Bruce M. Dyer

BREEDING NOMADISM IN SOUTHERN AFRICAN SEABIRDS-CONSTRAINTS, CAUSES AND CONSERVATION

Summary Crawford, R.J.M., Dyer, B.M. & Brooke, R.K. 1994. Breeding nomadism in southern African seabirds-constraints, causes and conservation. Ostrich 65:231-246. Fourteen species of seabirds representing three orders and five families breed in southern Africa. Nomadism in the breeding populations of 13 of these seabirds is examined. African Penguins Spheniscus demersus, Cape Gannets Morus capensis. Bank Cormorants Phalacrocorax neglectus, Whitebreasted Cormorants P. carbo and White Pelicans Pelecanus onocrotalus show strong fidelity to specific localities. Caspian Terns Sterna caspia change breeding localities at a low frequency; Cape Cormorants P. capensis, Hartlaubs Gulls Larus hartlaubii and Swift S. bergii and Roseate S. dougallii Terns at a higher frequency. At some localities, Bank Cormorants remain at the same breeding sites for extended periods, whereas Crowned Cormorants P. coronatus, Whitebreasted Cormorants, Kelp Gulls L. dominicanus, Hartlaubs Gulls, Damara Terns S. balaenarum, Swift Terns ...

Top predators in the Benguela ecosystem — implications of their trophic position

Many top predators in the Benguela ecosystem feed on prey species targeted by commercial fisheries. Their roles as indicators of the state of exploited prey resources, as competitors with commercial fisheries for resources, and as susceptible to impact from commercial fishing on those resources are briefly considered. Trends in the occurrence of anchovy Engraulis capensis and pilchard Sardinops ocellatus in the diet of Cape gannets Morus capensis off South Africas west coast are related significantly to survey estimates of the abundance of these fish species, and they provide useful confirmation of those estimates. In the 1980s, anchovy decreased in the diet of Cape gannets, but pilchard increased. In both the northern and southern portions of the Benguela system, groundfish were thought to eat most (66–73%) of the total quantity of cephalopods and vertebrates consumed by predators and man in the 1980s. South African fur seals Arctocephalus pusillus pusillus, predatory pelagic fish and man removed roughl...

Trends in numbers of Cape Cormorants (Phalacrocorax capensis) over a 50-year period, 1956–57 to 2006–07

Abstract The population trend of Cape Cormorants (Phalacrocorax capensis), a species endemic to southern Africa and that feeds mainly on shoaling pelagic fish, is described for a 50-year period, from 1956–57 to 2006–07. The main breeding localities for the species are grouped in three regions in the Benguela upwelling ecosystem: guano platforms off central Namibia, islands off southern Namibia and islands off South Africas Western Cape Province. From 1956–57 to 1978–79, the numbers breeding off Namibia increased, as a result of increased availability of breeding space and adequate supplies of food. In the same period, numbers remained stable in the Western Cape. Numbers decreased off southern Namibia in the early 1980s and off central Namibia in the early 1990s, when environmental perturbations reduced the availability of food. Numbers decreased in the Western Cape in the early 1990s, following periods of scarcity of anchovy (Engraulis encrasicolus), an important prey item, and an outbreak of avian cholera caused by the bacterium Pasteurella multocida. They remained low as cholera outbreaks continued and some pelagic fish were displaced to the east beyond the foraging range of breeding Cormorants. The overall population of Cape Cormorants was of the order of 100000 pairs in 1956–57, increased to ∼250000 pairs in the 1970s, but reverted to ∼100000 pairs in 2005–06.

Return to Robben Island of African Penguins that were rehabilitated, relocated or reared in captivity following the Treasure oil spill of 2000

Following an oil spill from the Treasure off the coast of South Africa in June 2000, about 19 000 oiled African Penguins Spheniscus demersus, including 14 825 from Robben Island, were caught for rehabilitation and subsequent release. A further 19 500 penguins that were not oiled — mostly birds in adult plumage, including 7 000 from Robben Island — were relocated some 700km to the east, to prevent them becoming oiled. Additionally, 3 350 orphaned chicks, including 2 643 from Robben Island — were collected for rearing in captivity and release to the wild. Some four years later — by the end of December 2004 — 70% of rehabilitated adults, 40% of relocated birds and 34% of captive-reared chicks had been seen back at Robben Island. Another 7% of birds relocated from Robben Island had been sighted at other localities. Rates of resighting rehabilitated birds were similar at Robben and Dassen Islands, but a greater proportion of relocated birds was seen at Dassen Island, where birds collected for relocation were mostly from breeding areas. The lower proportion of relocated birds seen at Robben Island is thought to result from this intervention causing some pre-breeding birds to move to other colonies. All three conservation interventions are considered to have been successful, but it is premature to assess their relative contributions to the conservation of the species. Three relocated birds tracked by satellite took 15–21 days to return to their home colonies. This rapid return may have resulted from breeding attempts being interrupted. After remaining at their home islands for 4–5 days, two of the tracked birds then left these islands for 19–36 days. We surmise that, after they had searched unsuccessfully for their mates, they abandoned breeding for the year 2000.

