Feeding Behavior of Four Arboreal Darwin’s Finches: Adaptations to Spatial and Seasonal Variability

In the Galápagos Islands climate and food abundance vary strongly among vegetation zones and between seasons. We studied the foraging behavior of four mainly insectivorous Darwin’s finch species on Santa Cruz Island. We compared foraging behavior between (1) the arid zone, where food is scarce, with the humid Scalesia zone, where food is abundant; and (2) within each zone between dry and wet seasons. The four species used different feeding substrates in the two vegetation zones and reacted flexibly to the seasonal variation by changing feeding techniques and substrates. Species mainly specialized in resource use and feeding techniques or showed no change in niche breadth when food became more limited in dry conditions. In the arid zone during the dry season, the Large Tree Finch (Camarhynchus psittacula) relied on its powerful biting beak to bite open the bark of dry twigs. The Woodpecker Finch (Cactospiza pallida) used twigs and cactus spines to access arthropods in tree holes and was the only species that significantly increased the diversity of feeding techniques. The use of tools extends the morphological properties of its beak temporarily without limiting behavioral versatility and flexibility. The Small Tree Finch (Camarhynchus parvulus) showed a shift in food types and had a high proportion of plant food in its diet. The Warbler Finch (Certhidea olivacea) was not present in our study site in the arid zone.