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Intraspecific variability in parasite virulence holds significant ecological and evolutionary implications as it can result in uneven costs incurred by individuals of a host species. Obligate brood parasites, birds that lay their eggs in the nest of another species and do not raise their own young, differ in interspecific virulence, as some species kill all host nestmates directly while other species do not. However, variation in the intraspecific virulence of a brood-parasitic species has rarely been investigated. One source of this variability could arise through sexual size dimorphism, because many brood-parasitic species are sexually dimorphic in size starting at the nestling stage, and nestling size often impacts competitive ability in the brood. Here, we investigated the sex-specific effects of nestling brood-parasitic brown-headed cowbirds, Molothrus ater , on one of their hosts, the prothonotary warbler, Protonotaria citrea. We predicted that larger male cowbird nestlings would cause host chicks to have lower survival and size and altered life history in the form of delayed fledging. Using experimentally parasitized broods, we found that although male brood-parasitic cowbird nestlings are heavier than females, there was no effect of cowbird sex on the survival, size or fledging phenology of the host nestlings. Furthermore, there were no differences in fledging phenology between the male and female cowbird chicks. Instead, we found that wing length, which was similar between the parasitic nestlings' sexes, was an important predictor for age and order of fledging. These findings show that the extent of development is critical for the timing of fledging of both parasitic and host species. Notably, the lack of effect of cowbird nestling sex on host chick survival and fledging suggests that the presence of a parasite is more influential for host nestlings than the size of parasites. • Nest-sharing obligate brood parasite chicks often outcompete smaller host nestmates. • Several brood-parasitic species display sexual size dimorphism at the chick stage. • Sex-specific virulence of larger male parasitic chicks could affect host demography. • Parasitic chick sex did not affect host chick survival or fledging. • Parasites decreased host chick survival and delayed fledging regardless of mass. [ABSTRACT FROM AUTHOR]

Parent–offspring communication mediates parental provisioning rates through nestling begging. Although begging can be energetically costly and it potentially attracts predators to the nest, it is critical to nestling survival. Parent-absent begging is a behavior that has similar costs as parent-present begging but lacks the immediate benefits and yet occurs among several passerine species. We recorded European Starling (Sturnus vulgaris) nestling begging vocalizations at 18 nest boxes on days 2, 7, 12, 17 of the nestling period and the day before fledging to examine whether parent-absent begging occurred, and if so, whether the frequency of parent-absent begging changed with nestling age. We predicted that, like other cavity-nesting species, European Starling nestlings would spend more time begging in the absence of parents as they aged. We found that the average proportion of time nestlings spent parent-absent begging increased significantly from days 2 and 7 to days 12 and 17, then declined significantly on the day prior to fledging. Offspring provisioning rates remained high on the day before fledging, when growth rates have slowed, and did not differ significantly from the early and middle stages of the nestling period. Parent-absent begging may function in advertising hunger. [ABSTRACT FROM AUTHOR]

Introduction: Multifarious selective pressures can interact to affect species' life history evolution, with predation and thermal exposure as selective pressures for nesting birds. Gray Vireos (Vireo vicinior) seemingly nest on the periphery of their nesting substrate because of lower predation rates, thereby increasing exposure to weather. We explored how nest placement and vegetation structure can be used to account for the increased weather exposure that Gray Vireos experience when nesting on the periphery of the nesting substrate to avoid predation. Methods: For each Gray Vireo nest, we placed temperature and light data loggers at three locations: at the nest site, at the opposite orientation of the nest within the nesting tree, and at the same orientation of the nest but in an adjacent tree. To measure nest orientation, we recorded the inverse compass azimuth (+/-1°) from the nest toward the trunk of the nesting tree, while accounting for declination. Nest temperatures and light exposure were compared across various dimensions of nest placement. Results: The orientation of nests was cooler than the opposite orientation in the mornings and in the late afternoons. When nests were placed in hotter orientations (e.g., south- or west-facing), nests surrounded by more foliage or placed closer to the interior of trees could compensate for the increased exposure. Discussion: Our findings suggest Gray Vireos accounted for the increased thermal exposure that comes from predator avoidance by using secondary dimensions of nest placement. Specifically, nests could be placed in orientations with cooler temperatures or in hotter orientations with greater shade potential. These results highlight how the interactive selection pressures of predation risk and microclimate can be tiered and shape life-history characteristics of birds. [ABSTRACT FROM AUTHOR]

The parent–offspring conflict in avian species encompasses resource allocation and a balance necessary for survival for both parties. Parental investment is modulated according to various factors, among which begging is important. Endogenous hormones, particularly corticosterone (CORT), play a role in modulating begging behavior. However, most studies on hormonal regulation of begging behavior induced elevated hormone levels in the offspring through feeding or injections, thus, limiting our knowledge of the evolution of the parent–offspring conflict under natural conditions. In this study, we aimed to identify the key signals that parents respond to during interactions with their nestlings in the wild, considering factors such as endogenous hormone CORT, nestling age, and brood size, which may affect nestling begging behavior. Begging performance was evaluated by measuring the begging frequency and score of the red‐whiskered bulbul (Pycnonotus jocosus), along with assessing CORT levels in feathers. CORT levels were significantly correlated with both the begging frequency and score of nestlings, while variables such as body mass and tarsus length did not influence parental feeding frequency. Additionally, factors such as the number of nestlings (brood size), age, and begging frequency were predictors of parental feeding frequency. Our findings indicate that begging frequency, nestling age, and brood size are signals that help navigate the intricacies of the parent–offspring conflict and that parents may rely on these key signals from the range of begging cues exhibited by nestlings to adjust their feeding strategies. [ABSTRACT FROM AUTHOR]

The avian vampire fly is an invasive species on the Galapagos Islands, where its hematophagous larvae utilize nestling birds as hosts. It poses a serious threat to populations and species of Darwin finches and other avian species. Prior studies suggest that the avian vampire fly larvae develop more rapidly in nests of small tree finches compared to sympatric green warbler finch nests. Here we investigate factors that may differentially influence larval growth in the two host species, including nest microclimate and nestling diet. We collected nest base temperature and humidity data as proxies for nest microclimate. As indicators of dietary composition and quality, we measured stable isotope δ13C and δ15N composition of nestling blood, used the C:N ratios as an indicator of relative protein content, and assessed the amino acid composition of the blood. The hematophagous larvae living off nestling blood were analyzed for the same parameters except amino acid composition. The effect of nest base humidity on nest base temperature significantly depended on bird species: at low humidity levels nest base temperature was higher in the small tree finch, and declined in both species as nest base humidity increased, which suggests higher stable heat capacity of small tree finch nests. The effect of age group based on the predicted onset of thermoregulation was marginally significant. Nest base temperatures were significantly higher in small tree finch nests during the predicted female brooding period before fully effective thermoregulation. Stable isotope δ13C levels were significantly higher in the blood of small tree finch nestlings compared to warbler finch nestlings, suggesting a difference in nestling food composition and source, while. δ15N levels were similar. The C:N ratios and amino acid composition of nestling blood were not significantly different between the two species, suggesting similar dietary quality. Thus, the faster development of larvae in small tree finch nests may be due to higher nest base temperatures during the early nestling phase rather than host blood quality parameters. [ABSTRACT FROM AUTHOR]

This document is a selection of poems titled "Seasons At The Patch" by Kerry Shawn Keys. The poems explore themes of nature, solitude, and reflection. The poet describes his experiences in a lettuce patch, his interactions with birds and animals, and his musings on life and mortality. The poems evoke a sense of tranquility and contemplation. [Extracted from the article]

Explaining variation in individual fitness is a key goal in evolutionary biology. Recently, telomeres, repeating DNA sequences capping chromosome ends, have gained attention as a biomarker for body state, physiological costs, and senescence. Existing research has provided mixed evidence for whether telomere length correlates with fitness, including survival and reproductive output. Moreover, few studies have examined how the rate of change in telomere length correlates with fitness in wild populations. Here, we intensively monitored an insular population of house sparrows, and collected longitudinal telomere and life history data (16 years, 1225 individuals). We tested whether telomere length and its rate of change predict fitness measures, namely survival, lifespan and annual and lifetime reproductive effort and success. Telomere length positively predicted short‐term survival, independent of age, but did not predict lifespan, suggesting either a diminishing telomere length—survival correlation with age or other extrinsic factors of mortality. The positive association of telomere length with survival translated into reproductive benefits, as birds with longer telomeres produced more genetic recruits, hatchlings and reared more fledglings over their lifetime. In contrast, there was no association between telomere dynamics and annual reproductive output, suggesting telomere dynamics might not reflect the costs of reproduction in this population, potentially masked by variation in individual quality. The rate of change of telomere length did not correlate with neither lifespan nor lifetime reproductive success. Our results provide further evidence that telomere length correlates with fitness, and contribute to our understanding of the selection on, and evolution of, telomere dynamics. [ABSTRACT FROM AUTHOR]

The house-farmed edible-nest swiftlet (Aerodramus sp.) is monogamous, produces nests from hardened saliva, and uses echolocation to navigate in the darkness. Most previous studies have focused on swiftlet nest building and incubation behaviour, but nestling provisioning behaviour, crucial for the survival of offspring during the breeding season, remains unclear. This study examined the nestling provisioning behaviour of house-farmed swiftlets at a swiftlet house farm in central Peninsular Malaysia. Complete focal video footage of the provisioning phase of swiftlets was analysed in detail. The overall feeding period decreased as the chick grew older. The parents alternately visited their nest 6-14 times a day from dawn to dusk to feed the nestling. The peak of this activity was from 07:00 to 08:00 and between 19:00 and 20:00. Nestling provisioning behaviour differed between pairs. The egg-laying interval of parents with two chicks was longer and affected the development of the second chick since the first chick more successfully competed for food and grew larger in size. Most second chicks with a smaller body size did not survive, because of being either purposely or unintentionally eliminated by the parents or sibling. The smaller-sized second chicks that survived took a longer time to fledge than the first chick; therefore, parents had to increase their foraging effort to ensure the survival of their chick until fledging. These behaviours may be influenced by physiological factors, such as age, experience, individual fitness, and abiotic factors, such as weather and food resources; therefore, different parental strategies may be established during the nestling provisioning phase. [ABSTRACT FROM AUTHOR]

Gape‐limited predators (e.g., snakes, many fish) are not generally expected to pose a predation threat to prey that are too large for them to swallow. However, the extent to which snakes predate on prey that exceed their gape limitation remains largely unknown. We conducted the first study to investigate the influence of both prey and predator sizes on the frequency of ingestion success by snakes in a natural system. We combined survival monitoring of an avian prey species (Aplonis opaca) via radio‐telemetry with a survey of the size distribution of their major predator (Boiga irregularis) on Guam. This allowed us to assess (1) the frequency of unsuccessful ingestion by the predator, (2) whether the size of the prey predicts ingestion success, (3) whether the size of the predator predicts ingestion success, and (4) the relationship between prey and predator sizes in successful ingestion attempts. We found that nearly half (47.95%) of ingestion attempts by snakes on fledgling birds were unsuccessful, and no instances where unsuccessful ingestion caused the mortality of the snake. Attempts to consume smaller fledglings were as likely to be unsuccessful as attempts to swallow larger fledglings. However, snakes that successfully ingested fledglings were among the largest snakes in the population, and larger than average conspecifics attracted to endothermic prey. The smallest snakes that successfully ingested fledglings attained remarkably high relative prey mass values for their species, consuming prey weighing up to 79.9% of their own mass. Our study indicates that B. irregularis routinely predate prey that are too large for them to successfully ingest, which causes mortality to the prey but poses little risk to the predator. The potential reward for snakes in consuming oversized prey may outweigh the inherent risks, while instances of predation that do not result in consumption may have considerable impacts on prey populations. [ABSTRACT FROM AUTHOR]

