Haliaeetus Vocifer Research Articles

Food procurement through piracy and scavenging in the African fish eagle in Queen Elizabeth National Park, Uganda

SummaryThe territorial adult African fish eagle Haliaeetus vocifer (Daudin, 1858) in Queen Elizabeth National Park (QEP) feeds almost exclusively on fish, which it catches live. However, it readily steals from conspecifics and other fish‐eating birds. With a success rate of only 17%–providing only 3% of the fish eaten by the territorial bird–piracy is a less successful method of food procurement than hunting, whose success rate is c. 66%. Even if restricted to depriving only conspecifics (success rate = 23%), piracy is still inferior to hunting. With its low success rate and high risk factor, piracy seems of little survival value to the territorial adult fish eagle. It contributes substantially (28%) to the food supply of the young. However, the fatalities due to injuries sustained during piracy could be of significant importance in the regulation of the population of the species.RésuméL'aigle pêcheur africain adulte Haliaeetus vocifer (Daudin, 1858) du Pare National Queen Elizabeth, se nourrit presque exclusivement de poissons qu'il attrape vivants. Cependant, il ravit volontiers la proie de ses congénères ou d'autres oiseaux piscivores. Avec un taux de réussite de 17%, procurant seulement 3% du poisson que mange cet oiseau territorial, ce piratage est une méthode moins effi‐cace pour se procurer de la nourriture que la pêche dont le taux de réussite est d'environ 66%. Même si Ton ne tient compte que des proies qu'ils volent à des congénères (réussite = 23%), cela reste moins efficace que la pêche. Vu son faible taux de réussite et le risque qu'il engendre, le piratage apparait comme de peu d'intérêt pour la survie de l'aigle pêcheur territorial adulte. II contribue de façon substancielle (28%) à l'apport de nourriture du jeune encore que Tissue fatale des blessures revues lors du piratage puisse compter de façon significative dans la régulation de la population de l'espèce.

Nestling growth in the African fish eagle in Uganda

SummaryNestling African fish eagles Haliaeetus vocifer (Daudin, 1858) in Queen Elizabeth National Park (QEP), Uganda, attained and exceeded the adult body weights of their respective sexes by fledging time. The growth curves conformed with the sigmoid form of most animal species. The overall growth rate, K (g/day), was low, averaging 0.077 ± 0.017 g/day and the time t10–90 required to complete growth from 10 to 90% of the asymptotic weight was c. 42 days. Brood size and hatching order did not significantly influence growth rates but the sex of the young did. The tarsus, femur and humerus reached adult sizes by fledging time but the standard wing did not.

Breeding seasonality of the African fish eagle in Queen Elizabeth Park, Uganda

SummaryThe African fish eagle Haliaeetus vocifer (Daudin) in Queen Elizabeth National Park, Uganda, breeds all‐year‐round. Only changes in temperature and water level are significantly but negatively correlated with this breeding seasonality. Social stimulation is not important in the breeding biology of the birds. In this area, the fish eagle exhibits an annual breeding cycle.RésuméL'aigle pêcheur africain (Haliaeetus vocifer (Daudin)) au Queen Elizabeth National Park (°) se reproduit tout au long de l'année. Seuls des changements de température et de niveau d'eau sont en correlation significative mais négative avec cette époque de reproduction. La stimulation sociale n'est pas importante dans la biologie de reproduction chez les oiseaux. Dans cette région, l'aigle pêcheur présente un cycle annuel de reproduction.

