Predation on artificial nests and caterpillar models across a disturbance gradient in Subic Bay, Philippines

Abstract

One possible mechanism underlying species losses in the tropics is an increase in predation due to habitat degradation. Relative levels of predation at three heights (ground, 1–1.5 m, > 5 m for nests and > 3 m for caterpillars) were compared across a gradient of disturbance in the Subic Bay Watershed Forest Reserve, Philippines over a 2-mo period. Four 750-m transects were established in each habitat type (closed-canopy forest, open-canopy forest, rural areas) where artificial nests and caterpillar models were placed within 10-m-radius plots and checked after a 5-d exposure period. Nests in open-canopy forest were least predated (16.7%), with predation in rural areas (58.3%) being higher than in closed-canopy forest (32.8%). Predation on nests at 1–1.5 m was significantly lower than ground nests. General linear mixed model analysis suggested that effects of habitat type on nest predation differed among heights. Attacks on caterpillars increased with disturbance (46.1–59.4%), but height was not found to have a significant effect on predation. Markings on plasticine models, camera traps and live traps were used to establish possible predators. Shifts in predator dominance among the habitats were observed. Vegetation cover, tree density and small mammal abundance were not correlated with mean predation in the transects.