THE MIGRATION SYSTEM OF THE CURLEW SANDPIPER CALIDRIS FERRUGINEA IN AFRICA

Elliot, C: C. H., Waltner, M., Underhill. L. G., Pringle, J. S. & Dick, W. J. A. 1976. The migration system of the Curlew Sandpiper Calidris ferruginea in Africa. Ostrich 47:191-213. Data on ringing and recoveries of Curlew Sandpiper, mainly from the Cape, South Africa are presented. Possible migration routes to the breeding grounds are considered in the light of these and other recoveries from the rest of Africa. Retraps show that the species exhibits ortstreue and some evidence is presented which suggests that some birds may travel together and stay in the south in the same flock during one and subsequent migrations. Sex ratio statistics show an excess of females. Adults complete a full primary moult in the Cape between September and February, taking about 140 days but there is a lot of individual variation. Data from Mauritania show primary moult starting faster, a month earlier than in the Cape, and arrested moult in a few adults. The difference may be because Mauritanian birds move on further south while the Cape is the end point of the migration. Kenyan moult records from the Rift Valley follow the Cape pattern except that some birds arrest moult and finish later. Juvenile moult is shown to be different from that of adults, involving only a moult of the outer primaries and taking place during the overwintering period, April to August. All juveniles in the Cape are thought to overwinter and the modified moult to be an adaptation to this behaviour. The weight of adults but not juveniles increases markedly in the six weeks before migration. Fat and protein analyses suggest that the increase is entirely due to deposition of migratory fat. Kenyan birds have lower mean weights and deposit fat about two weeks later than those at the Cape. The nearer the non-breeding quarters are to the breeding grounds, the earlier moult starts and the later fat deposition takes place.     

Disparity between Adult and Juvenile American Robins Turdus migratorius Foraging for Ground Invertebrates and Cherry Fruits

Although it has long been known that juveniles often have foraging skills inferior to those of adults, it has generally been assumed that animal prey are more difficult to capture than fruit, and thus that juveniles foraging on fruit should be similar to adults in their efficiency. To examine these ideas, we investigated the abilities of juvenile and adult American robins Turdus migratorius to forage for ground invertebrates and fruits of the black cherry tree Prunus serotina. We hypothesized that juveniles, lacking the experience of adults, would not have the skills of adults and therefore would be less proficient invertebrate and fruit foragers. Juveniles captured 69% of invertebrates at which they struck compared with 80% of adults’ strikes that ended in capture. However, juveniles made more strikes than adults, so mean prey capture per minute was the same. Juveniles were also less skilled fruit foragers. Juveniles were twice as likely as adults to fail to pick a cherry (55% of adults’ vs. 28% of juveniles’ attempts ended in success). However, there was no significant difference in the proportion of juveniles and adults that dropped a cherry once it was picked. As a result of their low levels of success, juveniles consumed about half the number of cherries per minute as did adults. Contrary to prior assumptions, skills involved in fruit foraging may not be so easily acquired and many omnivorous species, like the American robin, must learn both invertebrate and fruit foraging skills.     

How many juvenile Teal Anas crecca reach the wintering grounds? Flyway-scale survival rate inferred from wing age-ratios

Autumn postnuptial migration is critical in the dabbling duck annual cycle, when first-year birds in particular suffer high losses to natural and hunting mortality. Mortality rates in this age-class are generally unknown in Europe where winter ringing predominates. We used data from large-scale wing collections from hunters in Finland, Denmark and France to test the prediction that juvenile proportions among killed Teal (Anas crecca) would decline with distance along the flyway. As expected, this proportion decreased from 89% in Northern Finland to 58% in Western France. Potential biases linked with age determination from the wings, differential migration of age-classes, relative susceptibility to different forms hunting and gradual improvement of juvenile survival as they learn to avoid hunters could not explain the observed decline of juveniles in the shot population. This pattern was therefore considered to be genuine, the result of the cumulative depletion of first-years along the flyway, likely through hunting. On this assumption, combined with known adult monthly survival rates during August–November (94.2%), monthly juvenile survival rate was estimated at 52.8%, i.e. 14.7% (range 13.9–15.4% based on extreme values of adult survival) amongst Scandinavian juveniles reaching wintering quarters in Western France. Despite lack of precision in such estimates based on relative proportions, there is little doubt about the magnitude of autumn juvenile mortality and its consequences for the population dynamics of Teal. Lack of correlations between annual proportions of juveniles in the hunting bag and an index of Teal breeding success in Finland may result from such high and variable inter-annual mortality.     

