males consistently sang atypical songs and the odds of singing atypical songs increased with urbanization. We explored several explanations including habitat quality, population density, and bioacoustics. Future studies investigating causes and consequences of atypical singing will clarify effects of urbanization on Mountain Chickadees. [ABSTRACT FROM AUTHOR]

Most bird species exhibit biparental care, but the type of care provided by each sex may differ substantially. In particular, during the incubation phase in passerines, females perform most or all of the incubation, while the male cares for the brood indirectly by feeding the female. However, detailed descriptions of this male investment during the incubation period are missing. Here, we quantitatively describe female nest attendance and male incubation feeding throughout the ~ 14‐day incubation period in a population of Eurasian Blue Tits Cyanistes caeruleus breeding in nestboxes. Males and females progressively increased their daily activity at the nest over the incubation period. The amount of day‐time incubation, measured as the proportion of the active day (time interval between first nestbox exit in the morning and last entry in the evening) a female spent inside the nestbox, varied between 52 and 60% with an average of 55% per day. The frequency of male incubation feeding varied between 0 and 74 times per day with an average of 12 feeds per day. Both male feeding rate and female nest attendance were highest in the morning and declined rapidly throughout the day. Females were more likely to be off the nest during the warmest periods (15–21 °C), as expected based on thermal needs of the developing embryos, but also during the coldest periods (2–5 °C), presumably due to the energetic needs of the female. This was despite the fact that males fed their females more often at the nest when ambient temperatures were low. Females that received more feeds incubated more and their off‐nest bouts were shorter after a feed. The observed variation in female incubation and in male feeding rate was not linked to individual age or to variation in measures of reproductive success. However, direct observations showed that in some pairs a substantial amount of feeding by males occurred outside the nestbox. This suggests that the true male investment might have been underestimated, here and in previous studies. [ABSTRACT FROM AUTHOR]