COS 71-10 - Nest predation may be responsible for declines of understory insectivores in fragmented Neotropical rainforest

Wednesday, August 10, 2011: 4:40 PM
5, Austin Convention Center
Deborah M. Visco, Ecology & Evolutionary Biology, Tulane Universitry, New Orleans, LA

Tropical forest fragmentation threatens bird populations and has resulted in moderate to severe declines of many groups, particularly the highly specialized understory insectivores. Unfortunately from a conservation perspective, we do not know the specific mechanisms causing this ecological disruption. To address this problem, I investigated the hypothesis that increased frequency of nest depredation events in fragmented landscapes is the primary mechanism of decline. I quantified nest predation rates and identified the predators of a model species, the Chestnut-backed Antbird (Myrmeciza exsul), an understory insectivore that still persists in the Sarapiqui lowlands of Costa Rica, which have experienced substantial forest fragmentation as a result of land-use changes in the past 50 years. I used continuously-imaging digital video to document nest predation events across three populations in this landscape: a biological reserve (La Selva), a forest fragment (Rio Frio Colegio), and a national park (Braulio Carrillo). 


I observed a very high depredation rate of 88% (n = 16) for the population at La Selva Biological Station. All predators of eggs and nestlings were snakes, the majority being a single species, juvenile and adult forms of Pseustes poecilonotus; a remarkable result considering the diversity of potential nest predators in this region. Additional results from this site, along with results from fragment and control sites collected in Spring/Summer 2011 will also be presented. This novel comparative approach to nest predator identification in the tropics will focus conservation objectives by informing managers of the specific factors limiting M. exsul and, by extension, other birds of this guild. These results, in conjunction with high adult survival rates for this species, suggest that the nest-based juvenile stages are where these populations are limited and hence are the life stages where interventions should focus.

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