Life history traits and natural selection for small body size in a population of Darwin's finches.

Abstract

Darwin's medium ground finch Geospiza fortis juveniles, when close to fully grown, are often substantially smaller on average than the adult breeding population from which they are descended. Some weak selection favoring small body size was observed from age 2-4 mo to age 7-10 mo. It is likely that there is some selection against large juveniles. This opposes selection against small adults which is known to occur regularly. A plausible selection pressure is a metabolic disadvantage to large juveniles.-from Authors