Communal Roosts Research Articles

Common myna roosts are not recruitment centres.

We studied communal roosting in the Common Myna (Acridotheres tristis) in the light of the recruitment centre hypothesis and predation at the roost. The number and sizes of flocks departing from and arriving at focal roosts were recorded over a two year period. We also recorded the sizes and behaviour of foraging flocks. We found that flock sizes of birds departing from roosts at sunrise were larger than those at the feeding site, suggesting that there was no recruitment from the roosts. Flocks entering the roosts during sunset were larger on average than those leaving the following sunrise, suggesting no consolidation of flocks in the morning. Flocks entering the roosts at sunset were also larger on average than those that had left that sunrise, although there was no recruitment at the feeding site. There was no effect of group size on the proportion of time spent feeding. Contrary to expectation, single birds showed lower apparent vigilance than birds that foraged in pairs or groups, possibly due to scrounging tactics being used in the presence of feeding companions. Thus, the recruitment centre hypothesis did not hold in our study population of mynas. Predation at dawn and dusk were also not important to communal roosting: predators near the roosts did not result in larger flocks, and resulted in larger durations of arrival/departure contrary to expectation. Since flock sizes were smallest at the feeding site and larger in the evening than in the morning, but did not coincide with predator activity, information transfer unrelated to food (such as breeding opportunities) may possibly give rise to the evening aggregations.

Roosting behavior and group decision making in 2 syntopic bat species with fission-fusion societies

In many social species, individuals make group decisions to coordinate their actions. Despite the importance of group decisions for successful group living, few studies investigated how wild animals make group decisions in situations where group members have conflicting interests. This lack of empirical data is most evident for animal groups that regularly split into subgroups for some time. In groups with high fission–fusion dynamics, individuals can avoid group decisions that are not in their interest without foregoing benefits from being social. Here, we compare group decision making about communal day roosts in 2 syntopic bat species with a similar ecology and life history but a different fission–fusion behavior of their colonies. Daily roost monitoring during 3 breeding seasons showed that Bechstein’s bats formed subgroups 5 times more often than brown long-eared bats although both species occupied a similar number of bat boxes per colony and year. Bechstein’s bats were also significantly faster in discovering newly installed boxes and explored them further away from their established roosting areas compared with brown long-eared bats. In a field experiment where we created a conflict of interests among colony members where to roost, brown long-eared bats always achieved a colony-wide consensus about communal roosts. On the contrary, in Bechstein’s bats, individuals with conflicting interests often formed subgroups in different roosts according to their individual interests instead of reaching a consensus on a single communal roost. Our findings show that even ecologically similar species can use different group decision-making rules for solving an identical coordination problem.

Communal roosting sites are potential ecological traps: experimental evidence in a Neotropical harvestman

Situations in which animals preferentially settle in low-quality habitat are referred to as ecological traps, and species that aggregate in response to conspecific cues, such as scent marks, that persist after the animals leave the area may be especially vulnerable. We tested this hypothesis on harvestmen (Prionostemma sp.) that roost communally in the rainforest understory. Based on evidence that these animals preferentially settle in sites marked with conspecific scent, we predicted that established aggregation sites would continue to attract new recruits even if the animals roosting there perished. To test this prediction, we simulated intense predation by repeatedly removing all individuals from 10 established roosts, and indeed, these sites continued to attract new harvestmen. A more likely reason for an established roost to become unsuitable is a loss of overstory canopy cover caused by treefalls. To investigate this scenario, without felling trees, we established 16 new communal roosts by translocating harvestmen into previously unused sites. Half the release sites were located in intact forest, and half were located in treefall gaps, but canopy cover had no significant effect on the recruitment rate. These results support the inference that communal roost sites are potential ecological traps for species that aggregate in response to conspecific scent.

