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Abstract From fiddler crabs to humans, animals perform repetitive displays showing neuromotor skill and vigour. Consistent repetition of identical notes (vocal consistency) facilitates the assessment of neuromotor skills and is important in communication in birds. Most birdsong research has focused on song diversity as a signal of individual quality, which seems contradictory as repetition is extremely common in most species. Here we show that consistent repetition within songs is positively correlated with reproductive success in male blue tits (Cyanistes caeruleus). A playback experiment shows that females are sexually aroused by male songs with high levels of vocal consistency, which also peaks seasonally during the fertile period of the female, supporting the role of vocal consistency in mate choice. Male vocal consistency also increases with subsequent repetitions of the same song type (a warm-up effect) which conflicts with the fact that females habituate to repeated song, showing decreased arousal. Importantly, we find that switching song types elicits significant dishabituation within the playback, supporting the habituation hypothesis as an evolutionary mechanism driving song diversity in birds. An optimal balance between repetition and diversity may explain the singing style of many bird species and displays of other animals.

The zoo soundscape has important implications for animal welfare, management, and conservation. However, despite its importance, the zoo soundscape is yet to be examined in depth. Consistent human presence can influence the zoo soundscape. However, it is difficult to determine the specific impact of human presence, as visitors are usually present during the day when animals are active. The COVID-19 lockdown in 2020 provided a unique opportunity to study zoo soundscapes in the absence of visitors. The main aim of this study was to compare the sound environment across three zoo aviaries during the 2020 closure period to a comparable period in 2019 in which the zoo was open. We examined broad band frequency measures of sound pressure levels, sound pressure levels in defined frequency bands, and ecoacoustic indices (the Acoustic Complexity Index and Normalized Difference Soundscape Index) to describe the zoo soundscape. Ecoacoustic indices have not, to our knowledge, previously been used in the zoo setting, although they may provide a useful metric to assess zoo soundscapes. Therefore, we used this natural experiment to explore how successful these measures may be in assessing sound in zoo environments. We found that, during the zoo closure period, the overall sound pressure levels were lower (by 4.4 – 6.4 dB(Z) depending on aviary), and this effect was particularly pronounced in the lower frequency bands. The proportion of sound energy at low frequencies was also lower during the zoo closure period in two of the three aviaries. We argue that NDSI could be a useful index for determining the impact of human presence in zoos, although further information on how it is influenced by additional factors, such as human speech, would be beneficial. The use of multiple indices to assess the sound environment can provide additional information beyond traditional measures of sound levels in zoos, such as frequencies where sound energy is concentrated and characteristics of the soundscape, which could be used to better target management and mitigation.

Summary: In birds, song performance determines the outcome of contests over crucial resources. We hypothesized that 1) sustained performance is limited within song, resulting in a performance decline towards the end and 2) the impact of song length is compromised if performance declines. To test these hypotheses, we analyzed the songs of 597 bird species (26 families) and conducted a playback experiment on blue tits (Cyanistes caeruleus). Our multi-species analysis showed that song performance declines after sustained singing, supporting our hypothesis. If the performance decline is determined by individual attributes (i.e., physical condition), our results explain how trill length can honestly signal quality. Our experiment showed that longer trills of high performance elicited a stronger response during territorial interactions. However, long trills that declined in performance elicited a weaker response than short, high-performance trills. A trade-off between the duration and performance quality of a motor display can be an important aspect in communication across taxa.

Neonatal painful procedures causes acute pain and trigger long-term changes in nociceptive processing and anxiety behavior, highlighting the need for adequate analgesia during this critical time. Spinal serotonergic receptors 5-HT1a and 5-HT3 play an important role in modulating incoming nociceptive signals in neonates. The current study aims to attenuate acute and long-term hypersensitivity associated with neonatal procedural pain using ondansetron (a 5-HT3 antagonist) and buspirone (a 5-HT1a agonist) in a well-established rat model of repetitive needle pricking. Sprague-Dawley rat pups of both sexes received ondansetron (3 mg/kg), buspirone (3 mg/kg) or saline prior to repetitive needle pricks into the left hind-paw from postnatal day 0–7. Control animals received tactile stimulation or were left undisturbed. Acute, long-term, and post-operative mechanical sensitivity as well as adult anxiety were assessed. Neonatal 5-HT1a receptor agonism completely reverses acute hypersensitivity from P0-7. The increased duration of postoperative hypersensitivity after re-injury in adulthood is abolished by 5-HT3 receptor antagonism during neonatal repetitive needle pricking, without affecting baseline sensitivity. Moreover, 5-HT1a and 5-HT3 receptor modulation decreases adult state anxiety. Altogether, our data suggests that targeted pharmacological treatment based on the modulation of spinal serotonergic network via the 5-HT1a and 5-HT3 receptors in neonates may be of use in treatment of neonatal procedural pain and its long-term consequences. This may result in a new mechanism-based therapeutic venue in treatment of procedural pain in human neonates.

