Dispersion of seabirds at sea in the Southern Ocean
Master Thesis
1982
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University of Cape Town
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Abstract
The feasibility of obtaining information on the dispersion of seabirds at sea precise enough to reflect changes in their prey was investigated. A standardized technique for counting birds from a moving ship, designed to limit biases due to birds circling, following and/or deviating towards/from the ship, is suggested. An interspecific comparison of 31 seabird species was made to determine which species yielded the most accurate censuses. Although many species are attracted towards the ship, only the Wandering Albatross Diomedea exulans follows for long periods. Counts from a stationary ship are shown to be unsuitable for abundance and biomass estimates, because of the accumulation of birds around the ship. The avifauna at sea is described in terms of species richness, diversity, abundance, biomass and trophic groups of 42 pelagic species (penguins excluded). Birds eating plankton and cephalopods are the most abundant; few birds eat fish. Plankton- and cephalopod-eaters occur most abundantly in the south and north of the study area, respectively. An association between their distribution and the availability of their principal prey is proposed. The effect of five abiotic features on seabird distribution was investigated. Although significant preference for specific ranges of features is demonstrated, linear correlations are weak (maximum correlation coefficient (r = 0.325). Abiotic features associated with the distribution of the Snow Petrel Pagodroma nivea and the Antarctic Petrel Thalassoica antarctica were investigated in greater detail. Statistical relationships between the species' occurrence and measured oceanographic and meteorological features are inconclusive. Associations with prey are discounted, because of the birds' apparently unspecialized diet and opportunistic feeding. The two species occur in or near sea-ice. Their restriction to this area and the concomitant absence of other procellariiform species appears to be consequent on the species' flight characteristics. The merits of using seabirds at sea as biological indicators of prey resources are discussed.
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Bibliography: pages 57-66.
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Griffiths, A. 1982. Dispersion of seabirds at sea in the Southern Ocean. University of Cape Town.