Effect of food patch discovery on the number of American Crows (<em>Corvus brachyrhynchos</em>) using a flight lane

In winter, American Crows (Corvus brachyrhynchos) move back and forth between night roosts and foraging sites along flight lanes. If communal roosts act as information centres, we would expect more birds to use a particular flight lane after discovery of a new food patch on that route. In this study, I investigated how the number of crows using different flight lanes was affected by the establishment of artificial food patches, as well as how crows responded to multiple days of provisioning and to the location of the food patch relative to the flight lane. After discovery of a food patch, the number of crows using the flight lane closest to it increased, while numbers using adjacent flight lanes remained the same or decreased, particularly when the patch was in the path of the flight lane and when food provisioning occurred for 2 consecutive days. These results support the idea that crows using winter roosts may make use of information on food availability obtained at the roost.

Commonness of not-so-common birds: the need for baseline knowledge of actual population size for the validation of population size predictions

Capsule The hypothesized regional population size of a common species in Spain was found to be unreliable when compared with a complete and simultaneous single-species direct census.Aims To provide a regional census of Eurasian Jackdaws Corvus monedula as an example to highlight the crucial importance of baseline knowledge of actual population size of common species for validation and calibration of population size predictions derived from extrapolation.Methods Population size was measured by means of simultaneous counts of winter communal roosts after determining the best census date and other relevant information on flock routines, foraging areas and potential sources of count variability.Results A large discrepancy between hypothesized (∼330 000 individuals) and directly censused population size (∼15 000 individuals) was recorded.Conclusion Programmes aimed at establishing population size of wildlife by statistical inference should attempt to explicitly test their predictions by comparison with directly censused population sizes of particular species in control areas.

Congregations of wintering Egyptian Vultures Neophron percnopterus in Afar, Ethiopia: present status and implications for conservation

The Endangered Egyptian Vulture Neophron percnopterus congregates in communal roosts in the wintering areas and where food availability is high, where even a single threat might lead to substantial population declines. Thus, more research on the congregation sites is needed for timely detection of threats and effectively directed conservation measures. We studied bird numbers, use of roosting substrates and roosting habitat of wintering Egyptian Vultures in Ethiopia. Vultures were counted using the road-count technique in 2009, 2010 and 2013 along c. 600 km of roads in the Afar region. Over 1 000 individuals were counted each year and the sites with the highest congregations were identified. Nearly half of the birds were adults and the majority roosted on bird-safe types of electric pylons. Most of the Egyptian Vultures were found below 500 m above sea level, in bare areas, open savannas or grasslands, and their abundance was negatively related to the amount of cover of bush vegetation. The distribution of roosting birds was not affected by distance to human settlements. To avoid disasterous effects on the population of the Egyptian Vultures, we strongly recommend that the sites sheltering the highest numbers of roosting birds should be included in the Important Bird Area network, the use of poisons should be banned, and dangerous power lines should be insulated or substituted with safer types.

Behavioral drivers of communal roosting in a songbird: a combined theoretical and empirical approach

Communal roosting is a taxonomically widespread phenomenon, with considerable variation in patterns of roost dynamics. Some organisms roost together in different locations each night (or day), whereas others roost in traditional locations each night, sometimes switching between roosts in the roost network. The behaviors that drive roost-site selection and the resulting patterns are not well understood. We created an individual-based model that simulates the daily aggregation of organisms into communal roosts. In the model, individuals move according to a movement rule integrating 2 independently adjustable behavioral drivers: roost fidelity, which leads individuals back toward their previous nights’ roost, and conspecific attraction, which leads individuals to congregate toward nearest conspecific neighbors. The model predicts that variable levels of aggregation will emerge under different combinations of these drivers, ranging from no aggregation to complete aggregation of individuals into their previous roosts. We tested to see which combination of drivers best predicts patterns of roost use in our study system of Tree Swallows (Tachycineta bicolor) in southeastern Louisiana in fall. Using Doppler weather radar data, we show that Tree Swallow roost sites remain consistent from night to night, and the birds return to one of several traditional roosts. Using radio telemetry, we show that individuals switch between these traditional roosts at minimum 22% of the time. Our results suggest that the formation of large communal roosts in Tree Swallows is driven by a combination of moderate conspecific attraction and strong, but not perfect, roost fidelity.

