Nest site vegetation structure influences nest predators and nesting success of understory birds in a dry evergreen forest in northeastern Thailand

Nest predation is typically the main cause of nest failure in forest understory birds; thus, identification of primary nest predators is key to understanding nest predation patterns. Furthermore, responses of predators are likely affected by vegetation structure, but predator responses to micro-scale habitat characteristics are largely unknown, especially in tropical forests. We used a long-term study with one of the largest datasets of its kind to investigate the extent to which micro-habitat structure (5-m radius surrounding a nest) can predict the likelihood of predation and by which predator. In a secondary evergreen forest in northeastern Thailand, 2013–2021, we found 1,016 active nests of 13 species and 24-hr video-monitored 500 of them. We recorded 336 predation events from 16 nest predator species. From this and previous studies at our site, we identified the top 4 predator species/species-groups accounting for ~83% of predation events: Macaca leonina (northern pig-tailed macaque, 36% of predation events), cat snakes (Boiga cyanea [green cat snake] and Boiga siamensis [grey cat snake]) (20%), Lycodon cf. davisonii (Blandford’s bridle snake, 18%), and accipiters (A. trivirgatus [Crested Goshawk] and A. badius [Shikra]) (9%). These 4 predator species differed in their responses to vegetation structure likely reflecting differences in foraging behaviors. Macaque and accipiters, both diurnal and visually-oriented, tended to depredate more visible/open nests, but macaques depredated nests surrounded by more trees and short woody stems (<3 m tall) compared to raptors. For snakes, both nocturnal, cat snakes depredated nests with higher numbers of both short woody stems and woody climbers, whereas bridle snakes depredated nests with more trees and fewer climbers. As noted previously, nest predator identity is critical to understanding habitat-predation patterns. Our data suggest that nest site vegetation characteristics influence the likelihood of a given species of predator locating a nest and that even small changes in vegetation structure could significantly alter predation patterns.