Feeding ecology and territoriality of the Cactus Finch Geospiza scandens on Isla Daphne Major, Galápagos

Summary

In this study we investigated the relationship between food availability, feeding ecology and territoriality in a population of Cactus Finches, Geospiza scandens, on Isla Daphne Major, Galápagos, between 1979 and 1981.

We monitored the phenologies of the principal food types on the island and related them to changes in the feeding ecology of G. scandens. Feeding patterns closely tracked the availability of resources, with a similar pattern in each of the three years. Birds relied heavily on Opuntia fruits in the dry season.

G. scandens defends year-round territories based on Opuntia. Variation in Opuntia phenologies between individual territories and between years was documented in order to provide a measure of territory quality over the three years. A correlation was demonstrated between the area of cactus within a territory and mating success of the owner. We suggest that territory quality also affects the survival of the owners during periods of food scarcity and that the mating and survival advantage of a high-quality territory occur at different times and to different degrees in different years. Hence the importance of territorial quality can only be judged over a long-term period in these long lived and sedentary birds.