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Journal ArticleDOI

Some observations on black eagles in the matopos, rhodesia

01 Jul 1971-Ostrich (Taylor & Francis Group)-Vol. 42, pp 91-124
About: This article is published in Ostrich.The article was published on 1971-07-01. It has received 14 citations till now.
Citations
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Journal ArticleDOI
TL;DR: It is concluded that vervet alarm calls function to designate different classes of external danger, and context was not a systematic determinant of response.

876 citations

Journal ArticleDOI
TL;DR: This review places equal emphasis on production, usage, and comprehension of vocal production because these components of communication may exhibit different developmental trajectories and be affected by different neural mechanisms.

180 citations


Cites background from "Some observations on black eagles i..."

  • ...Others are given only when approaching an infant or when the group is moving from one area to another (e.g. Gargett, 1971)....

    [...]

  • ...For example, whereas vervets throughout Africa face avian predators, the exact predator species and its physical appearance can vary considerably from one local area to another (e.g. Gargett, 1971)....

    [...]

Journal ArticleDOI
01 Jun 1978-Ostrich
TL;DR: Comparisons are made between Matopos and Tanganyika observations on Black Eagles and between observations on sibling aggression in the Lesser Spotted Eagle Aquila pomarina where the second hatched chick lives longer and does not die directly from attack.
Abstract: Gargett, V. 1978. Sibling aggression in the Black Eagle in the Matopos, Rhodesia. Ostrich 49:57-63. A two-egg clutch of the Black Eagle Aquila verreauxii was observed from the hatching of the first...

56 citations

Journal ArticleDOI
TL;DR: Of 683 identified prey items from five sources of data, over 80% consisted of domestic livestock; about 60% of this was sheep and goats, and birds nesting within conservation areas derived more than half of their food from domestic stock.
Abstract: When offered a selection of food items, bearded vultures Gypaetus barbatus in southern Africa chose bones in preference to meat or to feeding from a fleshed carcass. Once a carcass had been stripped of soft tissue by Gyps vultures, bearded vultures disarticulated sections or individual bones (depending on the size of the dead animal) in the order: limbs, ribs, vertebrae, skull. Their overall diet was estimated as 70% bone with marrow, 25% meat and 5% skin. This diet is about 15% higher in energy than an equivalent mass of meat. Of 683 identified prey items from five sources of data, over 80% consisted of domestic livestock; about 60% of this was sheep and goats. Even birds nesting within conservation areas derived more than half of their food from domestic stock which they found by foraging over adjacent commercial and subsistence farming areas. Bearded vultures obtain all their food by scavenging, and reports of attacks on live animals and even humans are rejected.

41 citations


Cites background from "Some observations on black eagles i..."

  • ...Black eagles are common residents throughout the range of the bearded vulture in southern Africa (Brown in press b), and these eagles feed almost exclusively on the rock hyrax (Gargett 1971; Steyn 1982)....

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References
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Book
01 Jan 1968

686 citations

Journal ArticleDOI
01 Apr 1959-The Auk
TL;DR: I suggest that by "staggering" the ages of larger-brooded raptors, the task of sustaining a large and growing family of carnivorous young, instead of becoming progressively more difficult and perhaps ultimately impossible, is simplified, and to a great extent eased, by being spread over a prolonged period.
Abstract: For the majority of birds it is manifestly of considerable importance to synchronize, so far as is possible, the hatching date of their eggs. Indeed, this is essential if the entire brood is to leave the nest at approximately the same time, which, in most species, is necessary if they are all to survive. The approximate synchronization of the hatching date is, of course, normally effected by postponing full-time incubation until the clutch has been nearly, or wholly, completed; but it may be further assisted if the more recently laid eggs require a slightly shorter time to hatch than those deposited earlier (See Jourdain, in Witherby et al., 1: xxi; 1938). As a uniform hatching date is indubitably a desirable feature in the breeding biology of most birds, why is it that with the majority of raptors there is no synchronization in the hatching of the clutch? On the contrary with many of them, intervals of one, two, or more days commonly occur between the birth of each nestling. In large-brooded species, since incubation usually starts with the first egg laid, this may even result in differences of a fortnight or more between the ages of the first and last hatched nestling. What are the advantages gained by graduating the ages of their young in this way? I suggest, at any rate so far as the larger-brooded raptors are concerned, that the habit is beneficial for the following reasons. First, by "staggering" their ages, the task of sustaining a large and growing family of carnivorous young, instead of becoming progressively more difficult and perhaps ultimately impossible, is simplified, and to a great extent eased, by being spread over a prolonged period. And, secondly, as it is eugenically preferable to rear, let us say, one or two healthy well-nourished progeny rather than six or seven weaklings, this "staggering" is of the highest importance since it offers perhaps the only satisfactory way-namely by controlled cannibalism -of numerically reducing the family to a feedable size when this has become vitally necessary owing to a food shortage. As the food supply of some of the owls-and this is especially true of Asio flammeus-is often largely dependent on fluctuations in the population of certain rodents, a ready and rapid means of adjusting the size of the brood to the amount of food available is clearly desirable. Without a marked disparity in the age and size of the fledglings, fratricide would be virtually impossible and consequently no such

