Ecological conditions during winter affect sexual selection and breeding in a migratory bird

Populations of migratory birds have undergone marked declines, although the causes and mechanisms remain unknown. Because environmental effects on population dynamics are mediated by the effects of ecological factors on individuals, understanding changes in individual phenotypes in response to ecological conditions is key to understanding population trends. We show that breeding individuals of a declining population of trans-Saharan migratory barn swallows, Hirundo rustica, were affected by environmental conditions, as estimated from the normalized difference vegetation index (NDVI), reflecting primary production, in their winter quarters. The breeding dates of the same individuals in consecutive breeding seasons were advanced and clutch sizes were larger after winters with high NDVI in the winter quarters. Feather moult was also affected by winter conditions, with consequences for male sexual attractiveness. Length of tail ornament was positively correlated with NDVI during the previous winter, and males with large tail ornaments reproduced earlier and had larger clutches. The mean annual breeding date of the population was earlier and breeding success was increased after favourable winters, but this result was mainly determined by a single winter with very low NDVI. Thus, ecological conditions in Africa influence individual performance and productivity in a barn swallow population.     

Winter commingling of populations of migratory species can cause breeding range underpopulation

We build a model with large-scale demographic consequences for migratory species. The model operates where four elements co-occur, and we rely on empirical research using migratory birds to demonstrate them. First, breeding ranges have internal structure flowing from natal philopatry. Second, fecundity varies geographically. Third, populations of different breeding provenances commingle during winter. And fourth, a population-limiting carrying capacity operates during winter. In the absence of breeding season population-limitation, only the breeding population with maximum fecundity persists. Consequently, some potential breeding areas that offer suitable and productive habitat are bereft of breeding birds because of the interplay between the geographical fecundity gradient and the shared winter quarters. Where breeding season population-limitation also plays a role for at least one population, one (or more) breeding population becomes permanently depressed, resulting in a density well below the carrying capacity of the productive breeding habitat that is occupied. In either case, not all populations fare equally well, despite net positive breeding season productivity. Changes in winter carrying capacity, for example habitat degradation in winter quarters, can lead to uneven effects on geographically defined breeding populations, even though there has been no change in the circumstances of the breeding range.     

Changes in migration phenology and biometrical traits of Reed,Marsh and Sedge Warblers

Global environmental processes like climate change could severely affect population level migratory behaviour of long range migrant birds. We analyzed changes in migration phenology and biometrics of three closely-related long-distance migrant Acrocephalus species. We used the records of 12 063 Sedge, 12 913 Reed, and 5 409 Marsh Warblers caught and ringed between 1989–2009, at a Hungarian stopover site. Quantile regressions were used to analyse the changes in spring and autumn migration phenology. Median spring arrival date of Sedge and Reed Warblers shifted 6.5 and 7.5 days earlier, respectively. Autumn arrival of all species shifted one (Reed and Marsh Warblers) or two (Sedge Warbler) weeks later. Mean body mass of adult Reed and Marsh Warblers decreased in spring (by 0.3 and 0.2 grams, respectively) and in autumn (by 0.8 and 0.2 grams, respectively) while body mass of adult Sedge Warblers decreased only in autumn (by 0.4 grams). Mean wing length of all species increased significantly (range of change: 0.6–1 mm). Despite the fact that the studied species are closely related, all three have remarkably different migration strategies. However, similar patterns can be observed in the studied parameters, indicating that global processes may have general effects on these species, albeit through markedly different mechanisms.     

Population limitation in Palaearctic-African migrant passerines

We report the results of key factor analyses for Sedge Warbler Acrocephalus schoenobaenus, Blackcap Sylvia atricapilla, Whitethroat Sylvia communis and Willow Warbler Pftylloscopus Irochilus based on extensive data from the United Kingdom gathered by the British Trust for Ornithology. These results are compared with those from published key factor analyses based on intensive studies of Swallows Hirundo ruslica, Redstarts Phoenicurus phoenicums and three populations of Pied Flycatchers Fiiedula hypoleuca. Variation in losses between fledging and the following breeding season lk₄ ) accounted for most of the variation in total losses (K_T) for all populations. Breeding performance was poorly correlated with population changes. Density-dependence was found mainly in 6₄, its strength decreasing as average rate of population change increased. There was also evidence of weak density-dependence in the clutch size of Swallows and in Willow Warbler egg losses. Fluctuations in k₄ were correlated with conditions on the wintering grounds in Sedge Warblers, Whitethroats and Swallows, for the first two species these relationships being confirmed by analyses of independent survival estimates based on mark-recapture data. Populations of Sedge Warblers and Whitethroats appear to be limited by competition for resources on the wintering grounds. Removal experiments suggest that Willow Warblers, Pied Flycatchers and perhaps Blackcaps are limited through recruitment to the breeding population, in the case of Pied Flycatchers this limitation being in relation to the availability of nest sites.     

The Relationship Between Census Results and Breeding Populations of some Marshland Passerines

Censuses employing the mapping method, ancillary to an intensive population study of Reed Buntings, Sedge Warblers and Reed Warblers, revealed some limitations of the technique, which requires modification if the aim of the census work is an absolute estimation of the breeding population.     

Warming winter effects,fat store accumulation and timing of spring departure of Greenland White-fronted Geese <Emphasis Type="Italic">Anser albifrons flavirostris</Emphasis> from their winter quarters

Migratory geese accumulate energy and nutrient stores in winter to fly to refuelling spring staging areas before onward migration to breeding areas. Mean ground temperatures at two important Greenland White-fronted Geese wintering sites rose in winter and spring by 1.0–1.3°C during 1973–2007. Greenland White-fronted Geese departed the Wexford winter quarters on 3rd April 2007 for Icelandic spring staging areas, the earliest on record, representing a mean advancement of 15 days since 1973, mirrored amongst mean dates of departure amongst Scottish wintering birds that have advanced by 12 days during 1973–2007. Icelandic temperatures at critical midway staging areas en route to Greenland showed no significant change since 1973, suggesting that it is warming on the winter quarters that enable geese to depart earlier, rather than elevated temperatures at ultimate spring staging areas. However, Wexford departure date did not correlate with spring temperature. Data presented here show that Greenland White-fronted Geese have accumulated threshold body stores progressively earlier in spring migration, especially during 1995–2007. Although this did not correlate with ambient temperature, the mean degree of accumulated fat stored by 1st April in each year was a statistically significant predictor of departure date for the wintering population at Wexford. These data support the hypothesis that it is intrinsic factors (i.e. improvements in internal body state resulting from better feeding conditions) that has permitted progressively earlier departure of these geese from Wexford on spring migration, rather than amelioration of spring conditions in Iceland or solely the result of warming of the winter quarters.     

Food constraints explain the restricted distribution of wintering Lesser White‐fronted Geese Anser erythropus in China

More than 90% of the Lesser White‐fronted Geese Anser erythropus in the Eastern Palearctic flyway population winter at East Dongting Lake, China. To explain this restricted distribution and to understand better the winter feeding ecology and habitat requirements of this poorly known species, we assessed their food availability, diet and energy budgets at this site through two winters. Lesser White‐fronted Geese maintained a positive energy budget when feeding on above‐ground green production of Eleocharis and Alopecurus in recessional grasslands in autumn and spring to accumulate fat stores. Such food was severely depleted by late November and showed no growth in mid‐winter. Geese fed on more extensive old‐growth Carex sedge meadows in mid‐winter where they were in energy deficit and depleted endogenous fat stores. Geese failed to accumulate autumn fat stores in one year when high water levels prevented the Geese from using recessional grassland feeding areas. Fat stores remained lower throughout that winter and Geese left for breeding areas later in spring than in the previous year, perhaps reflecting the need to gain threshold fat stores for migration. Sedge meadows are widespread at other Yangtze River floodplain wetlands, but recessional grasslands are rare and perhaps restricted to parts of East Dongting Lake, which would explain the highly localized distribution of Lesser White‐fronted Geese in China and their heavy use of these habitats at this site. Sympathetic management of water tables is essential to maintain the recessional grasslands in the best condition for Geese. Regular depletion of fat stores whilst grazing sedge meadows in mid‐winter also underlines the need to protect the species from unnecessary anthropogenic disturbances that enhance energy expenditure. The specialized diet of the Lesser White‐fronted Goose may explain its highly restricted winter distribution and global rarity.     

