Foraging ecology of temperate-zone and tropical woodpeckers

The foraging behavior of II species of woodpeckers in Guatemala, Maryland, and Minnesota was studied in order to test the seasonal stability hypothesis. This hypothesis predicts that specialization and species richness should be no greater for tropical wood-excavators than for those in the temperate zone because wood-excavators in both regions are buffered against seasonal change. Niche breadth values for six variables that describe foraging methods and perches were calculated by two methods. Unweighted niche breadth values were similar for tropical and temperate woodpeckers for all variables except foraging technique; in this case the temperate species are more specialized. With weighted niche breadth values temperate species are more specialized for two variables and less specialized for two others. Thus there is no consistent tendency for tropical species to be more specialized. However, the excavating guild includes twice as many species in Guatemala as in either of the northern study sites. Two of the three "additional' species in Guatemala use a configuration of foraging methods and perches not used by northern woodpeckers. Hence the larger number of tropical woodpecker species can be attributed partly to the greater range of resources available in the structurally complex rain forest.