摘要:

The occurrence of feathers in stomachs of 407 Great Crested GrebesPodiceps cristatusfrom Lake IJsselmeer, The Netherlands, is described. Only four of the 8718 identified stomach feathers originated from a species other than Great Crested Grebes. In all, 68% were breast and belly feathers and 19% were flank feathers. Flank feathers were positively selected from those becoming available during moult, and also occurred more in the ejected feather pellets than expected from the intake. This suggests that flank feathers, which are long and curved and have a black tip, may be especially suited for the formation of pellets. Feather ingestion was more than balanced by feather production. Feathers were most abundant in stomachs in autumn and were least numerous in winter. Most of this variation can be explained by seasonal differences in the intensity of body moult. In addition, the type of prey was related to the number of ingested feathers. When the diet consisted of smelt, which leave little indigestible matter, more feathers were eaten than with a diet of perch and pikeperch, which leave more fish debris. We suggest the hypothesis that ingested feathers, in the absence of other indigestible matter, contribute substance to the stomach content, enabling the formation of pellets that can be ejected. The habit of regularly ejecting the stomach contents minimizes the chance that any serious population of gastric parasites will build up in the upper part of the alimentary tract.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04784.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The population dynamics of tundra‐nesting Peregrine FalconsFalco peregrinus tundriuswas studied over 7 years on a 450 km2study area in the Keewatin District of Canada's Northwest Territories. Peregrines showed strong fidelity to nest sites; none of 25 males ringed changed territories, while five of 38 females ringed were recorded changing territories. Such changes usually occurred after nesting failure. Annual turnover of territorial adults was estimated to be 22% (15% for males and 26% for females). Annual mortality of adults was estimated to be 17% (15% for males and 19% for females). If we assumed that territory vacancies, in addition to mate replacements, were indicative of mortality, then maximum annual mortality was estimated at 24% for each sex. Territories were held only by adult Peregrines. The oldest male on territory was at least 7 years old, the youngest was 2. The oldest female on territory was at least 7 years old, the youngest was 3. Territories were held by individuals of each sex for at least 6 years. One pair remained together for at least 4 years. Less than 4% of all young Peregrines produced on the study area in the first 5 years of the study were recruited into the breeding population. More male than female young were recruited despite an even sex ratio among nestlings. Peregrines did poorly in their first breeding attempts. The single young female recruited into the study population dispersed more than three times the median dispersal distance of six recruited males, suggesting that other females probably dispersed beyond the boundaries of the study are

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04785.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Data on the breeding success of LapwingsVanellus vanelluson unimproved and improved grassland, with comparative data for arable land, were obtained from a study on 760 Lapwing clutches. The study was undertaken in the Eden Valley, Cumbria, and Teesdale, Co. Durham, between 1985 and 1987. First clutches were larger on unimproved grassland with a mean of 3.73 eggs compared to 3.61 eggs on improved grassland. In contrast, replacement clutches were larger on improved areas (3.90 eggs) than on unimproved (3.47 eggs). On average, 40% of eggs laid on unimproved pastures hatched compared to only 17% on improved pastures. No significant difference in hatching success was found between unimproved and improved meadows with 32% and 22% of eggs hatching, respectively. Overall, 73% of unsuccessful first clutches were replaced on unimproved pastures, whereas on meadows and improved pastures combined, only 32% were replaced. Survival of small chicks was highest on unimproved areas. Production on unimproved areas was sufficient to replace adult losses and so maintain numbers, whereas on improved land production was too low to maintain existing breeding densities. Hatching success on unimproved areas was similar for the four species of wader considered. On improved areas, Redshank hatching success was relatively high, with 54% of pairs producing chicks, compared to 35% for Lapwing and 23% for Curlew.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04786.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The breeding biology of Black GuillemotsCepphus gryllewas studied from 1982 to 1984 in Shetland, on islands lacking introduced mammalian predators. Adult survival (94%), clutch size (1.75‐1.92) and breeding output (1.05‐1.34 young fledged per breeding pair) were very high, indicating that conditions were relatively favourable on the islands studied. The timing of breeding varied significantly between years and was somewhat later than in other temperate parts of the range. In 1984 food was probably more readily available (possibly due to better weather conditions) in the pre‐breeding period, which enabled more inexperienced birds to reach the condition threshold for breeding. It is likely that these birds tended to lay single‐egg clutches in more open sites which were more susceptible to egg predation by crows. Nest‐site quality and food availability were the key determinants of breeding pro

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04787.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Seven pigeon species fed on figs from at least 22Ficustaxa at a lowland forest site in Peninsular Malaysia. Forest pigeons of the genusTreronare fig‐eating specialists. Although these are important fig‐seed predators, at least some of the population, and pigeons from other genera, potentially disperseFicusseeds to distant si

