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.     

Use of Restored Small Wetlands by Breeding Waterfowl in Prince Edward Island, Canada

Abstract Since 1990 under the Eastern Habitat Joint Venture over 100 small wetlands have been restored in Prince Edward Island, Canada. Wetlands were restored by means of dredging accumulated sediment from erosion to emulate pre‐disturbance conditions (i.e., open water and extended hydroperiod). In 1998 and 1999 we compared waterfowl pair and brood use on 22 restored and 24 reference wetlands. More pairs and broods of Ring‐necked Ducks, Gadwall, Green‐winged Teal, and American Black Ducks used restored versus reference wetlands. In restored wetlands waterfowl pair density and species richness were positively correlated with wetland/cattail area, percent cattail cover, and close proximity to freshwater rivers. In addition, a waterfowl reproductive index was positively correlated with percent cattail cover. Green‐winged Teal pair occurrence in restored wetlands was positively correlated with greater amounts of open water and water depths. American Black Duck pairs occurred on most (86%) restored wetlands. Restored small wetlands likely served as stopover points for American Black Duck broods during overland or stream movements, whereas they likely served as a final brood‐rearing destination for Green‐winged Teal broods. We suggest that wetland restoration is a good management tool for increasing populations of Green‐winged Teal and American Black Ducks in Prince Edward Island.     

Using infrared thermography to detect night‐roosting birds

Most birds sleep while roosting at night. Although a widespread behavior, few investigators have studied the nocturnal roosting behavior of birds. Studies conducted to date have either focused on species that roost communally or used radio‐telemetry to locate sleeping individuals of a few focal species. Portable thermal cameras capable of detecting infrared (IR) heat signals may provide a more efficient and less invasive means of detecting nocturnal‐roosting endotherms such as birds. Our objective was to assess the efficacy of using thermal cameras to detect roosting birds in a woodland bird community in southeastern Australia. To better understand the limitations of using thermography to detect roosting birds, paired bird surveys were conducted along 44 transects from May to September 2016 using both traditional survey techniques during the day and surveys with a thermal camera at night. We detected 195 birds representing 21 species at nocturnal roosts using IR thermography, with the detection rate of birds during nocturnal surveys approximately one‐third (29.1%) that during diurnal surveys. Detection rates during nocturnal surveys declined more steeply with distance from observers than for diurnal surveys. Detection rates were significantly higher during diurnal surveys for 14 species of woodland birds, but did not differ between diurnal and nocturnal surveys for eight other species. Roost height, roost visibility, bird mass, and cluster size (i.e., two or more birds in physical contact) did not differ between species categorized as having high or low detectability during nocturnal surveys. Variability among species in nocturnal‐detectability could not be attributed to roost‐site visibility, roost height, or bird size. Positive detection biases associated with diurnal behavior, such as movement and vocalizations, and limitations of current IR technology, e.g., low resolution, likely contributed to overall lower detection rates during nocturnal surveys. However, our results suggest that infrared thermography can be an effective and useful technique for detecting roosting birds and studying roosting behavior, as well as for population monitoring under certain conditions.     

Selection of winter roosts in the Great Tit Parus major: influence of microclimate

The success in energy saving in roosting Great Tits (Parus major) is potentially influenced by roost microclimatic characteristics. We tried to learn about the pattern in cavity microclimate influence on night roosting of birds, under natural weather conditions. An experimental aviary offered two artificial tree-roosts with different microclimatic conditions which varied according to the outdoor conditions (mainly due to solar radiation) and microclimate retention capability of roosts. Birds actively explored roosts before the final choice of sleeping site. Two hours prior to sunset, there were significant differences between the roosts (n = 11 adult males tested, each six nights). Selected roosts had higher average temperature (Wilcoxon matched pairs test, P = 0.017) and temperature at the time of sunset (P = 0.028). Simultaneously, inside temperature decreased slowly (P = 0.047). During the night, when birds slept in one of the roosts, the average temperature was higher (P < 0.001) and the fluctuation range of temperatures was smaller (P = 0.003) there. Moreover, at the morning twilight, the temperature of the occupied roost was higher (P < 0.001). Humidity did not have a significant influence at all. The effect of metabolic heating was demonstrated. When birds slept in the insulated roost (n = 30 nights), the indoor average temperature significantly differed from the non-insulated and outdoor temperatures (Kruskal–Wallis ANOVA, P = 0.0001). Selection of an actually warmer and thermally more stable roost according to the course of weather indicates demand for a wide spectrum of potential roosts in the natural environment.     

