Temporal, spatial and social segregation of red-billed choughs between two types of communal roost: a role for mating and territory acquisition

Effects of the environmental conditions and seasonality on a population survey of the Andean condor Vultur gryphus in the tropical Andes

Background

Among the New World vultures, the Andean condor is considered one of the most culturally and ecologically important species. However, their populations are declining over their entire distributional range. In response, conservation strategies have been implemented in many countries to reverse the increasing extinction risk of this species. The initiatives rely on extensive population surveys to gather basic information necessary to implement policies and to intervene efficiently. Still, there is a need to standardize the surveys based on seasonality and suitable environmental conditions throughout the species distribution. Here, we provide the first assessment of how daily temperature, rainfall, and seasonality influence surveys of Andean condors on a communal roost in the central Peruvian Andes.

Methods

Using an autoregressive generalized linear model, we associated environmental variables with visual surveys of adult and young condors at three different times of the day and three times a week between June 2014 and March 2015.

Results

We found that both adults and young Andean condors showed a threefold reduction in the use of the communal roost after the beginning of the rainy season. Colder and drier days (dry season) are preferable for surveying, as we expect the total number of condors using communal roosts to reduce under rainy (rainfall = -0.53 ± 0.16) and warmer days (temperature = -0.04 ± 0.02) days. Therefore, the significant variation in the use of roosts across seasons and hours should be carefully accounted for in national surveys, at the risk of undermining the full potential of the communal roost surveys. Moreover, we also found a strong bias towards immatures (about 76%) in the adult:immature ratio and a remarkable absence of Andean condors during the wet season. These results suggest that the species might be using other unknown communal roosts hierarchically. Such results provide key information for selecting priority areas for conservation and selecting the best time to survey this species in the tropical Andes. Finally, it may open a fruitful avenue for further research on the protection of the Andean condor.

Discriminant Criteria for Field Sexing in the Eurasian Tree Sparrow by Combining Body Size and Plumage Features

The Eurasian tree sparrow (Passer montanus) is a monomorphic passerine, for which it is impossible to differentiate between males and females based on external characteristics. Being a species frequently captured for ringing, having a reliable method to determine sex from conventional biometric measurements would facilitate its study and be very useful for the correct management and conservation of this declining species. In the present study, we used biometric measurements recorded in 66 individuals captured with mist nets in communal roosts in northern Spain during the winter and sexed them using molecular techniques. We conducted a discriminant function analysis (DFA) to derive equations that allowed us to determine the sex of the specimens from some of the measurements recorded in the field. Significant differences were found between males and females in wing length, third primary length, badge width and height and body weight. The DFA provided two functions that correctly classified the sex of 94.7% of the individuals using wing length and badge width, and 98.2% if weight was added to the analysis. Our results allow sexing from measurements that can be easily recorded in the field with the tools commonly used in banding sessions and without the need for additional training. Considerations of Bergmann’s and Allen’s rules on body size and the use of DFA in different populations are discussed.

Roosting patterns of House Sparrow Passer domesticus Linn., 1758 (Aves: Passeridae) in Bhavnagar, Gujarat, India

The House Sparrow Passer domesticus is widely distributed across the world, and local alarming declines in sparrow populations have prompted studies focused on this species. An understanding of fundamental life history aspects such as roosting patterns is necessary for the development of efficient conservation strategies. This study examined House Sparrow roosting patterns in urban, suburban and rural areas of Bhavnagar during 2017–2018. Potential roosting sites were identified, and peak arrival/ departure times and roosting duration of sparrows were recorded. We found that peak arrival and departure times were correlated with solar timings, indicating a strong influence of photoperiod on sparrow behaviour. Little variation was observed in sparrow arrival and departure times across the urban, suburban and rural gradient. However, arrival duration was significantly larger in urban and suburban areas. This may be due to the restricted availability of suitable patches within these habitats, requiring birds to spend more time foraging. House Sparrows mostly preferred thick vegetation for pre-roosting activities and roosting, and the loss of thick vegetation poses a threat to sparrow populations worldwide. In addition to increasing nesting opportunities by providing artificial nest sites, the importance of retaining appropriate habitats should be a major focus of conservation strategies.

Night Capture of Roosting Cave Birds by Neanderthals: An Actualistic Approach

Evidence is accumulating on the regular and systematic Neanderthal exploitation of birds. However, the motivations, mechanisms, and circumstances underlying this behavior remains little explored despite their potential implications on Neanderthal ecology and capabilities. Fossil remains of choughs (Pyrrhocorax, Corvidae) are among the most abundant in cave sites with Mousterian technology. We reviewed the evidence showing that Neanderthals processed choughs for food, and confirmed that it occurred frequently over a widespread spatial and temporal scale. This lead us to propose the hypothesis that the cave-like refuge is the keystone resource connecting Neanderthals and choughs captured at night in rocky shelters eventually used by both species. By adopting an actualistic approach, we documented the patterns of refuge use and population dynamics of communally roosting choughs, the strategies and technology currently used to capture them, and their behavioral response against experimental human predators at night. Actualistic experiments showed that large numbers of choughs can be captured without highly sophisticated tools at night regularly and periodically, due to their occupation year-round during long-term periods of the same nocturnal shelters, the constant turnover of individuals, and their high site tenacity at these roost-sites even after recurrent disturbance and predation. Captures even with bare hands are further facilitated because choughs tend to flee confused into the cavity in darkness when dazzled and cornered by human (experimental) predators. Given the extreme difficulty of daylight chough capturing in open country, nocturnal hunting with the help of fire in the roosting caves and consumption in situ are proposed as the most plausible explanations for the strong association of choughs and Neanderthals in fossil assemblages. Night hunting of birds has implications for the social, anatomical, technological, and cognitive capacities of Neanderthals.

Phenotypic and environmental correlates of natal dispersal in a long-lived territorial vulture

Natal dispersal, the movement between the birth and the first breeding site, has been rarely studied in long-lived territorial birds with a long-lasting pre-breeding stage. Here we benefited from the long-term monitoring programs of six populations of Egyptian vultures (Neophron percnopterus) from Spain and France to study how the rearing environment determines dispersal. For 124 vultures, we recorded a median dispersal distance of 48 km (range 0-656 km). Linear models were used to assess the effect of population and individual traits on dispersal distance at two spatial scales. Dispersal distances were inversely related to vulture density in the natal population, suggesting that birds perceive the abundance of conspecifics as a signal of habitat quality. This was particularly true for declining populations, so increasing levels of opportunistic philopatry seemed to arise in high density contexts as a consequence of vacancies created by human-induced adult mortality. Females dispersed further than males, but males were more sensitive to the social environment, indicating different dispersal tactics. Both sexes were affected by different individual attributes simultaneously and interactively with this social context. These results highlight that complex phenotype-by-environment interactions should be considered for advancing our understanding of dispersal dynamics in long-lived organisms.

Winter movement patterns of a globally endangered avian scavenger in south-western Europe

Partial migration, whereby some individuals migrate and some do not, is relatively common and widespread among animals. Switching between migration tactics (from migratory to resident or vice versa) occurs at individual and population levels. Here, we describe for the first time the movement ecology of the largest wintering population of Egyptian Vultures (Neophron percnopterus) in south-west Europe. We combined field surveys and GPS tracking data from December to February during four wintering seasons (2014–2018). The wintering population consisted on average of 85 individuals (range 58–121; 76% adults and 24% subadults). Individuals were counted at five different roosting sites located near farms, unauthorized carcass deposition sites and authorized carcass deposition sites. Our results show that vultures tend to remain close to the roosting site. Moreover, we observed that females exhibited smaller home range sizes than males, which suggests a possible differential use of food sources. Overall, birds relied more on farms than other available food resources, particularly subadult individuals which exploited more intensively these sites. Our results showed that Egyptian Vultures congregate in significant numbers at specific sites throughout the winter period in south-west Spain and that these roosting and feeding sites should be given some level of legal protection and regular monitoring. Furthermore, predictable food sources might be driving the apparent increase in the non-migratory population of Egyptian Vultures, as observed in other avian species which are also changing their migratory behavior.