Why do Juvenile Chinese Pit‐Vipers (Gloydius shedaoensis) Select Arboreal Ambush Sites?

Ontogenetic shifts in habitat use are widespread, especially in ectothermic taxa in which juveniles may be an order of magnitude smaller than large adult conspecifics. The factors that generate such habitat shifts are generally obscure, but we studied an unusual system that allowed us to compare consequences of habitat selection between adults and juveniles. Pit‐vipers (Gloydius shedaoensis) on a small island in north‐eastern China feed almost entirely on seasonally migrating birds. During the spring bird‐migration period, individual snakes consistently re‐used either arboreal or terrestrial ambush sites. Snakes in trees were smaller (and more philopatric) than snakes on the ground. This ontogenetic shift in habitat use may reflect the difficulty of capturing birds on the ground, especially by small snakes. In laboratory trials, large (adult) pit‐vipers struck faster, further and more accurately than did small (juvenile) snakes. In experiments with free‐ranging snakes, the proportion of strikes hitting the bird was lower for juveniles than for adults, and lower for terrestrial snakes than for arboreal snakes. Additionally, adult snakes generally seized the bird by the head whereas juveniles frequently struck the body or wings (and thus, obtained a less secure grip). Arboreal ambush sites may facilitate prey capture not only because they give access to smaller birds but also because they render the bird's location more predictable and, hence, enable the snake to position itself optimally prior to the prey's arrival. Because juvenile pit‐vipers are less capable strikers, and are small relative to available prey items, they may benefit from the greater ease of prey capture from branches. Thus, the ontogenetic shift in habitat selection within this species may be because of ontogenetic shifts in the vipers’ ability to capture and ingest large, mobile prey.     

Long‐term phenological shifts and intra‐specific differences in migratory change in the willow warbler Phylloscopus trochilus

Climate change can influence many aspects of avian phenology and especially migratory shifts and changes in breeding onset receive much research interest in this context. However, changes in these different life‐cycle events in birds are often investigated separately and by means of ringing records of mixed populations. In this long‐term study on the willow warbler Phylloscopus trochilus, we investigated timing of spring and autumn migration in conjunction with timing of breeding. We made distinction among individuals with regard to age, sex, juvenile origin and migratory phase. The data set comprised 22‐yr of ringing records and two temporally separated data sets of egg‐laying dates and arrival of the breeding population close to the ringing site. The results reveal an overall advancement consistent in most, but not all, phenological events. During spring migration, early and median passage of males and females became earlier by between 4.4 to 6.3 d and median egg‐laying dates became earlier by 5 d. Male arrival advanced more, which may lead to an increase in the degree of protandry in the future. Among breeding individuals, only female arrival advanced in timing. In autumn, adults and locally hatched juvenile females did not advanced median passage, but locally hatched juvenile males appeared 4.2 d earlier. Migrating juvenile males and females advanced passage both in early and median migratory phase by between 8.4 to 10.1 d. The dissimilarities in the response between birds of different age, sex and migratory phase emphasize that environmental change may elicit intra‐specific selection pressures. The overall consistency of the phenological change in spring, autumn and egg‐laying, coupled with the unchanged number of days between median spring and autumn migration in adults, indicate that the breeding area residence has advanced seasonally but remained temporally constant.     

Intraspecific variation of wing pointedness index in juvenile Acrocephalus warblers in the southeastern Baltic

Variation of wing pointedness index between groups of juveniles captured in different months (July, August, and September) and at different stages of juvenile moult was studied in three Acrocephalus warbler species captured on the Courish Spit on the Baltic Sea. Sedge warblers (Acrocephalus schoenobaenus) captured in July had less pointed wings than sedge warblers captured in August or September. Marsh warblers (A. palustris) showed no significant difference between birds in early and in late moult. No differences in wing pointedness were found between different cohorts of reed warblers (A. scirpaceus), including known locally hatched birds and late migrants captured in September. It is hypothesised that reed warbler populations in the northeastern Baltic are too evolutionarily young to have evolved a different wing shape as compared with the local Courish population.Communicated by F. Bairlein     

Migration routes from Lombardy,Northern Italy,to Africa,covered by birds ringed during eighteen years of ringing activity in five Pre-alpine Ornithological stations

Vigorita, V. 2000. Migration routes from Lombardy, Northern Italy, to Africa, covered by birds ringed during eighteen years of ringing activity in five Pre-alpine Ornithological stations. Ostrich 71 (1 & 2): 341.

