Twenty years of understorey bird extinctions from Amazonian rain forest fragments: Consistent trends and landscape-mediated dynamics

Abstract

Aim: We analysed presence/absence data for understorey bird species in rain forest fragments sampled from 1979 through 2001. Here we consider extinctions between 1992, when most fragments had been isolated for at least 8 years, and 2001. Our objectives were to determine whether high extinction rates documented soon after isolation continued through up to 20 years after isolation, and to examine fragment size and landscape effects on extinction. Location: Biological Dynamics of Forest Fragments Project, near Manaus, Brazil. Methods: Through 1992, birds were surveyed with standardized mist net sampling in ten 1- to 100-ha fragments. We repeated the mist net protocol in 2000-01. We also added remote taping of the dawn chorus and tape playback surveys for species captured in 1991-92 but not in 2000-01. Results: Between 1992 and 2001, 37 species went extinct in at least one fragment. As expected, extinction rate decreased with increasing fragment size. Over 30% of species went extinct in 1-ha fragments, compared to about 5% in 100-ha fragments. Extinction followed a predictable pattern: most species lost from 100-ha fragments between 1992 and 2001 had already gone extinct in smaller fragments before 1992. Despite extinctions, fragments gained species between 1992 and 2001, apparently due to species moving through the developing second growth matrix. Fragments surrounded by old second growth had lower extinction rates than predicted based on fragment size alone. Main conclusions: Sequential extinctions occurred for at least 20 years. Some additional species previously lost from smaller fragments may continue to go extinct in 100-ha fragments. At the same time, species assemblages in 1- and 10-ha fragments mostly reflect second-growth dynamics by 20 years after isolation. High species loss predicted from the first few years after isolation has not occurred, almost certainly because of recolonization. © 2008 The Authors.