ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb04743.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Biological conservation is increasingly concerned with advocacy and lobbying. But its practical politics must stand on a firm basis of scientific fact and understanding: about the behaviour and ecology of species and about the workings of the habitats that are their life‐support systems. For Africa, a solid foundation was laid by R.E. Moreau in two scholarly analyses of the continent and its birdlife:The Bird Faunas of Africa and its Islands(1966) andThe Palaearctic‐African Bird MigrationSystems (1972). Hence the title of this paper: a generation having passed, my objectives are to emphasize the salient observations of Moreau (1972), and to review subsequent changes in the face of Africa as they might affect migrant birds from the Palaearctic that winter th

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb04744.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

In this paper we compare ecological attributes of tropical migrant passerines from the Nearctic and western Palaearctic, focusing particularly on habitat association patterns during both breeding and wintering seasons. Three regions were compared: Europe, western and eastern North America. Breeding bird census data from 32 studies (each including at least four stages of forest succession) were used to assess the association patterns of breeding habitats among tropical migrants. For each species we calculated an index of habitat diversity and habitat preference.Tropical migrants preferred earlier successional stages than other birds in Europe. The opposite was true in eastern North America. In eastern North America, tropical migrants tended to be associated with a smaller range of serai stages than other passerine species. In their winter quarters, Palaearctic migrants live primarily in open habitats, such as savannas, whereas eastern Nearctic migrants make more frequent use of evergreen forests. Migrants from western North America show the greatest match between breeding and wintering habitats.We relate the results to the taxonomy and probable history of contemporary avifaunas and vegetation formations of the Old and New World. Taxonomically, tropical migrants from different parts of the Holarctic are less closely related to each other than residents and short‐distance migrants. Tropical and temperate avifaunas are more closely related to each other in the New World than in the Old World. Conservation implications of the between‐continent differences are briefly discus

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb04745.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

In the past decade, a major trawl fishery for the squid Loligo gahi has developed in the vicinity of Beauchêne Island, an internationally important breeding site for the Black‐browed Albatross Diomedea melanophris. The breeding season diet of this albatross in the Falklands and its use of discards generated by the Loligo fishery were investigated. Albatross chicks are fed extensively on commercially exploited species of squid and fish including Loligo gahi and southern blue whiting Micromesistius australis. The quantity of waste generated by the Loligo fishery amounts to c. 5% of the reported catch and just over 50% of this waste, mainly Loligo and nototheniid fish, is scavenged by adult Black‐browed Albatrosses. The total quantity scavenged during the chick rearing period amounts to 1000–2000 tonnes per year. This is equivalent to 10–15% of the total food requirement of the breeding Black‐browed Albatross population on Beauchene Island during the period when the fishery is operating. Although the Loligo fishery currently provides a significant quantity of food to these albatrosses, its net effect may be detrimental to them, as it is a much greater predator of Loligo stocks than the albatrosses are estimated to have been prior to the fishery's d

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb07223.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

We analysed patterns of breeding habitat use in migrant and resident passerines on a broad geographical scale in Britain. Migrants were less widely distributed than residents and used fewer habitats. Although resident genera that were more widespread used more nesting habitats, this did not hold for migrant genera though it did at the species level. Although migrancy status in Europe has been associated with the use of ‘open’ structural habitat types (e.g. scrubland), evidence from Britain was contradictory. Within lowland woodlands the ratio of migrants to residents and the density of migrants was highest in habitats with large areas of young growth. The highest migrant ratios of all, however, were recorded in mature upland woods, with little or no undergrowth. These upland woods carried the lowest densities of residents. Regression models accounting for variation in the migrant ratios and densities in woodland habitats varied according to the geographical scale on which they were constructed. The extent of young growth was a strong predictor of migrant ratios and densities in south‐east England but not for woods in the north and west. Resident densities in northern and western woods were inversely related to alt

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb04746.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A multivariate analysis of data from a wide range of avian species revealed that migratory distance was related to a high aspect ratio, long and pointed wings and well‐developed distal wing segments. Migration also appeared to set limits on the development of the hind limb and on the wing muscles not involved in forward flight. AmongSylviawarblers it is shown that habitat use and migration may constrain each othe

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb04747.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The paper reports the occurrence of whitish ‘leucistic’ forms in populations of Barnacle Geese Branta leucopsis. A total of 15 (including 11 in the last 21 years) have been reported in the population breeding in Svalbard and wintering in the Solway Firth, northern Britain, whereas the two other populations, though much larger, have produced only one bird of the same type between them in the last 30 years. Leucism is controlled by a single, recessive allele.The median lifespan of leucistic birds is 2–3 years, compared to 8–10 years for normal plumaged birds. This is because they are sought out by (illegal) hunters. There is no evidence that there is any difference in pairing or breeding performance between white and normal birds, though one male, which is still alive aged 18 years, has produced 13 young; this performance is matched fay less than 2% of normal geese.It is suggested that the Svalbard population was established recently, from a few founders from the Siberian population; if one or two of these carried the allele controlling leucism, this would explain its much higher prevalence in this population than in the other discrete groups of Barnacl

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb07224.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The diets of Sea Eagles Haliaeetus albicilla and Golden Eagles Aquila chrysaetos living sympatrically in western Scotland were studied using pellets and prey remains collected at roosts and nest sites throughout the year. Both species showed changes in diet between winter and summer, and there were differences between species in both seasons. As a rule, Sea Eagles took proportionately more seabirds, waterfowl (ducks and waders) and fish, whilst Golden Eagles took proportionately more rabbits and hares. Sea Eagles had a broader diet than Golden Eagles but a measure of dietary overlap based on taxonomic composition indicated an overlap of more than 90% between the two species.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb07225.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

This paper addresses the question of how to diagnose the causes of a population decline of a migratory bird so that conservation action can be taken. Diagnosis may be through study of habitats or population factors. Different approaches are illustrated with examples from the more threatened migratory species which breed in Europe. Gaps in knowledge of how to make conservation diagnoses and of the circumstances of some of Europe's few migratory and globally endangered birds are shown.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb04748.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Complete adoption of unrelated broods by foster parents is surprisingly common among birds and the behaviour appears to be maladaptive in several species. In a small, marked, southern African population of African Marsh Harriers Circus ranivorus, studied over 4 years, a young male took over the complete parenting (provisioning and defence) of an unrelated brood, and several times fed the brood in preference to the soliciting maternal parent. This female then deserted and deceitfully courted (out of season) a third male, whose provisioned food she took to feed to her own young. Since the adopting male retained the territory and bred successfully for at least two further years, he suffered no expected loss in fitness and hence this case of fostering was neither maladaptive nor apparently altruistic.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1992.tb07226.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY