OBSERVATIONS ON THE COMMUNAL ROOSTING OF AFRICAN BLACK OYSTERCATCHERS

Hockey P. A. R. 1985. Observations on the communal roosting of African Black Oystercatchers. Ostrich 56: 52–57.

There are currently three main hypotheses for the adaptive significance of avian communal roosts: physiological advantages, predator avoidance and information centres. The African Black Oystercatcher Haematopus moquini is territorial throughout the year and forms communal roosts during the nonbreeding season, but does not breed communally. Roosts generally are small, and site fidelity is high. Roosts are normally sited on a rocky promontory with adjacent offshore rocks (west coast), or in flat areas with extensive all-round visibility. The main predators of African Black Oystercatchers are nocturnal terrestrial mammals and nocturnal communal roosts are larger and more tightly packed than daytime roosts. Breeding birds do not roost communally during the breeding season and at this time of year mortality due to mammal predators at a study site in Saldanha Bay was greatest (X² = 9.46; p<0.01). It appears therefore that predator avoidance is an important adaptive feature of communal roosting in this species.     

OBSERVATIONS ON SOME KENYA EAGLES

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.     

NOTES ON THE BIOLOGY OF THE MAURITIUS BLACK BULBUL HYPSIPETES OLIVACEUS

Safford, R.J. 1996. Notes on the biology of the Mauritius Black Bulbul Hypsipetes olivaceus. Ostrich 67: 151–154.

The Mauritius Black Bulbul Hypsipetes olivaceus is a threatened passerine endemic to Mauritius. Direct observations of food items indicate that it is an arboreal omnivore. Animal prey consists mostly of insects and native day-geckoes (Phelsuma spp.). A wide variety of native and exotic fruits is also taken. The species is apparently monogamous, with an egg-laying season extending from at least November to February, usual clutch and brood sizes of two to three, ability rapidly to lay repeat clutches in a new nest, and post-breeding complete moult. In these respects, its annual cycle resembles that of the other native Mauritian passerines. It occurs at very low population density compared to its Indian Ocean congeners; possible reasons for this are given.     

THE FEEDING HABITS OF THE WHITEWINGED BLACK TERN ON LAKE KARIBA

Bego, G. W. 1973. The feeding habits of the Whitewinged Black Tern on Lake Kariba. Ostrich 44: 149–153.

The stomach contents of 33 Whitewinged Black Terns were examined over the period 26 August 1971 to 6 January 1972. The most important single food item was the sardine, Limnothrissa miodon. This sheds new light on the habits of this fish. The terns fed primarily during calm weather. Sardines are caught by hovering and diving. Fishes of the genera Haplochromis and Synodonlis, also appeared in the stomach contents. Terns taken from marginal localities appear not to feed on fish. Of the insects eaten Odonata are the most important aquatic source of food, while many terrestrial insects are eaten (Orthoptera, Hemiptera, Coleoptera, Isoptera). Such insects could have been found drifting on mats of Salvinia on which the terns rest, otherwise insects are either hawked or skimmed from the surface of the water.     

BLACK LESIONS OF THE SKIN

Benign melanocytic lesions include lentigo, ephelid (freckle), pigmented nevus, sacral spot, blue nevus, and combined nevus and blue nevus.Malignant melanocytic lesions are melanomas, which arise from melanocytes at the epidermodermal junction, or, rarely, from blue nevi. They usually originate in brown plaques known as lentigo maligna, in pigmented nevi, or in normal skin.Melanoma is diagnosed clinically in less than 50 per cent of instances. Biopsy is therefore of great importance, since practically all melanoma can be cured by adequate early resection.     

THE CAPTURE AND TRANSLOCATION OF THE BLACK RHINOCEROS

Black rhinoceroses were hunted on foot, from a vehicle, or from a helicopter throughout their range of habitats. Animals weighing 370–1,260 kg could be handled an average of 13 min after darting with a mixture of etorphine (1.9 μg/kg) and acepromazine (19 μg/kg). Cases of respiratory depression at this dosage were reversed soon after immobilisation by the intravenous injection of cyprenorphine (1.0 μg/kg). The captured animal was transported to camp, lashed on its side to a sledge, for periods of up to 515 min without mishap. A rhinoceros that was unloaded 180 min after darting rose to its feet and tried to push its way through the corner of the pen until antidote was administered at 215 min. This action was not observed in animals that received a total dose of 3.4 μg/kg of cyprenorphine before being unloaded 90–413 min after darting. The addition of hyoscine (at doses as low as 18 μg/kg) to etorphine and acepromazine improved the tractability of rhinoceroses that were only partially immobilised. However, sometimes at this dosage and always at doses above 35 μg/kg, hyoscine prolonged the ‘pushing’ phase for 175–410 min after darting despite the administration of cyprenorphine (4.0 μg/kg). There were no mortalities due to drug action in the series of 59 healthy rhinoceroses that were dart-immobilised, but there were two deaths due to mishandling and one caused by subsequent mismanagement.     

饲料营养成分对草鱼,团头鲂和青鱼鱼种阶段的饲料可消化能值的影响

为了探讨饲料可消化能值同饲料营养成分之间的关系,用Ｃｒ２Ｏ３作指示物,分别测定了鱼粉和大豆粕等饲料原料的草鱼（Ｃｔｅｎｏｐｈａｒｙｎｇｏｄｏｎ　ｉｄｅｌｌａ）团头鲂（Ｍｅｇａｌｏｂｒａｍａ ａｍｂｌｙｏｃｅｐｈａｌａ　Ｙｉｈ）青鱼（Ｍｙｌｏｐａｒｙｎｇｏｄｏｎ　ｐｉｃｅｕｓ）鱼种饲料的可消化能,用微机计算分析测试结果,发现饲料可消化能值随饲料蛋白质和／或脂肪食量增加而增加;随饲料无氮浸出物和／或纤维含量增加而降低。同时,“优选”出了有一定实用价值的估算草鱼、团头鲂和青鱼鱼种饲料可消化能值的回归方程。     

THE INFLUENCE OF RAINFALL ON BLACK EAGLE BREEDING OVER 31 YEARS IN THE MATOBO HILLS,ZIMBABWE

Gargett, V., Gargett, E. & Damania, D. 1995. The influence of rainfall on Black Eagle breeding over 31 years in the Matobo Hills, Zimbabwe. Ostrich 66: 114–121.

The effect of rainfall from 1964 to 1994 on the annual reproductive rate and number of resident pairs of Black Eagles Aquila verreauxii in the Matobo Hills, Zimbabwe, and on the abundance of their staple prey, hyrax, Procavia capensis and Heterohyrax brucei is reviewed. The number of resident pairs of Black Eagles increased with increased rainfall, when hyrax numbers were estimated to be at a very high level. Subsequent poor rainfall years coincided with a decrease in the number of resident pairs, a smaller proportion of pairs breeding, a lower reproductive rate and a dramatic decline in prey numbers.     

THE VALIDITY OF CENSUSING BLACK RHINOCEROS POPULATIONS FROM THE AIR

The efficacy of censusing black rhinoceros ( Diceros bicornis Linnaeus) populations from the air was tested. Repeated aerial counts were made of the black rhinoceros population centered on Qlduvai Gorge, Tanzania, where the number of rhinoceros on the ground is known accurately. Even under the most ideal conditions only 50% of the population was detected by observers in an aircraft, and factors accounting for this are considered. It is concluded that the light aircraft is of limited value in providing estimates of black rhinoceros populations, and estimates based purely on aerial counts are subject to considerable variation.