For most birds that exhibit delayed dispersal (remaining on the natal territory rather than dispersing to seek a breeding opportunity), siblings appear free to stay or leave the natal area. However, in rare cases, delaying dispersal is determined via conflict among siblings, with the dominant individual remaining on the natal territory. We used radio-tracking to examine brood reduction, and subsequent juvenile survival, of first-year Canada Jays (Perisoreus canadensis) in Algonquin Provincial Park, Ontario, Canada. Soon after juveniles become nutritionally independent, intra-brood struggles lead to one "dominant juvenile" remaining on the natal territory after permanently expelling the subordinate siblings ("ejectees"). Males in above-average condition when nestlings were the most likely to become the dominant juveniles and females did so only when broods were all-female at the time of the expulsion. Dominant juveniles were much more likely to survive their first summer compared to ejectees (survival probabilities = 0.84 and 0.45, respectively), suggesting that ejectees are especially vulnerable to mortality risk in the critical interval between their expulsion from the natal territory and their settlement on a new territory. However, if ejectees lived to autumn, they had only a slightly lower probability of first-winter survival (0.73) than dominant juveniles (0.85). These results suggest that the survival advantage gained by dominant juveniles is greatest during the first summer after hatching, with a much smaller difference over the first winter after ejectees have settled on non-natal territories. Our work provides insight into potential evolutionary and ecological mechanisms driving social dominance hierarchies in wild birds. [ABSTRACT FROM AUTHOR]

The red-crested cardinal (Paroaria coronata) is an emblematic bird of the southern cone of South America that has been traditionally classified as sexually monomorphic and monochromatic from a human visual perspective. Using reflectance spectrometry, we analyzed sexual differences in the coloration of the red head plumage patch of adult wild red-crested cardinals in central-eastern Argentina. We also described sexual differences in body size and determined the onset of morphometric differences by comparing morphological measurements and growth rate between male and female nestlings. Adult males had on average longer wings and brighter red plumage relative to females. Similar to adults, nestlings were sexually dimorphic at fledging and presented sex-specific growth curves. Male nestlings grew faster and reached a larger size at the fledging time. Both for adults and nestlings, wing length was the trait that expressed sexual differences in body size. Our results are consistent with recent studies in passerines indicating that many birds considered sexually monochromatic are likely dichromatic when considering avian visual capacities. This study allows the red-crested cardinal to be re-categorized as sexually dimorphic and dichromatic. [ABSTRACT FROM AUTHOR]

Symptoms of illness offer insights into an organism's condition, altering social signals that affect others' behavior. Nestling birds employ begging signals to solicit parental care, but the extent to which begging reflects nestling health beyond hunger remains controversial. We investigated how experimentally induced changes in health affect begging signals in spotless starling (Sturnus unicolor) nestlings. To alter health status, we challenged nestlings by injecting lipopolysaccharide (LPS) -an antigen that elicits an immune response- or a control substance (PBS) and observed begging behavior under controlled food deprivation conditions. LPS-treated nestlings exhibited delayed gaping, reduced stretching, and less begging time compared to control nestlings. Moreover, LPS-treated nestlings produced calls with higher spectral entropy, particularly when deprived of food for longer. Our findings indicate that begging signals are sensitive to induced sickness. However, addressing mechanistic issues is crucial for effectively testing whether begging reflects nestling condition as a signal of quality in future experimental setups. Significance statement: This study demonstrates that begging signals of nestling birds reflect their health status beyond mere hunger, addressing a longstanding debate in behavioral ecology. By experimentally inducing sickness in spotless starling nestlings, we reveal that changes in health affect postural and acoustic begging behavior. However, ascertaining the implications of this finding for current begging theory proves challenging without information about the causal mechanisms underlying sickness behavior. Understanding how nestlings communicate their condition to parents through begging signals holds implications for comprehending parental care dynamics and lays the groundwork for future research in parent-offspring communication. [ABSTRACT FROM AUTHOR]

Parental care in birds encompasses many behaviours, from selecting nest‐sites and supplying eggs with nutrients to incubation and offspring provisioning. Unlike the early stages, where offspring are passive receivers of care, chicks actively solicit care after hatching. This may lead to either parent–offspring conflict or coadaptation, or both, if there is genetic variance in both parental provisioning and offspring begging. However, given that parental provisioning is highly responsive to brood size and age, its genetic determination is questioned. In this study, we used a multigenerational pedigree and 11 years of provisioning data to dissect the variation in this trait in the Collared Flycatcher Ficedula albicollis, and to examine whether offspring provisioning changes as parents age. We found that the parental provisioning rate was weakly repeatable (r = 0.088–0.213) and heritable (h2 = 0.052–0.158). Higher values were obtained when calculated based on within‐individual averages rather than individual measurements, and after adjusting for fixed effects. Older parents provisioned offspring at a lower frequency than younger ones. An additive genetic component in provisioning indicates potential for the evolution of parental care, parent–offspring coadaptation and indirect genetic effects on offspring traits. Future studies employing new tracking technologies, including accelerometers, radars and radio‐frequency identification readers, may help to determine whether senescence or increased experience causes the lower rate of offspring provisioning observed in older parents. [ABSTRACT FROM AUTHOR]

In many bird species, nestling begging signals play a key role in the interaction between parents and their offspring during development. The information conveyed by begging calls can be disrupted by anthropogenic noise, which is one of the major threats to biodiversity in increasingly urbanized landscapes. Here, we describe the developmental change in acoustic structure of begging calls in nestling Eurasian Blue Tits Cyanistes caeruleus; begging calls are pure‐tone, low‐frequency, soft calls during the first days of development and gradually turn into white‐noise, hiss‐like, powerful calls of broadband frequency. This strong developmental variation highlights the importance of an extended sampling scheme in developmental studies. Furthermore, we pinpoint two phases where begging calls could be most vulnerable to masking by anthropogenic noise. First, during early development, begging calls are very soft and low‐pitched, closer to high‐intensity noise bands of traffic noise. Secondly, around day 11, begging calls show reduced tonality, which implies higher degradation, and relatively low amplitude, which implies reduced signal range. We encourage future research to describe acoustic development of begging calls in other species, to provide a robust foundation that will make noise mitigation policies more effective. [ABSTRACT FROM AUTHOR]

