Ibis

Natal dispersal is a multi-step process. It commences when a juvenile departs from its natal site and concludes when it settles to breed for the first time. During this interim period, dispersing individuals of long-lived species undergo a wandering phase, which may span years. This phase remains one of the least studied aspects of species life history. We utilized a unique GPS-telemetry dataset on a slow-life history migratory bird of prey - the European honey buzzard, tracked for multiple years after fledgling. Our aim was to assess how phenology, ranging behaviour and philopatry change as individuals gain experience. Individuals exhibited variability in the age at which they first returned to their breeding range, yet all survivors settled at sites proximate to their natal nests. In subsequent returns, immatures increased the time spent within the breeding range and narrowed down their ranging to smaller areas situated even closer to their natal nests. Our study unveils the complexity and protraction inherent in natal dispersal, emphasizing the importance of individual experience and migratory improvement for successful recruitment in long-lived species. HIGHLIGHTSO_LIWe used a unique GPS telemetry dataset on honey buzzards to track their natal dispersal and recruitment in this long-lived avian migrant. C_LIO_LIAll individuals gradually decreased their ranging areas, moved closer to natal sites, and increased the time spent on the breeding grounds to synchronize with adults and begin recruitment. C_LIO_LIMortality during return migration was high and acted as a bottleneck. C_LIO_LIWe found both processes to be complex and lengthy, with the overall duration depending on individual decisions regarding the timing of return migration. C_LI

The ongoing growth of the human population will increase the rate of wildlife-human interactions. High levels of animal tolerance and flexible responses towards human presence seem to be among the key mechanisms behind successful wildlife-human coexistence, but this behaviour remains unexplored for most populations and species of animals. Here, we investigate the escape behaviour (measured as flight initiation distance) of the Crimean population of a charismatic and declining bird species, the lesser grey shrike (Lanius minor). We examined its relationship with starting distance of the approaching human, directness of that approach (direct or tangential), habitat type (rural or suburban), and height of the perch used by shrikes. We found that the starting distance was significantly associated with escape responses of shrikes to approaching humans. In contrast, we found no significant association between escape responses and directness of approach, habitat type, or height of perch. Our results indicate that the lesser grey shrike may exhibit low flexibility in their escape responses towards humans which may have implications for their conservation management. Our results also indicate that the widely used 30 metres threshold for minimum starting distance may be insufficient for rural populations, even of small passerines.

Infanticide, the killing of dependent young by adult conspecifics, is an extreme form of conflict that remains poorly understood. Previous studies suggest that it is associated with reproductive benefits, either by making breeders newly available for reproduction or by increasing offspring care and reducing competition for resources. In addition, infanticide may result from a reproductive trade-off, where parents kill their offspring if environmental conditions compromise their reproductive value. Here, we combine video, genetic and individual-level reproductive data collected over 12 years to describe infanticide in a highly social, cooperative bird, the sociable weaver Philetairus socius and to establish whether direct reproductive benefits or life-history trade-offs are possible motivators for this behaviour. We documented 50 cases of infanticide and identified 27 aggressors with known histories. These were mostly born outside the colonies where they committed infanticide (63%) and there was a bias towards younger individuals. Aggressors were usually not part of the victims breeding group (74%), but in two cases infanticide was committed by the breeding female, and in five by helpers. In most cases, aggressors were not reproducing at the time of the infanticide, were not recorded mating with any of the breeders or helpers from the attacked nest, nor occupied the nest from where the chicks were evicted. Only 13 of the known aggressors were confirmed as breeders after the attacks, and these mostly reproduced at the colony where the attacks were committed. Overall, we found no evidence for direct reproductive benefits of infanticide in sociable weavers. However, the younger age of aggressors, lack of genetic relatedness to the victims and future breeding at the colony suggest that competition between breeding groups, and hence indirect reproductive benefits, could provide motivation for infanticide in this population. Additional work over longer periods is needed to identify these possible indirect fitness benefits of infanticide.