Understanding population change in migratory songbirds: long-term and experimental studies of Neotropical migrants in breeding and wintering areas

Effective conservation and management of migratory bird species requires an understanding of when and how their populations are limited and regulated. Since 1969, my colleagues and I have been studying migratory songbird populations in their breeding quarters at the Hubbard Brook Experimental Forest in north-central New Hampshire, USA, and since 1986, in their winter quarters in the Greater Antilles (Jamaica). Long-term data on the abundance and demography of these populations, coupled with experimental tests of mechanisms, indicate that processes operating in the breeding area (e.g. density-dependent fecundity, food limitation) are sufficient to limit and regulate the local abundance of these species. At the same time, limiting factors operating in the non-breeding season (e.g. climate-induced food limitation in winter quarters and especially mortality during migration) also have important impacts on migrant populations. Furthermore, recent studies have shown that limiting processes during the winter period can carry over into the breeding season and affect reproductive output. These findings clearly demonstrate that to understand changes in abundance of long-distance migrant species requires knowledge of events operating throughout the annual cycle, which presents a challenge to researchers, managers and others concerned with the welfare of these species.     

Double brooding and polygyny in Sedge Warblers Acrocephalus schoenobaenus breeding in north-west England

Sedge Warbler breeding was studied at a site in Greater Manchester, UK, during 1991 and 1993. Birds were individually colour-ringed and, in the 2 years of the study, 18 pairs and 38 nesting attempts were observed. In both years, the majority of pairs (> 90%) attempted a second brood after successfully raising their first. Overall nest survival was 44% and the median reproductive output of individual males was 6.5 fledglings in each year (range 0–10 and 0–15 in 1991 and 1993, respectively). After fledging, one or both parents continued to feed the young for up to 15 days (median 11, range 0–15 days). One male was apparently bigamous in 1991 and in 1993, raising four broods successfully in 1993 and 25 fledglings over the 2 years. These observations suggest that double brooding is the normal strategy for Sedge Warblers in this population and that polygyny may be common, although easily overlooked.     

Understanding population change in migratory songbirds: long‐term and experimental studies of Neotropical migrants in breeding and wintering areas

Effective conservation and management of migratory bird species requires an understanding of when and how their populations are limited and regulated. Since 1969, my colleagues and I have been studying migratory songbird populations in their breeding quarters at the Hubbard Brook Experimental Forest in north‐central New Hampshire, USA, and since 1986, in their winter quarters in the Greater Antilles (Jamaica). Long‐term data on the abundance and demography of these populations, coupled with experimental tests of mechanisms, indicate that processes operating in the breeding area (e.g. density‐dependent fecundity, food limitation) are sufficient to limit and regulate the local abundance of these species. At the same time, limiting factors operating in the non‐breeding season (e.g. climate‐induced food limitation in winter quarters and especially mortality during migration) also have important impacts on migrant populations. Furthermore, recent studies have shown that limiting processes during the winter period can carry over into the breeding season and affect reproductive output. These findings clearly demonstrate that to understand changes in abundance of long‐distance migrant species requires knowledge of events operating throughout the annual cycle, which presents a challenge to researchers, managers and others concerned with the welfare of these species.     

丹顶鹤的越冬地特点与保护研究

丹顶鹤是濒危的国家1级重点保护动物。本文结合我们的观察,综述了丹顶鹤的生态习性,重点介绍了其越冬习性,提出了保护越冬地的措施。     

SPRING WEIGHTS OF SOME PALAEARCTIC MIGRANTS AT LAKE CHAD

A visit was made to Malamfatori, on the western shore of Lake Chad, Nigeria, from 22 March to 13 April 1967, with the principal aim of studying Palaearctic migrants in relation to the environment. About 2,400 Palaearctic migrants of 29 species were mist-netted in beds of bulrush Typha australis and thickets of saltbush Salvadora persica. Some 300 of these were collected for fat analysis; the remainder were released after measurement and ringing, and provided 275 retraps during the course of the study. Data were supplemented by further netting by A. J. Hopson in late April and May. Yellow Wagtails Motacilla flava, Sedge Warblers Acrocephalus schoenobaenus and Whitethroats Sylvia communis were abundant and were studied in greater detail than other species. Yellow Wagtails fed almost exclusively on midges, particularly the abundant Tanytarsus spadiceonotatus. Sedge Warblers fed on small insects and spiders, and Whitethroats on Salvadora fruits. Sedge Warblers and some other chiefly insectivorous species turned to a diet including berries shortly before emigrating. Changes in weight during the course of the day were difficult to investigate, but were probably bimodal. Good correlations of weights with wing-lengths were obtained for species for which many data were available. Pre-migratory fattening did not occur synchronously in all populations of a species, but once it started in an individual it proceeded at a constant rate of 0.2 g/day in Sedge Warblers and 0.6 g/day in Whitethroats. Predation pressure probably ensured that individuals emigrated immediately they attained their maximum pre-migratory weight, although some Sedge Warblers and Whitethroats left the area before attaining maximum weight. Differences between the mean weight curves of first-caught and retrapped birds are discussed, and it is concluded that in some species there were both through-migrant and temporarily-resident populations at Malamfatori. The mean weights per day of Whitethroats, Sedge Warblers and also Reed Warblers A. scirpaceus were falling in late March, and slight changes in the weather, particularly temperature, may have been responsible. In mid-April there was a “rush” of lean Whitethroats, which are thought to have originated to the SW in Nigeria. Yellow Wagtails, Sedge Warblers and Whitethroats deposited up to 40% fat/live weight; Sand Martins Riparia riparia had up to 28%, and a small sample of Ruffs Philomachus pugnax up to 17%. In the case of Sedge Warblers, fat reserves were sufficient for crossing the Sahara both to the north and to the northeast. Contrary to the findings in some previous lipid studies, the fat-free dry weight and water content increased during fattening. The fat-free dry weight increase was about 34% in Yellow Wagtails, 18% in Sedge Warblers, and 35% in Whitethroats. The tissues involved in this increase were not investigated, but a study of Yellow Wagtails at Malamfatori in 1968 (in prep.) suggests that the pectoral muscles hypertrophy during fat deposition sufficiently to account for nearly all of the increase in fat-free dry weight and water fraction.     

