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1.
The distribution of breeding ducks versus three other bird species (Mute Swan Cygnus olor, Black-headed Gull Larus ridibundus and Purple Heron Ardea purpurea) among waterbodies was investigated in the Dombes area, Eastern France, where breeding duck populations have undergone a severe decline following a large-scale transformation of meadow habitat into cropland. Higher Pochard Aythya ferina, Tufted Duck Aythya fuligula, Red-crested Pochard Netta rufina and Gadwall Anas strepera pair densities were recorded in fishponds where Black-headed Gulls were nesting. In these ponds however, nesting success (assessed by the number of broods divided by the number of pairs) was not significantly higher. Similarly, Pochard pair density was higher in ponds with a Purple Heron colony, but brood densities were not. We hypothesise that, in the study region, clutch concentration in the most attractive areas could compensate for the anti-predation effect of gull colonies or overwater nesting in shore vegetation. We could not confirm the expected negative impact of Mute Swan aggressive behaviour on duck distribution. Even though Mallard Anas platyrhynchos pair density was lower in ponds with breeding swans, we did not observe difference for Mallard broods. Moreover, Red-crested Pochard pair density and nesting success were higher in ponds where swans were breeding, probably as a consequence of shared habitat preferences.  相似文献   

2.
Sexual selection theory predicts that sexually selected ornaments are costly to maintain and, as condition-dependent signals, are likely to vary in attractiveness with season and age. Mute swans Cygnus olor possess a black, fleshy knob at the base of the bill, which is present in both sexes. Using measures calculated from digital photographs taken over two years we monitored changes in the size of the bill knob in individual swans throughout the breeding season. Our longitudinal data show that bill knob size is highly dynamic. Relative bill knob size was larger in males than females and was consistently greater for breeding males than for non-breeders. For males, relative bill knob size peaked during cygnet hatching, when male protection of the brood is most important, and was smallest during moult. In females, breeders had larger bill knobs than non-breeders at all times apart from immediately after egg-laying and incubation, when the reverse was true, presumably reflecting the costs of reproduction. Body mass was a highly significant predictor of relative bill knob size in both sexes, as was age, with an initial increase and then later a decline in relative ornament size across the lifetime of male birds. The bill knob ornament in mute swans thus appears to be a condition-dependent, highly malleable trait. It accurately reflects the differing pressures experienced by individual birds as they progress through the breeding season, suggesting selection by both intra- and inter-sexual forces.  相似文献   

3.
The weights of Mute Swans contain useful information on individuals' prospects for survival and breeding but to interpret them one needs to know what 'typical' weights would be. This paper uses multiple linear regression to predict such 'typical' weights: 1968 zveighings of 957 Mute Swans, from south Staffordshire, England, are analysed with respect to sex, age, moultstage, month of capture and breeding status. Because of marked sexual dimorphism, knowing a swan's sex is fundamental to interpreting its weight; age from hatching and stage of primary feather growth affect cygnets' weights near fledging; weights of young swans change with age during their first years of life; primary feather moult significantly depresses the weights of first year males but not, in this study area, of older males or females; monthly, seasonal changes are generally small; breeding adults are significantly heavier. The results and their biological implications agree well with other, less comprehensive, analyses. The method described could facilitate both the identification of other factors that should be investigated and comparisons between different study areas.  相似文献   

4.
Monthly surveys of Bewick's Swans Cygnus columbianus bewickii , Whooper Swans Cygnus cygnus and Mute Swans Cygnus olor in Britain and Ireland were made during the 1990–1991 winter to determine factors affecting the swans' selection of feeding sites. Geographic location and habitat both influenced site selection. Whooper Swans occurred in greatest numbers at sites in Scotland, northeastern England and Northern Ireland, whereas Bewick's Swans had a more southerly distribution, reflecting differences in the migratory routes used by these two species. The resident Mute Swans were more widespread, with large flocks occurring in southeastern England and in parts of Scotland. Whooper and Mute Swans were found mainly on permanent inland waters (68% and 61%, respectively), but the majority of Bewick's Swans (60%) were on arable land. The percentage of Bewick's Swan flocks found on permanent inland waters (42%) was higher than that found on arable fields (23%), indicating that the large number recorded on arable land was a result of the birds congregating at a comparatively small number of sites. Overall, less than 15% of Whooper Swans and 3% of Mute Swans were on arable crops during the winter, but the largest flocks were associated with arable land for all three species. Thus, although the occurrence of large flocks at particular arable sites may give an impression that swans feed mainly on farmland, the swans are in fact more widely dispersed. Regional variation in the percentage of juveniles present was recorded for all three species. Changes during the winter in the distribution of juveniles, and of the swans as a whole, are considered in relation to food supply and to migratory routes for the Bewick's and Whooper Swans.  相似文献   

