The influence of light intensity on the roosting times of the rook (Corvus frugilegus)

Little work has been done on the roosting behaviour of Corvidae, particularly the influence of light-intensity on its timing. This paper describes the effects of light-intensity on the roosting times of rooks (Corvus frugilegus) from a large roost during winter. Light intensity was measured and its influence on the departure of birds from the feeding grounds, arrival at the roost, entry into the roost and morning departure was found to be significant. Departure from feeding areas (and arrival at the roost) was earlier at lower light-intensities and later at higher light-intensities. Control of responsiveness to light-intensity by circadian rhythm for rooks from different feeding grounds was discussed.     

Effect of weather conditions on the communal roosting behaviour of common ravens <Emphasis Type="Italic">Corvus corax</Emphasis> with unlimited food resources

Avian time–activity budgets are known to be affected by many environmental factors. The aim of this study was to examine whether roosting times of common ravens Corvus corax are affected by inclement weather conditions in response to increased energy demands. The study was conducted at a communal roost of ravens in Thuringia, Germany, from August 2003 to January 2005. The number of roosting ravens fluctuated substantially, ranging from zero individuals in summer to 574 in winter. During the entire study period, a composting facility served as the main feeding ground for roosting ravens. There, the feeding-to-resting ratio did not depend on flock size, indicating the ravens were not food limited. Ravens arrived at the preroost and the roost later relative to sunset on cloudless evenings and on days with shorter length of daylight. Weather conditions measured as ambient temperature, wind speed, and cumulative daily precipitation had no effect on arrival times at the preroost and the roost. Likewise, moonlight did not affect roosting times. Apparently, flexible time–activity budgets resulting from a superabundant food supply may have enabled ravens to moderate the effects of environmental conditions on arrival times at the preroost and the roost.     

Synchronous nocturnal activity and gregarious roosting in the neotropical skipper butterfly Celaenorrhinus fritzgaertneri (Lepidoptera: Hesperiidae)

Gregarious roosting behaviour and nocturnal activity is virtually unknown within the family Hesperiidae. Observations on Celaenorrhinus fritzgaertneri (Bailey) from Guanacaste Province, Costa Rica, are presented which demonstrate that, during the dry season, individuals roost gregariously in cave-like situations during the day and are nocturnally active. Circadian behaviour is highly synchronized with regard to timing of departures and arrivals at the roosting site, and appears to be regulated by light levels. Individuals on the roost are in reproductive diapause and show marked roost-site fidelity and longevity. The break-up of roosts appears to be mediated by the onset of the first rains of the season. These observations are compared and discussed in relation to gregarious roosting in other Lepidoptera. Two possible life history strategies to explain roosting in C. fritzgaertneri , with appropriate experiments, are suggested for future studies.     

Microhabitat use and social structure in Linnet Carduelis cannabina and Corn Bunting Miliaria calandra at a winter roost in central Spain

Capsule Both species selected particular patches for roosting, and Linnets but not Corn Buntings showed a social structure with males occupying the preferred roosting positions.

Aims To evaluate microhabitat preferences of Linnet and Corn Bunting within a winter communal roost, and to examine roost structure according to sex, age and body size.

Methods We captured Linnets and Corn Buntings along a habitat gradient in a reed-bed in central Spain when they were coming to roost. Each bird was sexed, aged, and several body traits were measured. We also characterized the habitat patches where the birds were trapped and grouped patches according to their similarity.

Results Three groups of patches were defined according to reed structure. Linnets preferred patches with low density of high and thick shoots, while Corn Buntings preferably used patches with intermediate values for these variables. Interspecific competition for preferred positions was not evident. Male Linnets were proportionately more abundant in the preferred patches, and individuals in lower body condition, independent of sex, age or body size, occupied the non-preferred patches. Male Corn Buntings were less abundant, bigger in size, and showed better condition than females, although differences in body size and condition were not apparent among patches within the roost.