Heterogeneity in stable isotope profiles predicts coexistence of populations of barn swallows Hirundo rustica differing in morphology and reproductive performance

Population studies assume that individuals belonging to a study population are homogeneous for natal and breeding origin, although this assumption is rarely tested. We tested for heterogeneity in stable-isotope profiles (delta15N, delta13C, deltaD) of feathers grown in the African winter quarters from a Danish breeding population of adult barn swallows, Hirundo rustica. Deuterium isotope values did not provide useful information on population segregation of wintering swallows in Africa. However, both delta15N and delta13C values showed a clearly bimodal distribution with 6% belonging to one category and the remaining birds belonging to another category, resulting in this population comprising three categories of birds. Adults belonging to the two categories of delta13C isotope profiles differed weakly in morphology for several different characters. The frequency and the size of second broods differed between categories of delta13C isotope profiles. Phenotypes of nestlings from the first brood in terms of tarsus length, body mass and T-cell response differed significantly between the two delta15N isotope categories, suggesting that conditions during winter carried over to the breeding season at least as late as the first brood. Polymorphism can be maintained only if fitness is similar for birds from categories of isotope profiles. We suggest that fluctuating selection or migration-selection balance may maintain the observed polymorphism.     

A wild Marsh Warbler?×?Sedge Warbler hybrid (Acrocephalus palustris?×?A. schoenobaenus) in Norway documented with molecular markers

We present photographic and molecular evidence of a wild Marsh Warbler × Sedge Warbler (Acrocephalus palustris × A. schoenobaenus) hybrid that occurred over three breeding seasons (2007–2009) near Trondheim, Central Norway. The bird had the appearance of a Marsh Warbler but with some typical Sedge Warbler plumage traits. DNA analyses of a few plucked body feathers, using the COI barcode region (mtDNA) and conserved microsatellite loci, confirmed that the bird was a hybrid, with a Marsh Warbler mother and a Sedge Warbler father.     

Long-term satellite tracking of white stork ( Ciconia ciconia) migration: constancy versus variability

During satellite-tracking investigations of 140 white storks (Ciconia ciconia), one individual, the long-term world record holder among birds, was followed along 12 migratory journeys over a period of 10 years. This long-term study confirms what previous several-year tracking studies of white storks had indicated: there can be great variability from year to year in the choice of winter quarters as well as in the routes and times of migration, intermediate destinations and stop-over periods, but constancy of winter quarters and migration routes is also possible. The variability may well be caused by external factors, of which food supply is probably predominant.Communicated by F. Bairlein     

Satelliten-Telemetrie beim Wei?storchCiconia ciconia: Wanderung eines Ost-Storchs westlich bis Nigeria

A male White Stork, for the first time equipped with a mini-transmitter operated by a solar battery, was tracked on the eastern migration route from E Germany to central African winter quarters and during part of the return migration, for a total distance of about 10 000 km. The individual moved westward into Nigeria, i.e. into the wintering area of western Storks. Since a number of other eastern Storks were tracked as far as Chad, the possibility is discussed that individuals migrating to central Africa along the eastern or western route may eventually return on the opposite route when attracted to flocks of the population from the other side of the migration divide. Some ringing recoveries are consistent with a U-shaped abmigration.     

