A comparison of giving-up densities of five species of granivorous birds

Abstract

The foraging efficiencies of four sympatric southern African seed-eating birds, namely Bronze Mannikin Spermestes cucullatus, Cape Sparrow Passer melanurus, Southern Red Bishop Euplectes orix and Thick-billed Weaver Amblyospiza albifrons, and a domesticated species, the Bengalese Finch Lonchura domestica, were measured and compared using giving-up densities (the amount of food remaining following patch exploitation) in experimental food patches. Foraging efficiency was quantified using giving-up densities by offering individual birds equal foraging opportunities. A low giving-up density displays the ability of a forager to profitably harvest food at low resource densities and to gainfully exploit the foraging opportunities overlooked by a less efficient forager. Ten individuals of each of the five species were allowed to forage on six different seed types. Thick-billed Weavers had significantly lower giving-up densities for all seed types except the smallest, namely red manna. Bronze Mannikins showed the converse trend, foraging most efficiently on the smallest seeds. The results of the present study revealed that Thick-billed Weavers were the most efficient foragers (i.e. had the lowest giving-up densities on seeds in feeding trays).

Ostrich 2008, 79(1): 101–104