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ECOLOGICAL SEPARATION BETWEEN WHITE AND PINK‐BACKED PELICANS IN THE RUWENZOFU NATIONAL PARK, UGANDA
Author(s) -
Din N. A.,
Eltringham S. R.
Publication year - 1974
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/j.1474-919x.1974.tb00221.x
Subject(s) - pelican , flock , white (mutation) , national park , geography , hippopotamus , breed , fishery , ecology , population , biology , archaeology , demography , biochemistry , sociology , gene
Summary The number and distribution of the White Pelican Pelecanus onocrotalus roseus and the Pink‐backed Pelican P. rufescens were studied in the Ruwenzori National Park, Uganda, by means of aerial surveys carried out at approximately weekly intervals between May 1968 and December 1969. The White Pelican is migratory and was present in the Park at highest numbers in August 1968 and May 1969 when 2510 and 3927 respectively were recorded. It does not breed within the Park. The Pink‐backed Pelican is resident, with a population averaging about 1350 birds. Pelicans are distributed in discrete flocks on loafing grounds. Flocks of the White Pelican tend to be bigger than those of the Pink‐backed. Forty‐three loafing grounds were recognized in the Park, and it is shown that there is no difference between the species in the frequentation of these grounds. The areas favoured by both species are characterized by flat, open stretches close to water; steep slopes and heavily vegetated shore‐lines are avoided. The feeding behaviour was studied by direct observation and through cine‐photography. Only the White Pelican feeds communally in coordinated groups; this species also often feeds singly. The feeding sequence of both species is described, and is divided into four phases:searching, trapping, catching and swallowing. The searching phase lasts about six times longer in the Pink‐backed Pelican than in the White. The White Pelican feeds further from the shore than does the Pink‐backed. There is little difference between the species in the daily feeding pattern. Feeding takes place throughout the day but mostly from dawn to about 10.00 hrs and from 17.00 hrs until dusk. The rest of the day is spent mainly in preening, resting or bathing. The food of pelicans is exclusively fish. The White Pelican takes mainly large Tilupia , and Haplochromis and fish fry to a lesser extent. The Pink‐backed Pelican feeds largely on fish fry, but Tilapia and Haplochromis are frequently taken and by weight are more important than the fry. However, the Tilapiu are smaller than those taken by the White Pelican. Ecological separation between the two species is achieved through these differences in their feeding behaviour. It is estimated that the White Pelican takes 1201 g and the Pink‐backed Pelican 776 g of fish each day. The total amount of fish eaten by both species from Lake George during 1969 was calculated to be 591 709 kg. This is small ( c . 3%) compared with the estimated total fish production of the lake but quite appreciable (12.7%) as a proportion of the total caught by man. It is concluded that the pelican populations are probably not important as a link in the chain whereby organic matter transferred from land to water by the Hippopotamus is returned to the land.