首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 93 毫秒
1.
Ewins  P. J.  Weseloh  D. V.  Groom  J. H.  Dobos  R. Z.  Mineau  P. 《Hydrobiologia》1994,(1):39-55
In the Great Lakes, the Herring Gull (Larus argentatus) is a prominent member of the aquatic bird community, and has been used to monitor spatial and temporal trends in contaminant levels. To understand more fully contaminant loading outside the breeding season, we analysed the contents of 1298 freshly regurgitated pellets and 179 fresh faeces, collected in March and early April 1978–83, and between late December and late February 1990–91, from the vicinity of breeding colonies in Lakes Ontario and Erie, the Niagara River, Detroit River, and south-eastern parts of Lake Huron. Most adult Herring Gulls from the Great Lakes population winter in these areas, but there is no published account of their food habits other than during the breeding season. Most pellets from colonies close to large urban centres contained remains of garbage, as well as various fish species. Small mammals, notably Deer Mice (Peromyscus maniculatus) dominated the early spring diet at Lake Huron colonies near agricultural areas. At all other sites fish predominated in pellets and faeces, but garbage items were also recorded regularly. The species of fish consumed varied regionally, probably reflecting local availability. In Lake Ontario, Rainbow Smelt (Osmerus mordax) and Alewife (Alosa pseudoharengus) occurred most frequently in samples, whereas Freshwater Drum (Aplodinotus grunniens) was the main fish prey in Lake Erie and the Detroit River. Dietary differences were apparent between years, within seasons, and amongst areas. While these may have reflected some real differences in food availability, interpretation of these results was confounded by various biases inherent in the sampling of pellets and faeces to determine diet in such an opportunistic species. Therefore, it would be unwise to draw rigid conclusions as to regional or seasonal differences in the diets of piscivorous birds, based upon analyses of diet from only a small sample of sites or years. Herring Gulls appear to feed mainly on fish and garbage in winter and early spring on the lower Great Lakes (much as during the breeding season), but any locally abundant food source is probably exploited opportunistically.  相似文献   

2.
Reducing resource competition is a crucial requirement for colonial seabirds to ensure adequate self‐ and chick‐provisioning during breeding season. Spatial segregation is a common avoidance strategy among and within species from neighboring breeding colonies. We determined whether the foraging behaviors of incubating lesser black‐backed gulls (Larus fuscus) differed between six colonies varying in size and distance to mainland, and whether any differences could be related to the foraging habitats visited. Seventy‐nine incubating individuals from six study colonies along the German North Sea coast were equipped with GPS data loggers in multiple years. Dietary information was gained by sampling food pellets, and blood samples were taken for stable isotope analyses. Foraging patterns clearly differed among and within colonies. Foraging range increased with increasing colony size and decreased with increasing colony distance from the mainland, although the latter might be due to the inclusion of the only offshore colony. Gulls from larger colonies with consequently greater density‐dependent competition were more likely to forage at land instead of at sea. The diets of the gulls from the colonies furthest from each other differed, while the diets from the other colonies overlapped with each other. The spatial segregation and dietary similarities suggest that lesser black‐backed gulls foraged at different sites and utilized two main habitat types, although these were similar across foraging areas for all colonies except the single offshore island. The avoidance of intraspecific competition results in colony‐specific foraging patterns, potentially causing more intensive utilization of terrestrial foraging sites, which may offer more predictable and easily available foraging compared with the marine environment.  相似文献   

3.
This study evaluates the trophic position of adult Yellow-legged Gulls Larus michahellis atlantis resident in the Azores archipelago in the past (1921–1928) and in the present (2009–2010), and analyses the decadal variation in the diet of breeding birds from the 1990s to the 2000s for three main colonies (Topo Islet, Baixo Islet and Mistério da Prainha). Using mixing models, we compared stable isotope signatures of nitrogen and carbon in adult breast feathers between birds from 1921 to 1928 (held in museum collections) and 2009 to 2010, jointly with both isotopic signatures of their main prey groups (fish, goose barnacles (Lepas anatifera), seabirds, mammals and refuse). The diet of breeding birds was analysed using pellets collected in 1989, 1995, 1996, 2004, 2009 and 2010. Stable isotopes analysis (SIA) results were in accordance with the results provided from the analysis of pellets, showing a relatively recent and significant change in the diet of adult gulls. In particular, SIA revealed a significant decrease in the trophic position of Yellow-legged Gulls in the Azores, over the last 89 years in response to the decrease in the consumption of seabirds and fish and, an increase in the consumption of marine invertebrates (goose barnacles) and refuse. The analysis of pellets confirmed the significant decrease in the fish ingested, whereas the ingestion of lower trophic level prey (i.e. goose barnacles, mammals and refuse) increased. Both methods reflect the feeding plasticity and opportunistic foraging behavior of this species, and are in accordance with patterns described for continental Europe.  相似文献   