The size and growth patterns of nestling birds are key determinants of their survival up to fledging and long‐term fitness. However, because traits such as feathers, skeleton and body mass can follow different developmental trajectories, our understanding of the impact of adverse weather on development requires insights into trait‐specific sensitive developmental windows. We analysed data from nestling Alpine swifts in Switzerland measured throughout growth up to the age of 50 days (i.e. fledging between 50 and 70 days), for wing length and body mass (2693 nestlings in 25 years) and sternum length (2447 nestlings in 22 years). We show that the sensitive developmental windows for wing and sternum length corresponded to the periods of trait‐specific peak growth, which span almost the whole developmental period for wings and the first half for the sternum. Adverse weather conditions during these periods slowed down growth and reduced size. Although nestling body mass at 50 days showed the greatest inter‐individual variation, this was explained by weather in the two days before measurement rather than during peak growth. Interestingly, the relationship between temperature and body mass was not linear, and the initial sharp increase in body mass associated with the increase in temperature was followed by a moderate drop on hot days, likely linked to heat stress. Nestlings experiencing adverse weather conditions during wing growth had lower survival rates up to fledging and fledged at later ages, presumably to compensate for slower wing growth. Overall, our results suggest that measures of feather growth and, to some extent, skeletal growth best capture the consequences of adverse weather conditions throughout the whole development of offspring, while body mass better reflects the short, instantaneous effects of weather conditions on their body reserves (i.e. energy depletion vs. storage in unfavourable vs. favourable conditions). [ABSTRACT FROM AUTHOR]

The early life movement patterns of long-lived, large raptors, such as the white-tailed eagle (Haliaeetus albicilla), remain largely unexplored. In this study, we have tracked 22 individuals of white-tailed eagles hatched in Denmark to investigate key parameters, including survival rates, causes of death, nest site fidelity, geographical distribution, and dispersal behaviors. Our analyses are based on approximately 340,000 GPS/GSM telemetry positions from the 22 individuals. We found that survival rates were lower in the first year of life, especially among females, but increased in subsequent years. The primary causes of death were wind turbine collisions and avian influenza. Movement analyses revealed that juvenile eagles frequented nest sites in August and September, with females showing earlier exploratory flights and dispersal. Both males and females spent most of their first calendar year near their nest sites. In the second calendar year, a significant proportion of their time was spent at well-known white-tailed eagle resting areas in Denmark, as well as visiting neighboring countries. Notably, one individual set a new distance record for a Danish GPS-tagged white-tailed eagle, venturing at least 1750 km away from its nest site to visit Sweden, Finland, Russia, and Norway. Our results, indicating that juvenile white-tailed eagles continue to utilize nest sites into September, suggest an extension of the recommended time period for nest protection zones provided by BirdLife Denmark (DOF). [ABSTRACT FROM AUTHOR]

The allocation of parental care behaviors between the sexes may be influenced by the species' mating system, degree of sexual size dimorphism, and predictability of food resources. Biparental care (i.e., both parents contributing to raising young) has been documented in raptors, including those with minimal sexual size dimorphism and/or whose food resources are unpredictable in time (e.g., scavengers). The Chimango Caracara (Milvago chimango) is a common raptor with slight sexual size dimorphism and a scavenging lifestyle. During two breeding seasons, we performed focal observations at nests in a Chimango Caracara colony in central Argentina to assess the division of labor between the sexes. For males and females separately, we measured the time spent incubating and brooding, and the food delivery rate to nestlings; then we used GLMMs to assess various factors that may influence these behaviors, including parental sex, time of day, clutch or brood size, and nestlings' age. We used GLMMs to test the influence of time spent brooding and food delivery rate (both parents combined for these variables) on nest success and productivity. Although both sexes contributed to all parental care activities, females spent more time incubating and brooding than males. Brooding time decreased as nestlings aged. Food delivery rate did not differ between the sexes. Food delivery rate was higher during the middle of nestlings' development but declined thereafter. Nest success and productivity were higher at nests with higher food delivery rates. Adults spent more time incubating and brooding during morning and midday, and food delivery rate was higher during the afternoon. La división de roles entre sexos en el cuidado parental puede estar determinada por el sistema de apareamiento, el grado de dimorfismo sexual de tamaño y la predictibilidad de los recursos alimenticios. El cuidado biparental, en el que ambos progenitores contribuyen a la crianza de la descendencia, se ha documentado en rapaces, incluso en aquellas con escaso o nulo dimorfismo sexual de tamaño y/o cuyos recursos alimenticios son impredecibles en el tiempo, por ejemplo, las aves carroñeras. Milvago chimango es un ave rapaz común que presenta un ligero dimorfismo sexual de tamaño y tiene un estilo de vida carroñero. Durante dos temporadas reproductivas, se realizaron observaciones focales en los nidos de una colonia de M. chimango en el centro de Argentina para evaluar la división de tareas entre sexos. Para machos y hembras por separado, medimos el tiempo dedicado a la incubación y a la cría, y la tasa de aporte de alimento a los polluelos. Utilizamos modelos lineales generalizados mixtos (GLMM por sus siglas en inglés) para evaluar diversos factores que pueden influir en estos comportamientos, incluyendo el sexo de los progenitores, la hora del día, el tamaño de la puesta o la nidada, y la edad de los polluelos. Se utilizaron GLMM para comprobar la influencia del tiempo de cría y la tasa de aporte de alimento (de ambos adultos combinados) en el éxito y la productividad del nido. Aunque ambos sexos contribuyeron a todas las actividades de cuidado parental, las hembras pasaron más tiempo incubando y criando que los machos. El tiempo de cría disminuyó a medida que aumentaba la edad de los polluelos. No encontramos diferencias en la tasa de aporte de alimento entre sexos. La tasa de aporte de alimento fue mayor en la mitad del periodo de desarrollo del polluelo, pero disminuyó a partir de entonces. El éxito y la productividad de los nidos fueron mayores en los nidos con tasas de alimentación más elevadas. Los adultos pasaron un mayor porcentaje de tiempo incubando y cuidando a los polluelos durante la mañana y el mediodía, y la tasa de aporte de alimento fue mayor durante la tarde. [Traducción de los autores editada] [ABSTRACT FROM AUTHOR]