Systematic bird ringing in Lombardy, northern Italy, was started in 1977. In total 661 979 birds of 168 species were ringed in the period 1977–1994. The recoveries were 3 660. The ringed species in five Prealpine Ornithological stations wintering and recovered in Africa, during eighteen years were 14: Anthus trivialis, Anthus pmtensis, Motacilla Java, Motacilla alba. Erithacus rubecula. Phoenicum phoenicurus, Turdus merula. Turdus philomelos, Sylvia borin, Sylvia atricapilla, Ficedula hypoleuca, Sturnus vulgaris, Fnngilla coelebs, Carduelis spinus. Accordingly, with ringing and recoveries data in Lombardy and recoveries data in Africa, we can get some more detailed information on migration routes. A better knowledge of migration routes allows the study of correlation among trends of populations and quality- quantity variation of habitats and meteorological dynamics in Afiica. The collection of data is expected to continue with more standardised methods for field research, data storage and their processing. Detailed migration routes, based on analysis of ringing data, are shown.     

Tracking from the Tropics Reveals Behaviour of Juvenile Songbirds on Their First Spring Migration

Juvenile songbirds on spring migration travel from tropical wintering sites to temperate breeding destinations thousands of kilometres away with no prior experience to guide them. We provide a first glimpse at the migration timing, routes, and stopover behaviour of juvenile wood thrushes (Hylocichla mustelina) on their inaugural spring migration by using miniaturized archival geolocators to track them from Central America to the U.S. and Canada. We found significant differences between the timing of juvenile migration and that of more experienced adults: juveniles not only departed later from tropical wintering sites relative to adults, they also became progressively later as they moved northward. The increasing delay was driven by more frequent short stops by juveniles along their migration route, particularly in the U.S. as they got closer to breeding sites. Surprisingly, juveniles were just as likely as adults to cross the Gulf of Mexico, an open-water crossing of 800–1000 km, and migration route at the Gulf was not significantly different for juveniles relative to adults. To determine if the later departure of juveniles was related to poor body condition in winter relative to adults, we examined percent lean body mass, fat scores, and pectoral muscle scores of juvenile versus adult birds at a wintering site in Belize. We found no age-related differences in body condition. Later migration timing of juveniles relative to adults could be an adaptive strategy (as opposed to condition-dependent) to avoid the high costs of fast migration and competition for breeding territories with experienced and larger adults. We did find significant differences in wing size between adults and juveniles, which could contribute to lower flight efficiency of juveniles and thus slower overall migration speed. We provide the first step toward understanding the “black box” of juvenile songbird migration by documenting their migration timing and en route performance.     

Influence of environmental variables on foraging by juvenile American Robins

ABSTRACT.   Juvenile birds lack the experience of adults and, as a result, are typically less efficient foragers. Environmental factors can influence how birds forage and the outcome of foraging bouts, but few investigators have considered the effects of such factors on the foraging behavior of juveniles. We examined the effects of two environmental factors, sunlight and soil moisture, on the foraging behavior of juvenile and adult American Robins ( Turdus migratorius ). Both factors had a significant effect on robin foraging, with robins more effective at capturing arthropods in the sun and worms in moist soils. However, juveniles were less successful than adults across all conditions. Juveniles were less successful than adults at capturing arthropods and were less efficient at capturing worms. Juveniles captured an average of one worm per minute, whereas adults captured nearly two worms per minute. Additionally, the high failure rates of juveniles (0.44/min) as compared to adults (0.20/min) may be indicative of their inability to choose suitable prey items. Finally, we found that juveniles tended to forage with other robins more than did adults, suggesting that they may use other individuals as cues for locating favorable foraging sites.     