ASPECTS OF THE BIOLOGY AND ECOLOGY OF THE OSPREY IN'THE CAPE PROVINCE, SOUTH AFRICA

Summary Boshoff, A. F. & Palmer, N. G. 1983. Aspects of the biology and ecology of the Osprey in the Cape Province, South Africa. Ostrich 54:189-204. Information gathered opportunistically on the distribution, habitat, density, seasonality, timing of migration, food spectrum, feeding and hunting behaviour and periodicity, flight mode, influence of weather on hunting activity, interspecific and intraspecific interaction, general behaviour and conservation status of the Osprey Pandion haliaetus in the Cape Province, South Africa, is presented. The species is confined mainly to the coastal region and was recorded most frequently from the larger estuaries. Although it is basically a non-breeding migrant to the area, with peaks of occurrence during the austral summer, birds were recorded throughout the austral winter. A maximum density of 0,0028 Osprey/ha of surface water was determined; there is some evidence for an increase in the number of birds in the main study area from 1980 to 1982. The birds are persistent hunters and forage mainly in the littoral zone at water depths of up to 1,5 m, with a hunting activity peak at mid morning and at late afternoon. The food spectrum comprised 84–91% mullet (Mugilidae) of 20–700 g and 9–14% Mozambique Tilapia Oreochromis mossambicus. Flapping flight was preferred for hunting purposes and the implications of this are discussed. The study area is considered to provide optimal foraging conditions of windspeed and cloud cover for Ospreys. There was little aggressive interaction between Ospreys and resident Fish Eagles Haliaeetus vocifer and competition between these two species was not a major factor. Kelp Gulls Larus dominicanus harassed Ospreys with grey. The conservation status of Ospreys in the Cape Province is considered to be satisfactory at present.

Book Reviews

Book reviewed in this article: The African Fish Eagle. By Leslie Brown. East African Mammals. An Atlas of Evolution in Africa. Vol. III Part B. Large Mammals. By Jonathan Kingdon.

The African Fish Eagle, by Leslie Brown. Bailey Bros & Swinfen, £8.50.

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Capacités prédatrices et budgets d’activité chez l’Aigle pêcheur Haliaeetus vocifer

Ten pairs of Fish Eagles Haliaeetus vocifer taken among a dense population in Uganda, were followed at the end of the breeding season to compare the time and energy budgets of breeding and non breeding adults. Fish are usually obtained by diving from a waterside tree. If unsuccessful, the bird searches in flight, an energy-expensive but very rewarding method. The additional food necessary to feed the young is provided mainly by the male through fishing flights. Another source of increase in energy expenditure related to breeding activities is the more active territorial defense by adults with young than without young. The food consumption of the former is higher than that of the latter ; but the difference is smaller than the increase of the energetic cost of breeding (42 % and 64 % for 1 and 2 fledged young). Thus brood size seems to be limited by the ability of the parents to feed their young and maintain a territory of adequate size or quality, even in the optimal conditions studied. Immature birds suffer heavily from the adults’ territorial behaviour, which forces them to make extensive flights and confines them to marginal food sources. This may explain their high mortality rate (83 % during the first four years).

Densité, taille des territoires et production dans une population d’aigles pêcheurs Haliaetus vocifer (Daudin)

A very dense population of African Fish Eagles, Haliaetus vocifer (100 pairs within a 120 km2 area) has been studied in the Rwenzori National Park (South West Uganda) at the end of the breeding season (February-March 1976). Each territory covered an area of 20 to 50 hectares and had an average diameter of 200 to 900 meters All the coast line is fully occupied, several adult birds, even mated, being unable to secure a territory of their own. Only 37 % of the pairs produced fledged young (average of 1.13 per successful pair and 0.42 per established pair). The whole population was made of 70.2 % adults, 17.2 % juveniles, 6.9 % first and second years immatures and 5.7 % subadults (3rd and 4th years), giving an overall mortality rate of 80 % during the first two years, 17 % during the two last years of immature stage and a mean adult life expectancy of 25 years. Density and breeding success have been correlated with seve¬ ral territory features through a multivariate statistical analysis. Though a higher density reduces production of young, the most favorable habitat for a breeding pair includes a rather steep and well wooded slope, along shallow and calm coastal waters.

Territory size and distribution in the African fish eagle

The fish eagles along 32 km of shoreline were counted regularly from a launch. The territory size was found to be 0.6 km of shore with a density of 3.5 eagles per km. A single aerial count along 323 km of shore returned a density of 1.9 eagles per km with a territory size of 1.0 km of shore. The distribution of fish eagles is related to the relative availability of trees as perches and probably also to the abundance of fish. The quantity of fish taken by the fish eagles is shown to be negligible compared either with the total production or with the yield harvested by man.