We investigate the impact of anthropogenic noise on the foraging efficiency of leafcutter ants (Acromyrmex octospinosus) in a controlled laboratory experiment. Anthropogenic noise is a widespread, pervasive and increasing environmental pollutant and its negative impacts on animal fitness and behaviour have been well documented. Much of this evidence has come from studies concerning vertebrate species with very little evidence for terrestrial invertebrates, especially social living invertebrates. We compare movement speed, forage fragment size, and colony activity levels of ants exposed to intermittent elevated noise and in ambient noise conditions. We use intermittent and temporally unpredictable bursts of white noise produced from a vibration speaker to create the elevated noise profile. Ant movement speed increased under elevated noise conditions when travelling to collect forage material and when returning to the colony nest. The size of individually measured foraged material was significantly reduced under elevated noise conditions. Colony activity, the number of ants moving along the forage route, was not affected by elevated noise and was consistent throughout the foraging events. Increased foraging speed and smaller forage fragments suggests that the ants had to make more foraging trips over an extended period, which is likely to affect energy expenditure and increases exposure to predators. This is likely to have significant fitness impacts for the colony over time.

Social learning of vocalizations is integral to song inheritance in oscine passerines. However, other factors, such as genetic inheritance and the developmental environment, can also influence song phenotype. The relative contributions of these factors can have a strong influence on song evolution and may affect important evolutionary processes such as speciation. However, relative contributions are well-described only for a few species and are likely to vary with taxonomy. Using archived song data, we examined patterns of song inheritance in a domestic population of Java sparrows (Lonchura oryzivora), some of which had been cross-fostered. Six-hundred and seventy-six songs from 73 birds were segmented and classified into notes and note subtypes (N = 22,972), for which a range of acoustic features were measured. Overall, we found strong evidence for cultural inheritance of song structure and of the acoustic characteristics of notes; sons’ song syntax and note composition were similar to that of their social fathers and were not influenced by genetic relatedness. For vocal consistency of note subtypes, a measure of vocal performance, there was no apparent evidence of social or genetic inheritance, but both age and developmental environment influenced consistency. These findings suggest that high learning fidelity of song material, i.e., song structure and note characteristics, could allow novel variants to be preserved and accumulate over generations, with implications for evolution and conservation. However, differences in vocal performance do not show strong links to cultural inheritance, instead potentially serving as condition dependent signals.

Older males tend to have a competitive advantage over younger males in sexual selection. Therefore, it is expected that signals used in sexual selection change with age. Although song repertoire size in songbirds is often mentioned as an age-related trait, many species, including the banded wren (Thryothorus pleurostictus), do not increase their repertoires after the first year. Here, we show that banded wrens reproduce the trill notes in their songs with less variability between them (i.e. more consistently) when they grow older. In a playback experiment, we also show that banded wrens discriminate between younger and older birds based on structural aspects of their song. In a second experiment, banded wrens also respond differentially to natural songs versus songs with artificially enhanced consistency. We argue that consistency in trill note reproduction may be achieved through practice. Sexual selection in the form of male–male competition may therefore operate on a phenotypic trait, the expression of which is enhanced by practice. [ABSTRACT FROM AUTHOR]

Migratory birds are assumed to be under stronger sexual selection pressure than sedentary populations, and the fact that their song is more complex has been taken as confirmation of this fact. However, this assumes that sexual selection pressure due to both male competition and female choice increase together. A further issue is that, in many species, songs become less complex during competitive encounters; in contrast, female choice selects for more complex song, so the two selection pressures may drive song evolution in different directions. We analysed song in two sedentary and two migratory populations of blackcaps (Sylvia atricapilla), a species in which different song parts are directed to males and females. We found that migratory populations produce longer, female-directed warbles, indicating sexual selection through female choice is the strongest in these populations. However, the part of the song directed towards males is shorter and more repetitive (as observed in individual competitive encounters between males) in non-migratory populations, indicating sedentary populations, are under stronger selection due to male competition. We show for the first time that the intensity of selection pressure from male competition and female choice varies independently between populations with different migratory behaviours. Rapid alterations in the migration patterns of species are thus likely to lead to unexpected consequences for the costs and benefits of sexual signals. [ABSTRACT FROM AUTHOR]