5.
Mike  Birkhead 《Journal of Zoology》1983,199(1):59-73
In this paper blood lead levels in three categories of Mute swan are examined, (i) flock birds (ii) breeding birds and (iii) cygnets. From these regional, seasonal and sex variation for both 1980 and 1981 was examined. In addition a portable haematofluorometer was assessed to determine its possible use as an alternative to atomic absorption and spectrophotometry for determining a measure of lead exposure.
Very few swans on the River Thames had blood lead levels below the maximum acceptable level of 40 mgg/100 ml. In general lead levels increased with proximity to London and the swans on the tributaries consistently had the lowest levels which were always below the maximum acceptable level. Blood lead levels in flock birds were shown to be highest during the coarse fishing season and it was only during the close season that levels dropped to around 40 g/1OO ml. Breeding females had significantly higher lead levels than males and females with lead levels in excess of 200 g/1OO ml seemed to have a poor chance of producing cygnets or surviving to the next breeding season. Cygnet mortality was significantly higher on the lower Thames where blood lead levels were also known to be at their highest.  相似文献   

6.
Foragers in patchy environments do not only select sites for single patch characteristics, but also have to consider the local environment of such patches. We studied habitat selection by mute swans Cygnus olor in a wide and heterogeneous fishpond region (the Dombes, eastern France). In this study, we considered fishpond isolation, resource quality within fishponds and breeding status of mute swans during both summer and winter. Mute swans did not select aquatic habitat randomly within the landscape. During summer, the population spread preferentially on medium to large fishponds, in subregions with numerous or closely related waterbodies, without generating a clumped distribution of birds. In addition to a positive effect of local fishpond number (2 km radius), breeding birds also responded positively to fishpond size. Non‐breeders selected fishponds mainly according to their size. Intraspecific territoriality did not appear to limit the presence of non‐breeders (i.e. moulting flocks), since both breeders and non‐breeders could coexist on the larger fishponds. During winter, mute swans used medium to large reflooded fishponds after summer drainage. The surrounding aquatic environment of fishponds played a minor role in determining flocking, compared to actual patch quality. Flocking occurred on large fishponds that had reflooded after having dried the summer before, whatever the agricultural cultivation practiced in the summer following drainage. The results suggest that geographical aspects should be taken into account when considering the potential impact of this expanding species within such ecosystems, and also in more general management policies dealing with aquatic habitats for waterbird populations.  相似文献   

7.
In some avian species, young birds capable of reproducing diminish their prospects of doing so by molting into a subadult plumage that accurately signals their subadult status. Several hypotheses have been proposed to explain the evolution of delayed plumage maturation, but testing them usually has involved interspecific comparisons that are hard to interpret. Mute swans (Cygnus olor) exhibit two phenotypes that differ in whether the birds have a gray subadult plumage (SAP phenotype) or molt immediately into an all white adult plumage (AP phenotype). The AP phenotype results from a recessive allele on the X chromosome; both phenotypes occur in the same population and even in the same brood. We compared costs and benefits of both phenotypes in mute swans on the Chesapeake Bay in 1972-1980 and on Long Island Sound in 1982-1989. Swans with the SAP phenotype had higher survival rates from hatching to fledging than AP swans. In the fall, when AP cygnets began to molt into their white plumage, their parents often attacked and drove them off while allowing SAP cygnets from the same brood to remain on their territories for several more months. SAP males had higher survival rates during their first 2 yr of life than AP males, but AP swans bred at a younger age than SAP swans. The only proposed hypothesis for the evolution of delayed plumage maturation that can explain its occurrence in mute swans is the status-signaling hypothesis. This hypothesis argues that males with subadult plumage honestly advertise their age and subordinate status while AP swans are cheaters and engaging in dishonest communication. SAP males acquire a longer period of parental care, suffer less aggression from older birds, and increase their survival but forgo the opportunity to breed at an early age. This is a unique example of how a single gene resulted in either honest or dishonest communication, changed a bird's relationship with its parents and potential mates, and altered the bird's chances to survive and to reproduce.  相似文献   