Conclusion Our results suggest that among-patch differences in structure and location within a reed-bed generate microhabitats that differ in quality for roosting passerines. This habitat heterogeneity in turn seems to be responsible for the social spatial structure observed in Linnets, in which females and individuals in poor physiological condition were displaced, possibly through competition, towards non-preferred positions. The relatively small body size of Linnets compared to Corn Buntings might explain Linnets' preference for patches that seem to provide more protection against harsh weather conditions.     

The effects of season,sex, age and weather on population-level variation in the timing of activity in Eurasian Blue Tits Cyanistes caeruleus

All birds sleep and many do so in a specific location, the roost. Thus, every day each individual needs to decide when to go to (enter) and leave the roosting place. This determines the timing of activity, a trait shaped by both natural and sexual selection. Despite its importance in a variety of contexts, including foraging, predation, mating success and parental care, variation in the timing of activity has rarely been studied. Here, we describe this variation in a population of Eurasian Blue Tits Cyanistes caeruleus roosting in nestboxes using data collected over 7 years. We investigate seasonal changes in the start and end of activity and assess to what extent these parameters are sex- and age-specific and affected by weather. We show that the start of activity is relatively constant in relation to sunrise during winter but undergoes drastic changes during the breeding season. The end of activity is markedly later relative to sunset in mid-winter and is also strongly influenced by breeding behaviour. Females generally start their activity later and end it earlier than males. The duration of daily activity is shorter during periods of rain and longer when temperatures are relatively high for the time of year.     

Communal roosting behaviour of the black kite (<Emphasis Type="Italic">Milvus migrans govinda</Emphasis>) in an urban metropolis

Research on raptors in general in India is scanty, and it is practically non-existent on black kites (Milvus migrans govinda) which are the major scavenging raptor in many urban areas. The aim of this study was to analyse the seasonal abundance and roosting behaviour of black kites in an urban metropolis. Data on the abundance and behaviour of roosting black kites in this setting were collected using evening roost counts and ad-libitum sampling, respectively. Analysis was performed using separate generalized linear models considering roosting kite abundance, number of black kites arriving to roost and number of black kites showing pre-roosting display as response variables, respectively. We found that black kites roosted communally and that their number varied in different years and seasons, with the abundance highest in the summer and lowest during the winter. Pre-roosting displays also varied seasonally, being highest during the monsoon and at a minimum in the winter. In our urban setting, black kites arrived at the roosting sites mostly after sunset, and their arrival was influenced by sunset time, temperature, relative humidity and season. Some behavioural aspects of black kites within the roosts were also documented. This is the first quantitative assessment of roosting black kite abundance in Kolkata, India, and our data provide insight on the roosting behaviour of these birds relative to various environmental parameters.     

Roosting behaviour is related to reproductive strategy in brood parasitic cowbirds

Shiny Cowbirds Molothrus bonariensis and Screaming Cowbirds Molothrus rufoaxillaris are closely related brood parasites but the former is socially polygynous or promiscuous and an extreme host generalist, whereas the latter is socially monogamous and parasitizes almost exclusively one host. Females of both species lay in relative darkness, before dawn, relying for host nest location on previous days’ prospecting activity, or possibly on following better‐informed roost associates. We studied the temporal and spatial patterns of roosting behaviour in these species to test the hypothesis that roosting behaviour of cowbirds is related to their breeding strategy (brood parasitism) and reflects differences in strategies between species. We recorded fidelity to a roost, location fidelity within a roost, inter‐individual spatial associations and timing of roost departures and parasitic events, using tagged individuals. Female Shiny Cowbirds and both sexes of Screaming Cowbirds showed marked fidelity in roosting location, and roost departures occurred both during and after the known time window for parasitism, with earlier departures probably corresponding to laying days. Screaming Cowbird females and males that were trapped together and showed high levels of association during the day, also showed high levels of association in the roost. We describe the spatial and temporal patterns of a relatively poorly known aspect of avian ecology in general and the behaviour of brood parasites in particular.     

Roosting associations of flat-headed bats, Tylonycteris species (Chiroptera: Vespertilionidae) in Malaysia

Roosting associations of Tylonycteris pachypus and T. robustula were studied in West Malaysia. Both species roosted within the internodes of one species of bamboo, but were only once found together at roost. Roosting groups, which formed before entry in the morning, were not limited in size by the dimensions of the roost site. In both species the sexes exhibited different roosting behaviour, the males tending to be solitary and the females gregarious. Seasonal variations in associations occurred correlated with the reproductive cycle. Banding demonstrated that the populations were highly mobile, that the bats frequently changed roost sites, and that the roosting associations were of an ephemeral nature.     

WINTER ROOSTING AND FEEDING BEHAVIOUR OF PIED WAGTAILS MOTACZLLA ALBA NEAR OXFORD, ENGLAND

This study presents data on the roosting and feeding behaviour of Pied Wagtails around Oxford, England. During the winter of 1977–78, from two to 1200 wagtails roosted in a Phragmites reed-bed. Use of this roost was greatest during mild, windless weather and the birds apparently used alternate roosts during harsh weather. Movement between roosts sometimes occurred between sunset and sunrise. Morning ‘departure group’ size, number leaving per unit time and diversity of departure directions increased with roost size. Wagtails quickly left the vicinity in the morning. In the afternoon, they joined one or more pre-roost gatherings before entering the roost for the night. Behaviour upon arrival at the roost was variable: birds might enter the reeds quickly or circle in large groups before landing. Aerial revolutions and generally ‘restless’ behaviour often accompanied increases in roost size. Wagtail feeding rates varied significantly between and within habitats. Number of wagtails feeding on the flooded Port Meadow, located 2–3 km south of the main roost, varied from about five to over 60 on different days; these numbers were not correlated with feeding rates. In contrast, the number of birds feeding at a sewage farm was nearly constant all winter. Some wagtails show high fidelity to feeding areas but others do not. Five short-term food supplementation experiments indicated that wagtails knowledgeable about a dense food source are not followed in the morning by naive birds. Results of this study are discussed in relation to the predation, physiology and information centre hypotheses that have been suggested to explain communal roosting in birds. I conclude that the communal roosting system of Pied Wagtails has physiological and anti-predator functions. Wagtails appear to choose certain roosts because of the protection that they provide from adverse climate and predation.     

Roosting in tree foliage by Common Swifts Apus apus

Common Swifts Apus apus have occasionally been reported roosting overnight by hanging in the foliage of trees. However, roosting in foliage, which is often associated with food shortage as a result of adverse weather, appears to be an important alternative to aerial roosting. Thirty-nine observations of the behaviour have been recorded previously in Europe, some of them concerning two or more birds. Furthermore, each August from 1982 to 2000, within a restricted area of c . 300 × 300 m in southern Sweden, Swifts (118 total) were observed to roost in the foliage of trees or on a latticework mast, whereas others (230 total) were observed making 'fly-ins' typical of the behaviour preliminary to roosting. Of those roosting, 39 Swifts could be aged, and all but one of these were newly fledged juveniles. The Swifts perched late at dusk with maximum frequency about 30 min after sunset, but tended to perch earlier in cloudy weather and later in clear weather. Numbers of roosting Swifts were correlated with low mean temperatures in August, and appearances of roosting Swifts were correlated with low local evening temperatures. During May–July 1982–2000, within the same small area, 18 Swifts were observed to roost in this manner and 29 other Swifts made preroost fly-ins. It is concluded that the behaviour is used more frequently and is more widespread geographically than thus far published observations indicate. This applies especially to newly fledged young on their first migration. Adaptive explanations for this are suggested, with the implication that the behaviour may be widespread in swifts of the tribe Apodini.     

