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Journal ArticleDOI

Supplementary notes on the biology of the large biros of prey of embu district, kenya colony

03 Apr 2008-Ibis (Blackwell Publishing Ltd)-Vol. 97, Iss: 1, pp 38-64
TL;DR: The fluctuations of population in an area of 146 square miles in Embu district, where a census of eagles was carried out in 1950, are described and discussed and the inter-relations of various species are discussed.
Abstract: Summary. 1 The present paper is supplementary to that in ‘Ibis’ 94 and 95. 2 The fluctuations of population in an area of 146 square miles in Embu district, where a census of eagles was carried out in 1950, are described and discussed fur 951–52. 3 The inter-relations of various species are discussed, particularly for Aquila wahlbergi and Lophaetus occipitalis. 4 General accounts of breeding biology are given for Sagittarius serpentarius, Aquila wahlbergi, Hieraaetus ayresi and Terathopius ecaudatus, and supplementary data for Aquila verreauxi, Hieraaetus spilogaster, Polemaetus bellicosus, Stephanoaetus coronatus, Lophaetus occipitalis, Circaetus cinereus and Circaetus pectoralis. These accounts are given under the following heads:— 1 General notes on adults. 2 Nests and nest-building. 3 The incubation period. 4 The fledging period: (a) general, (b) development of the young, (c) parental behaviour, (d) food. 5 The post-fledging period. 5 Special problems of breeding biology are discussed under the following heads: (1) Display; (2) Eagle-weaver-bird nesting-associations; (3) Feeding rates of female and eaglet; (4) Breeding seasons; (5) Breeding success and replacement rate.
Citations
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Journal ArticleDOI
01 Dec 1977-Ostrich
TL;DR: There was no significant difference between the mean reproductive success of five African eagle species that lay two eggs and that of fiveAfrican eagle species laying one egg, even excluding inequalities due to sample size, and other factors.
Abstract: Summary Brown, L. H., Gargett, V. & Steyn, P. 1977. Breeding success in some African Eagles related to theories about sibling aggression and its effects. Ostrich 48:65-71. Previous explanations for fatal inter-sibling strife in eagles (lack of food, extra aggressiveness which enhances survival, and an expression of the innate aggressiveness or territoriality of raptors) can not be supported by recent evidence. The latest theory, that the second egg acts as a “reserve”, is examined. If so, eagles normally laying two eggs should have better reproductive success than eagles laying a single egg. However there was no significant difference between the mean reproductive success of five African eagle species that lay two eggs and that of five African eagle species laying one egg. Even excluding inequalities due to sample size, and other factors, the overall finding is the same. In Verreaux's Eagle Aquila verreauxi for which the largest number of records is available there was a significantly higher total loss in...

36 citations

Journal ArticleDOI
01 Mar 1972-Ostrich
TL;DR: In this paper, the age classes and population dynamics of the BATELEUR and AFRICAN FISH EAGLE were discussed, and a study was conducted to understand the differences between the two groups.
Abstract: (1972). AGE CLASSES AND POPULATION DYNAMICS OF THE BATELEUR AND AFRICAN FISH EAGLE. Ostrich: Vol. 43, No. 1, pp. 1-16.

31 citations

Journal ArticleDOI
TL;DR: In this article, the division of parental activities during breeding (nest-building, incubation, brooding, food provisioning and feeding) was found to be significantly different in the tasks of nest-building and incubation of chicks.
Abstract: Capsule The sexes make significantly different contributions in the tasks of nest-building, incubation and food provisioning to chicks. Aims To determine the division of parental activities during breeding (nest-building, incubation, brooding, food provisioning and feeding). Methods Between 1991 and 1998 focal observations were made at nests using 20–60× telescopes. During the incubation period, 11 pairs were studied involving a total of 2812 observation hours over 269 days. During the chick-rearing period, seven pairs were studied involving a total of 5499 observation hours spread over 503 days. The birds were sexed and identified individually on the basis of size, position during copulation, vocalization and plumage differences. Results Significant differences were found between the sexes in parental behaviour. Males scarcely participated in incubation and contributed significantly more than the females only in food provisioning, both during incubation (food transfers to feed the female) and during chic...

28 citations

Journal ArticleDOI
01 Oct 1993-Ibis
TL;DR: It is concluded that population density influences most aspects of breeding in Wahlberg's Eagles, and reduced food resources do not appear to explain these trends, and adaptive restraint may account for decreased annual reproduction in this species.
Abstract: Increased population density often reduces reproductive output in breeding birds, but the underlying mechanisms (adaptive restraint v reduced food resources) behind decreased productivity are poorly understood. Here I correlatively and experimentally investigated the roles of food, breeding density, latitude, altitude and rainfall in limiting productivity of Wahlberg's Eagles Aquila wahlbergi throughout Africa. Breeding success in equatorial and subtropical Africa (0°–30°S) was highly density-dependent but showed no latitudinal or rainfall-related trends. Pairs in dense populations produced half as many young annually as pairs in low-density populations. Density (but not rainfall or latitude) also explained much of the geographic variation in the mean proportion of pairs attempting to breed each year and the incidence of two-egg clutches. Breeding within populations was consistent with these density-dependent trends: incidence of two-egg clutches increased in a declining population, and productivity was inversely related to breeding density and rainfall combined. To determine if reduced food resources accounted for reduced output in dense populations, eight pairs were food supplemented: supplementary food failed to induce nonbreeding pairs to breed: nor did it induce earlier laying or increase egg size or clutch-size. Population density itself was unrelated to two correlates of food resources, rainfall and latitude. I conclude that population density influences most aspects of breeding in Wahlberg's Eagles, and reduced food resources do not appear to explain these trends. Hence, adaptive restraint may account for decreased annual reproduction in this species.

27 citations

Journal ArticleDOI
01 Jun 1972-Ostrich
TL;DR: In this article, the author discusses at a black eagle nest in the MATOPOS, RHODESIA, discussing the discovery of a black eagle nest in a white eagle nest.
Abstract: (1972). OBSERVATIONS AT A BLACK EAGLE NEST IN THE MATOPOS, RHODESIA. Ostrich: Vol. 43, No. 2, pp. 77-108.

20 citations

References
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Journal ArticleDOI
03 Apr 2008-Ibis
TL;DR: The observed timing of breeding seasons can be secured only by external factors regulating an internal rhythm, and in some communities and categories of birds the “reasons” for the observed breeding seasons are intelligible.
Abstract: Summary. 1 For the present purpose Africa is divided into everyreen, semi-arid and intermediate (deciduous) types of count?, all of which occur in all latitudes south of the Sahara. 2 “Breeding season” is limited to the months during which eggs are laid by the species concerned in the given area and all records are interpreted accordingly. As a basis for ascertaining the curve of breeding activity in a given area through the year the number of species laying in each month has been ascertained and calculated as a percentage of the total for all species for the whole year. 3 A definite peak in the curve of breeding activity is evident everywhere except in certain areas within about four degrees of the Equator. 4 In one part of this inner tropical belt there may be no distinct breeding season for must groups of birds (Congo), but in East Africa a double breeding season is the rule, with peaks coinciding with the two rainy seasons. 5 Even so close to the Equator as 5°s. the (single) breeding season in evergreen forest is as restricted as in other types of country and its time-relation to the rains varies locally. 6 In the “ intermediate” type of country characterized by 4–6 months drought each year the timing of the peak breeding season varies from the end of the rains, at Cape Town, to the start of the rains in Natal and several weeks before the rains in areas 23° - 10° S. 7 The key to this local difference is that at Cape Town the rains fall in the cold season, so that vegetation and insects are slow to flush. In the warmer conditions in which the rains begin in Natal the flush comes at once. And further north the dominant vegetation and its associated insects flush towards the end of the drought and well in advance of the rains. 8 From Natal northwards the breeding season for all birds combined shows a progressively less marked peak. The reason is that the seasons of certain ecological categories (1) water birds, (2) raptors and scavengers, (3) ground birds, (4) grass birds, (5) the other birds, tend to diverge. 9 The raptors and scavengers are everywhere the earliest breeders, the biggest species laying by the middle of the dry season. The water birds lay to a large extent towards the end of the rain, and after. The ground birds tend to lay as soon as the grass fires are over and before the heavy rains have induced a lush growth of herbage. The grass birds lay later than most-others, when the grass has grown high. 10 In semi-arid areas the breeding seasons are on the whole similar to the foregoing, with most birds breeding when the vegetation flushes, whether just before or after rain has fallen. But the “semi-and” birds are notably sensitive to rainfall; breeding that has begun is checked if the rains are interrupted. 11 In some communities and categories of birds the “reasons” for the observed breeding seasons are intelligible, the best food-supply or the safest nesting apparently being secured. In others the reasons are not obvious; and the degree to which the breeding seasons are restricted is often incomprehensible. 12 The observed timing of breeding seasons can be secured only by external factors regulating an internal rhythm. Day-length, rainfall and humidity, temperature and visual stimuli are each considered briefly. Each may be effective on some species in some areas, but no one generally.