Population structure and dynamics in the African Fish Eagle Haliaeetus vocifer (Daudin) at Lake Naivasha, Kenya

Summary(1) The population structure and breeding success of the Fish Eagle Haliaeetus vocifer (Daudin) at Lake Naivasha was assessed in 1970‐71, as part of a wider pesticide residue survey. The figures obtained have been combined with those of an earlier population and breeding survey in 1968‐69.(2) Population structure was assessed by plumage criteria, dividing the total adults, subadults (early and late), 2 year‐olds, and recent immatures. Between 1968 and 1971 there was an increase of about 40% in the adult population on the lake, but immatures increased by only 11 %. The adult/immature ratio was 83: 17% in 1968‐69 and 85‐6: 14‐4% in 1970‐71.(3) From these data it appears that the age of Fish Eagles as adults lies between 16 and 24 years, with a total age of 20–28 years. This is much longer than observed wild life spans in some other eagles.(4) Although the total population rose, the number of breeding pairs was constant, fifty‐six in each year of survey, with minor changes.(5) Breeding success overall is about 0–47 young/pair/annum for both years combined, varying greatly between different parts of the lake and from year to year. As only two thirds of all pairs lay, and some of these fail, this equals 0–74 young/pair which bred and 1–28/successful nest.(6) Breeding success at Lake Naivasha is considered to be unaffected by human interference, either deliberate or casual.(7) Analysed by habitat, pairs which bred near wide lagoons within the papyrus were markedly more successful than those with access only to open water (0–55 young/ pair/annum overall cf. 0–29). The possibility that this is due to superior food opportunities in the lagoon habitat is discussed. Fish Eagles can catch birds and fish, and pirate other species kills in lagoons, whereas they must catch all their own fish prey in the open lake sites.(8) Preliminary observations of diurnal behaviour do not indicate that Fish Eagles with access only to open water have any more difficulty in catching prey than those in lagoons, so that the relation between food supply, habitat, and nesting success remains obscure.

Dual infection of an African fish eagle with acid-fast bacilli and an Aspergillus sp.

Clinical, post-mortem and histological findings are described for an African fish eagle (Haliaeetus vocifer), which was naturally infected with acid-fast organisms. In addition to this infection, there was an invasion of the air sacs and, to a lesser extent the lungs, by an Aspergillus sp. The predominant clinical sign was dyspnoea and there were acid-fast organisms in lesions in the liver and kidney in addition to the respiratory tract.

THE AFRICAN FISH EAGLE HALIAETUS VOCIFER ESPECIALLY IN THE KAVIRONDO GULF

SUMMARY1. The African Fish Eagle Haliaetus vocifer is discussed, with especial reference to the Kavirondo Gulf area of Lake Victoria.2. Numbers in I his and adjacent areas are given, and reference is made to possible movements on Lake Victoria.3. Territories and home ranges of seven pairs breeding on a group of islands overlap somewhat, with a tendency towards mutual stimulation by adjacent pairs, and the possibility of breeding and hunting difficulties through overcrowding.4. Some pairs appear to be permanently resident in certain areas without breeding at all.5. The data on food indicate that the African Fish Kagle eats more birds than has generally been supposed, especially Hamingos; the diet may be summed up as fish when abundant, otherwise water‐birds and some carrion.6. The breeding cycle is discussed under the heads Display, Nests and Nest‐building, Eggs and Incubation, the Fledging period, and the Post‐Hedging period.7. Breeding seasons, and their possible relations to food supplies and climate are discussed.8. Three years' data on breeding success indicate a mean annual replacement rate in the Kavirondo Gulf of 0–6 young per pair per annum, with wide variations in the performance of individual pairs.

HABITS OF THE AFRICAN FISH EAGLE

IbisVolume 100, Issue 4 p. 624-624 HABITS OF THE AFRICAN FISH EAGLE First published: October 1958 https://doi.org/10.1111/j.1474-919X.1958.tb07967.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume100, Issue4October 1958Pages 624-624 RelatedInformation