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 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.     

鸟类夜栖地选择研究进展

夜栖地可以为鸟类提供安全、舒适、温暖的夜间栖息场所。昼行性鸟类夜间视觉能力较差,对夜栖环境中潜在的威胁感知程度较低,导致其夜栖时常常处于被动和危险的环境中。鸟类通过选择适宜的夜栖地,进而达到充分利用夜栖地空间资源的目的。本文从鸟类夜栖地选择的行为适应性以及保温性、食物因子和安全性(隐蔽性)等3个影响因素,对国内外鸟类夜栖地选择相关研究进行综述,为今后该领域的研究提供更多思路。     

Mechanisms of dusk orientation in white-throated sparrows (Zonotrichia albicollis): Clock-shift experiments

Summary Several species of night migrating birds, especially North American emberizines, exhibit markedly different orientation behaviour when tested in circular cages under clear skies at dusk as compared with tests performed after complete darkness. During the period between sunset and the first appearance of stars, birds tend to show high levels of well-oriented hopping; birds deprived of exposure to clear skies at dusk hop less and their activity is usually not oriented. There is evidence that visual cues available during the dusk period, but not later, are responsible for this difference, but details of the orientation mechanisms involved are unclear. We performed 3-h fast and slow clock shifts on white-throated sparrows (Zonotrichia albicollis) to address two questions concerning migratory orientation at dusk: (1) Is the better orientation of sparrows tested at dusk a function of the visual cues available at that time, or does it result from circadian changes in motivation?; and (2) Is the dusk orientation based on a time-compensated sun compass?Sparrows subjected to a 3-h slow clock shift were tested with controls on clear, moonless nights beginning immediately after lights-off in the clock shift room and thus about 3.5 h after local sunset. Individuals of both groups performed poorly oriented hopping typical of tests performed after complete darkness. The pooled data from each group were not significantly oriented. These results show that the visual cues available shortly after sunset, not temporal changes in the motivation of the birds, are responsible for the qualitative differences in orientation.Birds exposed to a 3-h fast clock shift were tested with controls on clear evenings between sunset and the first appearance of stars. Both groups showed well-oriented hopping. The mean direction of the pooled tests of controls was 325°, a typical spring orientation direction for this species. The mean direction of the pooled tests of the clock shifted birds (274°) was significantly different from that of controls and the 51° counterclockwise shift is consistent with that predicted by a time-compensated sun compass model.     

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.     

Artificial light at night affects the timing of roosting by Chimney Swifts

Understanding the impact of anthropogenic threats, such as light pollution, on biodiversity is necessary to establish effective guidelines to protect diminishing wildlife. In this study, we examined the effect of artificial light at night (ALAN) on the roosting behaviour of Chimney Swifts Chaetura pelagica, a highly threatened migratory bird species that lives commensally with humans, where it often breeds and roosts in artificial structures such as chimneys. Although Chimney Swifts are known to use time of sunset in combination with temperature, wind and season to coordinate roost entry, we predicted that high ALAN exposure would override these natural cues and lead to a delayed entry compared with sites with less light pollution. To test this, we examined the effects of ALAN on the start and end times of entry to 21 roosting sites located along a light pollution gradient in New Jersey and the New York Metropolitan area. We found that ALAN was a significant predictor of roosting entry time, with birds entering later in sites with more light pollution. While Chimney Swifts initiated roosting earlier in the summer months compared with the autumn, this effect was absent in areas with high light pollution. These findings highlight the need to determine the causes and consequences of light pollution effects.     