Quantifying long-term phenological patterns of aerial insectivores roosting in the Great Lakes region using weather surveillance radar

Organisms have been shifting their timing of life history events (phenology) in response to changes in the emergence of resources induced by climate change. Yet understanding these patterns at large scales and across long time series is often challenging. Here we used the US weather surveillance radar network to collect data on the timing of communal swallow and martin roosts and evaluate the scale of phenological shifts and its potential association with temperature. The discrete morning departures of these aggregated aerial insectivores from ground-based roosting locations are detected by radars around sunrise. For the first time, we applied a machine learning algorithm to automatically detect and track these large-scale behaviors. We used 21 years of data from 12 weather surveillance radar stations in the Great Lakes region to quantify the phenology in roosting behavior of aerial insectivores at three spatial levels: local roost cluster, radar station, and across the Great Lakes region. We show that their peak roosting activity timing has advanced by 2.26 days per decade at the regional scale. Similar signals of advancement were found at the station scale, but not at the local roost cluster scale. Air temperature trends in the Great Lakes region during the active roosting period were predictive of later stages of roosting phenology trends (75% and 90% passage dates). Our study represents one of the longest-term broad-scale phenology examinations of avian aerial insectivore species responding to environmental change and provides a stepping stone for examining potential phenological mismatches across trophic levels at broad spatial scales.     

RANGE EXPANSION AND MIGRATION OF THE CATTLE EGRET

Maddock, M. & Geering, D. 1994. Range expansion and migration of the Cattle Egret. Ostrich 65: 191–203.

The expansion of the range of the Cattle Egret Bulbulcus ibis from its origins in tropical Africa and Asia to Europe, the Americas and Australasia are summarised, and implications of research in Australasia based on birds marked with patagial tags on the spread of the species discussed.     

Nocturnal flights by Bearded Vultures Gypaetus barbatus detected for the first-time using GPS and accelerometer data

ABSTRACT

Capsule: We document previously undescribed nocturnal flight behaviour by Bearded Vultures Gypaetus barbatus using a combination of accelerometer and global positioning system (GPS) information.

Aims: To study the nocturnal flight activity of the Bearded Vulture and determine whether nocturnal flights could be linked to foraging behaviour.

Methods: We used both accelerometer and GPS location data of 11 Bearded Vultures in the Spanish Pyrenees along with 88 carcasses monitored with camera traps.

Results: Over half (55%, n?=?11) of the individuals tracked were recorded flying between 0.7 and 6.1?km on at least 19 different nights, including 37% that occurred when less than 20% of the moon was illuminated. Bearded Vultures displayed feeding activity in only 8.2% of the 146 feeding events existing during the hour after dawn and the hour before dusk.

Conclusions: Our findings suggest that foraging benefits do not explain the nocturnal flights. Disturbances or adverse weather conditions may result in the abandonment of an overnight roosting site. This could also explain why individuals recovered in the field showed impact injuries.     

Role of exotic tree stands on the current distribution and social behaviour of Swainson's hawk, Buteo swainsoni in the Argentine Pampas

Aim The Argentine Pampas was extensively and abruptly altered by European colonization. Between 1880 and 1885 the indigenous human inhabitants were completely displaced, and native grasslands were replaced by exotic pasture plants and crops. One of the most important ecological changes in the Pampas landscape, the introduction of tall exotic tree species, has received little attention, and its effect on wildlife has never been assessed. We have made an intensive survey of habitat use of Swainson's hawk, Buteo swainsoni in its most important non‐breeding quarters, the Pampas of Argentina, aiming to characterize the sites used by hawks for communal roosting. Location Pampas grasslands, Argentina. Methods We surveyed 30,000 km of roads by car during the austral summer from 2001 to 2004, covering the main non‐breeding area occupied by Swainson's hawks. Their roost sites were located by direct observation of birds roosting in tree stands close to the roads, by surveying potential roost sites around places where groups of pre‐ and post‐roosting hawks were recorded, and by gathering information from local farmers. Results Swainson's hawks exclusively used stands of exotic tree species for roosting. Eucalyptus viminalis was present in all 34 roosts surveyed, and in 59% of them it was the only species present. The remaining exotic tree species were the Siberian elm, Ulmus pumila, pines (Pinus spp.) and cypress (Cupressus spp.). Flock sizes at roost sites were unusually high for a raptor, with an average of 658 individuals (range 8–5000 hawks, n = 27 flocks). Main conclusions The introduction of exotic trees may have resulted in the expansion of the suitable habitat for Swainson's hawks, permitting a recent colonization of the Argentine Pampas. Tree stands may have also changed the communal roosting behaviour of this raptor, by virtue of their providing new structural elements in a region that almost completely lacked trees prior to European occupation.     