Communal Roosting inHeliconiusButterflies (Nymphalidae): Roost Recruitment, Establishment, Fidelity, and Resource Use Trends Based on Age and Sex

ABSTRACT. Heliconius passion-vine butterflies form communal roosts on a nightly basis as an anti-predatory defense. Although past studies have evaluated various components of this behavior, much remains unknown about many basic aspects of roost dynamics. To learn more about communal roosting I examined roost establishment, recruitment, roost-mate resource use, roosting participation in a population, and roost arrival, departure, and perch preferences in natural populations of Heliconius erato petiverana in Panama. My observations suggest that 1) younger butterflies are recruited more readily than older butterflies, 2) roosts are first established by a single butterfly roosting consecutively in the same location that later recruits butterflies, 3) males depart roosts earlier than females in the morning, 4) older butterflies tend to roost on the same perch in the same roost every night, 5) roost-mates share the same resource traplines, and 6) most butterflies in a population participate in roosts. These obs...

A Communal Roosting of the Great Horned Owl (Bubo virginianus)

A Communal Roosting of the Great Horned Owl (<i>Bubo virginianus</i>)

Long-Term Dynamics of Long-Eared OwlsAsio otusat a Northern Winter Roost in European Russia

We investigated the factors influencing the dynamics of Long-eared Owls Asio otus wintering in Moscow. The study was carried out in 2001–2011. Twelve communal roosts and 14 solitary wintering owls were found. Number of active roosts was positively correlated with the total number of wintering owls per year. The four largest roosts were active for many years, with up to 16 individuals in a single winter (9.9 ± 1.3 on average). Generalized linear models indicated that the number of wintering owls was influenced simultaneously by the abundance of Common Vole Microtus arvalis in the previous autumn and in spring, and the owls' breeding numbers in the study plot. The most important factor was vole abundance in early spring indirectly indicating food supply in late winter. The influence of weather was investigated on the regularly surveyed local site in Moscow. The maximum number of owls at the roosting site varied from 0 to 9 individuals (2.1 ± 0.4 on average). Among weather factors, the most important influence on the dynamics of owls was by snow cover and wind jointly, though the snow was undoubtedly of greatest significance. Air temperature and precipitation turned out to be almost of no importance for owl dynamics at the roosting site.

Avian roosting behavior influences vector-host interactions for West Nile virus hosts.

BackgroundExtensive work has shown that vectors almost never feed at random. Often, a subset of individual hosts and host species are fed on much more frequently than expected from their abundance and this can amplify pathogen transmission. However, the drivers of variation in contact patterns between vectors and their hosts are not well understood, even in relatively well-studied systems such as West Nile virus (WNV).MethodsWe compared roosting height and roost aggregation size of seven avian host species of WNV with patterns of host-seeking mosquito (Culex pipiens) abundance at communal and non-communal roost sites.ResultsFirst, host-seeking mosquito abundance increased with height and paralleled increased mosquito feeding preferences on species roosting higher in the tree canopy. Second, there were several hundred-fold fewer mosquitoes per bird trapped at American robin (Turdus migratorius) communal roosts compared to non-communal roost sites, which could reduce transmission from and to this key amplifying host species. Third, seasonal changes in communal roost formation may partly explain observed seasonal changes in mosquito feeding patterns, including a decrease in feeding on communal roosting robins.ConclusionsThese results illustrate how variation in habitat use by hosts and vectors and social aggregation by hosts influence vector-host interactions and link the behavioral ecology of birds and the transmission of vector-borne diseases to humans.

Communal roosting and the seasonal dynamics of the hen harrier Circus cyaneus in the Záhorie region

Abstract A count of hen harriers Circus cyaneus was carried out at roost sites in south-western Slovakia from 1 992-2013. The number of sites and also the frequency of survey visits were different in different years. A total of 1 03 counts were carried out. Hen harriers were not seen roosting at the sites in 13 cases. In all, 10 localities with 14 roost sites were checked. Hen harriers roosted in sedge (5) or in ruderal associations (6) and meadows (3). A total of 634 individuals were recorded roosting. There were 483 brown birds (adult females and immature birds in the first calendar year) and 151 grey birds (males in the second calendar year and older). The average number of hen harriers at the roost sites ranged from 3 to 9 individual birds. The maximum number was at least 27 individuals (December 15, 2011 ; a minimum of 18 brown birds and 9 grey birds, Moravský Svätý Ján, Pacitov locality). The percentage of roosting males was 23.76%. The time period of roosting was also recorded. The last individuals were observed flying over the site from six minutes before sunset to 40 minutes after sunset. The average time of the last observation was approximately 1 7 minutes after sunset. The average luminosity at the last observation of an active individual bird was 28 lux. Hen harriers migrate from October to March in the study area. Occurrences in September, respectively in April and May, were very rare. Most registration and the highest number of individual birds were recorded in October, but especially in December and February.