BODY MEASUREMENTS,PLUMAGE AND MOULT OF THE SACRED IBIS IN SOUTH AFRICA

Lowe, K. W., Clark, A. & Clark, R. A. 1985. Body measurements, plumage and moult of the Sacred Ibis in South Africa. Ostrich 56: 111–116.

Body measurements, plumage and moult of Sacred Ibis Threskiomas aethiopicus were studied at Pretoria from July 1973 to June 1974. Adult and immature Sacred Ibises are sexually dimorphic in size. Bill length alone can be used to sex most birds. Body mass, wing, tarsus and tail lengths overlap greatly between the sexes but males are generally larger than females. The sexes show similar patterns of variation in body mass and gonad size throughout the year. Juveniles follow a different pattern of variation in these parameters. The plumages of adults, immatures and juveniles are described and compared. There is no sexual dimorphism in plumage pattersn. Moult in adults occurs mainly in the post-breeding period from January to August, and in juveniles and immatures throughout the year. Adult Sacred Ibises have an-extensive, irregular and asymmetrical moult. Factors affecting sexual size dimorphism in African and Australian populations are discussed.     

Pair bond characteristics and maintenance in free‐flying jackdaws Corvus monedula: effects of social context and season

Most birds rely on cooperation between pair partners for breeding. In long‐term monogamous species, pair bonds are considered the basic units of social organization, albeit these birds often form foraging, roosting or breeding groups in which they repeatedly interact with numerous conspecifics. Focusing on jackdaws Corvus monedula, we here investigated 1) the interplay between pair bond and group dynamics in several social contexts and 2) how pair partners differ in individual effort of pair bond maintenance. Based on long‐term data on free‐flying birds, we quantified social interactions between group members within three positive contexts (spatial proximity, feeding and sociopositive interactions) for different periods of the year (non‐breeding, pre‐breeding, parental care). On the group level, we found that the number of interaction partners was highest in the spatial proximity context while in the feeding and sociopositive contexts the number of interaction partners was low and moderately low, respectively. Interactions were reciprocated within almost all contexts and periods. Investigating subgrouping within the flock, results showed that interactions were preferentially directed towards the respective pair partner compared to unmated adults. When determining pair partner effort, both sexes similarly invested most into mutual proximity during late winter, thereby refreshing their bond before the onset of breeding. Paired males fed their mates over the entire year at similar rates while paired females hardly fed their mates at all but engaged in sociopositive behaviors instead. We conclude that jackdaws actively seek out positive social ties to flock members (close proximity, sociopositive behavior), at certain times of the year. Thus, the group functions as a dynamic social unit, nested within are highly cooperative pair bonds. Both sexes invested into the bond with different social behaviors and different levels of effort, yet these are likely male and female proximate mechanisms aimed at maintaining and perpetuating the pair bond.     

Integration of environmental stimuli in the migratory orientation of the savannah sparrow (Passerculus sandwichensis)

Two ‘cue-conflict’ experiments were designed to evaluate the role of (1) solar cues at sunset and stars, and (2) solar cues at sunset and geomagnetic stimuli, in the migratory orientation of the savannah sparrow (Passerculus sandwichensis). A sunset and stars experiment exposed birds in the experimental group to a mirror-reflected sunset followed by an unmanipulated view of stars. Experimental birds shifted their migratory activity in accordance with the setting sun despite exposure to a normal night sky. The sunset and geomagnetism experiment exposed birds in the experimental group to a simultaneous shift in both the position of sunset and the earth's magnetic field. Again experimentals shifted their activity in accordance with the setting sun rather than the artificially shifted magnetic field. Savannah sparrows probaly use stars as celestial landmarks to maintain a preferred direction and do not reorient their activity when exposed to an alternative cue once a direction is established. Moreover, savannah sparrows with experience of migration do not require geomagnetic information in order to use the solar cues available at sunset to select a migratory direction.     

5. LIVINGSTONE IN NORTH-EASTERN RHODESIA

Sugg, M. St. J. 1974. Mensural and moult data from a breeding colony of Pied Kingfishers. Ostrich 45: 227–234.