Effects of consecutive,contrasting, winters on the bird population of an Anglesey pine plantation

Capsule European Nightjars Caprimulgus europaeus breeding in southern England were found to over-winter in the Democratic Republic of Congo.

Aims To ascertain the wintering areas and migration routes of European Nightjars breeding in southern England.

Methods The wintering areas of three Nightjars were mapped using light geolocation tags (two in 2008 and one in 2010). For one of these birds, details of the timing and route of migration were determined. The impact of the birds' behaviour on location accuracy was measured and data on the timing of emergence and roosting was collected.

Results All three Nightjars were found to be wintering in the south and east of the Democratic Republic of Congo, in an area not previously considered to be part of the wintering range of this species. The route of migration differed in each period. Autumn migration was across central Sahara, whereas in spring the route was to the west of the Sahara. Aberrations in the light curve caused by the roosting and emergence of the birds were found to affect the estimated location of the wintering areas, shifting them approximately 1° south, and reducing the estimated accuracy of the locations. The timing of these aberrations showed that roosting and emergence roughly follow the timing of dawn and dusk.

Conclusions Current distribution maps for the wintering areas of Nightjars in Africa probably under-represent the true distribution of the species in the continent. The wide dispersal of birds from the same breeding area in the UK may be an indication of mixing of breeding populations during the wintering period. Further study is needed to understand how these results fit into the larger picture of Nightjar migration both from the UK and the wider Eurasian breeding range, and to determine locations of stopovers.     

Novel cross-stage solitarising effect of gregarious-phase adult desert locust (Schistocerca gregaria (Forskål)) pheromone on hoppers

Previous studies had demonstrated stage differentiation in the cohesion (aggregation) pheromone systems of the desert locust, Schistocerca gregaria. In laboratory arena, the nymphal and adult stages responded aggregatively to their own pheromone, but dispersed evenly within the arena in the presence of the other. In the present study, we explored the effects of longer-term contact of field gregarious hopper bands and laboratory crowd-reared nymphs with the major constituent of the adult pheromone. During the first few days, hoppers in treated bands became relatively hyperactive. Over the next few days, their movements became random and they stopped marching as coherent groups, they started to roost for longer periods on vegetations, and they fragmented into smaller and smaller groupings and individuals. When attacked by birds, they demonstrated subdued levels of collective defensive behaviour compared to normal hoppers, and there were clear signs of increased predation and cannibalism at the roosting sites. In cage experiments, crowd-reared nymphs treated with the pheromone component became hyperactive, showed abnormal diel patterns and reduced feeding on plants but increased cannibalism. Our observations show that the major adult pheromone constituent has a solitarising effect on gregarious hoppers. The mechanism underlying this effect and the potential of the agent in desert locust control are discussed.     

The effect of extreme weather events on breeding parameters of the White Stork Ciconia ciconia

Capsule Although the White Stork avoids adverse weather conditions by modifying its arrival and breeding, it cannot avoid extreme weather events during the breeding season.

Aims To show how extreme weather conditions can influence breeding attempts of a large, long-lived species, the White Stork.

Methods We analysed data on arrivals of White Storks in Western Poland from 2005 to 2013 and detailed breeding biology parameters from 2009 to 2013 in relation to weather conditions. We analysed breeding success and breeding failure rate from 1974 to 2013.

