Population density estimates and key microhabitat parameters for two endangered tropical forest understory insectivorous passerines from the Pernambuco Endemism Center

Abstract

The Pernambuco Endemism Center (PEC) is the most fragmented and degraded tract of the Atlantic Forest, considered to be a hotspot within a hotspot. Recent bird extinctions and the high number of endangered taxa have called the attention of conservation practitioners all over the world to this area. Among the most vulnerable groups of birds are the insectivorous passerines of the forest understory, yet empirical information on demography and habitat requirements are unavailable for these taxa. Here, we provide population density estimates and microhabitat selection information for two endangered insectivorous passerines endemic to the PEC, the Pernambuco Fire-eye, Pyriglena pernambucensis, and the Black-cheeked Gnateater, Conopophaga melanops nigrifrons. Distance-sampling estimates resulted in population densities of 0.15 and 0.35 individuals/ha, respectively, in an Atlantic Forest fragment of approximately 1000 ha. Extrapolations of population densities to 39 fragments where the occurrence of these taxa was confirmed resulted in population estimates of 4936 individuals for the Pernambuco Fire-eye and 12,679 individuals for the Black-cheeked Gnateater, but these may be underestimates because other fragments where they could potentially occur were never surveyed. Although extrapolating data from only one fragment to other areas is problematic, these are the first rough minimum population size estimates for birds from the PEC. Microhabitat preference analyses revealed that both species selected sites with denser forest understory vegetation, which is associated with areas in regeneration. This is evidence that these taxa can tolerate certain levels of habitat disturbance and that their limited distributions and habitat loss may be more important causes of threat than habitat requirements. In the face of ongoing PEC fragmentation, our data will serve to parameterize other studies and may contribute to practical conservation policies.