Movements of a juvenile red kite Milvus milvus in the border zone of Aaustria, Slovakia and the Czech Republic

Abstract One juvenile female red kite was tracked during 2011-2013. The bird was tagged with a leg-mount radio transmitter in a nest in the Záhorská nížina Lowland in western Slovakia. Movements were monitored in the natal area and in the temporary settlement area (TSA). These areas were 40 km apart. The location of the TSA in the border zone ofAustria, Slovakia and the Czech Republic confirmed information about the wintering of local birds in the region. The temporary settlement area (MCP = 402.0 km2, 95% FKP = 622.8 km2, 50% FKP = 68.6 km2) was mainly situated in Austria. The natal area was significantly smaller (MCP = 34.7 km2, 95% FKP = 32.3 km2, 50% FKP = 5.0 km2). The juvenile hunted an average of 12.5 km from the communal roost place.

Factors influencing the selection of communal roost sites by the Black Vulture Coragyps atratus (Aves: Cathartidae) in an urban area in Central Amazon

Increasing populations of the Black Vulture, Coragyps atratus (Bechstein, 1793) and the capacity this bird has to live near humans has resulted in vulture-human conflicts. These conflicts increase the need for the effective management of vultures. Improved understanding of communal roosting dynamics is a key aspect of vulture biology that provides information for effective management that can mitigate conflicts. Here we investigated factors influencing roosting site selection by Black Vultures in Manaus. We monitored 40 native vegetation remnants (VR), visiting each VR twice (two independent observers) between 5:00 p.m. and 6:00 p.m. once every two-three months from June to November 2011. Using maximum-likelihood analysis and information-theoretic multimodel inference, we investigated the effects of VR covariates (size, shape, and location relative to feeding sites, to thermal power plants, and to other VRs) on VR occupancy by roosting Black Vultures. Distance to feeding sites (mainly garbage-dumping sites) was identified as the most important covariate (model-averaged β = -0.62, SE = 0.26) and the other variables had no significant effects. Our results indicate that Black Vultures adjusted to the nearest possible roost to the food source to reduce the cost of movement. This suggests that reducing Black Vulture access to food through simple waste management and sanitation policies, including public education, may help reduce vulture-human conflicts in Manaus.

Female Bechstein’s Bats Adjust Their Group Decisions about Communal Roosts to the Level of Conflict of Interests

Most social animals depend on group decisions for coordination. Recent models suggest that the level of interindividual conflict strongly influences whether groups reach a consensus during decision making. However, few experimental studies have explored how wild animals make group decisions in situations with conflicting interests. Such experimental data are particularly lacking for animal societies with regular fission and fusion of subgroups. In this long-term study, we varied the level of conflict of interest among members of three wild Bechstein's bat (Myotis bechsteinii) colonies with high fission-fusion dynamics experimentally to explore whether the bats adapt their group decisions about communal roosts accordingly. In situations with low levels of conflict of interest, a minority of bats experiencing a roost as suitable was sufficient for a group consensus to use it communally. In contrast, if their interests diverged strongly, the bats no longer sought a compromise, but based their roosting decisions on individual preferences instead. Our results demonstrate that the rules applied to make group decisions can vary with the level of conflict among the individual interests of group members. Our findings are in agreement with predictions of the models and provide evidence for highly flexible group decisions within species.