Urban areas—characterized by high human densities, buildings, and impermeable surfaces—are increasing globally and represent a leading threat to wildlife by drastically altering the natural resources wildlife species are accustomed to. Prior work suggests that living in urban habitats can cause wildlife to show increased cholesterol levels. In biomedical research, elevated cholesterol is linked to disease, but the consequence of elevated cholesterol in wildlife remains unclear. We measured total cholesterol in European Starlings (Sturnus vulgaris), an urban-adapted species, across an urban and a rural site. We asked: (1) Do urban starlings have elevated cholesterol? and (2) Is elevated cholesterol correlated to negative physiological outcomes in starlings? We found that nestlings from the urban (N = 16) and rural (N = 98) sites showed similar cholesterol, but adult starlings from the urban (N = 5) habitat showed elevated cholesterol compared to rural (N = 36) birds. However, elevated cholesterol was not correlated with increased oxidative damage to DNA, lowered body condition, or increased baseline glucocorticoids across any age class, suggesting that elevated cholesterol did not come at a physiological cost to starlings. Future work is needed to explore what mechanism(s) drive variation in cholesterol across urban and rural birds, as well as whether any long-term consequences of elevated cholesterol exist. Les zones urbaines, caractérisées par de densités humaines élevées et des bâtiments et des surfaces imperméables, augmentent au niveau mondial et représentent une menace majeure pour la faune sauvage en modifiant radicalement les ressources naturelles auxquelles les espèces sont habituées. Des travaux antérieurs suggèrent que vivre dans des habitats urbains peut entraîner une augmentation des taux de cholestérol chez la faune sauvage. Dans la recherche biomédicale, un taux de cholestérol élevé est lié à la maladie, mais les conséquences d'un taux de cholestérol élevé chez la faune sauvage ne sont pas claires. Nous mesurâmes le cholestérol total chez l'étourneau sansonnet (Sturnus vulgaris), une espèce adaptée à la ville, sur un site urbain et un site rural. Nous demandâmes: (1) est-ce que les étourneaux sansonnets urbains ont un taux de cholestérol élevé? et (2) est-ce qu'un taux de cholestérol élevé est corrélé à des résultats physiologiques négatifs chez les étourneaux? Nous constatâmes que les oisillons des sites urbains (N = 16) et ruraux (N = 98) présentaient un taux de cholestérol similaire, mais que les étourneaux adultes de l'habitat urbain (N = 5) présentaient un taux de cholestérol élevé par rapport aux étourneaux adultes de l'habitat rural (N = 36). Cependant, un taux de cholestérol élevé n'était pas corrélé à une augmentation des dommages oxydatifs de l'ADN, à une condition corporelle réduite ou à une augmentation des glucocorticoïdes de base dans toutes les classes d'âge, ce qui suggère qu'un taux de cholestérol élevé n'a pas eu de coût physiologique pour les étourneaux. Des travaux futurs sont nécessaires pour explorer le(s) mécanisme(s) qui déterminent la variation du cholestérol chez les oiseaux urbains et ruraux, ainsi que pour déterminer s'il existe des conséquences à long terme d'un taux de cholestérol élevé. Mots-clés: condition corporelle, dommage à l'ADN, glucocorticoïdes, urbanisation. [ABSTRACT FROM AUTHOR]

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The article discusses the diversity of parental care in animals, focusing on the provision of mucus as a form of nourishment for offspring. While maternal care through lactation is common in mammals, there is growing evidence that nonmammal vertebrates, such as fish and amphibians, can also nurture their young with milk-like substances. The study specifically highlights the discovery of mucus provisioning as "milk" in a species of caecilian, a less-studied amphibian. The researchers provide evidence of this behavior and discuss its implications for understanding the evolution of parental care across different animal taxa. [Extracted from the article]

Background: Exploring the dynamics of gut microbiome colonisation during early-life stages is important for understanding the potential impact of microbes on host development and fitness. Evidence from model organisms suggests a crucial early-life phase when shifts in gut microbiota can lead to immune dysregulation and reduced host condition. However, our understanding of gut microbiota colonisation in long-lived vertebrates, especially during early development, remains limited. We therefore used a wild population of common buzzard nestlings (Buteo buteo) to investigate connections between the early-life gut microbiota colonisation, environmental and host factors. Results: We targeted both bacterial and eukaryotic microbiota using the 16S and 28S rRNA genes. We sampled the individuals during early developmental stages in a longitudinal design. Our data revealed that age significantly affected microbial diversity and composition. Nest environment was a notable predictor of microbiota composition, with particularly eukaryotic communities differing between habitats occupied by the hosts. Nestling condition and infection with the blood parasite Leucocytozoon predicted microbial community composition. Conclusion: Our findings emphasise the importance of studying microbiome dynamics to capture changes occurring during ontogeny. They highlight the role of microbial communities in reflecting host health and the importance of the nest environment for the developing nestling microbiome. Overall, this study contributes to understanding the complex interplay between microbial communities, host factors, and environmental variables, and sheds light on the ecological processes governing gut microbial colonisation during early-life stages. [ABSTRACT FROM AUTHOR]

The temperature experienced by avian embryos during development has important impacts on their growth and post‐hatching phenotypes. Ambient temperature can directly affect avian nest temperature and indirectly affect it through its impact on parental incubation behaviours. Because the nests of uniparental incubators are usually left unattended more frequently than the nests of biparental incubators whose nests can be attended by another bird when one bird leaves the nest, we predict that the effect of ambient temperature on nest temperature and thus on embryonic development (specifically, incubation period length and hatching success) and post‐hatching phenotype (i.e. potential carry‐over effect on nestling body mass and condition) should be greater in uniparental incubators than in biparental incubators. To test this prediction, we studied two congeneric species, the biparental incubating black‐throated tits Aegithalos concinnus and the uniparental incubating silver‐throated tits A.glaucogularis. We found that although the embryos of the two species both developed faster (shorter incubation period length) when ambient temperature was higher, the slope was significantly greater for silver‐throated tits than for black‐throated tits, consistent with our prediction of a greater effect of ambient temperature on embryonic development in silver‐throated tits. However, the result was not due to a greater effect of ambient temperature on nest temperature, because nest temperatures of the two species had positive relationships with ambient temperature in a similar way. Therefore, it implies a greater response of silver‐throated tit embryos to temperature change. In addition, ambient temperature during the incubation stage did not affect either hatching success or nestling body mass and condition in both species. Although our predictions were not fully supported, our findings highlight the different responses of embryonic development to environmental changes between a uniparental incubator and a biparental incubator, and suggest further research to explore the mechanisms. [ABSTRACT FROM AUTHOR]

