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Relative abundance and microhabitat of four sympatric antpittas in an in-terandean valley of Southern Ecuador

Abstract:

Exploring mechanisms that determine species coexistence is a key step to understanding community organization and patterns of distribution of biodiversity. Antpittas of the genus Grallaria offer a great opportunity to quantify mechanisms of coexistence among closely related species. They are terrestrial insectivores with specialized foraging techniques and limited dispersal abilities, factors that may produce high levels of niche overlap and consequently reduce the chances of stable coexistence. We explored spatial niche partitioning among four sympatric antpitta species ? Rufous Antpitta (Grallaria rufula), Chestnut-crowned Antpitta (Grallaria ruficapilla), Undulated Antpitta (Grallaria squamigera), and Tawny Antpitta (Grallaria quitensis) ? in a tropical Andean valley located in southern Ecuador. We determined the abun-dance of each antpitta species in native forest, shrub, pasture, and páramo habitats, and gathered data about the microhabitat of each spe-cies. Abundance was determined using point counts, territories were located by triangulating on individual calls, and certain microhabitat characteristics were measured within each territory. We found no differences in the abundance or probability of occurrence of species among habitats for the Rufous Antpitta, the Chestnut-crowned Antpitta, or the Undulated Anpitta, but the Tawny Antpitta was restricted to páramo. At the microhabitat level, Rufous and Chestnut-crowned Antpittas shared similar vegetation characteristics, with the presence of shrubs being an important shared microhabitat feature. The Undulated Antpitta occurred in a microhabitat characterized by the presence of trees and a ground cover of mosses. In general, our results suggest that closely related birds could partition habitats into particular niches at different scales, which could promote the coexistence of species in the tropical Andes.