Animal cultures are learned behaviours, traditions, and collective knowledge that are maintained within populations through social learning. Global biodiversity decline can lead to the loss of animal culture within small and sparsely distributed populations, making the conservation of animal cultures increasingly important. The Critically Endangered regent honeyeater (Anthochaera phrygia) is an Australian songbird whose population is declining to the extent that song culture is being lost in the wild. Reintroduced, zoo-bred males that supplement the wild population sing songs that differ from all wild birds, representing a significant cultural barrier that may impact their fitness after release to the wild. Over three breeding seasons within the applied breeding system, we undertook adaptive song tutoring experiments using combinations of song broadcast and live tutoring from two wild-origin males to teach zoo-bred juveniles the wild song. The proportion of juveniles that learned the wild song increased from 0 before the experiment to 42% after three years. The entire population is predicted to sing the wild song within two years. The full version of the wild song taught to zoo-bred males disappeared from the wild over the course of the experiment, making the zoo population the only remaining repository of traditional song culture. Using just two wild founders, we show how animal cultures can be restored in ex-situ populations with simple modifications to husbandry protocols. Ex-situ populations can then play important roles in the maintenance and restoration of wild animal cultures through reintroductions.

The Great Snipe as a long-distant migrant wintering in Africa, faces the challenge of accumulating sufficient energy reserves before the departure from European breeding grounds. Despite possible trade-offs in resource allocation, this species additionally initiates moult of flight feathers before southward migration. Here we discuss the strategy of flight feather moult and fuelling, exploring their scheduling, constrained by the timing of breeding and departure for female and male Great Snipes from the European lowland population. We found significant intrasexual differences in both moult initiation date and moult duration. Males start flight feather replacement more than two weeks earlier and moult faster compared to females. However, neither sex completed this process on breeding grounds before the migration, as late in the season all males and half of the females had suspended their primary moult, with the remaining females not moulting at all. Moult of secondaries occurred exceptionally in the studied population. We observed a non-linear energetic stores gain in the studied period, where both sexes maintained a stable and low body condition until the end of July, coinciding with the primary moulting period. Subsequently, there was an increase in body condition, of approximately 1% of the lean body mass per day, indicating a shift towards fuelling for migratory flight. The overlap between stages of maintaining a stable and low body condition and moulting suggests a resource allocation towards feather growth before initiating fuelling. Our study describes moult strategy in Great Snipe conducted on their breeding grounds, highlighting the intrasexual differences, likely resulting from different parental duties of males and females of this lekking species.

The logistics of measuring activities that occur at fine temporal scales, such as short stopovers that last a few hours, has proven very challenging when studying small migratory birds. Here, we deployed multi-loggers equipped with an accelerometer and thermometer on Chilean Elaenia (Elaenia chilensis) to evaluate their activity patterns while they undertook their annual migration from their Patagonian breeding grounds to non-breeding zones in Brazil. Results show that elaenias can fly at altitudes of >1500 masl and migrate nocturnally, providing the first evidence of this behavior in a Neotropical austral migrant. Although most migration flights lasted less than 8 h, one individual flew non-stop for more than 28 h. Overall activity patterns (e.g., flight and stopover duration) were not substantially different between pre- and post-breeding migration. This technology offers a window into the migratory behavior of small birds that migrate within the Neotropics at a finer temporal scale than previously possible.