Predators affect the survival of developing young by eating them. More recently, the fear of being eaten has been uncovered as a powerful driver of offspring survival reducing recruited offspring numbers by 53%, but the mechanisms driving these effects are not well understood.We exposed song sparrows to predator or non‐predator playbacks throughout three breeding seasons. We followed offspring as eggs through development and into maturity. We quantified the repercussions of being reared in a fearful environment on body (fat, mass, size) and physiological condition using 12 different measures categorized into six systems (oxygen carrying capacity, energy reserves, immune function, antioxidant protection, oxidative stress/damage, glucocorticoids). We further tracked offspring survival in the nest to maturity and determined which measures of condition significantly predicted survival.We report that fear of predators affected offspring condition at all stages of life, with survival consequences. Predator‐playback offspring hatched from heavier eggs (8%) but quickly lost this advantage and never regained it. Nestlings reared by 'frightened' parents were as heavy and much leaner than non‐predator playback nestlings. This pattern extended throughout development into maturity where offspring reared by frightened parents were up to 31% leaner and 5% lighter. Predator‐playback nestlings also were evidently in poorer physiological condition, having shorter telomeres, while late dependency stage fledglings carried relatively less uric acid and more haptoglobin perhaps indicative of chronic susceptibility to infection.Only body condition (mass and fat) predicted survival during peak mortality periods (nestling and early fledging), with the leanest lightest offspring from the predator‐playback treatment being least likely to survive. Thereafter, mass predicted survival irrespective of playback treatment. Similarly, at this later stage, offspring with less telomere loss and high uric acid levels survived best regardless of playback group.Our findings reveal that fear of predators is a potent form of early life adversity which persistently alters the condition of offspring affecting early stage survival and the 'quality' of the survivors throughout their life. Development is fuelled by food and fear‐induced reductions in parental provisioning at the earliest stages likely instigated these effects, with consequences on the population growth rate. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

A greater knowledge of the intrinsic and extrinsic factors of animal home range (HR) formation can help us to understand the fundamental biological issues underlying, for instance, movement patterns, habitat selection and survival. However, very little is known about the HRs of birds of prey fledglings, even though the post-fledging phase is recognised as crucial due to the high mortality of juvenile birds. We radio-tracked 138 Tengmalm's owl (Aegolius funereus) fledglings from 43 broods to determine their HRs during the post-fledging dependence period and to investigate the factors affecting their sizes. The study was conducted during four breeding seasons in Czechia and two seasons in Finland. The mean fledglings' HR size calculated according to the 95% IID Kernel Density Estimation method was 63.7 ± 43.9 ha (± SD; n = 71) during nocturnal activity and 52.0 ± 46.1 ha (n = 63) during diurnal roosting. The sizes of both nocturnal activity and diurnal roosting HRs increased with the longer individual duration of the post-fledging dependence period and also the higher rank of hatching within a brood. Diurnal roosting HRs were two times smaller in the Czech site, probably because of the very limited number of dense forest patches suitable for roosting as a legacy of the air pollution calamity in the 1970s, during which most coniferous stands died out. There was no difference in the size of nocturnal activity HR between the two study areas, although they differed markedly in terms of night length, altitude, weather, and forest age, structure and composition. This suggests that environmental factors are not decisive in determining the size of nocturnal activity HRs of Tengmalm's owl fledglings. Since the diurnal HRs always occurred within the area of the nocturnal HRs, we suggest that conservation of the densest and preferably oldest forest stands within the areas of the study species occurrence may offer straightforward conservation tasks for protecting Tengmalm's owl fledglings and also other species. [ABSTRACT FROM AUTHOR]

The article focuses on the impact of extreme weather events, particularly a heat dome in 2021, on Barn Owl productivity in southwestern Canada. Topics include the heat dome's effects on young birds, the admission of heat-stressed raptors to a rehabilitation facility, and the significance of implementing conservation measures to protect Barn Owls from the increasing frequency of extreme weather events and other threats.

This editorial discusses the lack of representation of women in the field of coevolution and highlights the contributions that women have made to the field. It acknowledges the historical biases that have led to a male-dominated research landscape and emphasizes the importance of including diverse perspectives in scientific research. The editorial features a collection of articles written by women that explore various aspects of coevolution, such as symbiosis, microbial partnerships, and plant-pollinator interactions. The authors hope that this collection will inspire and support women in science. The article also addresses the issue of conflict of interest in research and emphasizes that the views expressed are solely those of the authors and do not necessarily represent their affiliated organizations or the publisher. Relevant references to other scientific studies and publications are provided. [Extracted from the article]

Conservation breeding programs are an increasingly important tool to help supplement declining wild populations, but captive-bred animals generally do not survive well post-release. Early life in captivity has the potential to influence growth and development, with impacts carrying over to affect survival. Understanding carryover effects of captivity and consequences on survival is critically important for conservation efforts globally but remains poorly understood. We examined the relationship between early-life environment, physical condition, and juvenile survival of wild and captive-bred critically endangered orange-bellied parrots (Neophema chrysogaster). Using nestling growth models, we calculated a body condition index for 1,039 wild and captive-bred orange-bellied parrots hatched over six breeding seasons. Nestling body condition varied with year, provenance, and brood position. Wild nestlings had consistently higher body condition than captive-bred nestlings, and first-hatched nestlings were typically heavier than later hatched siblings. We then investigated first-year survival for 298 wild-born and captive-bred released parrots in the wild. Overall, first-year survival was 27.5%, and individual body condition was more influential than provenance in predicting survival. Our findings could be used to aid the selection of individuals for release that have the best prospects of surviving in the wild. This study addresses important questions about the post-release fitness of captive-bred animals, and our metric of assessing physical condition provides a straightforward tool for other conservation breeding programs to adapt management techniques to improve survival outcomes. [ABSTRACT FROM AUTHOR]

In recent years, temperatures have increased globally, and nestlings of many bird species are likely regularly exposed to increased temperatures both pre‐ and post‐natally. Even small increases in nest temperature during incubation affect offspring growth and survival in a variety of species, one cause of which is thought to be increased production of pro‐oxidants in embryos and nestlings. Defences marshalled in response to this oxidative stress could, in turn, result in trade‐offs that lead to reduced survival or growth. If so, any downstream negative effects on nestlings of increased ambient temperatures during incubation could be counteracted by increasing their antioxidant intake. We predicted, therefore, that dietary supplements of an antioxidant would reduce or eliminate any detrimental effects on nestling growth and survival of experimentally increased nest temperature during the incubation period. We employed a split‐brood design in which we increased the nest temperature of entire clutches and, after hatching, provided dietary supplements of the antioxidant vitamin E to half of the nestlings within broods. We also recorded female incubation and provisioning behaviour to control for the possibility that heating nests might also influence maternal behaviour. There was a significant interaction between nestbox heating treatment and vitamin E treatment in their effect on nestling mass, a trait that is positively correlated with survival and future reproductive success in the study population. Vitamin E supplementation promoted increased nestling mass in heated nests, whereas it had the opposite effect in control nests but these effects were weak. Heating significantly affected female incubation behaviour, with females in heated nestboxes investing less in incubation than those in unheated boxes. These results suggest that within at least some range of expected increased ambient temperatures during the 21st century, effects of climate change on nestling bird development can be mitigated by adjustments in female incubation behaviour. [ABSTRACT FROM AUTHOR]