123 citations

Journal ArticleDOI
03 Apr 2008-Ibis
TL;DR: The species of eagles occurring in Embu district are detailed, with general notes on the methods and scope of the study, and the inter-relations of the various species are discussed from the points of view of territorial agressiveness and competition for prey.
Abstract: SUMMARY. 1 The species of eagles occurring in Embu district are detailed, with general notes on the methods and scope of the study. 2 The vegetation and climate of Embu district are described, and their effect upon eagles is discussed. 3 Population and inter-relations. The actual population of eagles and of the Secretary Bird in an area of approximately 146 sq. miles is given and their remarkable local concentrations are described. The inter-relations of the various species are discussed from the points of view of territorial agressiveness and competition for prey. 4 Detailed accounts are given of the breeding biology of Sagittarius serpentarius, Aquila verreauxi, A. wahlbergi, Hieraaetus spilogaster, Polmaetus bellicosus, Stephano-aetus coronatus and Circaetus cinereus, and some information for Terathopius ecaudatus, Circaetus pectoralis, and Aquila rapax, Hieraaetus ayresi, Lophaetus occipitalis, and Cuncuma vocifer. The headings for each species include: “Nests and nest-building”, “Incubation period”, “Fledging period” (with special attention to food), and “Post-fledging period”. 5 The following special aspects of breeding behaviour are described and discussed: (1) Display, (2) Use of green branches, (3) Breeding seasons, (4) Breeding success, (5) Breeding frequency.

39 citations

Journal ArticleDOI
03 Apr 2008-Ibis

22 citations

Journal ArticleDOI
03 Apr 2008-Ibis
TL;DR: Breeding records in Tropical Africa show, when analysed with reference to egg-dates, that as a rule in each area the young get through their fledging period, or at least the later, unbrooded part, during the local cool dry season.
Abstract: Summary An account is given of one hundred hours of observations at a Bateleur'a nest in north-eastern Tanganyike Territory. The adults were a white-backed bird and a chestnut-backed, with a sub-adult; probably over three years old, in association with them. The youngster took 130 dap to fledge. During at least part of the time all its food was brought by the white-backed adult. When the fledgling was about one month old its feeds averaged about one in eight hours; during its last week in the nest feeds were nearly three times as frequent. Literature and unpublished data are reviewed in relation to special points of interest, viz.:— Slow development and maturation accords with longevity. Fledging period apparently longer than authentically recorded for any land bird. First wing-moult may have started before first flight. Tail length is greater in proportion to wing in juveniles than in adults. Proportion of white-becks to chestnut-backs differs in parts of Africa, being least in South africa. White-tailed birds seem confined to Sudanese semi-desert belt. Voice, flight habits and wing-noises seem to differ in parts of Africa. Food comprises both carrion and live prey, especially snakes, but not poultry or other birds. Claws are not less sharp than those of Stephanoaetus and Polemaetus. Breeding records in Tropical Africa show, when analysed with reference to egg-dates, that as a rule in each area the young get through their fledging period, or at least the later, unbrooded part, during the local cool dry season. Psychologically the Bateleur is most peculiar: in the wild it is shy of man, sociable with big birdv of its own and other species, and breeding birds tolerate sub-adults: in captivity it becomes unusually tame, has a grecting ceremony for friends and likes to be handled.

11 citations