Effects of forest fragmentation on experimental nest predation in Andean cloud forest

Abstract

Large-scale forest fragmentation in the Colombian Andes has resulted in the decline and local extinction of bird populations. We used artificial nests to examine the effects of habitat fragmentation on bird nest predation in a cloud forest site in the western Andean range, where local extinction of understory birds has been documented. Rates of nest predation were higher in three small (11, 13 and 29 ha) than in two large (75 and 300 ha) forest fragments. High rates of predation were not due to an edge effect, as predation rates were not higher on the edge than in the interior of the large fragments. Egg remains, recovered from depredated nests, suggested that nest losses were attributable to medium-sized mammals in large fragments, while small rodents were probably responsible for most predation in small fragments. Thus, we argue that changes in the mammalian predator assemblage (increased abundance of small mammals in small fragments) may account for the increased predation rates.