Pied Kingfishers were ringed over two breeding seasons at a breeding colony on the Kenyan shore of Lake Victoria. Data were collected on weight, wing and bill length, injury and moult. Bill abrasion and breakage from nest excavation was found in both sexes and regeneration of worn and broken bills was recorded.

Adult birds of both sexes returned to the colony to breed but no juvenile was recaptured the year after hatching. Females are slightly larger than males (wing length) and both sexes showed a weight increase in the evening prior to roosting. Juveniles had shorter wings and bills than adults but their weights were similar. Their bills were short, soft, weak and the gape was salmon pink. No juveniles showed any moult. Adult moult records support the sequence and duration of moult suggested by Douthwaite (1971) though no overall decrease of moult activity was recorded during the breeding season.     

Distribution of sleep and wakefulness in 24-h light-dark cycles in the juvenile and adult magpie, Pica pica

The daily organization of sleep and wakefulness was examined electrographically under natural conditions in captive juvenile and adult magpies, Pica pica. Electrographic indices of sleep in the magpie were found to be similar to those of other avian species. The daily amount of TS in juveniles was 17% greater than in adults. The amount of paradoxical sleep (PS) in adults was one-fifth that of juveniles. In adults sleep was confined to darkness, while in juveniles it also occurred during the light period. SWS in adults was almost constant, while PS slightly increased across the night. No systematic trends were observed in juveniles. In both groups of birds, the longest sleep episodes appeared around midnight.     

Diversity of migration strategies among great frigatebirds populations

Migratory behavior varies extensively between bird taxa, from long distance migration to purely sedentary behavior. Variability in migratory behavior also occurs within taxa, where individuals within some species, or even populations, show mixed strategies. The same variability occurs in seabird species. We examined the migratory behavior of distinct populations of great frigatebirds Fregata minor in three distant oceanographic basins. Great frigatebird populations showed extensive variation in post‐breeding migratory behavior. Birds from Europa Island (Mozambique Channel) made long‐distance migration to numerous distinct roosting sites in the Indian Ocean, New Caledonia birds made shorter distance migrations to roosting sites in the southwestern Pacific Ocean, and Galapagos birds were resident within the archipelago year round. Juvenile birds from Europa Is. and New Caledonia dispersed widely whereas Galapagos juveniles were resident year round. The migratory behavior of Europa Is. and New Caledonia resulted in complete separation of foraging grounds between breeding adults, non‐breeding adults, and juveniles, whereas in the Galapagos the overlap was complete. We suggest that population variability in migratory behavior may have arisen because of different environmental conditions at sea, and also depends on the availability of suitable roosting sites on oceanic islands. The results also highlight the capacity of frigatebirds to remain airborne most of the time even outside the breeding season when they have to molt.     

SEX RATIOS,MORPHOLOGY AND GROWTH OF THE AFRICAN BUCK DUCK

Frost, P. G. H., Ball, I. J., Siegfried, W. R. & McKinney, F. 1979. Sex ratios, morphology and growth of the African Black Duck. Ostrich 50:220-233.

Black Ducks Anus sparsa were trapped regularly in the Eerste River Valley near Stellenbosch, South Africa. The sex ratio of adult Black Ducks did not differ significantly from parity. Males were larger and heavier than females and also had proportionately larger wing spurs which are used when fighting over mates and territories. Body mass fluctuated seasonally, being lowest during summer and highest in autumn-winter. In the southwestern Cape breeding took place from July to December after the peak of the early winter rains. Ducklings hatched when waters were dropping and there was an increase in the emergence of aquatic insects. The growth rate of ducklings in the Eerste River Valley was severely retarded compared with that of ducklings reared in captivitly. Black Ducks moulted their body feathers twice a year, the moults corresponding to the pre- and post-nuptial moults of northern hemisphere waterfowl. Moults were not accompanied by any change in plumage coloration. Body and rectrix moult took more than five weeks to complete while remex replacement required about 30 days. Males began wing moult about a month earlier than females which delayed moulting until after their young had been reared. Forty-six percent of Black Ducks trapped had noticeable plumage aberrations; individual recognition among Black Ducks appears to be an important element in their social behaviour.     

