Habitat structure affects nest predation of the Scaly-crowned Babbler (Malacopteron cinereum) by macaques and snakes in a Thai-seasonal evergreen forest

Nest success of forest birds is typically low due to high rates of predation, but little is known regarding how different nest predators affect nest-site selection and nesting success, particularly in the tropics. We studied nest-site selection and nest success of the understory-nesting Scaly-crowned Babbler (Malacopteron cinereum) in a seasonal evergreen forest in northeastern Thailand during four breeding seasons. We identified nest predators using video-monitoring and examined relationships between nest site vegetation structure and nest predation by dominant predators. Based on 71 video-monitored nests, 98.5% of failures were due to predation; 59 predation events from nine predator species were documented including Northern
Pig-tailed Macaque (Macaca leonina) (47.5%, n= 28), five avian predator species (32.2%, n= 19), and two snake species (18.6%, n = 11). Nest sites had significantly higher concealment and number of lianas than random sites. Higher concealment may represent selection against visually oriented predators which were responsible for approximately 80% of predation events. Vegetation parameters suggested opposing patterns for macaques versus snakes; nests surrounded by higher density of saplings and lower density of taller stems (5–10 m) were depredated by macaques, whereas snake depredated nests were associated with a lower density of saplings, a higher density of taller stems and a higher density of lianas. Nests depredated
by avian predators were not associated with any measured variables. Our data suggest that different vegetation structures perhaps facilitate or impede different predators and different predators may generate conflicting selection pressures for nesting birds within a given habitat. Our data also imply that impacts on nesting success from vegetation disturbance (e.g., logging, road edges, etc.) may be difficult to predict, as these effects are likely to vary among sites and regions depending on the foraging behavior of dominant local predators.