A principal finding in the food-caching literature is that species differences in hoarding propensity are positively correlated with species differences in degree of adaptations to caching behaviour, such as performance on spatial memory tasks and hippocampal volume. However, there are examples that do not fit this pattern. We argue that these examples can be better understood by considering the phylogenetic relatedness between species. We reconstruct the ancestral state for caching behaviour in corvids and assess when transitions in caching behaviour occurred within the corvid phylogeny. Our analysis shows that the common ancestor of all corvids was a moderate cacher. This result suggests that corvids followed a bi-directional evolutionary trajectory in which caching was secondarily lost twice and there were at least two independent transitions from moderate to specialized caching. The independent evolution of specialized cachers in the two groups must, therefore, be a case of convergent evolution. This is exemplified by the fact that specialized cachers show structurally different adaptations serving the same function to intense caching, such as different pouches to transport food. Finally, we argue that convergent evolution may have led to adaptations in memory and hippocampus that serve the same function but differ in design, and that these different adaptations may explain the examples that do not fit the pattern predicted by the adaptive specialization hypothesis. [ABSTRACT FROM AUTHOR]

A correlation between the degree of specialization for food hoarding and the volume of the hippocampal formation in passerine birds has been accepted for over a decade. The relationship was first demonstrated in family-level comparisons, and subsequently in species comparisons within two families containing a large number of hoarding species, the Corvidae and the Paridae. Recently, this approach has been criticized as invalid and excessively adaptationist. A recent test of the predicted trends with data pooled from previous studies found no evidence for such a correlation in either of these two families. This result has been interpreted as support for the critique. Here we reanalyse the original dataset and also include additional new data on several parid species. Our results show a surprising difference between continents, with North American species possessing significantly smaller hippocampi than Eurasian ones. Controlling for the continent effect makes the hoarding capacity/hippocampal formation correlation clearly significant in both families. We discuss possible reasons for the continent effect. [ABSTRACT FROM AUTHOR]

Abstract Food sharing among unrelated same-sex individuals has received considerable interest from primatologists and evolutionary biologists because of its apparent altruistic nature and implications for the evolution of complex social cognition. In contrast to primates, food sharing in birds has received relatively little attention. Here we describe three types of food sharing in jackdaws, with the initiative for the transfer either with the receiver or the giver. The latter situation is of particular interest because the food transfer takes place through active giving. Compared to primates, jackdaws show high rates of food sharing. Finally we discuss the implications of food sharing in jackdaws, and in birds in general. [ABSTRACT FROM AUTHOR]

Using the responses of territory owners to playback to infer the territorial function of acoustic signals is common practice. However, difficulties with interpreting the results of such experiments have obscured our understanding of territorial signalling. For instance, a stronger response to playback is often interpreted as more aggressive, but there is no consensus as to whether this should be in response to the least or most threatening simulated intruder. Rather than following a gradual increase or decrease, the relationship between signal intensity and response strength may instead describe a peaked curve. We manipulated banded wren (Thryophilus pleurostictus) songs to simulate low-, median-, and high-performance singers and used these songs as stimuli in playback experiments. Banded wrens were less likely to approach the high-performance stimulus compared with the low- and median-performance stimuli. However, the birds that did approach the high-performance stimulus sang more than those that approached the low-performance stimulus. In addition, birds were more likely to match the songs when exposed to the median- and high-performance stimuli compared with the low-performance stimuli, and song matching predicted approach behavior. These results are in accordance with theoretical models of aggressive encounters in which low-performance opponents are challenged without further assessment. Median- and high-performance opponents, however, may require further assessment, and the latter may be perceived as too intimidating for approach. [ABSTRACT FROM AUTHOR]

Secondary contact between closely related species can lead to hybridization. The fitness of hybrid individuals within and outside the hybrid zone determines whether the hybrid zone expands into the ranges of the 2 parental species or remains a stable, geographically narrow area in between the allopatric ranges of the parental species. In birds, vocalizations play an important role in male–male competition and female mate choice and are often affected by hybridization. One of the factors that will influence male hybrid fitness is the ability to defend a territory against competitors by vocalizing. We tested the efficacy of territorial signals of hybrids of 2 dove species, Streptopelia vinacea and Streptopelia capicola, compared with the vocalizations of the parental species. With playback experiments, we assessed the response to hybrid and the 2 parental species vocalizations in the hybrid zone and adjacent allopatric populations of each species. In the hybrid zone, males did not respond differently to the 3 vocalization types. In both allopatric populations, however, males responded more to conspecific than to heterospecific signals and the response strength to hybrid signals was intermediate. Therefore, in the allopatric populations, hybrid males may have a reduced success in defending territories. In male–male interactions in the hybrid zone, hybrids may not have a disadvantage compared with males of the parental species. The ability to defend a territory against competitors may thus help maintain a stable hybrid zone in the area of overlap. [ABSTRACT FROM AUTHOR]