Do adult and juvenile dunlins Calidris alpina form randomly mixed flocks during fall migration?

Many northerly breeding shorebird species show a separation in timing of adult and juvenile migration. If, in addition to genetic control of migration, learning from experienced conspecifics is advantageous, juveniles should join adult birds during their first fall migration when possible. We here present a method to test if juveniles mix with adults during the period of overlap during southward migration, using dunlin Calidris alpina migrating over southern Sweden as an example. While taking timing differences between age classes into account, we compare flock compositions observed in the field against randomized flock‐compositions based on the pool of available individuals derived from the field data. During both the early, the adult‐dominated, and later, the juvenile‐dominated, part of the season, age classes segregate. Applied to other shorebird species, our method could be used in a comparative sense to evaluate the potential for social learning of migration routes.     

A RINGING STUDY OF THE MIGRATORY BROWN SHRIKE IN WEST MALAYSIA

Wintering Brown Shrikes frequent open lowland country, a habitat that is largely man-made in Malaya. Individuals are sedentary during the winter season, each occupying a restricted area and exhibiting territorial behaviour. The earliest observations each year in different parts of Southeast Asia indicate that the southward migratory journey is relatively rapid. In Malaya, migrants arrive from the first week of September to the third week of October. At a lowland netting station during 1964–68 a major part of the total catch was taken in the months of September and October. Only a small proportion of these early shrikes wintered in the netting area. No distant recoveries were reported, and the subsequent movements of birds that were not retrapped are unknown. Shrikes netted in September—October comprised 29% adults, 54% full grown (i.e. immatures plus poorly—characterized adults), and 17% juveniles. The mean wing-length was significantly longer among adults than among both other classes, which did not differ significantly. During the winter, all ages showed a progressive decline in wing-length until the flight feathers were renewed in a premigratory moult falling in February—early April. Moult recorded in four Brown Shrikes taken in October-November is interpreted as the completion of a post-nuptial moult, commenced on the breeding grounds before autumn migration. In April, after the premigratory moult, confirmed adults constituted 70% of the total trapped and apparent immatures 30%. The mean weight of September birds was lower than any other month except November. The low weight in November is partly correlated with the shorter mean wing-length of the sample; it may also reflect the seasonally unfavourable weather of this month. The mean weight in February was high, although all birds were moulting; the weather in this month is typically hot and dry. Highest weights were recorded in April, indicating the premigratory deposition of fat. Weights of birds trapped more than once at different intervals showed a small initial weight loss (2 g), followed by a recovery within four days and no long-term adverse effects. A comparison of September weights in Taiwan and Malaya provides a tentative basis for the calculation of fat reserves utilized on the migratory flight. The proportion of returns after one year was 11%, and after two years 1 % only. Most returning birds were present in the netting area during the latter part of the winter of initial ringing; it is suggested tentatively that imprinting of the wintering grounds may occur during this period. Ecologically in Malaya the Brown Shrike occupies a new habitat only gradually being filled by the resident Rufous-backed Shrike. There is no evidence of interaction between the two species.     

The influence of climate on the timing and rate of spring bird migration

Ecological processes are changing in response to climatic warming. Birds, in particular, have been documented to arrive and breed earlier in spring and this has been attributed to elevated spring temperatures. It is not clear, however, how long-distance migratory birds that overwinter thousands of kilometers to the south in the tropics cue into changes in temperature or plant phenology on northern breeding areas. We explored the relationships between the timing and rate of spring migration of long-distance migratory birds, and variables such as temperature, the North Atlantic Oscillation (NAO) and plant phenology, using mist net capture data from three ringing stations in North America over a 40-year period. Mean April/May temperatures in eastern North America varied over a 5°C range, but with no significant trend during this period. Similarly, we found few significant trends toward earlier median capture dates of birds. Median capture dates were not related to the NAO, but were inversely correlated to spring temperatures for almost all species. For every 1°C increase in spring temperature, median capture dates of migratory birds averaged, across species, one day earlier. Lilac (Syringa vulgaris) budburst, however, averaged 3 days earlier for every 1°C increase in spring temperature, suggesting that the impact of temperature on plant phenology is three times greater than on bird phenology. To address whether migratory birds adjust their rate of northward migration to changes in temperature, we compared median capture dates for 15 species between a ringing station on the Gulf Coast of Louisiana in the southern USA with two stations approximately 2,500 km to the north. The interval between median capture dates in Louisiana and at the other two ringing stations was inversely correlated with temperature, with an average interval of 22 days, that decreased by 0.8 days per 1°C increase in temperature. Our results suggest that, although the onset of migration may be determined endogenously, the timing of migration is flexible and can be adjusted in response to variation in weather and/or phenology along migration routes.     

