Interspecific patterns of seed selection among granivorous passerines: effects of seed size, seed nutritive value and bird morphology

The relationships between seed characteristics (size and nutrient contents) and bird morphology were investigated in ten species belonging to three specialized families of granivorous passerines. Wild‐caught birds were exposed in captivity to a fixed mixture of thirteen seed types before measuring their consumption rates and seed preferences. A multivariate analysis of seed characteristics showed two principal and independent gradients of covariation, namely seed nutritive value and seed size. The smaller the birds, the more nutritive the seeds they selected, this result being largely independent of the family the bird belonged to. The selected seed size was directly related to both the body and bill sizes of the birds, hut these relationships varied between families, most probably as a consequence of interfamilial differences in the structure of the ramphotheca and the associated seed handling method.