Divergent foraging behavior in a hybrid zone: Darwin’s tree finches (Camarhynchus spp.) on Floreana Island

Hybrid speciation is increasingly recognized as a mechanism for novel evolutionary trajectories. However, we know very little about the ecology of a contact zone that has arisen in sympatry. This study examines the foraging behavior and fitness of two species of Darwin’s tree finches (Camarhynchus parvulus, C. pauper) and hybrid offspring on Floreana Island. Previous study showed that the percentage of hybrids in the tree finch population increased from 19% in 2005 to 41% in 2010, and their body and beak size increased by ~5% (parental phenotype did not change). In 2005–2006, all three tree finch groups (two parental species and hybrid birds) used the same foraging substrate, technique, and height. By 2010–2013, the small tree finch C. parvulus had changed its foraging technique and the medium tree finch C. pauper had changed its foraging height. Both parental species had higher body condition when foraging at (divergent) mean foraging heights per species but hybrid birds did not. We discuss the implications of conserving forest to facilitate vertical niche expansion and the role of hybridization for genetic persistence