Browsing by Author "Underhill, L G"
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- ItemRestrictedBreeding success of African penguins Spheniscus demersus at Dassen Island, especially after oiling following the Apollo Sea spill(2008) Wolfaardt, A C; Underhill, L G; Nel, D C; Williams, A J; Visagie, JThe reproductive success of African penguins Spheniscus demersus at Dassen Island from 1994 to 2000 was variable, but much higher than previously reported figures for the species. Breeding success was positively related to the abundance of anchovy Engraulis encrasicolus and sardine Sardinops sagax, and the high reproductive output during the study was attributed to the large biomass and high availability of these two species for much of the study period. De-oiled penguins from the Apollo Sea spill had a slightly lower hatching success but a significantly lower overall breeding success than that of un-oiled birds, driven mainly by the reduced number of chicks which fledged. Nests with two de-oiled Apollo Sea parents were less successful than nests with one de-oiled bird. There was increased mortality of chicks 40 days and older in nests with de-oiled birds. Chicks from nests with one de-oiled Apollo Sea parent grew at a similar rate to chicks from nests with no de-oiled parents. However, chicks from nests that comprised two de-oiled Apollo Sea birds had significantly slower growth rates than these other two groups. Breeding success and chick growth at nests with de-oiled birds were more negatively impacted when feeding conditions were less favourable. These results suggest that one of the main reasons for lower breeding success in de-oiled birds was their reduced ability to provision chicks, especially during the period in which the energy demands of the chicks is greatest. The rate of mate fidelity was lower in de-oiled birds than un-oiled birds, and there was a positive association between mate fidelity and breeding success.
- ItemOpen AccessImpact of flipper-banding on breeding success of African penguins Spheniscus demersus at Robben Island: comparisons among silicone rubber bands, stainless-steel bands and no bands(2008) Barham, P J; Underhill, L G; Crawford, R J M; Leshoro, T M; Bolton, D AFrom 2001 to 2006, two new designs of flipper bands made from silicone rubbers were tested on African penguins Spheniscus demersus at 365 nests on Robben Island, South Africa. We compared, over six years, the breeding success, from hatching to fledging, of three different groups of penguins: those with rubber bands (117 nests), with conventional stainless-steel bands (103 nests) and without bands (145 nests). There were no significant differences in breeding success between the three groups, suggesting that neither the currently used steel bands, nor either of the new rubber-band designs, were harmful during the seasons investigated. The rubber bands caused less wear of feathers and less drag on a model penguin than the steel bands. In captivity, the behaviours of African penguins fitted with rubber bands were not noticeably different to those of unbanded birds.
- ItemOpen AccessMaking sense of censuses and dealing with missing data: trends in pup counts of Cape Fur Seals Arctocephalus pusillus pusillus between 1972-2004(2007) Kirkman, S P; Oosthuizen W H; Meÿer, M A; Kotze, P G H; Roux, J-P; Underhill, L GTrends in the population of Cape fur seals Arctocephalus pusillus pusillus were estimated from counts of pups on aerial photographs of colonies taken between 1972 and 2004 to determine trends in the overall population and subpopulations. Incomplete coverage resulted in missing data in some years. Various methods of determining proxy values for missing data were assessed, and it was concluded that different methods were applicable to Namibian and South African colonies. This reflected variation in trends of pup counts between the countries, which was associated with differences in productivity between the southern and northern Benguela ecosystems. In Namibia, temporal changes in pup numbers were non-linear in some years and there was correspondence in fluctuations at most colonies. This appeared to be on account of an effect of periodic, wide-scale prey shortages that reduced birth rates. There was a northward shift in the distribution of seals in the northern Benguela system. In South Africa, pup counts were much less variable between years, probably on account of a relative stability of food supply. A linear approach was therefore suitable for determining proxy values for missing data at South African colonies. Pup counts suggest that there has been little change in the overall population of the Cape fur seals since 1993, when it was estimated at about two million animals.
- ItemRestrictedPopulations of surface-nesting seabirds at Marion Island, 1994/5-2002/3(2003) Crawford, R J M; Cooper, J; Dyer, B M; Greyling, M D; Klages, N T W; Ryan, P G; Petersen, S L; Underhill, L G; Upfold, L; Wilkinson, W; De Villiers, M S; Du Plessis, S; Du Toit, M; Leshoro, T M; Makhado, A B; Mason, M S; Merkle, D; Tshingana, D; Ward, V L; Whittington, P ADuring the 1990s and early 2000s, populations of surface-nesting seabirds at Marion Island showed different trends, but for the majority of species numbers decreased. Reduced numbers of gentoo penguins Pygoscelis papua, eastern rockhopper penguins Eudyptes chrysocome filholi, Crozet shags Phalacrocorax [atriceps] melanogenis and probably macaroni penguins E. chrysolophus are most plausibly attributed to an altered availability of food. Decreases in numbers of dark-mantled sooty albatrosses Phoebetria fusca, light-mantled sooty albatrosses P. palpebrata, southern giant petrels Macronectes giganteus and possibly northern giant petrels M. halli may have resulted from mortality of birds in longline fisheries. However, populations of wandering Diomedea exulans and grey-headed Thalassarche chrysostoma albatrosses fluctuated around a stable level. Numbers of Subantarctic skuas Catharacta antarctica and kelp gulls Larus dominicanus breeding at Marion Island also decreased. Kerguelen Sterna virgata and Antarctic S. vittata terns remain scarce at the island. Trends for king penguins Aptenodytes patagonicus were not reliably gauged, but numbers probably remained stable or increased. There were large fluctuations in numbers of king penguin chicks surviving to the end of winter.
