BILL MORPHOLOGY AND DIET OF A FILTER-FEEDING SEABIRD - THE BROAD-BILLED PRION PACHYPTILA-VITTATA AT SOUTH-ATLANTIC GOUGH ISLAND

One hundred and fifty diet samples collected from broad-billed prions Pachyptila vittata at South Atlantic Gough Island and Tristan da Cunha over four years during the breeding season showed that they fed almost exclusively on copepods (0.7-4.1 mm in size), consistent with a bill morphology adapted for filter-feeding. Food is sieved from the surface of the ocean by means of palatal lamellae, of which there are 112-136 on either side, 0.16 mm apart. The filtration area of both rows of lamellae together amounted to 785 mm2 and the bill held 4.1 ml of water with a maximally extended mandibular pouch. Both sexes of broad-billed prions look outwardly alike but morphometric measurements proved that males are slightly larger.