Mechanisms for the formation and maintenance of traditional night roost aggregations in a territorial damselfly

Communal roosting has been studied extensively in birds, but the mechanisms and functions of this taxonomically widespread behaviour pattern remain poorly understood. We studied the roosting behaviour of rubyspot damselflies, Hetaerina americana, in relation to sex and territorial status, and conducted field experiments to test for specific mechanisms of roost formation and maintenance. Both sexes tended to return close to their previous night's roost, but only males were significantly more roost site faithful than chance expectations based on individual day ranges. Males were more roost site faithful when they held mating territories. After acquiring a territory, males usually began roosting closer to the territory after a delay of a few days. Roosts were not located at sites that reduced the daily commuting distance between hunting areas and territories; males generally hunted closer to their territories than to their roosts. In field experiments, sites 'seeded' with synthetic models of male rubyspots attracted more recruits than vacant control sites and control sites seeded with nonrubyspot (clear-winged) damselfly models. Sites seeded repeatedly with rubyspot models often remained popular for roosting after the models were removed, suggesting that the models established new traditional roosts. These results indicate that conspecific attraction and individual spatial memory together may be sufficient to explain, at a proximate level, the traditional night roost aggregations of this species. We discuss these results in relation to functional hypotheses for roost site choice and fidelity. Copyright 2000 The Association for the Study of Animal Behaviour.     

Rediscovery of short-tailed bats (

Short-tailed bats (Mystacina sp.) were rediscovered in Nothofagus dominant rainforest in the Eglinton Valley in February 1997, representing the first records of these bats in Fiordland since 1871. Breeding females, adult males and juveniles were captured. This paper presents preliminary observations of taxonomy, echolocation calls, population size, habitat use, activity patterns, home range size, movements, roosting, and singing behaviour. Compared to lesser short- tailed bats (M. tuberculata) on Codfish and Little Barrier Islands, the Fiordland bats were heavier, had larger wings and smaller ears, and were sexually dimorphic. The Mystacina echolocation calls were of low intensity (quiet), making them difficult to detect. Call durations in free-flying bats were only 1.0-2.9 ms long. In a comparative trial the majority of calls that were detected at 25 kHz using the Batbox III bat detector were not recorded at 40 kHz, indicating that there was little overlap with the calls of long-tailed bats (Chalinolobus tuberculatus). In February, roosting groups numbered from 107 to 279 individuals and the bats ranged over 130 km(2) of the valley. Bats began emerging c. 20 minutes after sunset and were active at the roost sites throughout the night. Radio-tagged bats were active for an average of 372 minutes at a time. All roosts were in large diameter (67-146 cm dbh) red beech (N. fusca) trees.     

Recruitment to food in black vultures: evidence for following from communal roosts

Experimental and observational evidence from a 5-year study of a partially marked population of black vultures, Coragyps atratus, suggests that individuals can find food by following others from overnight roosting groups. Natural food sources usually lasted long enough for recruitment to occur. Black vultures formed larger roosting groups and had enhanced second-day recruitment during winter, when their main food source was least abundant. Successful foragers returned to experimental food sources on subsequent days and generally preceded new arrivals. Arrivals at bait were clumped on days of discovery and second days, but incoming groups were larger on second days and highly skewed towards early arrivals. In general, adults arrived at baited sites earlier than young adults and juveniles. During natural roost departures, adults were as likely to depart at the head of departing groups as at the rear, while young were concentrated in the rear. Birds removed experimentally from the population long enough to be naive about the location of food followed others from the roost when reintroduced. Control adults (birds caught and handled but not restrained for long) were not concentrated in the rear of roost-departing groups, as were experimental adults. Juveniles tended to follow regardless of recent experience. These results suggest that roost attendance facilitates foraging for black vultures; these roosts probably function as information centres.