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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 Sep 1972-Ostrich

9 citations

Journal ArticleDOI
01 Dec 1990-Ostrich
TL;DR: Observations were made on the breeding biology of the Bateleur Terathpoius ecaudataus between 1981 and 1984, in the central region of the Kruger Nabonal Park, and breeding failures were mainly due to failure to lay or predation.
Abstract: Summary Watson, R. T. 1990. Breeding biology of the Bateleur. Ostrich 61: 13–23. Observations were made on the breeding biology of the Bateleur Terathpoius ecaudataus between 1981 and 1984, in the central region of the Kruger Nabonal Park. Nests were uniformly distributed with a mean inter-nest distance of 5,1 km and density of 3,1 nests/100km2. Single-egg clutches were laid from January to June, and laying appeared to be suressed by unusually high rainfall events. The mean productivity was 0,47 young per pair per year, an a breeding failures were mainly due to failure to lay or predation. Breeding adults chaned nest sites within their territory on average once every 2,8 years, but territories and pairs were stable from year to year. Both members of a pair put equal time into care of the young.

8 citations

Journal ArticleDOI
TL;DR: There is no evidence that either an individual species or a combination of several could effectively limit the populations of certain prey species in East Africa, and it is concluded that real competition is likely to be slight and that such groups of nesting raptors must be due to a form of inter-specific gregariousness.
Abstract: Summary East Africa is a country very rich in birds of prey, both resident and migrant, partly because a majority of migrant Eurasian birds of prey enter Africa through Suez in winter. Diurnal birds of prey are both more numerous and more varied than nocturnal, especially among migrant species. The size range of birds of prey, both diurnal and nocturnal, in East Africa is nearly equivalent to that occurring in the whole world. The predator-prey relationship is thus exceedingly complex in East Africa. Diurnal birds of prey hunt by sight and nocturnal by the use of sight and hearing. Diurnal birds of prey can thus make use of both live and dead prey, but owls are only able to capture living prey and do not feed upon carrion. Almost all animals in East Africa, from elephants to small insects, are either eaten as carrion or preyed upon as live prey by some species of raptor. Most live animals in the size range from small insects to animals 5 kg in weight are preyed upon by a diurnal or a nocturnal bird of prey at some stage of the twenty-four hours. Carrion is not consumed by birds of prey at night. Comparison of the raptor avi-fauna of forests with that in savannah indicates that in forests raptors are much less likely to eat carrion than in open country, but that the size range of raptors preying upon live animals is much the same in forests and in open country. Nocturnal birds of prey are less successful in a forest environment than are diurnal species. The possible effect of individual species (Aquila wahlbergi and Polemaetus bellicosus) and of a combination of many species on the possible population of animals in home ranges of known size is discussed. It is concluded that there is no evidence that either an individual species or a combination of several could effectively limit the populations of certain prey species. Concentrations of several breeding pairs of large raptors in apparent association with one another are mentioned. The interrelations of such species, and the effects of possible competition between members of such associations, are discussed. It is concluded that real competition is likely to be slight and that such groups of nesting raptors must be due to a form of inter-specific gregariousness.

6 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