"The Albatross and the Ethnographer" is a document that explores the unique relationship between the protagonist and Lola, a wandering albatross, on Bird Island in the Southern Atlantic Ocean. The protagonist communicates with Lola through nonverbal means, highlighting the connection between different species. The document also delves into the significance of beauty in advocating for change, the mating rituals and partnerships of albatrosses, and the challenges they face due to climate change. It discusses the use of tracking devices by scientists to study albatross behavior and the threats they encounter. The document concludes with a powerful dream illustrating the devastating impact of human activities on albatrosses and other marine life. It is a journal entry written by an outsider who encounters a scientist studying plastic pollution's effects on sea turtles and albatrosses. The scientist shares the story of Lola, an albatross who tragically died entangled in fishing line, leaving her mate Seth to grieve. The text also references Samuel Taylor Coleridge's poem "The Rime of the Ancient Mariner," which tells the tale of a sailor cursed after killing an albatross. The journal entry ends with a discussion of Earthseed, a belief system that embraces change as an inherent part of the universe, and the concept of Earthseed Revolutionaries working towards positive transformation. [Extracted from the article]

Mimicry is widespread in the animal kingdom, with sound/or acoustic mimicry remaining less studied than visual mimicry. Some incubating female birds in cavity nests emit a hissing call when encountering nest predators, which sounds like a snake hiss and serves to scare off predators; this is considered a form of acoustic Batesian mimicry. Similarly, for nearly defenseless bird nestlings, using a hissing call to scare off predators can improve their survival; however, few studies have reported nestlings making hissing calls. In this study, we report on the hissing calls of nestlings of the open-nesting zitting cisticola (Cisticola juncidis) and compare their hissing calls with those of other animals, such as birds and snakes. The results showed that the hissing calls of C. juncidis nestlings closely approximate the sounds of snakes. This study is the first report of sounds that mimic snakes made by the nestlings of any open-nesting passerine bird species. [ABSTRACT FROM AUTHOR]

Some theoretical models predict that nestling begging must be a costly activity to transmit reliable information to parents about offspring hunger. One candidate cost is oxidative stress, which could impair growth or immune function. This hypothesis predicts that nestlings in a poor oxidative status should pay higher costs for a given amount of begging, hence beg at lower rates for a similar degree of hunger. To test this prediction, we experimentally induced a transient alteration of the oxidative status of Barn Swallow (Hirundo rustica) nestlings by administering them either a single dose of a pro-oxidant substance (BSO) or an antioxidant (vitamin E), and recorded their begging behaviour. Chicks treated with vitamin E increased their begging rates in the hours following treatment. However, and contrary to prediction, BSO nestlings did not decrease begging compared to controls. These inconsistent results are difficult to explain by the hypothesis that begging performance is mediated by the oxidative status of nestlings because chicks with an impaired oxidative status (the BSO group) begged the same as controls. Alternatively, vitamin E may alleviate the inhibitory effects on begging of stress responses mediated by glucocorticoids. This study suggests that oxidative costs of begging are minor or absent in this species. Future studies should consider alternative explanations for an association between oxidative status, antioxidant supplementation and begging behaviour, particularly those involving glucocorticoids. [ABSTRACT FROM AUTHOR]

Urban areas present thermal environments that may be challenging for altricial nestlings, particularly in early development. We aimed to evaluate whether altricial Bewick's Wren (Thryomanes bewickii) nestlings experienced thermal stress in the nest-box during the early- and late-developmental stages. We determined the thermoregulatory set point (thermoneutral range) of nestlings by measuring cloacal body temperature of five nestlings from three nests, every other day from hatching until they fledged. We also exposed nestlings to a thermal challenge from day 5 to determine the age of endothermy. We used dataloggers to determine the thermal environment inside and outside of three nest-boxes, and obtained the operative temperature for nestlings in the nest-box using 3D-printed models corresponding to early- and late-developmental stages. Ambient temperatures inside the nest box fluctuated throughout the day, being colder at night just before daybreak (min range: 10.4°C - 10.8°C), and hotter in the afternoon (max range: 25.8°C - 28.3°C). However, temperatures in the nest-box did not reach the extreme high and low outside temperatures, and were warmer at night. Nestlings reached age of endothermy at 9 ± 2.3 days after hatching, and showed a thermoneutral range of body temperature above ambient temperatures in the nest-box. Operative temperatures of models in the nest-box closely followed ambient temperatures, and were below nestlings' thermoneutral range. Therefore, nestlings could experience thermal stress when parents do not provide additional buffering while off the nest for foraging. Although nest-boxes provide limited thermal benefits for nesting birds in tropical cities, they still provide valuable nesting and roosting sites where natural cavities are limited in availability. [ABSTRACT FROM AUTHOR]

Human activity changes multiple factors in the environment, which can have positive or negative synergistic effects on organisms. However, few studies have explored the causal effects of multiple anthropogenic factors, such as urbanization and invasive species, on animals and the mechanisms that mediate these interactions. This study examines the influence of urbanization on the detrimental effect of invasive avian vampire flies (Philornis downsi) on endemic Darwin's finches in the Galápagos Islands. We experimentally manipulated nest fly abundance in urban and non‐urban locations and then characterized nestling health, fledging success, diet, and gene expression patterns related to host defense. Fledging success of non‐parasitized nestlings from urban (79%) and non‐urban (75%) nests did not differ significantly. However, parasitized, non‐urban nestlings lost more blood, and fewer nestlings survived (8%) compared to urban nestlings (50%). Stable isotopic values (δ15N) from urban nestling feces were higher than those from non‐urban nestlings, suggesting that urban nestlings are consuming more protein. δ15N values correlated negatively with parasite abundance, which suggests that diet might influence host defenses (e.g., tolerance and resistance). Parasitized, urban nestlings differentially expressed genes within pathways associated with red blood cell production (tolerance) and pro‐inflammatory response (innate immunological resistance), compared to parasitized, non‐urban nestlings. In contrast, parasitized non‐urban nestlings differentially expressed genes within pathways associated with immunoglobulin production (adaptive immunological resistance). Our results suggest that urban nestlings are investing more in pro‐inflammatory responses to resist parasites but also recovering more blood cells to tolerate blood loss. Although non‐urban nestlings are mounting an adaptive immune response, it is likely a last effort by the immune system rather than an effective defense against avian vampire flies since few nestlings survived. [ABSTRACT FROM AUTHOR]

Early‐life conditions impact fitness, but whether the combined effect of extrinsic stressors is additive or synergistic is not well known. This is a major knowledge gap because exposure to multiple stressors is frequent. Telomere dynamics may be instrumental when testing how stressors interact because many factors affect telomere shortening, and telomere shortening predicts survival. We evaluated the effect of manipulated brood size and natural infestation by the carnid fly Carnus hemapterus on nestling growth and telomere shortening of wild jackdaws (Corvus monedula). Telomere length, measured in blood using TRF, shortened on average by 264 bp, and on average, Carnus infection induced more telomere shortening. Further analyses showed that in enlarged broods, nestlings' telomeres shortened more when parasitized, while in reduced broods there was no effect of infection on telomere shortening. We conclude that there is a synergistic effect of number of siblings and Carnus infection on telomere shortening rate: blood‐sucking parasites may negatively impact telomeres by increasing cell proliferation and/or physiological stress, and coping with infection may be less successful in enlarged broods with increased sibling competition. Larger nestlings had shorter telomeres independent of age, brood manipulation or infection. Growth was independent of infestation but in enlarged broods, nestlings were lighter at fledging. Our findings indicate that (i) evaluating consequences of early‐life environmental conditions in isolation may not yield a full picture due to synergistic effects, and (ii) effects of environmental conditions may be cryptic, for example, on telomeres, with fitness consequences expressed beyond the temporal framework of the study. [ABSTRACT FROM AUTHOR]

Seabird populations are declining across their global range due to a variety of threats, including shifting food webs from climate change. The impact of these threats is exacerbated in long‐lived species with low reproductive output and high investment in a few offspring, where juvenile survival is of substantial importance to populations. Changes to post‐fledging survival and recruitment of adults are difficult to detect, necessitating better information to forecast juvenile survival before fledglings take to sea. To achieve this goal, we test the hypothesis that there is an ideal mass range for fledglings, outside of which survival is limited, providing an early warning signal for future recruitment failures. Here we present a long‐term study of chick banding, weighing and resighting of wedge‐tailed shearwaters, Ardenna pacifica, a globally widespread but declining tropical/subtropical seabird in a sea‐surface warming hotspot across a span of 43 years. We provide data on 1615 fledgling birds banded most years between 1977 and 2020, with 111 resighted as adults. We found that fledglings weighing 380–470 g have the best chance to survive to adulthood and those weighing 330–540 g have a possible chance of survival. We detected a gradual decline in masses since data collection began, with chicks fledging, on average, 1.6 g lighter each year. This decline has been sharpest since 1996, with fledging masses decreasing at an average rate of 3.8 g annually. Should this 1.6 g decline continue, the average fledgling will cross out of the 'survivable' mass range by 2047/2048. We contextualise these findings with observed declines reported in some populations across the species South Pacific range, adding to the conversation about challenges to seabirds in regions experiencing rapid change. [ABSTRACT FROM AUTHOR]

This article documents the discovery and observation of a Superb Lyrebird nest in Black Range, New South Wales, Australia. The author, Matthew Higgins, used a trail camera to capture the activities of the female Lyrebird as she built the nest, incubated the egg, and raised the chick. The article provides information about the nest construction, the presence of other animals in the area, and the unfortunate loss of the egg due to the disturbance caused by a Sugar Glider. The author acknowledges the natural behavior of the Sugar Glider and expresses uncertainty about the female Lyrebird's future breeding attempts. [Extracted from the article]

The article reports the first detailed documentation of intraguild predation involving a Northern Goshawk preying on Gyrfalcon nestlings, observed through wildlife camera monitoring in central Norway. Topics include the rarity of such predation events, potential impacts on Gyrfalcon reproduction, and the implications of changing habitats due to climate change, highlighting the need for further research and conservation efforts.

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The recovery of some predator species in recent decades has intensified conflicts between humans and predators. To mitigate these conflicts, knowledge of predator-prey relationships is needed. The aim of this study was to estimate the predation rate of common buzzards Buteo buteo on young brown hares Lepus europaeus and to compare the magnitude of this predation between two areas that differ in the type of agricultural landscape, i.e. the size of crop fields. In the years 2005–2014, the composition of buzzard diet was studied in western Poland by analysing pellets and prey remains of nestlings and adult birds (7971 prey items identified) and estimating the abundance of buzzards (searching for and observing their nests) and hares (spotlight counts) in two adjacent areas (75 km2 in total) with small and large fields. The diet of common buzzards was dominated by common voles Microtus arvalis, and the frequency of hares ranged from 1.1% of prey items in the nestling diet to 0.2% in the diet of post-breeding individuals. The total number of hares consumed by buzzards during the spring-summer season in the whole study area amounted to 2.94 per km2, which is equal to 7.8–15.3% of the young hares born per km2. However, the predation rate estimated based on the nestling food was 2.6 times lower in small fields than in large fields. Thus, this study suggests that reducing buzzard predation on young hares can be achieved by habitat management, i.e. the creation of agricultural landscapes with numerous field boundaries. [ABSTRACT FROM AUTHOR]

This article examines the similarities between birds and human babies in terms of their vocal learning abilities. It challenges the traditional view that both species learn in two distinct phases and suggests that the timelines for vocal learning need revision. The article also explores the role of social experience and interaction in vocal learning, finding that brain areas involved in attention and sensorimotor processing are more active during social interaction. This neural activity predicts language development in children. The article emphasizes the importance of comparing the neurobiology of communicative learning in babies and birds. [Extracted from the article]