摘要:

We describe parental feeding by Red‐throated DiversGavia stellatafrom 14.2–44.7 h of observation on each of eight pairs, coordinated with simultaneous observations at potential fishing lakes, in southwest Sweden. All pairs bred on small tarns (0.8–10 ha), normally devoid offish, and foraged in larger freshwater lakes 1.9–7.7 km away from the breeding site. Most pairs directed the majority of the foraging trips to the same lake. On average, parents made seven foraging trips per day per young. Both parents contributed to feeding activities and, in broods of two young, each chick obtained an equal amount of food. Cyprinid fish (mainlyRutilus rutilus) and salmonids (mainlyCoregonus albula) dominated. Qualitative predictions from central‐place foraging theory concerning relationships between the time for a foraging trip and the size of prey delivered by a single‐prey loader were not corroborated. The amounts of fish biomass delivered were in agreement with or lower than predictions from models on daily energy requirements; this result is related to the decreased abundance of fish in acidified freshwater lakes and the decline of Red‐throated Diver populations in

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01010.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01075.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

In Grey‐faced PetrelsPterodroma macroptera gouldiparental care during the 55‐day incubation period is mainly achieved by three long shifts (two by the male) when one partner is ashore while the other forages at sea. This situation would seem to carry high risks of parental desertion and failure of the hatching chick to receive a meal before its yolk sac is exhausted. We examined incubation routines of 51 pairs of Grey‐faced Petrels to investigate factors implicated in parental desertion and in the duration of the final foraging trip before hatching. The duration of the final long foraging trip (by the female) during incubation is not predicted by the time spent fasting on the nest but by the time elapsed since laying. Desertions accounted for 6.5% of egg losses. Eggs were deserted not after the delay of the foraging bird to return to the nest, but when the incubating bird departed early in the incubation spell. Desertions were not a response to critically depleted energy res

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01011.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Among the species of diurnal herons (Ardeinae) showing light‐dark colour polymorphism in plumage, colour phase is age‐related in one species, closely associated with geography in three species, and found in most populations in three closely related species of reef herons. In Pacific Reef HeronsEgretta sacrawhite‐phased birds sought prey by a flight, land, and freeze hunting style in breaking surf, while dark birds pursued prey by actively walking or running on reef flats. On Mangaia, in the southern Cook Islands, more white‐phased birds used the windward side of the island and more dark‐phased birds used the lee side. On Rarotonga, 204 km from Mangaia, reef herons foraged almost exclusively in shaded streams and no entirely white‐phased bird was encountered. These results provide the first evidence of differences in hunting techniques associated with colour morph and only the second observation of differences in habitat use by white‐ and dark‐phased herons at single localities. As such they support Murton's (1971) idea that colour polymorphism serves herons in their role as predators. For reasons discussed in the text such differences are more expected in reef herons than in most other colour‐p

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01012.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The population of the White StorkCiconin ciconiain Alsace (northeastern France) has decreased considerably since 1961. Using recent captureerecapture models, we analysed resighting data on ringed birds resulting from a long‐term ringing programme carried out in 1947–1985. Time‐dependence and age‐dependence in annual survival rates are examined with reference to environmental variables in the Sahel wintering area. Our results show a decrease in adult annual survival rate linked to the severity of the drought in the Saheli

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01013.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Breeding by Rüppell's Griffon VulturesGyps rueppelliiis synchronized but the time of breeding of colonies in the Serengeti region of Tanzania has changed by 5 months over the period between 1969–1970 and 1985. During this interval there have been considerable changes in the ungulate populations within the feeding range of the vultures, resulting in an increase to the food supply available to the birds. It is suggested that this species may have two alternative breeding seasons, the selective value of each depending on the magnitude of the food supp

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01014.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Our aim was to investigate how ecologically similar species with different evolutionary adaptations may coexist in a moist Guinean savanna, which is the optimal habitat of the Lizard BuzzardKaupifalco monogrammicuswhereas the Grey KestrelFalco ardosiaceusand the Grasshopper BuzzardButastur rufipennisare of more Sudanian origin. Activity budgets, foraging behaviour and success were assessed by focal sampling and were related to habitat parameters and prey availability. Each species had its own daily foraging pattern which seemed to be related to the activity patterns of their main prey, grasshoppers or lizards. Interspecific habitat segregation reflected their morphological and behavioural adaptations and their respective tolerance to grass height, the most important factor in habitat selection. The resident Lizard Buzzard selected the densest woodlands, whereas the Grey Kestrel was restricted to the most open areas and the dry season migrant Grasshopper Buzzard to intermediate, recently burnt, savanna types. The main foraging variables (perch height, inter‐perch distance and frequency of moves) differed significantly between species. Maximum detection distances increased with perch height but decreased with increasing grass cover. Perch height was lower when the grass became too high. When attack rates increased, birds tended to move more often, but for shorter distances, and stayed longer within restricted patches. The highly insectivorous Grasshopper Buzzard had the highest and least variable attack rates, negatively correlated with grass height. It exhibited a behaviour typical of a migrant—superficial and opportunistic exploitation of superabundant, easily accessible, and seasonal food sources. Conversely, the residents were associated with denser, more stable habitats and larger, less abundant, but more predictable p

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01015.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Juvenile and adult behaviour was studied at eight nests of Black KitesMilvus migranswithin the Doñana Biological Reserve, Spain. Parental investment in vigilance and defence of offspring progressively decreased during the post‐fledging dependence period. The number of feeds was also slightly reduced towards the end of the period. However, this does not seem to be the main factor which leads to juvenile independence. The fact that the family rupture is sudden and that the post‐fledging dependence period tends to shorten as the season progresses suggests that juvenile and adult migratory urgency may be as important a factor as reduced parental investment in breaking the family

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01016.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Weight losses incurred by incubating birds of both sexes, and weight changes at the beginning and end of shifts between successive incubation and brooding shifts were studied in the Antarctic FulmarFulmarus glacialoidesin Adélie Land, Antarctica. The overall rate of weight loss during incubation fasts was 4.46% per day in both sexes but 3.91% per day after the first 2 days of fast once the stomach contents had been digested. Antarctic Fulmars appear to have rates of body‐weight loss significantly greater than the rates of weight loss observed in any other species of albatross or petrel. The validity of methods using the rate of weight loss to estimate incubation metabolic rates is discussed, and it appears that for birds incubating for periods of less than 2–3 days the digestion of the stomach contents can bias the estimation. The absence of change in weight at the beginning of shifts during incubation and brooding, together with the short time spent on foraging trips, suggests that food availability is high and/or food is readily accessible to Antarctic Fulmars. The availability of food allows the Antarctic Fulmar to compensate for the high energy cost of breeding that could be due to the cold Antarctic environment and perhaps also to a higher intrinsic metabo

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01017.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Scarlet RobinsPetroica multicolorand Flame RobinsP. phoeniceaoccurred sympatrically during the breeding season in southeastern Australia. Scarlet Robins that occur territories in forest habitat remained there throughout the year, while those, mostly first‐year birds, that occupied territories in grassland habitat were present only during the non‐breeding season. Flame Robins were present for 9 months of the year and were territorial for 6 of those months. The migratory Flame Robin did not show more intense or prolonged territorial or courtship behaviour than the sedentary Scarlet Robin, despite having to obtain territories and mates when it returned each year. It is suggested that the similarities between the two species' social organizations arise partly from high adult survivorship (70–75%) and lengthy breeding seasons (4–5 months). High adult survivorship and scarcity of suitable breeding habitat also caused intense competition for territories and mates, and appears to have led to the evolution of bright, signalling plumages among female and young male Scarlet Robins. Scarcity of females and breeding habitat may have caused delayed maturation of plumage among male Flame

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1990.tb01018.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY