With Atlantic Forest conversion to open farmland, cavity-nesting birds increasingly rely on woodpecker excavation in snags

COCKLE, KRISTINA L.; BONAPARTE, EUGENIA BIANCA; IBARRA, JOSÉ TOMÁS

Congreso; North American Ornithological Conference; 2020

Understanding nest-site selection is critical to conserving tree-cavity-nesting wildlife, but nest-site use may vary across landscapes. We examine variation in the characteristics of trees and cavities used by cavity-nesting birds from globally-threatened primary Atlantic Forest to open farmland. We used a stratified case-control design and 20 random plots to assess variation in characteristics of trees and cavities (used and available) across gradients of canopy cover and distance to forest edge in Argentina. For secondary cavity nesters, nest cavities were more likely to occur in larger-diameter trees across all stand conditions, but more likely to occur in snags as canopy cover declined (in open farmland; n = 123 nest trees). For primary excavators, nest cavities were more likely to occur in larger snags, regardless of stand conditions (n = 54 nest trees). Available cavities declined from 4/ha in primary forest to 0.4/ha in open farmland. Available cavities and those used by secondary-cavity nesters were increasingly of excavated origin in open farmland, which indicates that avian excavation may partly compensate for the loss of decay-formed on farms. As forest landscapes shift toward a predominance of agroecosystems, snags and primary cavity nesters may take on important roles in conserving cavity-nesting communities and their ecosystem functions. However, nest cavities declined in height and depth, and increased in entrance size toward open farmland, raising the possibility that birds increasingly use suboptimal cavities as forest cover declines. Conservation of cavity-nesting birds should include retention of large trees and recruitment of native young trees across all landscapes but especially on farms.