Results In years with a cold March White Storks arrived later than when March was warmer. Frost during incubation negatively influenced the hatching success. Extreme weather events caused high late mortality even for nestlings older than 30 days. Data from 27 breeding seasons showed a significant increase in mean breeding success but also a significant increase in the proportion of pairs which lost broods in the nestling stage.

Conclusion The White Stork can modify its arrival in response to current weather conditions on the breeding grounds but it cannot respond to extreme weather events. Due to increasing frequency of extreme weather events caused by climate change, White Stork breeding success may decrease in the future.     

Chemically-Mediated Roostmate Recognition and Roost Selection by Brazilian Free-Tailed Bats (Tadarida brasiliensis)

Background

The Brazilian free-tailed bat (Tadarida brasiliensis) is an exceptionally social and gregarious species of chiropteran known to roost in assemblages that can number in the millions. Chemical recognition of roostmates within these assemblages has not been extensively studied despite the fact that an ability to chemically recognize individuals could play an important role in forming and stabilizing complex suites of social interactions.

Methodology/Principal Findings

Individual bats were given a choice between three roosting pouches: one permeated with the scent of a group of roostmates, one permeated with the scent of non-roostmates, and a clean control. Subjects rejected non-roostmate pouches with greater frequency than roostmate pouches or blank control pouches. Also, bats chose to roost in the roostmate scented pouches more often than the non-roostmate or control pouches.

Conclusions/Significance

We demonstrated that T. brasiliensis has the ability to chemically recognize roostmates from non-roostmates and a preference for roosting in areas occupied by roostmates. It is important to investigate these behaviors because of their potential importance in colony dynamics and roost choice.     

NOTES ON THE ECOLOGY OF THE CATTLE EGRET ARDEOLA IBIS AT ROKUPR, SIERRA LEONE

SUMMARY
The Cattle Egret is a dry season visitor to Rokupr in Sierra Leone during the bird's non-breeding season. There are no cattle in the area to attract the herons and they obtain nearly all their food from small isolated areas of vegetable gardens which are associated with all the villages. The number of herons associated with each garden is closely correlated with the area of that garden and is about two birds per acre.
The daily life of the birds is discussed, in particular the pre-roosting assemblies and the flight to roost, and it is shown that each flock leaves for the roost at the same time each day, about 30–35 min. before dusk.
Observations made at a particular roost showed that all the Cattle Egrets reached the roost before dusk and from these observations, combined with those made on the feeding grounds, it is concluded that the number of Cattle Egrets using the roost is determined by the number and area of the feeding grounds that lie within 30–35 minutes flying time (about 12 miles) of the roost.
Other species using the roost are briefly discussed.     

Sociality influences thermoregulation and roost switching in a forest bat using ephemeral roosts

In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoid interferences with reproduction. In forest‐roosting bats, deep tree cavities buffer roost microclimate from abrupt temperature oscillations and facilitate thermoregulation. Forest bats also switch roosts frequently, so thermally suitable cavities may be limiting. We tested how barbastelle bats (Barbastella barbastellus), often roosting beneath flaking bark in snags, may thermoregulate successfully despite the unstable microclimate of their preferred cavities. We assessed thermoregulation patterns of bats roosting in trees in a beech forest of central Italy. Although all bats used torpor, females were more often normothermic. Cavities were poorly insulated, but social thermoregulation probably overcomes this problem. A model incorporating the presence of roost mates and group size explained thermoregulation patterns better than others based, respectively, on the location and structural characteristics of tree roosts and cavities, weather, or sex, reproductive or body condition. Homeothermy was recorded for all subjects, including nonreproductive females: This probably ensures availability of a warm roosting environment for nonvolant juveniles. Homeothermy may also represent a lifesaver for bats roosting beneath loose bark, very exposed to predators, because homeothermic bats may react quickly in case of emergency. We also found that barbastelle bats maintain group cohesion when switching roosts: This may accelerate roost occupation at the end of a night, quickly securing a stable microclimate in the newly occupied cavity. Overall, both thermoregulation and roost‐switching patterns were satisfactorily explained as adaptations to a structurally and thermally labile roosting environment.