4.
The world's oceans have undergone significant ecological changes following European colonial expansion and associated industrialization. Seabirds are useful indicators of marine food web structure and can be used to track multidecadal environmental change, potentially reflecting long‐term human impacts. We used stable isotope (δ13C, δ15N) analysis of feathers from glaucous‐winged gulls (Larus glaucescens) in a heavily disturbed region of the northeast Pacific to ask whether diets of this generalist forager changed in response to shifts in food availability over 150 years, and whether any detected change might explain long‐term trends in gull abundance. Sampled feathers came from birds collected between 1860 and 2009 at nesting colonies in the Salish Sea, a transboundary marine system adjacent to Washington, USA and British Columbia, Canada. To determine whether temporal trends in stable isotope ratios might simply reflect changes to baseline environmental values, we also analysed muscle tissue from forage fishes collected in the same region over a multidecadal timeframe. Values of δ13C and δ15N declined since 1860 in both subadult and adult gulls (δ13C, ~ 2–6‰; δ15N, ~4–5‰), indicating that their diet has become less marine over time, and that birds now feed at a lower trophic level than previously. Conversely, forage fish δ13C and δ15N values showed no trends, supporting our conclusion that gull feather values were indicative of declines in marine food availability rather than of baseline environmental change. Gradual declines in feather isotope values are consistent with trends predicted had gulls consumed less fish over time, but were equivocal with respect to whether gulls had switched to a more garbage‐based diet, or one comprising marine invertebrates. Nevertheless, our results suggest a long‐term decrease in diet quality linked to declining fish abundance or other anthropogenic influences, and may help to explain regional population declines in this species and other piscivores.  相似文献   

5.
Understanding the use of feeding sources at the local scale is crucial in comprehending the factors driving population dynamics, dispersal and territory use. Many gull (Larus spp.) populations have increased sharply, which is partly promoted by their use of landfills as a food resource. Although at the large scale it is known that birds from mainland colonies feed more on landfills than those from offshore colonies, at the local scale, this distance‐dependent exploitation has been little studied. Here, then, we study whether the extent of gulls’ use of landfill is distance‐dependent through the study of 3 different gull colonies and five separate landfill sites within a relatively small geographical area. After controlling for bird numbers by both age cohort and colony, we observed that the number of gulls found at each landfill was colony dependent and that it decreased non‐linearly with increased distance to place of birth.  相似文献   

6.
Prey availability is known to limit reproduction of some species of nesting birds, but identifying the primary prey types of a species with a flexible diet can be challenging. For the White Ibis Eudocimus albus, a tactile feeding, medium‐sized wading bird, nestling prey composition is suggested to depend on landscape water depths/availability of foraging habitat at the time of nesting and on historical drying events affecting prey production. We collected and compared inter‐ and intra‐annual diet variation of White Ibis chicks reared in the Everglades over two years that were independently identified as being relatively good (2006) and poor (2007) nesting seasons. We collected 127 nestling boluses and analysed the temporal variation in biomass of eight functional prey groups using multivariate techniques. The boluses from 2006 in the central Everglades were dominated by fish, but in 2007, after fish had been reduced by the previous year of drying, the boluses from the same region were more variable and dominated by garbage (i.e. scavenging). Analysis of five different collections taken from a different colony in the northern Everglades indicated that boluses were characterized by crayfish and had fewer fish or less garbage when landscape water depths were relatively higher and more preferred habitat was available. At lower landscape water depths in 2007 the bolus composition shifted away from crayfish towards small fish and urban food (terrestrial insects and garbage). Our results support the suggestion of depth‐dependent diets; prey composition depends on the current landscape water levels around the colonies, and also suggests that previous drying events can lead to increased reliance on alternative food sources. White Ibis partially compensated for unavailable aquatic prey with alternative urban foods, but their nesting success appears to have suffered.  相似文献   

7.
M. P. Harris 《Ibis》1965,107(1):43-53
The food of L. argentatus on Skomer and Skokholm Islands (Wales) was studied by the analysis of stomach contents, pellets and direct observation. L. argentatus is mainly a scavenger and exists for the most part on fish-waste and garbage discarded by man. At Ncwborough Warren argentatus feeds more on arable land and on the shore than do the Skokholm and Skomer birds.
Although argentatus frequently eats limpets Patella spp., there is little competition for food between them and Oystercatchers Haematopus ostralegus because the two species eat different sized limpets.
A summary of previous studies into the food of argentatus is given.
L. marinus is mainly a predator feeding on the young of other gulls, sea-birds and Rabbits but it also eats carrion, offal and fish-waste when available and during the winter. The numbers of Manx Shearwaters Procellaria puffinus killed on Skokholm and Skomer are discussed.
L. fuscus obtains most of its food on the shore and on arable land. There appears to be little competition, at least in the areas studied, between .fuscus and argentatus for food.  相似文献   

8.
Analyses of the contents of pellets of Grey herons from different breeding colonies and breeding seasons indicated that the mammal and invertebrate species included in the heron diet varied between colonies and between years. The large differences in mammal species found in neighbouring heronries suggested the existence of important small-scale variability in the exploitation of mammals. Almost no fish and bird remains were found in the pellets. We believe that most invertebrates, even the smallest ones, were actively taken by the herons. Identification of mammal species composition by means of skulls and hair remains gave different results. The shape of a pellet seemed to be dependent upon the (moisture?) conditions during its formation.  相似文献   

9.
The UK Farm Scale Evaluations (FSEs) have shown that the use of broad spectrum herbicides on genetically modified herbicide-tolerant (GMHT) crops can have dramatic effects on weed seed production compared to management of conventional varieties. Here, we use FSE data and information on bird diets to determine how GMHT cropping might change the food resources available to farmland birds. More than 60 fields of each of four crops, spring- and winter-sown oilseed rape, beet and maize, were split, one half being sown with a conventional variety, the other with a GMHT variety. Seed rain from weeds known to be important in the diets of 17 granivorous farmland bird species was measured under the two treatments. In beet and spring oilseed rape, rain of weed seeds important in the diets of 16 bird species was significantly reduced in GMHT compared to conventional halves; for no species did it increase. In winter oilseed rape, rain of weed seeds important in the diets of 10 species was significantly reduced in GMHT halves; for only one species did it increase significantly. By contrast, in maize, rain of weed seeds important in the diets of seven species was significantly greater in GMHT halves; for no species was it reduced. Treatment effects for the total weed seed energy available to each bird species were very similar to those for seed rain alone. Measuring the effects on individual bird species was outside the scope of this study. Despite this, these results suggest that should beet, spring and winter rape crops in the UK be largely replaced by GMHT varieties and managed as in the FSEs, this would markedly reduce important food resources for farmland birds, many of which declined during the last quarter of the twentieth century. By contrast, GMHT maize would be beneficial to farmland birds.  相似文献   

10.
We tested discriminatory ability and food choice in relation to protein content of the diet in wild-caught Blue-gray Tanagers (Thraupis episcopus), a generalist tropical frugivorous bird. In two sets of experiments we offered to five individual birds in pair-wise choice trials two nearly iso-caloric experimental diets differing in their protein content only. Protein contents of the experimental diets were 4.6 vs. 1.4% in the first experiment and 3.2 and 1.5% (dry matter basis) in the second experiment. Response varied among individual tanagers, but 6 of the 10 birds showed a clear preference for the food highest in protein. Two individuals displayed a strong positional preference. When testing each treatment group, birds ate daily significantly more of the food that had higher protein content. We conclude that Blue-gray Tanagers prefer richer nitrogen foods. Our results also demonstrate that Blue-gray Tanagers have remarkable discriminatory abilities, they reacted to differences in protein content as small as 0.09% fresh matter. We show for the first time discriminatory ability and preference of wild frugivorous birds for foods richer in protein under controlled conditions. Our findings support the hypothesis that frugivorous birds can act as selective agents for fruit pulp composition.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号