110 citations

Book
01 Jan 1961

78 citations

Journal ArticleDOI
28 Jun 2008-Ibis
TL;DR: The continuation of work on eagles in Embu district, Kenya, especially at Eagle Hill, which has now been under observation continuously since 1949, is described and possible life spans in the wild state of adults of H. dubius and S. coronatus are suggested.
Abstract: SUMMARY This paper describes the continuation of work on eagles in Embu district, Kenya, especially at Eagle Hill, which has now been under observation continuously since 1949. Observations in other parts of Kenya have been included. The ecological changes possibly affecting eagles on Eagle Hill are discussed. The population fell from a pair each of Circaetus cinereus, Aquila verreauxi, Hieraetus fasciatus spilogaster, H. dubius, Polemaetus bellicosus and Stephanoaetus coronatus in 1952 to a pair each of H. dubius, P. bellicosus and S. coronatus in 1965. Possible causes of the decline are discussed. The species of eagles are not normally aggressive to one another, in contrast to other resident species such as Falco peregrinus and Buteo rufofuscus. Although the eagles appear to be ecologically separated by food preferences and habitat this is apparently not the whole explanation for the unusual concentration of eagles on this hill. Additional breeding data are given for H.f. spilogaster, H. dubius, P. bellicosus and S. coronatus. These species rear respectively 0.56, 0.65, 0.42 and 0.44 young per pair per annum. S. coronatus breeds in alternate years and cannot breed every year because of a protracted post-fledging period in which the young is fed for up to 350 days. P. bellicosus, with about the same annual reproductive rate, does not have the same breeding rhythm. Data on reproductive rates combined with other data suggest possible life spans in the wild state of adults of H.f. spilogaster 10–11 years, H. dubius nine years, P. bellicosus 14 years, and S. coronatus 16 years. At nests of H. dubius and S. coronatus changes of mates have been recorded for 16 and 17 years respectively. In S. coronatus a change occurs about every six years and in H. dubius about every four years, indicating that S. coronatus may live about 1.5 times as long as H. dubius in the wild state. One female S. coronatus was known to live for 8.5 years as an adult. Other incomplete life spans are eight and eight years for two male S. coronatus, and eight for one female of this species. Two male H. dubius have each lived for at least eight years but no female of this species has lived for more than five years. Two proven cases of re-laying after a natural disaster are recorded, one each in H. dubius and S. coronatus. Other instances are suspected in H. dubius. The habit may be commoner than is supposed in large eagles. The history of four pairs of S. coronatus, each observed for four years or more, totalling 34 pair/ years is given. S. coronatus breeds regularly every second year unless some unusual occurrence, such as a change of mates or a failure during incubation, upsets the rhythm. S. coronatus females lay 1–2 eggs at dates varying from June–October in Kenya; breeding is not confined to the dry season. Laying dates of individual females may vary by two months between one year and another. Incubation takes 48–49 days, fledging 105–116 days. The elder of two young hatched invariably kills the younger so that no more than one young is reared. Female adults are dangerously aggressive, especially during days 30–60 of the fledging period. In 86% of cases where eggs are laid a young bird is reared. Since clutches of two in practice do not result in more than one young this represents a breeding success of 86% of the potential, a very high percentage. The sex ratio of young leaving the nest is about equal, seven males to five females, in known cases. The post-fledging period in S. coronatus is 330–350 days, and the total breeding cycle about 560 days, making it impossible for the eagles to breed every year, if they rear a young bird to independence. In the post-fledging period the young S. coronatus remains within half a mile of the nest, where it is fed by the parents, the female bringing most of the prey. The adults call to attract the young bird, which flies into the nest receiving the prey there, or rarely on a tree nearby. If the adult obtains no response from the young it may carry the prey away. Although regularly fed by its parents the young eagle kills some of its own food from at least day 61 of the period onwards, but most often in the last third of the period, being then apparently stimulated by unusual periods of privation. Almost 100% of young eagles that leave the nest are reared to independence at about 15 months old. The possible biological advantages of this protracted adolescence in survival and economy of prey are discussed. The main prey of S. coronatus is antelopes, followed by hyrax. Monkeys are rarely taken. Killing methods, times, and relations with prey are discussed. The eagles usually kill in early morning or evening, but also at other times. They may cache portions of large kills. Most prey is brought to the nest between hours 4–6 of daylight. The male S. coronatus feeds his incubating mate about once every 3–3 days. Once the young has hatched his killing rate rises to about one kill per 1.7 days. The killing rate falls slowly to one kill per two days later in the fledging period. At normal times the killing rate of adults is apparently controlled by their own appetites, and the increased killing rate of the male after hatching is an exception to this rule. During the post-fledging period the feeding rate varies from 1: 2.0 days to 1: 6.2 days, averaging 1: 3 days in 130 cases. Periods of privation may last from 5–13 days. Alternatively several kills may be brought in a day, possibly from cached portions of large kills in some cases. Long foodless periods may stimulate the young eagle to kill for itself, especially in the last third of the post-fledging period. Final independence of the young is not brought about by aggressive parental behaviour, but is probably due to increasing indifference of the young to food-bringing adults. This indifference may act as a release to the adults, breaking the rhythm of bringing food to the young, and so stimulate the onset of a new breeding cycle.

50 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