Roosting Site Usage, Gregarious Roosting and Behavioral Interactions During Roost-assembly of Two Lycaenidae Butterflies

Lycaenidae is one of the larger of the world's butterfly families, based on number and diversity of species, but knowledge of roosting in this group is sparse. Zizina otis riukuensis and Zizeeria maha okinawana are two small lycaenids that are commonly found in urban settings and widely distributed across much of Asia. We conducted experiments on a university campus to determine the plant species and plant structures commonly used by these two blues when roosting. We also tested the hypothesis that gregarious roosting exists in these two blues by demonstrating the non-random distribution of roosting blues and the tight mapping of their roosts to the spatial distribution of specific plant species and/or specific plant structures, as well as by demonstrating behavioral interactions among individuals during roosting-assembly. We found that both Z. otis and Z. maha roosted primarily on flowers and fruits of Tridax procumbens and Vernonia cinerea. We also found that these blues formed conspicuous roosting aggregations with significant positive associations between the flowers and fruits of both T. procumbens and V. cinerea and the blues. Moreover, our behavioral observations showed that these blues expressed various levels of interaction during roosting gatherings. Based on these findings, we conclude that gregarious roosting exists in both Z. otis and Z. maha. To our knowledge, this paper represents one of the first demonstration of nocturnal gregarious roosting in lycaenids. This study also highlights the importance of institutional estates in providing roosting resources for butterflies in urban ecosystems.

Food predictability and social status drive individual resource specializations in a territorial vulture

Despite increasing work detailing the presence of foraging specializations across a range of taxa, limited attention so far has been given to the role of spatiotemporal variation in food predictability in shaping individual resource selection. Here, we studied the exploitation of human-provided carrion resources differing in predictability by Canarian Egyptian vultures (Neophron percnopterus majorensis). We focussed specifically on the role of individual characteristics and spatial constraints in shaping patterns of resource use. Using high-resolution GPS data obtained from 45 vultures tracked for 1 year, we show that individual vultures were repeatable in both their monthly use of predictable and semi-predicable resources (feeding station vs. farms) and monthly levels of mobility (home range size and flight activity). However, individual foraging activities were simultaneously characterized by a high degree of (temporal) plasticity in the use of the feeding station in specific months. Individual rank within dominance hierarchy revealed sex-dependent effects of social status on resource preference in breeding adults, illustrating the potential complex social mechanisms underpinning status-dependent resource use patterns. Our results show that predictable food at feeding stations may lead to broad-scale patterns of resource partitioning and affect both the foraging and social dynamics within local vulture populations.

Extreme genetic structure in a social bird species despite high dispersal capacity

Social barriers have been shown to reduce gene flow and contribute to genetic structure among populations in species with high cognitive capacity and complex societies, such as cetaceans, apes and humans. In birds, high dispersal capacity is thought to prevent population divergence unless major geographical or habitat barriers induce isolation patterns by dispersal, colonization or adaptation limitation. We report that Iberian populations of the red-billed chough, a social, gregarious corvid with high dispersal capacity, show a striking degree of genetic structure composed of at least 15 distinct genetic units. Monitoring of marked individuals over 30 years revealed that long-distance movements over hundreds of kilometres are common, yet recruitment into breeding populations is infrequent and highly philopatric. Genetic differentiation is weakly related to geographical distance, and habitat types used are overall qualitatively similar among regions and regularly shared by individuals of different populations, so that genetic structure is unlikely to be due solely to isolation by distance or isolation by adaptation. Moreover, most population nuclei showed relatively high levels of genetic diversity, suggesting a limited role for genetic drift in significantly differentiating populations. We propose that social mechanisms may underlie this unprecedented level of genetic structure in birds through a pattern of isolation by social barriers not yet described, which may have driven this remarkable population divergence in the absence of geographical and environmental barriers.

Cliffs used as communal roosts by Andean condors protect the birds from weather and predators

The quality and availability of resources influence the geographical distribution of species. Social species need safe places to rest, meet, exchange information and obtain thermoregulatory benefits, but those places may also serve other important functions that have been overlooked in research. We use a large soaring bird that roosts communally in cliffs, the Andean condor (Vultur gryphus), as a model species to elucidate whether roost locations serve as a refuge from adverse weather conditions (climatic refuge hypothesis, CRH), and/or from predators or anthropogenic disturbances (threats refuge hypothesis, TRH). The CRH predicts that communal roosts will face in the opposite direction from where storms originate, and will be located in climatically stable, low precipitation areas. The TRH predicts that communal roosts will be large, poorly accessible cliffs, located far from human-made constructions. We surveyed cliffs used as communal roosts by condors in northwestern Patagonia, and compared them with alternative non-roosting cliffs to test these predictions at local and regional scales. We conclude that communal roosting places provide refuge against climate and disturbances such as, for instance, the threats of predators (including humans). Thus, it is not only the benefits gained from being aggregated per se, but the characteristics of the place selected for roosting that may both be essential for the survival of the species. This should be considered in management and conservation plans given the current scenario of global climate change and the increase in environmental disturbances.

Genetic composition of communal roosts of the Eurasian Magpie (Pica pica) inferred from non-invasive samples

Many animal species form communal roosts in which they aggregate and sleep together. Several benefits of communal roost have been suggested, but due to lack of data on relatedness among group members, it is unknown whether these benefits can be amplified by the formation of kin-based communal roosts. We investigate the genetic composition of two winter roosts of Eurasian Magpies (Pica pica), using microsatellite markers on non-invasive samples. Using permutation tests by reshuffling the alleles presented in the roosts, we determined that individuals in the communal roosts of magpies were not more related than expected by chance, suggesting that kinship may not be a driving force for the formation of communal roosts in magpies. However, the pairwise relatedness and estimated relationship based on a maximum likelihood approach revealed that the roosts involve both kin and non-kin. Relatedness coefficients varied widely within a roost, indicating that family subgroups form a small proportion of the total number of birds in a roost. Our results suggest that ecological benefits of communal roost in animals are sufficient for the evolution of communal roosts without any involvement of kinship.

Captive husbandry and socialization of the red-billed chough (Pyrrhocorax pyrrhocorax)

Since the 1970s, Paradise Park Wildlife Sanctuary in Cornwall, United Kingdom, has built up a captive flock of red-billed choughs Pyrrhocorax pyrrhocorax and over 30 years has developed successful methods of keeping, breeding, and appropriately socializing them in captivity. A total of 77 nests reached the egg stage with 27 nests producing at least one young and 48 young fledging in total. Several components are important in achieving successful breeding and socialization. Provision of live food, especially ant's eggs and small mealworms and crickets, in the first days after hatching is essential, improving the condition of adults and survival of nestlings. Situating aviaries in quiet areas, away from public view, is important. Socialization in family groups during the winter months and allowing choughs to choose partners induces better compatibility. Introduction of nest cameras greatly improved young survival through early identification of health problems enabling treatment of young between hatching and 10-days old, when mortality is otherwise highest, and enabling precautionary medication shortly after hatching. We show that clutch size increases significantly with female age and that direct intervention such as artificial egg incubation and hand rearing can be successful and worthwhile, but its requirement is reduced by closer monitoring. Red-billed choughs provide a good model species to further develop captive management and release techniques that can then be applied to critically endangered species that show similar social and long-learning behaviors. Captive breeding programs can play an important role in such work through provision of suitable birds and supporting avicultural expertise.