Equal nonbreeding period survival in adults and juveniles of a long‐distant migrant bird

In migrant birds, survival estimates for the different life‐history stages between fledging and first breeding are scarce. First‐year survival is shown to be strongly reduced compared with annual survival of adult birds. However, it remains unclear whether the main bottleneck in juvenile long‐distant migrants occurs in the postfledging period within the breeding ranges or en route. Quantifying survival rates during different life‐history stages and during different periods of the migration cycle is crucial to understand forces driving the evolution of optimal life histories in migrant birds. Here, we estimate survival rates of adult and juvenile barn swallows (Hirundo rustica L.) in the breeding and nonbreeding areas using a population model integrating survival estimates in the breeding ranges based on a large radio‐telemetry data set and published estimates of demographic parameters from large‐scale population‐monitoring projects across Switzerland. Input parameters included the country‐wide population trend, annual productivity estimates of the double‐brooded species, and year‐to‐year survival corrected for breeding dispersal. Juvenile survival in the 3‐week postfledging period was low (S = 0.32; SE = 0.05), whereas in the rest of the annual cycle survival estimates of adults and juveniles were similarly high (S > 0.957). Thus, the postfledging period was the main survival bottleneck, revealing the striking result that nonbreeding period mortality (including migration) is not higher for juveniles than for adult birds. Therefore, focusing future research on sources of variation in postfledging mortality can provide new insights into determinants of population dynamics and life‐history evolution of migrant birds.     

Does intraspecific competition facilitate age separation in timing of southward migration in waders?

In many Palaearctic wader species there is a clear separation in the timing of adult and juvenile southward migration. This phenomenon is traditionally explained by the selection on adults to depart early from breeding grounds and necessity of juveniles to prepare longer for migration. In this study we hypothesize that late departure from natal grounds may also be adaptive for juveniles, as it allows them to avoid intensified interference competition at stopover sites with adult, usually more dominant conspecifics. To test this hypothesis we analysed long-term data on stopover behaviour of juvenile wood sandpipers (Tringa glareola) staying at a central Polish stopover site under varying levels of competition from adult birds. The results clearly indicated that juveniles were highly disadvantaged by the simultaneous presence of adults at the same staging site, as under intense competition from older conspecifics they refuelled more slowly and attained lower fat reserves. It was also found that juveniles which were forced to compete with adults left the site quickly and possibly searched for more favourable staging places. All these imply that delayed departure from natal grounds may be adaptive for juvenile waders, allowing them to mismatch the timing of their first migration with the peak of adult passage and, thus, reduce the negative consequences of intraspecific competition during migration.     

Seasonal distribution of juvenile Atlantic cod in the southern Gulf of St Lawrence

Seasonal changes in the geographic distribution of juvenile (ages 1–4) Atlantic cod Gadus morhua were determined from research surveys conducted in the southern Gulf of St Lawrence during 1986–87, 1990–91, and 1994. From late June to early October, juvenile cod were most abundant in shallow water (<50 m deep). By early November, all age groups (adults and juveniles) had migrated to deep (>100 m) offshore waters for the winter. For most juveniles, this represented a minimum migration of >225 km (each way). Age 3 and 4 cod migrated greater distances than age 1 and 2 fish. Some age 3 and 4 cod migrated as far as 650 km from their summer and early autumn areas. Although there was partial geographic segregation of juvenile and adult fish during summer and winter, all age groups were found together during the migration. No cod were present in the shallow waters (<80 m deep) of the south-western Gulf during April due, in part, to later than average ice-melt. Large numbers of all age-classes were present in most of the south-eastern Gulf by mid-May.     

Social learning of hunting skills in juvenile marsh harriers <Emphasis Type="Italic">Circus aeruginosus</Emphasis>

The impact of social factors on the improvement of hunting skills of juvenile marsh harriers during their first autumnal migration were studied in SE Poland. While foraging with adult birds, juveniles performed more dives on prey both in terms of number of trials and rates. Hunting sessions of juveniles were more efficient in the presence of adults than in the absence of adults. Juveniles hunting with adults and other juveniles could select adequate habitat patches in which access to prey is easier. The role of vertical and horizontal transmission of information in the development of hunting skills in juvenile marsh harrier were confirmed because faster development of hunting ability was achieved in the social hunting after the end of their postfledging dependency period.     

Leaving on migration: estimating departure dates of Barn Swallows Hirundo rustica from summer roosts using a capture–mark–recapture approach

Capsule Capture–mark–recapture data can be used to predict departure dates of Barn Swallows Hirundo rustica from summer roosts.

Aims To investigate how long Barn Swallows remain at their breeding grounds before migration by estimating departure dates.

Methods A capture–mark–recapture approach was applied to an extensive data set (65?303 ringed and 710 recaptured birds) from two summer roosts. Multiple-day constancy models were used to estimate apparent survival, which was subsequently translated to residence time.

Results The longest intervals between ringing and recapturing were between 66 and 67 days; estimated mean minimum durations were between 16.3 and 18.5 days. Apparent survival was high over most of the summer, indicating that there is little emigration during this period and was followed by a sharp departure-related decline in late August and September. Expected residence time, derived from apparent survival estimates, declined linearly from about 80 days in early July to less than 10 days in September. Estimated departure dates were highly consistent between years and occurred in late September.

Conclusions Barn Swallows stay much longer at post-breeding roost sites than is necessary to build up their fat reserves for migration. We suggest that the birds are likely to derive a number of benefits from such a prolonged stay that are not directly related to preparation for migration; for example, minimizing predation risk by foraging in familiar areas, and gathering information on the quality of future breeding sites.     

Annual dynamics variation of a landlocked Galaxias maculatus (Jenyns 1842) population in a Northern Patagonian river: occurrence of juvenile upstream migration

Galaxias maculatus, broadly distributed in the southern hemisphere, presents both diadromic and landlocked populations. The upstream migration of larvae and juveniles from the sea to freshwater habitats is a characteristic phenomenon of diadromous populations, but upstream migration has never been reported in those that are landlocked. The objective of this study was to establish the population dynamics of a peculiar riverine landlocked population that presents an upstream migration at the larvae–juvenile transition from the Piedra del Águila Reservoir to the Caleufú River (Argentina). A spawning season from September to November and the arrival of shoals of metamorphic larvae and juveniles from February to April to the adult habitat were coincidental with lacustrine landlocked populations, but not with diadromous populations. Growth rate and age at migration, 147 ± 22.6 days, were also similar to other landlocked and diadromous populations. The arrival of these shoals produced a 20‐fold increase in fish density while the two cohorts of G. maculatus overlapped in time and space. No significant differences in morphology or vertebrae number were detected when riverine and reservoir adults were compared. The great life history plasticity of G. maculatus, shown to be even greater in our results, could be the key to explain the wide distribution of this species in the southern hemisphere. Likewise, discovering this juvenile potamodromous behaviour in a landlocked population will provide a new view for the analysis of the ways of this species’ dispersion in continental waters.     

Trends in trappability and stop-over duration can confound interpretations of population trajectories from long-term migration ringing studies

We examined ringing data for three common passerines at a migration monitoring site with the objective of determining how closely the numbers of birds captured reflected the actual numbers of birds passing through this site. Mark–recapture analyses were used, fitting smooth inter-annual changes in re-trapping probability and apparent survival (continued presence within the study area). For all three species we found systematic declines in re-trapping probability over the roughly three decades of our study; one species showed systematic increases in daily apparent survival over this same time period. Within individual years, daily variation in wind and rainfall were found to affect re-trapping probability and apparent survival. The result of all of these effects was that long-term trends in the numbers of unique individual birds captured systematically over-estimated the declines for all three species, providing clear indication that the biological interpretation of these raw capture totals from ringing stations will not necessarily reflect actual changes in the abundance of species passing through these sites.     

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.