Inter-individual recognition is crucial for stable social relationships and it is frequently mediated through vocal signatures. In socially complex species, recognition may additionally require additional levels corresponding to other layers of social organisation such as the pair, family, social group or colony. Additional vocal signatures may encode these different levels of social organisations for recognition. We investigated this hypothesis in the calls of the rook (Corvus frugilegus), a highly social corvid. Rooks form large breeding colonies where multiple pairs nest in clusters. We recorded the calls of five colonies located in France and in Great Britain, including both wild and captive colonies. To exclude variations due to different call types, we focused on the loud nest call produced exclusively by nesting females during the breeding season. We compared the acoustic distance of calls from each individual and between individuals at various levels of nest proximity, i.e. from the same nest cluster, from different nest clusters, from colonies within the same country, and from colonies in different countries. The only vocal signatures we found were at the individual level, but not at the nest cluster or colony level. This suggests a lack of vocal convergence in this species, at least for the nest call, which may be important for pair recognition in large colonies. Further studies should now evaluate if types of calls other than the nest call better carry vocal signatures as markers of different layers of sociality in this species, or if vocal divergence is a more general vocal phenomenon. In that case, applying new methods of monitoring vocal signatures in wild individuals should help understand the cognitive, social and environmental mechanisms underlying this vocal singularisation. 1. Significance statementInter-individual recognition is crucial for social relationships in animals, and is often mediated by individual-specific acoustic characteristics in vocalisations, called a vocal signature. High levels of social organisations, such as a social group of familiar conspecifics or a breeding colony, may likewise be signalled by vocal signatures shared by multiple individuals. We used machine-learning techniques to investigate vocal signatures at multiple social levels in the nest call of brooding female rooks, a corvid species that breeds colonially but lives year-round in social groups. We find evidence of a strong individual vocal signature, but no common vocal signature even in females that nest close together, or in the same colony. A strong individual vocal signature may be a potent tool to monitor populations in this species with minimal disturbance and minimal material, especially as corvids are frequently targeted by human-fauna conflicts in continental Europe.

Like many bird species associated with agricultural habitats in the UK, the Twite Linaria flavirostris has undergone severe declines over recent decades due to habitat degradation, with populations in England, Wales and Ireland now restricted to a few small pockets. However, the demographic drivers of these declines are still largely unresolved. We estimated the survival of Twite from a small population at the southernmost edge of the English range in Derbyshire using capture-mark-recapture data from 2016-2019. Annual apparent survival for juveniles (0.14-0.34) was lower than for adults (0.29-0.56) and less than that of other Cardueline finches. Our results suggest that low juvenile survival may be one demographic driver underpinning the recent decline of the Derbyshire Twite population, although we also cannot rule out the possibility that differences in emigration of juveniles and adults from the population also contribute to the observed age-specific apparent survival rates.

Conspecific brood parasitism (CBP) has been reported in many altricial avian species, yet its prevalence and underlying behavioural mechanisms remain poorly understood. We studied CBP in the barn swallow (Hirundo rustica), a species in which conspecific brood parasitism has been reported. We conducted parentage analysis on 1945 barn swallow broods involving 7816 offspring. Samples were collected over 12 breeding seasons at 5 colonies/populations. Contrary to expectations, we identified only six cases of CBP (0.3 % of broods). By identifying all individuals involved, i.e. the parasitic females, the female hosts and the males that fathered the parasitic eggs, we determined these cases of CBP resulted most likely from either a failed nest take-over (three times), the disappearance of a female partner or a disruption caused by researchers while only one case could be interpreted as a result of females mixed reproductive tactic. Based on a review of the literature on CBP in seven other Hirundinidae, we conclude that the only reliable evidence for CBP comes from cliff swallows (Petrochelidon pyrrhonata). Studies on other species either failed to identify the parasitic females or do not present sufficient evidence supporting the occurrence of CBP. Several studies relied on the appearance of two eggs in a nest within 24 hours to conclude that CBP occurred. However, based on the parentage analysis, we show that CBP only occurred in one out of 11 such cases in our barn swallow data. Our findings highlight that CBP is rare in our barn swallow populations, and have been likely overestimated in other studies. We emphasize the importance of frequent nest checks and rigorous genetic validation in CBP research. Overall, our results challenge existing assumptions about the prevalence of CBP and provide insights into the behavioural mechanisms that lead to CBP, with ecological and evolutionary implications.

Island endemic birds are under greater threat than their mainland counterparts. Sedentary living and historically reduced predation may affect island bird sociality and inform their conservation and management. However, detailed studies on their sociality are uncommon. The federally- endangered koloa maoli (Anas wyvilliana, Hawaiian duck, or koloa) is primarily threatened by hybridization with feral mallards and avian botulism outbreaks. We used capture-mark-recapture and genetic data on koloa on the island of Kaua i, a stronghold of remaining koloa, to construct social networks and examine their associations (inferred from co-occurrence in traps) and spatial genetic structure. Information on associations might shed light on preferences for or against mallards and hybrids, and inform planned translocation efforts. Microgeographic spatial genetic structuring where relatedness among individuals scales with geographic distance is a potential liability for maintaining koloa genetic diversity, and would particularly be detrimental during highly localized outbreaks of botulism that could result in the removal of entire lineages. While we found persistent social associations among adult koloa, they were not apparently influenced by plumage traits or body mass, suggesting a lack of social preference for mallard-like individuals. Importantly, we found no spatial patterns of relatedness within the largest refuge. Therefore, botulism outbreaks remain a demographic threat but are unlikely to remove correlated genetic diversity. There were no sex differences in spatial genetic structure and both sexes moved within a refuge. The lack of spatial genetic structure and the presence of many unrelated conspecifics may enable koloa to limit inbreeding and retain genetic diversity without sex-biased dispersal. In the context of future translocations, our results suggest that translocating koloa captured in the same trap together will reduce disruption of preferred associations while also retaining genetic diversity among translocated individuals. LAY SUMMARYO_LIThe koloa maoli (Hawaiian duck, or koloa) is a federally-endangered, island endemic bird. Like other Hawaiian waterbirds, koloa are threatened by introduced predators and habitat loss, but also specifically by hybridization with feral mallards and localized avian botulism outbreaks. Currently, the island of Kaua i has the largest population of non-admixed koloa. We used capture-mark-recapture and genetic data of koloa at two wetland sites on Kaua i to examine their sociality and spatial genetic structure. C_LIO_LIKoloa formed preferential social associations, but they were not based on plumage traits, body mass or genetic relatedness. C_LIO_LIThere was no spatial genetic structure for males and females within a wetland site. Our results suggested that 1) koloa have no preference for mallard-like plumage that might increase hybrid pairing, 2) localized (within-refuge) botulism outbreaks are unlikely to remove close relatives and unique genetic lineages, and 3) translocation of groups could maintain social associations without limiting genetic diversity. C_LI

Habitat selection is a key mechanism that enables animals to optimize their fitness in response to varying environmental conditions. Differences in habitat selection between populations in different geographical areas may indicate behavioral adaptations to local environmental conditions. Understanding the adaptive potential of species across broad geographical ranges is of primary interest to anticipate possible changes in species behavior or distribution in the context of climate change. In this study, we investigated the habitat selection and the daily movement patterns of the Eurasian Woodcock, Scolopax rusticola, a bird species that winters across widely varying climatic zones. We tracked 84 individuals wintering in the Mediterranean regions with GPS-VHF transmitters, where climate and habitat conditions differ significantly from the regions with Atlantic climate influence, which have formed the main background for the ecology and behavior of this species in winter. To assess how woodcocks responded to varying habitat and environmental conditions, we collected data across three geographical regions spanning a gradient of Mediterranean climatic influence -- ranging from northern subareas with denser forest and deeper soil to southern subareas characterized by less productive forests, garrigues, and rocky soil. In the northern Mediterranean region, woodcocks visited open habitats at night less than 53% of the time and less than 40% of the time in the two other regions with a stronger Mediterranean climate influence. This behavior was much less frequent than reported in studies conducted in areas with Atlantic climate influence (>80%). Woodcocks also changed their day/night activity patterns, as illustrated by their daily movements. They increased their daytime movements (11 to 29% higher) and reduced their nocturnal movements (12 to 18% lower) in the two regions with the strongest Mediterranean climate influence. During the day, when birds used only forested areas, denser forests were preferred in all studied Mediterranean subareas. Birds used different forested habitats between subareas, especially at night. For example, denser but shorter vegetation and higher rock cover were more strongly used at night in southern subareas. These forested habitats contrasted sharply with those in areas with Atlantic climate influence, the latter being plots rich in humus and deep soils. Our findings highlight that basic ecological knowledge of species can be biased towards those known in certain types of habitats. They also underscore the remarkable behavioral flexibility of woodcocks, highlighting their potential to adapt to global change. However, the occurrence of escape movements under the driest conditions suggest that this change in behavior and habitat selection may be an early warning sign of the effects of climate change on the wintering areas. Overall, our study emphasizes the need to study the ecology of species across diverse environmental conditions to better understand their habitat requirements and adaptive capacity.

Understanding the breeding success of European Turtle Doves is crucial for their conservation, helping to address the threats they face, and optimizing the species prospects for future successful reproduction and survival. However, data on breeding success of this species in Germany are missing due to the low density and poor accessibility of nests and chance to disturb nesting efforts during direct nest searches. We therefore used two indirect methods to obtain data on breeding success. First, we analyzed field age ratios, i.e. the proportion of juveniles from Citizen Science data. We observed a marked decrease in observed fledglings from 1.28 in the years 1957-1989 to 0.44 in 1990-2009 and to 0.32 in 2010-2023. This suggests a sharp decline in breeding success. Very low juvenile numbers in July further suggest that first broods were especially affected. Second, nesting sites were determined from GPS data, and the breeding constancy was checked at these sites. Based on data from 32 GPS-marked birds representing 28 breeding pairs, we obtained values of maximum breeding success of 1.5 chicks per potential breeding pair at hatching and 0.7 chicks per potential breeding pair at fledging. This is an optimistic calculation for fledglings, as it assumes that two chicks per nest survive until fledging. Overall, these data highlight an urgent need to improve the habitat conditions in the breeding areas to conserve this once common species.

In species that learn their song, cultural transmission of song components can lead to the accumulation of variants that differ among populations, resulting in the formation of dialects. Three avian clades are thought to have independently evolved song learning - parrots, oscine passerines, and hummingbirds. Dialects have mainly been studied in passerines. We extend the study of dialects to the bee hummingbird clade, focusing on Annas and Costas hummingbirds (Calypte anna and C. costae). Both species are vocal learners. Annas produces complex, three phrase, multi-syllable songs and Costas produces simple, one phrase songs. We recorded 5-24 males per population (5 Costas and 6 Annas populations) across the species ranges in the Western United States and tested for evidence of geographic variation in song. We found minor population differences in frequency measures of Costas song, but song form was invariant across populations. Annas song was contrastingly variable with population differences in both syllable use and multiple spectral and temporal measures. The most strongly differentiated Annas population in our study, Seattle (Washington State), is the product of a recent northward range expansion facilitated by human activities that provide additional food sources for hummingbirds. The loss and modification of syllables in this population is suggestive of a founder effect on song. This study provides insight into song evolution in non-passerine vocal learners and contributes to understanding of how complex signals evolve.

Geographic differences in vocalisations provide strong evidence for animal culture, with patterns likely arising from generations of social learning and transmission. The current knowledge on the evolution of vocal variation has predominantly focused on fixed repertoire, territorial song in passerine birds. The study of vocal communication in open-ended learners and in contexts where vocalisations serve other functions is therefore necessary for a more comprehensive understanding of vocal dialect evolution. Parrots are open-ended vocal production learners that use vocalisations for social contact and coordination. Geographic variation in parrot vocalisations typically take the form of either distinct regional variations known as dialects or graded variation based on geographic distance known as clinal variation. In this study, we recorded monk parakeets (Myiopsitta monachus) across multiple spatial scales (i.e. parks and cities) in their European invasive range. We then compared calls using a multi-level Bayesian model and sensitivity analysis, with this novel approach allowing us to explicitly compare vocalisations at multiple spatial scales. We found support for founder effects and/or cultural drift at the city level, consistent with passive cultural processes leading to large scale dialect differences. We did not find a strong signal for dialect or clinal differences between parks within cities, suggesting that birds did not actively converge on a group level signal, as expected under the group membership hypothesis. We demonstrate the robustness of our findings and offer an explanation that unifies the results of prior monk parakeet vocalisation studies.

Climate change is significantly affecting animal distributions and phenology, with migratory birds experiencing notable shifts in migration timing. There are complexities to changes in migration timing, considering variations due to monitoring locations or definitions of migration timing. Previous studies have focused on differences between traits in the magnitude of change and agreed that migration distance has an effect, although distribution has not been considered. This study investigates the factors influencing phenological changes in spring migration, focusing on First Arrival Date (FAD) and Last Departure Date (LDD) in eastern Japan. Using community science data from Sendai and Tokyo, we examine the effects of species characteristics, including trophic level, migration distance, and breeding and wintering areas, in addition to climatic variables. Consistent with other studies, FAD was advanced and LDD was delayed with climate. Notably, the magnitude of change in FAD differed depending on the distribution of wintering areas. Birds use many areas during their life cycle, and our results suggest that distribution, as a simple indicator, may be key to predicting responses to climate change.

Anthropogenic noise pollution has a variety of negative consequences for animals, with observed effects ranging from physiological processes to community structures. Sound waves from anthropogenic noise can mask animal signals, creating challenges for animal communication. Songbirds have been observed to combat noise pollution by changing their song rate, duration, frequency, or amplitude, with different species employing different strategies. We examined whether Swainsons thrushes (Catharus usulatus) adjust their song structure under different traffic noise regimens using both population level surveys and individual level noise playback experiments. Swainsons thrushes song frequency varied with background traffic noise levels across the surveyed population, but other song parameters did not. When confronted with realistic levels of experimental traffic noise playback, individual thrushes rapidly changed their song structure, increasing both the duration and the minimum frequency of their songs, before quickly returning towards baseline levels after the noise playback ended. Together, these results suggest that Swainsons thrushes are adjusting their singing to reduce acoustic masking in noisy areas and further indicate that some songbirds might continually assess ambient noise levels and only adjust their signals when necessary.

While the function of bird song has been well studied in male songbirds, the function of female song is less well understood. This is partly due to a historical view of females occupying a passive role compared with males, which led to ignoring female song even in some well-studied species. We report one such case in yellow warblers (Setophaga petechia), as no other study investigated female song in 35 years after the first documentation of solo female songs. We interrogate the seasonal patterns and functions of female song in Galapagos yellow warblers (Setophaga petechia aureola), in which females perform solo song and produce duets with their male social partners. We carried out simulated territory intrusions by broadcasting male, female, or duet songs during breeding and non-breeding seasons, and conducted a territory retention survey for over a year. We measured the association between aggressive response and singing behaviour, sex-specific patterns of response, and territory retention across years. Females sang mostly during the non-breeding season and predominantly in male-led duets. Although females were strongly aggressive towards female song playback, they gave the weakest singing response towards them. There was no association between female aggressive behaviour and song output in response to a simulated intruder. Moreover, the probability of territory retention across years was not explained by song output or aggression in response to intruders, though evidence for this was weak due to the small sample size. We suggest that female song in this year-round resident island system does not function for territory defense or intrasexual competition, but may have other functions. HighlightsO_LIGalapagos Yellow Warbler females produce solo songs and duets with their male partners. C_LIO_LIFemale song and aggression were mainly restricted to the non-breeding season. C_LIO_LIWhile females were equally aggressive to all intruders, they had the lowest song rate in response to females. C_LIO_LIIn contrast to males, aggressive behaviour didnt predict song output in females. C_LIO_LIFemale singing behaviour did not increase the probability of territory retention. C_LI

The ecological processes that determine how individual animals become hosts to zoonotic pathogens is a topic of rapidly growing interest. However, how such exposure is mediated by context (e.g., season, location), host behavior (e.g., migration distance) and host demographics is generally poorly understood. We evaluated seasonal exposure to West Nile Virus of American robins sampled in Indiana and compared our results to those of previous studies. Because robins that breed in Indiana are partial migrants (i.e., only a portion of the population migrates), we evaluated their probability of exposure to WNV as a function of whether they migrated or not and of their movement distance. We also tagged a subset of breeding robins with tracking devices to evaluate their potential to disperse the virus between Indiana and other regions of the continent. We found that robins that breed in Indiana are exposed to WNV at a higher rate than that detected in previous studies, but found no correlation between robin exposure and whether a robin migrated or not, nor with migration distance, season, sex, and breeding latitude (for robins overwintering in Indiana). Our tracking data indicate that robins that breed in Indiana migrate several hundred miles to overwinter in the southeastern US. The mean duration of their return to Indiana in spring is 10.3 days, which is less than the maximum infectious period found for robins in previous studies, suggesting that they have the capacity to move WNV long distances in spring. However, we still know little about the physiological capacity of robins to migrate while being infectious, which could inhibit the dispersal of the virus through robin migration. Future research on the physiological, ecological and behavioral factors mediating the exposure of birds to WNV will lend insight into the role that robins and other birds play in the transmission ecology of the virus.

Ecological restoration projects provide excellent opportunities to study how animals adapt their life-history strategies in response to changeable environments. A fundamental way animals can optimise reproductive success in changing conditions is trading-off aspects of their breeding system. The New Zealand bellbird (Anthornis melanura) has had a long-term presence on the small restoration island, Tiritiri Matangi Island (Tiri), spanning the islands degraded agricultural past to its current extensively restored state. We studied the breeding biology of this bellbird population to assess how their reproductive life-history strategies have responded over time to the restoration on Tiri. We compared the current breeding data (2012-2016) of the bellbirds with data from between 2001-2010 (including Baillie, 2011, Cope, 2007), and from 1977-1978 (Anderson and Craig, 2003), prior to the islands restoration. We also explored associations between abiotic/biotic factors and bellbird reproductive success for the most recent period (2012-2016). Our main finding was that clutch size significantly declined over time from a mean of 3.6 to 2.4 eggs per nest and this decline correlated with increasing population density. This is consistent with a density dependent effect, although further data are required to empirically test this conclusion. Overall, the earliest spring laying dates were in late August and the latest extended to January, with all chicks fledged by the end of February. Nest success was 47% (range 40 - 54%) across 2012-2016, falling within a similar range as previous studies. We found little effect of year, weather, parental age or morphometrics on reproductive success. We observed directional change in patterns of parental investment between 1977-1978 and 2012-2016; in 2012-2016, parents persisted with raising single broods rather than abandoning and re-nesting to raise larger broods. These results suggest that the bellbirds life-history traits are plastic in response to local conditions which provides an advantage when repopulating a regenerating or changing habitat.

Vocal distinctiveness is expected to occur more often in colonial-breeding species as the parents need to recognize their offspring in a large group of conspecifics. Territorial species like the Scops Owl are expected to exhibit low distinctiveness. Contrary to what was expected, spectrographic analysis of the food-begging calls of young Scops Owls revealed previously unknown, complex acoustic structure. Within recording sessions, call duration exhibited the highest repeatability (average R 0.82), followed by the peak frequency in the last third of the call (0.61). Other spectral measures showed low to moderate repeatability (0.32 - 0.57), while the time between subsequent calls was the least repeatable (0.15). When comparing recordings made on different nights, Linear Discriminant Analysis assigned 55.7% of the calls to the correct individual, and 73.1% when restricting analysis within broods. When analyzing variability across recordings, individuals explained most of the variation in Call duration and Peak frequency in the last third of the call (89.5 % and 81.2 %, respectively), while recordings explained little variation (3.4 % and 1.3 %, respectively), suggesting that those acoustic features were the most important in vocal stability and distinctiveness. The calculated information capacity HS was 4.48 bits, i.e. within the range of values found in loosely-colonial species. The results suggest that the vocalizations of young Scops Owls show moderate individuality that could only help offspring recognition among a small number of individuals. However, the functional significance of call distinctiveness remains unclear; a few hypotheses are discussed. Keywords: Acoustic signature, coloniality, fledglings, individuality, Otus scops, repeatability.