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 ...
BelIy-soaking in the Whitecrowned PloverMaclean (1975, J. Bombay nat. Hist. SOC. 72(1):??) reviewed the phenomenon of belly-soaking in the Charadriiformes. The Whitecrowned Plover Vanellus albiceps is one of several plover species known to wet their abdominal feathers by crouching down in water, and then to go to the nest and wet the eggs. The function of the behaviour is presumably to cool the eggs, since it is manifested only on hot days.Some observations were made at nests of the Whitecrowned Plover on the shore of Lake Kariba in the Matusadona Game Reserve. On 27 September 1973 a clutch of four was observed for three hours on a hot afternoon. Fragments of aquatic plants were found draped over the eggs at 11 :OO and again at 14:30 when observations were begun from a hide at the nest. The parent began to pant vigorously as soon as it returned to incubate. After about 45 min the parent left the nest, walked quickly to the edge of the lake and squatted in the shallow water. It got up, moved and squatted several times before finally standing up and preening. The belly-soaking posture ( Fig. 1) is quite characteristic, with wings and tail held well up. It does not resemble bathing at all. Cooling of the parent by such behaviour must be significant. Neither parent returned to the nest during the remainder of the observation period, despite high ambient temperatures. On 5 October this nest was again visited briefly. The eggs were wet and had drops of water on them. FIGURE 1White-crowned Plovers belly-soaking in shallow water near their nests (drawn from photographs by G. W. Begg).At another nest on 12 September one of the parent birds was seen to squat in the water for a moment, but it did not return to the eggs.Although none of the parents wetted their eggs during these observations, they exhibited typical belly-soaking behaviour and might have been inhibited from egg-wetting by the presence of the observation hide. The covering of an egg with plant material may have been deliberate as it has occasionally been recorded in other Vanellus spp. (Maclean 1974, Ostrich 45:167-174). The fact that on the same day, three species of aquatic plants were found freshly draped upon the eggs suggests that this behaviour may be regarded as a cooling mechanism. However, closer observations on the care of eggs by waders at high ambient temperatures are needed. The finding of wet eggs at the same nest is circumstantial evidence that the belly-soaking seen at Lake Kariba is for this purpose. G. W. 66 SHORT NOTESOSTRICH 47 Extent of overlap in two races of the Fiscal ShrikeOn a journey by road between Natal and the Kalahari Gemsbok National Park in July 1972, we counted the numbers of Fiscal Shrikes with and without white eyebrows, in order to see what degree of overlap exists between the more easterly form, Lanius collaris collaris and the more westerly form, Lanius collaris subcoronatus. L. c. subcoronatus has a broad white eyebrow which is easily visible in the field. The results of our counts on the forward and return journeys are ...
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