Competition for space: Recolonising seals displace endangered, endemic seabirds off namibia

Abstract South Africa (Cape) fur seals Actocephalus pusillus pusillus recolonised Mercury Island off South West Africa/Namibia in the early 1980s. By 1986, many endemic seabirds, including endangered and scare species, had been displaced from their breeding sites. The seabirds, already stressed because food resources have been depleted by fisheries, appear unable to compete for space against the heavier seals. Guano scraping has led to a loss of potential refuges and, by lessening the availability of nesting material and the attractiveness of nest sites, may also have weakened the inclination of birds to defend territories. As depleted seal populations recover worldwide, competition between pinnipeds and seabirds for breeding space is likely to increase.

The efficacy of hand-rearing penguin chicks: evidence from African Penguins ( Spheniscus demersus ) orphaned in the Treasure oil spill in 2000

Some 2,000 orphaned chicks of African Penguins Spheniscus demersus were hand-reared and released back into the wild on Robben and Dassen Islands following the Treasure oil spill in June 2000. Of these chicks, 1,787 were flipper banded. This paper reports on the subsequent survival rate and breeding success of those individuals seen on Robben Island from 2001–2006. Survival to breeding age and their subsequent breeding success of hand-reared chicks was no different from that of naturally-reared chicks. Over a four-year period, pairs where at least one partner was a hand-reared chick produced an average of more than 1.6 chicks per year. Combining the data on survival with that on breeding success indicates that 1,000 hand-reared chicks will produce around 1,220 chicks themselves over their lifetimes, making this a worthwhile conservation intervention.

Longevity, inter-colony movements and breeding of Crested Terns in South Africa

Abstract The nominate race of the Crested Tern, Sterna bergii bergii, first breeds when aged three years, but may not be fully recruited to breeding colonies until six years old because many birds do not breed in years of food scarcity. A 21-year-old bird breeding at Dassen Island was the oldest record for the species. There are 109 records in South Africa of birds alive when aged 15 years or older. Of birds whose colony of origin was known, 18% of those breeding and 27% of those present at colonies were at their natal localities. Most cohorts bred at several localities and breeding at most colonies was by birds fledged at several localities. Crested Terns in the Western Cape mainly breed between January and June. Most eggs are laid between January and April. Mean clutch size is 1.02 eggs. At Robben Island in 1987 and 1988 the average number of chicks fledged per breeding pair was estimated to be between 0.48 and 0.59.

Trends in numbers of Kelp Gulls Larus dominicanus off western South Africa, 1978-2007

The number of Kelp Gulls Larus dominicanus breeding at 11 islands in South Africas Western Cape province increased during the period 1978 to 1999–2000 and then decreased. The increase came after removal of controls on gulls and was associated with supplementary food provided by fish factories and rubbish tips. The decrease resulted from predation of gull chicks at some colonies by an increased population of Great White Pelicans Pelecanus onocrotalus. At Dassen Island, the density of gull nests remained constant as the colony doubled, but decreased by 50% as the colony decreased. At Dassen and Schaapen islands, the clutch size increased after pelicans started eating chicks. Numbers of gulls at two southern colonies where pelicans are seldom encountered have increased recently. This may have been influenced by shifts to the south and east of several fish stocks and their associated fisheries.

Seasonal pattern of breeding by Cape and Crowned Cormorants off western South Africa

Crawford, R.J.M., Dyer, B.M. & Upfold, L. 1999. Seasonal pattern of breeding by Cape and Crowned Cormorants off western South Africa. Ostrich 70(3&4): 193–195. At Bird Island, Lamberts Bay, and Malgas Island, South Africa, small numbers of Cape Cormorants Phalacrocorax capensis may breed at any time of the year, but the main breeding season is from September to February. At Malgas Island, Crowned Cormorants P. coronatus may also breed throughout the year, but mostly from December to March. Counts of the breeding population of Cape Cormorants should be undertaken between October and December, and of Crowned Cormorants in January or February.

Absence of breeding by African penguins at four former colonies

African penguins Spheniscus demersus no longer nest at four suspected previous breeding localities: Neglectus Islet (Hottentot Bay), North Reef and Albatross Island off Namibia and Jacobs Reef off South Africa. This brings to 10 the number of localities where breeding does not now occur. Breeding also ceased at Robben Island, which has now been recolonized. It is uncertain that penguins bred at Cape Recife. Of the other 10 localities, breeding probably stopped at five as a result of competition with South African fur seals Arctocephalus pusillus pusillus for space and at four because of exploitation and disturbance by man. The reason for the loss of the important colony at North Reef, where there were more than 1 000 penguins in 1956, is unclear, but a scarcity of food may be implicated.