Dominance, not kinship, determines individual position within the communal roosts of a cooperatively breeding bird

Kin selection has played an important role in the evolution and maintenance of cooperative breeding behaviour in many bird species. However, although relatedness has been shown to affect the investment decisions of helpers in such systems, less is known about the role that kin discrimination plays in other contexts, such as communal roosting. Individuals that roost communally benefit from reduced overnight heat loss, but the exact benefit derived depends on an individual's position in the roost which in turn is likely to be influenced by its position in its flock's dominance hierarchy. We studied the effects of kinship and other factors (sex, age, body size and flock sex ratio) on an individual's roosting position and dominance status in captive flocks of cooperatively breeding long-tailed tits Aegithalos caudatus. We found that overall, kinship had little influence on either variable tested; kinship had no effect on a bird's position in its flock's dominance hierarchy and the effect of kinship on roosting position was dependent on the bird's size. Males were generally dominant over females and birds were more likely to occupy preferred roosting positions if they were male, old and of high status. In this context, the effect of kinship on social interactions appears to be less important than the effects of other factors, possibly due to the complex kin structure of winter flocks compared to breeding groups.

Avian Hosts of West Nile Virus in Arizona

West Nile virus (WNV) causes sporadic outbreaks of human encephalitis in Phoenix, Arizona. To identify amplifying hosts of WNV in the Phoenix area, we blood-sampled resident birds and measured antibody prevalence following an outbreak in the East Valley of metropolitan Phoenix during summer, 2010. House sparrow (Passer domesticus), house finch (Haemorhous mexicanus), great-tailed grackle (Quiscalus mexicanus), and mourning dove (Zenaida macroura) accounted for most WNV infections among locally resident birds. These species roost communally after early summer breeding. In September 2010, Culex vector-avian host contact was 3-fold greater at communal bird roosts compared with control sites, as determined by densities of resting mosquitoes with previous vertebrate contact (i.e., blood-engorged or gravid mosquitoes). Because of the low competence of mourning doves, these were considered weak amplifiers but potentially effective free-ranging sentinels. Highly competent sparrows, finches, and grackles were predicted to be key amplifying hosts for WNV in suburban Phoenix.

Social ordering of roosting by cooperative breeding buff-throated partridges Tetraophasis szechenyii

The benefits of communal roosting are unlikely to be acquired equally by all roosting birds, and it has been suggested that individual ordering during roost formation can be determined by factors such as social status. However, to date there have been no published data on this issue among precocial, cooperative breeders. We examined social ordering of roosting by buff-throated partridges Tetraophasis szechenyii, a typical cooperative breeding Galliform species newly found where group members roost in a linear huddle. We revealed that the breeding male was normally the first to enter roosting trees and a helper entered last, regardless of whether groups had young or not (n = 50 observations from seven groups). In a linear huddle, a helper frequently occupied the outermost position, especially in groups with young, and young birds were often squeezed into the center (n = 48 observations from seven groups). For buff-throated partridges, we suggest that while structuring of communal roosts confers the greatest energy benefits and protection from predators to young birds, helpers, rather than the breeding male, may face higher costs in terms of lookout and thermoregulation. To further understand social ordering of roosting by buff-throated partridges, future studies need to examine quantitatively the relative value of predation risk and/or thermoregulatory costs among roosting members placed in certain ordering, and determine the relatedness indices among group members.

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.

Variability in size of groups in communal roosts: influence of age-class, abundance of individuals and roosting site

Many birds roost communally but their patterns of use of communal roosts is generally poorly known. For conservation purposes, and to better understand communal roosting generally, it is important to know the factors that influence the size of groups at roosts. I studied the effect of age-class, number of individuals and roosting site on the patterns of variation in the size of communally roosting groups of Andean Condors (Vultur gryphus). I fitted a variance-mean relationship (Taylor's Power Law, TPL) to the number of individuals that roosted daily at seven communal roosts, and made temporal (in each roost) and spatial (among roosts) comparisons of the relationship. The abundance of individuals at a roost fitted the TPL well, both temporally and spatially. The variation in the abundance of individuals was significantly influenced by the roosting site selected, independent of the effect of the mean number of individuals. Moreover, the effect of roosting site on the variability of abundance of individuals was stronger than the effect of age-class. Accordingly, I highlight the importance of the roosting site in modulating variation in the size of groups of communally roosting individuals. This understanding of the patterns of variation in the use of communal roosts could aid in determining the importance of sites for the conservation of a species.