WHY DO GREAT WHITE PELICAN CHICKS DIE SUDDENLY ON AREL ISLAND, BANC DARGUIN, IN MAURITANIA

The status of the Great White Pelican in Africa in the 1980s is review ed. During this period the size of the colony of Pelecanus onocrotalus located on the Mauritanian coast at the bane d'Arguin increased ten-f old owing to an influx of birds coming from newly installed colonies i n Senegal. Great White pelicans are absent from the Bane d'Arguin from February to June. The first birds install on the Bane in July, coinci ding with the arrival of warm waters from the Gulf of Guinea. The peli cans lay their eggs in successive waves from mid-August to the end of November. The clutch size is unusually low for the species (mean 1.25 eggs/nest). There is a positive relation between clutch size and the s ize of the breeding cohort (r = 0.87, P < 0.01). Heavy mortality of ch icks of all ages is recorded from mid-December onwards, together with a massive departure of adults towards the south. This mortality appear s to be due to the upwelling of cold water which displaces the warm wa ter towards the south: this hypothesis was tested from supporting evid ence. Observations on the composition of chick regurgitates, the behav iour of adults on the foraging grounds (both during the day and at nig ht, but exclusively at low tide) and the timing of breeding of other f ish-eating bird species confirmed this hypothesis.