8.
Colonies of co-operatively breeding African mole-rats have traditionally been thought to be composed of a single breeding female, one or two breeding males, and their offspring. In the naked mole-rat (Heterocephalus glaber), the occurrence of facultative inbreeding means incest avoidance cannot prevent reproduction in subordinate group members, and physiological suppression of reproductive function by the breeding female occurs in both sexes. In contrast, previous studies of captive colonies of the Damaraland mole-rat (Cryptomys damarensis) suggest that breeding within a colony is restricted to a single breeding pair, simply because all other colony members are highly related (first- or second-order relatives) and this species is an obligate outbreeder. Using microsatellite markers, we investigated parentage and colony composition in 18 wild Damaraland mole-rat colonies to determine whether inbreeding avoidance alone can explain the high levels of reproductive skew in this species. Multiple and unidentified paternity was widespread within colonies and immigrants of both sexes were regularly identified. Unrelated, opposite-sex nonbreeders were found coexisting in two colonies. These results suggest that, in the wild, conditions exist where nonreproductive females can come into contact with unrelated males, even when they do not disperse from their natal colony. Inbreeding avoidance alone is therefore insufficient to maintain the high levels of reproductive skew identified in this species suggesting that the breeding female somehow suppresses the reproductive function in nonbreeding females.  相似文献   

9.
Investigating the extent (or the existence) of local adaptation is crucial to understanding how populations adapt. When experiments or fitness measurements are difficult or impossible to perform in natural populations, genomic techniques allow us to investigate local adaptation through the comparison of allele frequencies and outlier loci along environmental clines. The thick‐billed murre (Uria lomvia) is a highly philopatric colonial arctic seabird that occupies a significant environmental gradient, shows marked phenotypic differences among colonies, and has large effective population sizes. To test whether thick‐billed murres from five colonies along the eastern Canadian Arctic coast show genomic signatures of local adaptation to their breeding grounds, we analyzed geographic variation in genome‐wide markers mapped to a newly assembled thick‐billed murre reference genome. We used outlier analyses to detect loci putatively under selection, and clustering analyses to investigate patterns of differentiation based on 2220 genomewide single nucleotide polymorphisms (SNPs) and 137 outlier SNPs. We found no evidence of population structure among colonies using all loci but found population structure based on outliers only, where birds from the two northernmost colonies (Minarets and Prince Leopold) grouped with birds from the southernmost colony (Gannet), and birds from Coats and Akpatok were distinct from all other colonies. Although results from our analyses did not support local adaptation along the latitudinal cline of breeding colonies, outlier loci grouped birds from different colonies according to their non‐breeding distributions, suggesting that outliers may be informative about adaptation and/or demographic connectivity associated with their migration patterns or nonbreeding grounds.  相似文献   

10.
The Little Penguin, Eudyptula minor, is a seabird that nests in colonies throughout New Zealand and southern Australia. Individuals from different colonies in southeast Australia differ significantly in morphology and ecology, suggesting that some genetic structuring may exist among colonies. In contrast, the marking of individuals with flipper bands has revealed some, albeit infrequent, movement between colonies. To determine the extent of genetic structuring, we tested the null hypothesis of substantial gene flow within southeast Australia by examining patterns of genetic variation across seven colonies separated by up to 1,500 km. Phylogeographic structuring was absent for mitochondrial control region sequences (2–3 individuals per colony). Microsatellite allele frequencies at five loci and mitochondrial haplotype frequencies (50 individuals per colony) were also homogenous among the majority of colonies sampled, although two colonies at the western periphery of the sampling range were distinct from those to the east. The genetic homogeneity among the majority of colonies can be explained by low but consistent contemporary gene flow among them, or a recent founder event in Bass Strait following the last marine transgression. The genetic break towards the western end of the sampling distribution appears best explained by differences in sea surface temperature and, consequentially breeding phenology, the latter hindering genetically effective migration.  相似文献   

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