Spatial heterogeneity in resource distribution promotes facultative sociality in two trans-Saharan migratory birds

Background

Migrant populations must cope not only with environmental changes in different biomes, but also with the continuous constraints imposed by human-induced changes through landscape transformation and resource patchiness. Theoretical studies suggest that changes in food distribution can promote changes in the social arrangement of individuals without apparent adaptive value. Empirical research on this subject has only been performed at reduced geographical scales and/or for single species. However, the relative contribution of food patchiness and predictability, both in space and time, to abundance and sociality can vary among species, depending on their degree of flexibility.

Methodology/Principal Findings

By means of constrained zero-inflated Generalized Additive Models we analysed the spatial distribution of two trans-Saharan avian scavengers that breed (Europe) and winter (Africa) sympatrically, in relation to food availability. In the summering grounds, the probability of finding large numbers of both species increases close to predictable feeding sources, whereas in the wintering grounds, where food resources are widespread, we did not find such aggregation patterns, except for the black kite, which aggregated at desert locust outbreaks. The comparison of diets in both species through stable isotopes revealed that their diets overlapped during summering, but not during wintering.

Conclusions/Significance

Our results suggest that bird sociality at feeding grounds is closely linked to the pattern of spatial distribution and predictability of trophic resources, which are ultimately induced by human activities. Migrant species can show adaptive foraging strategies to face changing distribution of food availability in both wintering and summering quarters. Understanding these effects is a key aspect for predicting the fitness costs and population consequences of habitat transformations on the viability of endangered migratory species.

Density-dependent productivity depression in Pyrenean Bearded Vultures: implications for conservation

The main objective of many conservation programs is to increase population size by improving a species' survival and reproduction. However, density dependence of demographic parameters may confound this approach. In this study we used a 25-year data set on Bearded Vultures (Gypaetus barbatus) in Spain to evaluate the consequences of population growth on reproductive performance. Unlike its coefficient of variation (cv), mean annual productivity decreased with increasing population size. After controlling for territorial heterogeneity, productivity also was negatively related to the distance to the nearest conspecific breeding pair and to supplementary feeding points where floaters congregate. These results suggest that vulture populations are regulated as posited by the site-dependency hypothesis: as the population increases, average productivity decreases because progressively poorer territories are used. The combined effects of the shrinkage of territories and the presence of floaters around supplementary feeding points seem to be the main causes of productivity decline and are therefore the main determinants of territory quality. This has conservation implications, especially concerning the role of supplementary feeding points. Supplementary feeding should be reviewed given that its usefulness in reducing preadult mortality has not yet been proved and its effect on productivity, as our results suggest, is negative.

Ignorant hooded crows follow knowledgeable roost-mates to food: support for the information centre hypothesis

Communal roosting in birds may function to enhance foraging efficiency as explained by the information centre hypothesis, which predicts that successful foragers return from the roost to the rewarding food patch and that birds ignorant of this food follow knowledgeable roost-mates. We tested these predictions by exposing 34 radio-tagged, free-ranging, flock-living hooded crows (Corvus corone cornix) to a novel experimental set-up mimicking a superfluous food patch with maximum temporal and spatial unpredictability Each replicate lasted two days and was located on a new site. Data were collected during ten replicates over three years. First, a crow was more likely to visit the experimental food patch on the second day when it had been there on the first day. Second, when a crow had not been at this food patch on the first day, it was more likely to visit it on the second day if it had roosted together with a crow that had been there on the first day, but only if this knowledgeable roost-mate returned to the food patch on the second day. Our results support the information centre hypothesis and suggest that communal roosting might function to enhance foraging efficiency in hooded crows.

Sexual Size Dimorphism and Positive Assortative Mating in Alpine Choughs (Pyrrhocorax graculus)

The degree of sexual size dimorphism in a number of different morphological characters was examined in a social corvid, the Alpine Chough, using measurements taken on 178 males and 144 females. A small amount of size dimorphism appeared in all morphological characters, and weight was the most dimorphic character. To identify if Alpine Choughs mate assortatively, measurements of mates were compared in 76 pairs. A positive assortative mating was found on tarsus length, and a small positive trend is suggested between body condition of partners, but that needs to be confirmed with a larger sample size.