- ItemOpen AccessRange expansion of the Red-billed Quelea, Quelea quelea, into the Western Cape, South Africa(2006) Oschadleus, H D; Underhill, L GThe red-billed quelea, Quelea quelea, is a serious problem bird of cultivated grain throughout Africa. It has expanded its range in different parts of southern Africa. Recent sightings over the last seven years in the Western Cape indicate that this species is appearing more frequently here. If queleas do become established in the Western Cape as a breeding species, this could have a serious impact on the economy of the wheat farmers.
- ItemOpen AccessRestoration of oiled African penguins Spheniscus demersus a decade after the Apollo Sea spill(2008) Wolfaardt, A C; Underhill, L G; Altwegg, R; Visagie, JThe bulk ore carrier Apollo Sea sank south-west of Dassen Island off western South Africa in June 1994, oiling approximately 10 000 African penguins Spheniscus demersus, most of which were collected from Dassen Island. A total of 4 076 de-oiled penguins was released with flipper bands. From 1994 to 2005, follow-up research using re-sighting and capture-mark-recapture methods indicated that about 73% of the de-oiled penguins observed back at Dassen Island attempted to breed, and were thus successfully restored into the breeding population. For de-oiled breeders, the median interval between their first recorded sighting and first recorded breeding attempt was 11 months, indicating a short-term delay in restoration. At least 45% of the de-oiled breeders were still being re-sighted five years after their release, and a minimum of 4% survived into their ninth year. These results represent the most successful restoration estimates anywhere in the world. The proportion of de-oiled juvenile penguins re-sighted back at Dassen Island and recorded breeding was lower than that of birds in adult plumage. De-oiled non-breeders spent significantly more time along the shore and less time within breeding colonies than de-oiled breeders. The mean proportion of de-oiled breeders that abstained from breeding each year during the study period was greater than expected. There was a negative relationship between breeding and subsequent survival and breeding, suggesting a cost of reproduction for de-oiled birds.
- ItemRestrictedThe management of Avian Cholera Pasteurella multicida outbreaks on Dyer Island, South Africa, 2002-2005(2007) Waller, L J; Underhill, L GIn 2002 there was a widespread epizootic involving seabirds on five of the offshore islands of the Western Cape, South Africa. Since then, avian cholera Pasteurella multocida outbreaks have been occurring annually on one of these islands, Dyer Island. This paper reports on the three subsequent summers, 2003/04, 2004/05 and 2005/06, during which further avian cholera outbreaks were recorded. It focuses on the outbreak in 2004/05, which was the largest in extent and the most closely monitored. The mortalities during 2005/06 were not as extensive as expected. The management measures used to bring these outbreaks under control are described. Removal of all the carcasses from the entire island in one day is important in reducing mortality. Management intervention is required to reduce the negative impacts of disturbance due to kelp gull Lasus dominicanus predation on other breeding seabirds, primarily the African penguin Spheniscus demersus, during the carcass collection process.
- ItemOpen AccessThe seminal legacy of the Southern African Bird Atlas Project(2008) Harrison, J A; Underhill, L G; Barnard, PThe first Southern African Bird Atlas Project was launched in 1986 and gathered bird distribution data from six countries of southern Africa. The project culminated with the publication of The Atlas of Southern African Birds in 1997. The database generated by the project, seven million bird distribution records, has been widely used by four groups: environmental consultants (for example, to locate electricity transmission lines), conservationists (planning conservation strategies), research scientists (especially macro-ecologists and biogeographers) and birders (ecotourism materials). By 2007, the database had spawned 50 research publications and eight Ph.D.s and master's degrees. These products are a tribute to the more than 5000 'citizen scientists', who gathered the bulk of the data. The atlas concept has been extended to frogs, reptiles, spiders and butterflies; a second bird atlas started in 2007 and will, for example, facilitate knowledge of the impact of environmental change on birds. The South African National Biodiversity Institute is playing a lead role in initiating these new projects.