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04788.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The breeding behaviour of two similarly sized sympatric cuckoos, Horsfield's Bronze‐CuckooChrysococcyx basaltsand the Shining Bronze‐CuckooC. lucidus, was studied over four breeding seasons at Gooseberry Hill, Western Australia. Both cuckoos usually began laying in late August; Shining Bronze‐Cuckoos laid for up to 13 weeks and Horsfield's Bronze‐Cuckoos for up to 15 weeks. Four host species were parasitized and major hosts were parasitized throughout most of their laying periods. The frequency of parasitism varied between hosts and between years, but Splendid Fairy‐wrensMalurus splendensand Yellow‐rumped ThornbillsAcanthiza chrysorrhoa(major hosts) were always parasitized more heavily than Western ThornbillsA. inornataand Scarlet RobinsPetroica multicolor.Western Thornbills were parasitized by both cuckoos. Horsfield's and Shining Bronze‐Cuckoos laid monomorphic eggs; those of Horsfield's Bronze‐Cuckoos were highly mimetic whereas those of Shining Bronze‐Cuckoos were non‐mimetic and dark in colour. Both cuckoos laid one egg per host nest, deposited eggs directly into the nest, laid very quickly in the early morning, removed at least one host egg at laying, laid eggs small for the size of the birds, hatched after 12 days and evicted nest companions shortly after hatching. Laying was well synchronized with the start of incubation by hosts. Field observations and experiments with egg models indicated that neither of the major hosts, nor the secondary host in common, discriminate against foreign eggs. The nestling period for Horsfield's Bronze‐Cuckoo was 17 days, and for the Shining Bronze‐Cuckoo 20 days. There was a corresponding difference in nestling growth rate between the cuckoo species. About 50% of cuckoo eggs produced fledglings. Reproductive success for both cuckoos was highest in nests of the secondary host in common, the Western Thornbill. Young cuckoos reached independence 5–6 weeks after hatching. The adaptive significance of competition between cuckoos as a selective agent for cuckoo egg morphology and host

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04789.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Two hummingbird species inhabit the Juan Fernández Islands, nearly 700 km off the Chilean coast in the Pacific Ocean—the endangered endemic Juan Fernández FirecrownSephanoides fernándensisand the continental Green‐backed Firecrown S.sephaniodes.In terms of body size, the endemic species is the most sexually dimorphic species of hummingbird known; it also displays an extraordinary degree of sexual dichromatism. Both sexes hold feeding territories, within which courtship probably occurs. It is suggested that sexual selection, and selection for gender recognition and the absence of indigenous predators may explain the evolution of sexual dimorphism and dichromatism in the Juan Fernández Firecrown. In spite of a more than twofold difference in body size, the bill lengths of both sexes in both species are nearly identical and closely match the flower tube length of the several species of endemic plants they pollinate.The endemic Juan Fernández Firecrown has become extinct on one of the two main islands (Isla Alejandro Selkirk) and its population on the other main island (Isla Róbinson Crusoe) has greatly declined in recent decades. In contrast, the population of the Green‐backed Firecrown has probably increased on Róbinson Crusoe and the species has recently become established on Alejandro Selkirk. Because historical records show that Green‐backed Firecrown survived centuries of potential competition from Juan Fernández Firecrown, massive habitat destruction, plagues of rats, feral cats and dogs and the effects of feral livestock before beginning its recent decline, it is suggested that the introduction earlier in this century of the brambleRubus ulmifalius, the coatiNasua nasuaand possibly the rabbitOryctolagus cuniculusmay have differentially favoured the Green‐backed Firecrown at the expense of the Juan Fe

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04790.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The female Black‐and‐white Casqued HornbillBycanistes subcylindricususes mud to seal herself into a nest cavity and remains there until the nesting attempt has ended. The male hornbill is solely responsible for food provisioning and external defence of the nest. Data on hornbill nests in a Ugandan rain forest were used to test Martindale's (1982) model of nest defence and central place foraging. As predicted, nest guarding by the resident male hornbill during intrusions by conspecifics altered foraging patterns; the resident male foraged closer to the nest, made a larger number of shorter visits, and brought smaller food loads. There was a significant change in size composition of fruits brought before, during, and after intrusions. For short intrusions, the volumes of food brought per unit time did not change. However, if intrusions lasted for days or weeks, food delivery rates declined. Nest‐sealing by the Black‐and‐white Casqued Hornbill appears to function primarily to protect the nest from conspecifics rather than from interspecific

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04791.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Variation in clutch‐size of the Pied FlycatcherFicedula hypoleucawas studied simultaneously in relation to latitude, longitude, altitude, laying date and habitat, using data from 103 areas from north Africa to north Norway (latitudinal range about 3900 km). Clutch‐size variation was significantly related to altitude and habitat, small clutches being laid at high altitude and in coniferous forests. In contrast to some earlier studies, latitudinal or longitudinal clutch‐size trends were not

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04792.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The breeding ecology of White and Japanese Wagtails,Motacilla albaandM. grandis, was studied along a river in central Japan. The home ranges of the two species greatly overlapped along the river, but no interbreeding occurred.M. grandisspent more time on the river thanM. albaand defended territories there.M. albaused the river as part of the entire home range, and did not defend the river areas as territories. Singing activity and breeding started earlier inM. grandisthan inM. alba.The early breeding ofM. grandiswas related to the lack of moulting in spring, less necessity for pair formation due to the existence of pairs in the winter, and the greater dependency on larval than on adult insects. Songs were very different between the two species. The bowing display that preceded the pre‐copulation display was found only inM. alba.During the pre‐copulation display, maleM. grandislifted both wings above the horizontal while maleM. albadrooped both wings. The pre‐copulation display ofM. grandiswas similar to that of Large Pied WagtailsM. maderaspatensisin India, suggesting a closer relationship of the two species than toM.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1989.tb04793.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY