摘要:

SummaryThe diet of young Red Grouse was studied from the crop contents of 211 chicks caught on a moor in northeast Scotland. The food was more varied than that of adults, but shoot tips of heather usually formed at least 75% (by dry weight) of their diet, as in adults. Arthropods, particularly Diptera, were taken frequently by chicks up to three weeks old, but they formed less than 5% (by dry weight) of the diet then. The chicks ate more invertebrates when more were available. There was no evidence that chick survival was related to the abundance of invertebrates. The chicks ate heather containing more nitrogen and phosphorus than that eaten by adults at the same time of year.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02039.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryThe feeding ecology of three Costa Rican finches occurring in mixed flocks,Tiaris olivacea, Sporophila aurita corvinaandSporophila torquella, was investigated by measuring both behavioural and ecological variables. Observations on foraging height, rate of hopping and pecking rate, as well as the identity, proximity and number of nearest neighbours were recorded. In addition the duration of all feeding and perching episodes were timed. Comparisons were also made between the abundances of food items (grass seeds) consumed and those potentially available for consumption.The analysis of variance of the feeding behaviour revealed that the presence or absence of neighbouring birds, whether of the same or different species, influenced the duration of feeding bouts more significantly than did either differences in habitat or species‐characteristic behaviour. In addition the dietary comparisons revealed overlap in both species and size of seed consumed. Such similarities suggest that these species are not partitioning fields in the classical sense.We propose that the increase in the duration of the feeding bout associated with the presence of mixed species aggregations leads to increased feeding efficiency and is the result of intra‐ and inter‐specific social learning. Certainly flocking is often advantageous, since searching in a group facilitates finding clumped resources; mixed species flocking, by increasing exposure to a diversity of foraging places and patterns, can further augment feeding effic

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02040.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryTen Barn Owls were tested in a sound‐room with recordings of various alarm calls and noise. The owls readily responded with head movements to the majority of stimuli and correctly oriented to their source. Theseeetalarm call and the ‘warning’ call elicited the least responses, but they were properly localized by all owls which did respond. This suggests that rather than non‐localizability accounting for the fewer observed responses to theseeetand ‘warning’ calls, there is either something else in the quality of those sounds, or in the manner in which they are processed by the bird, which does not elicit responses to the degree that transient sounds with broad frequencies do. Selection in these predators for non‐responsiveness is suggested as a counter‐strategy to minimize futile energy expenditure in attacking, or otherwise responding to an alerted prey.An additional hypothesis, consistent with Darwin's antithesis principle, is proposed whereby intraspecific and interspecific selection, rather than predator selection for non‐localizability, has led to the evolution ofseeet

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02041.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryDuring spring and autumn 1970 and 1971 the movements of terns off the coast of Ghana near Accra were studied by radar. In autumn, dense movements were recorded within 22 km of the coast both day and night from July to early December. Fluctuations in the magnitude of the movements suggest that the terns were on passage through the Gulf of Guinea. Simultaneous to these movements were roosting flights into shore roosts and both movements appeared independent.In contrast, no spring movements along the coastline were detected either by radar or visually from the land. Although small tern flocks probably moved westwards within 22 km of the coast, but outside their detectable radar range, the results suggest that the majority of terns return through the Gulf of Guinea by a different route from that taken in autumn.The difference between spring and autumn movements correlates well with the seasonal variation of the terns' food sources. In autumn, upwellings result in an abundant fish supply (sardines) in the surface waters close to land, whereas in spring, fish is abundant only well off shore such as at fronts (convergences) and upwellings (divergences) both of which have been located as far as 600 km from the coast.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02042.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryMore extensive collections of subfossil bird bones from Ascension Island in the South Atlantic further confirm that the former seabird populations of the main island were composed of tropical species still present in greatly reduced numbers, mostly on offshore islets. A single specimen ofPuffinus lherminieriprovides the first fossil evidence of that species from the island. The extinct flightless railAtlantisia elpenorwas the only land bird certainly known to have been native. A femur, apparently from a vagrant individual, is referred toPorphyrula alleni, A specimen ofNycticorax, much smaller than any recent examples ofN. nycticoraxseen, is either from an unusually small vagrant or possibly indicates an undescribed endemic species.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02043.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryThe occurrence, chronology of breeding and wing‐moult, and feeding habits of seven commonly occurring species of filter‐feeding ducks on the Kafue Flats in Zambia are described, based on 20 aerial surveys over the central section of floodplain and intensive observations on the ground at Lochinvar National Park, between October 1970 and January 1974.At high flood levels ducks were almost restricted to areas heavily utilized by lechwe; this association persisted until the floodplain became dry, but during the dry season ducks were also found on vegetated lagoons. Five species—Dendrocygna bicolor, Dendrocygna viduata, Thalassornis leuconotus, Netta erythropthalmaandAnas erythrorhyncha—were most abundant between June and September; a sixth—Anas punctata—was most abundant between December and March, while the seventh—Anas undulata—was probably resident. At times the numbers ofD. bicolor, D. viduataandA. erythrorhynchaprobably exceeded 25 000; those ofN. erythropthalmareached 6500, but the numbers ofT. leuconotus, A. punctataandA. undulatawere much lower and at Lochinvar did not exceed 500.Small numbers ofD. bicolor, N. erythropthalma, A. punctataandA. undulatanested on the floodplain in the vicinity of Lochinvar between March and July. All seven species completed their wing‐moult between April and October in the area; large numbers, particularly ofA. erythrorhynchaandD. bicolor, were involved.At Lochinvar,A. punctatafed mainly on aquatic invertebrates; the remaining species fed largely on shed fruits and seeds. The most important food plants were a terrestrial herb,Ambrosia maritima(January–April), two aquatic herbs,Nymphaea capensisandNymphoides indica(May–August), and two aquatic grasses,Echinochloa stagninaandVossia cuspidata(September–December). The herbs grew where grassland had been suppressed by lechwe; fruits of the aquatic grasses were found where lechwe had removed the overlying mat of stems. Despite similarities in diet the ducks differed from each other in feeding behaviour and/or preferred habitat.Five other species of filter‐feeding ducks,Anas capensis, Anas smithii, Anas clypeata, Anas acutaandAnas querquedula, have been recorded from th

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02044.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02045.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02046.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02047.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1977.tb02048.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY