Birds at Lake Ngami, Botswana

Fraser, William C.

doi:10.1080/00306525.1971.9634564

Cited by 5 publications

(2 citation statements)

References 2 publications

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“…If anything, there is an indication of a slight range contraction at the southern edge of this population's range. Although recorded from Lake Ngami by Wahlberg in the 1850s (Gyldenstolpe 1934) the species has not been recorded there in recent years (Fraser 1971;Dawson & Jacka 1975). The area is thOUght to have recently become drier (Smithers 1964;Dawson & Jacka 1975).…”

Section: Botswanamentioning

confidence: 99%

Range expansion of the hadeda ibisBostrychia hagedashin southern Africa

Macdonald

Richardson

Powrie³

1986

South African Journal of Zoology

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The southern African range of the habeda ibis Bostrychia hagedash has expanded from 530 900 km2 in 1910 to 1 323300 km 2 in 1985. Major range expansions have occurred in the fynbos biome of the southwestern Cape, the Karoo, the grasslands of the eastern Cape, the Orange Free State and the Transvaal highveld. Smaller expansions are documented for Lesotho, eastem Zimbabwe, central Mozambique and westwards along the Zambezi, Okavango, Limpopo and Orange rivers. The reasons for this expansion were investigated. Important factors include reduction in human persecution following the introduction of legislation in the period 1934 to 1941 and an increase of alien trees in formerly treeless areas. The increases in artificial impoundments and areas under irrigation are thought to have played a smaller role.

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Section: Botswanamentioning

confidence: 99%

Range expansion of the hadeda ibisBostrychia hagedashin southern Africa

Macdonald

Richardson

Powrie³

1986

South African Journal of Zoology

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“…There are two previous records from Lake Ngami (Smithers 1964;Fraser 1972). At least 13 different birds were recorded between 1958 and 1969 at Barberspan (Milstein 1975).…”

Section: Sightings Of Pectoral Sandpiper Knot Redshank and Bartailementioning

confidence: 99%

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Robertson

Begg²,

Dick

et al. 1981

Ostrich

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The Blacknecked Grebe Podiceps nigricollis is the most gregarious of the three southern African grebe species (pers. obs.). Besides nesting colonially, it occurs in flocks in the non-breeding season on large sheets of water and in even bigger flocks off the coast of South West Africa/ Namibia (McLachlan & Liversidge 1978; Ryan 1980). Migration occurs but it is not well understood (Broekhuysen 1967). I observed Blacknecked Grebes at sea in November 1978, while on a joint Sea Fisheries Branch-FitzPatrick Institute expedition to the guano islands off the coast of South West Africa, and briefly studied their behaviour and activity.A flock of up to 41 birds was observed along the leeward shore of Possession Island (27 01 S; 15 12E) from 4-7 November 1978. The elongate island lies 2,7 km off the coast of South West Africa; it is rocky and has a band of kelp Ecklonia maxima along its perimeter extending out at least 5 m. The flock foraged within about 40 m and along about 800 m of the coastline. Observations were made on the birds' general behaviour and diving times were recorded with a stopwatch. The diurnal activity of the group was recorded using group-scan sampling (Altmann 1974) in moderately calm weather on 7 November from 07hOO to 19h00, with a break from 11 h50 to 12h40. Scans were made at 1-min intervals. Six activities were recorded: swimming on the surface, diving, preening and bathing, resting, flying and "alert". The last activity was usually an intermediate state between foraging, and resting and preening. A complete scan lasted from 2-15 s, depending on the activity of the group. During each scan the fraction of the flock performing each activity was noted. However, in calculating the activity budget, the flock as a unit was assigned a single activity category at each scan based on the predominant activity (over 50% of individuals involved). This procedure would tend to emphasize the major activities of the group and ignore the minor activities.Individual activity budgets can therefore not be extrapolated from it.The basic activity rhythm throughout the day was foraging, in which the group swam and dived for food, alternating with preening, bathing and resting bouts undertaken close inshord. The flock was cohesive while foraging (about 0,3 m between individuals) and each group dive would be initiated by a member swimming in the lead, other members diving in accelerating succession after it. Forty-one percent of all dives were completed by the entire flock, 90,6% by more than 50% of the flock (Fig. 1). Flocks of Blacknecked Grebes observed briefly at Liideritz and Walvis Bay within the same month were also observed diving synchronously.When resting, each bird placed its neck across its back and faced forwards. Asynchronous diving by individuals was recorded for 23 % of the time when most of the flock was resting, preening and/or bathing. The group flew on five occasions, once when a Jackass Penguin Spheniscus demersus surfaced nearby, but otherwise for no apparent reason. After settling again on the water ...

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Strukturierung natürlicher und anthropogen beeinflußter Avizönosen im Okavango-Delta, Botswana

Utschick

Brandl

1987

J Ornithol

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Birds at Lake Ngami, Botswana

Cited by 5 publications

References 2 publications

Range expansion of the hadeda ibisBostrychia hagedashin southern Africa

Range expansion of the hadeda ibisBostrychia hagedashin southern Africa

Short Notes

Strukturierung natürlicher und anthropogen beeinflußter Avizönosen im Okavango-Delta, Botswana

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