Does migration promote or restrict circumpolar breeding ranges of arctic birds?

Aim Migration has been suggested to promote large breeding ranges among birds because of the greater mobility of migratory compared with non‐migratory species, but migration has also been suggested to restrict breeding ranges because of evolutionary constraints imposed by the genetically based migration control programme. We aim to investigate the association between migration and the breeding ranges of both land birds and pelagic birds breeding in the Arctic region. Location The Arctic region. Methods Information on breeding and wintering ranges and migratory status of bird species breeding in the arctic tundra biome was compiled from the literature. The association between breeding range, migration distance and primary winter habitat was tested using multivariate generalized linear models and pair‐wise Mann–Whitney U‐tests. Phylogenetic effects were tested for using Mantel’s permutation tests. Results We found different relationships depending on the species’ major winter habitat. Among birds that are pelagic during winter, long‐distance migrants have the largest breeding ranges, while among terrestrial birds, residents and short‐distance migrants have the largest breeding ranges. Breeding ranges of coastal birds of all migratory distance classes are comparatively restricted. Main conclusions As a new explanation for this pattern we suggest that the possibility of colonizing large winter ranges is a key factor for the subsequent expansion of breeding ranges in arctic bird communities and possibly also in bird communities of other regions of the world. Because of the reversal in the relative extent of continents and oceans between the hemispheres, longitudinally wide winter ranges are more likely for long‐distance than short‐distance migrants among pelagic birds, while the reverse holds true for birds that use terrestrial winter habitats. For coastal birds both continents and oceans form barriers restricting colonization of extensive winter quarters and consequently also of extensive breeding ranges, regardless of the distance to the winter quarters.     

Zostera marina population genetics in Barnegat Bay, New Jersey, and implications for grass bed restoration

Within Barnegat Bay, New Jersey, Zostera marina populations have declined by 62% over the last 20 years, and restoration efforts have met with mixed success. We have completed a microsatellite-based genetic investigation of eight populations of Z. marina within Barnegat Bay to determine whether the genetic stock origins of the plants used in management projects may affect restoration success. Additionally, we assessed the genetic diversity of Z. marina in Barnegat Bay to better understand its population structure. Clonal diversity ranged from 0.70 to 0.95 for the populations studied. Individually, Barnegat Bay populations are not genetically diverse, and there is also little divergence among populations. The Atlantic populations had mean Hobs values (0.20–0.34) that were far lower than the Hexp values (0.69–0.83). Also, the F _IS values in all of the eastern populations indicate a surfeit of homozygotes over heterozygotes, suggesting a low degree of outcrossing in the Barnegat Bay populations. Six of the ten populations studied (Ham Island, Manahawkin Bay, Shelter Island, Marsh Elder, Harvey Cedar Sedge, and Long Island) show evidence of historical bottlenecks. Mean estimated F _ST values would suggest that most alleles are undergoing moderate genetic differentiation, with values that range from 0.06 to 0.13. Oyster Creek and Sedge Island demonstrate the largest estimated effective population sizes and may be the most appropriate populations for use in future eelgrass restoration projects.     

Winter quarters of wetland ground beetles (Coleoptera,Carabidae) in South Scandinavia

Sites at various distances from eutrophic and mesotrophic lakes and fens on the island Öland in southern Sweden were systematically surveyed in summer (May–August) and autumn (late September–October) to elucidate the hibernation sites of wetland carabid beetles. Thirty-five of 47 wetland species were found in their winter quarters. In areas ≤50 m from the lakes and fens, the observed as well as the estimated number of hibernating wetland species was higher in mesic to dry sites than in wet or moist open sites. Very few overwintering beetles were detected far (≥120 m) from the water. There was no significant difference in the frequencies of macropterous and dimorphic (brachypterous) species and individuals hibernating close to, and more distantly from, water. Individuals of small species hibernated closer to water than larger ones. At least in Scandinavia, there is no convincing evidence that wetland species hibernate far away from water, migrating by flight. A considerable number of the species that were collected in their winter quarters are rare and red- listed in at least one of the Scandinavian countries. Winter quarters situated in mesic and dry meadows and woodland close to lakes and fens had the highest number of red-listed species. Therefore, it is of fundamental importance to protect such sites. Threats to the integrity of the current habitats are logging and various transformations of meadows, e.g. digging and removal of large objects such as stones. Cessation of grazing by cattle may also have a negative effect.