7. SHORT NOTES

Randall, R. and Ross, G. J. B. 1979. Increasing population of Cape Gannets on Bird Island, Algoa Bay, and observations on breeding success. Ostrich 50:168-175.

The South African Gannet Sula capensis on Bird Island has doubled in numbers between 1956 and 1974 and the process is continuing. The increase is similar to that of the two closely related species S. serrator and S. bassana. We estimated from the colony surface area and nest density that the number of birds with nests in 1974/5 was approximately 77 000. Making allowance for non-breeders, there were about 100 000 adults in 1974/5. Guano harvests from 1938–75 show considerable annual fluctuations with an overall downward trend. Poor agreement was found when relating guano harvests to population estimates, when the latter are gauged by colony surface area. We suggest that guano harvests are not good indicators of gannet population trends on Bird Island, primarily because of harvesting methods and environmental conditions. The number of chicks which fledged in the 1976/7 season in a section of the colony was far fewer than expected, even when allowances were made for egg-loss and chick mortality. A combination of heavier-than-usual rainfall and poor management techniques have resulted in high egg-loss and low chick numbers.     

7. SHORT NOTES

Raseroka, B. H. 1974. Diet of the Hadedah Ibis. Ostrich 45:51-54.

The diet of the Hadedah Ibis in Victoria East, Cape Province is described. 60% of the weight of the diet is composed of animals obtainable from the surface of the soil, indicating that the birds can survive in dry areas where the hardness of the ground would prevent probing for the collection of food.     

SHORT NOTES ON BIRDS FROM KLIP RIVER VALLEY

Watkins, B. P. &; Furness, R. W. 1986. Population status, breeding and conservation of the Gough Moorhen. Ostrich 57: 32–36.

The Gough Moorhen Gallinula comeri holds territories of about 5000m² on Gough Island, where there may be 2 000–3 000 pairs. Scavenging from petrel carcasses partly eaten by Subantarctic Skuas Catharacta antarctica seems to be an important feeding method. Nests are constructed in tussocks with a tunnel entrance. Nest, egg and adult biometrics are given together with observations of incubation behaviour, and we discuss potential threats to this flightless endemic species.     

8. SHORT NOTES

Stutterheim, C. J. 1980. Moult cycle of the Redbilled Oxpecker in the Kruger National Park. Ostrich 51:107-112.

This paper describes the pattern and rate of the complete moult cycle in the Redbilled Oxpecker Buphagus er ythrorhynchus. The average duration of primary moult in adult birds was 340 days and the mean time to replace a primary feather was calculated as 34 days. The moult of the secondaries is initiated at two points, at the first secondary and at the innermost secondary. Secondary moult takes seven months. The differentiated inner secondaries moult in the normal middle/inner/outer passeriform fashion. The rectrices moulted only once annually. The two body moult cycles correspond with the moult of the differentiated inner secondaries. First-year birds undergo a partial postjuvenile feather replacement at three months of age.     

6. SHORT NOTES

Feare, Christopher J. 1981. Breeding schedules and feeding strategies of Seychelles sea-birds. Ostrich 52:179–185.

A comparison of the breeding schedules of Seychelles seabirds with their feeding strategies showed no relation between synchronous breeding and the ranges over which the birds forage, but there was a relation with flock feeding. Flock feeding birds are largely dependent upon schools of predatory fishes that drive prey species to the surface, and food is thus localized and transient. Synchronous colonial breeding probably helps individuals to locate these localized food sources, but species that are dependent mainly on dispersed prey would derive no benefit from synchrony, and they do, in fact, breed throughout the year.

Within shoals of prey, food is probably superabundant, but feeding space may be limiting. The dark backs of flock feeding birds render them inconspicuous to foraging birds (conspecifics and other species), thereby tending to reduce competition for space within the feeding flocks. The white plumage of species that feed on dispersed prey appears to act as a spacing out mechanism, reducing interference between feeding birds.     

SHORT NOTES

Hockey, P.A.R., Plagényi, É.E., Turpie, J.K. &; Phillips, T.E. 1996. Foraging behaviour of Crab Plovers Dromas ardeola at Mida Creek, Kenya. Ostrich 67:33-44.

The foraging behaviour of Crab Plovers is directly analogous to the ‘walk-stop-search-walk’ hunting behaviour of true plovers, and changes slightly depending whether the birds are foraging on sand or in water: they are nonterritorial when foraging. Crabs dominate the diet, but other invertebrates and fish are also eaten. Foraging efficiency increases with age and adults and subadults are able to satisfy their daily energy requirements in a single tidal cycle. The population of Crab Plovers at Mida Creek was much larger in 1994 than in 1992, but in 1994 adults achieved much higher intake rates than in 1992, suggesting considerable year-to-year variation in the carrying capacity of Mida Creek for Crab Plovers. The world population of 43–50 000 birds breeds at very few colonies and the species is thus a potential conservation concern. Because of the relative accessibility of large concentrations of Crab Plovers away from the breeding grounds, we suggest that a programme to monitor numbers and population demography should be targeted at nonbreeding aggregations.