Avian responses to reduced-impact logging in the southwestern Brazilian Amazon

Reduced-impact logging (RIL) involves several techniques that try to minimize changes to forest structure from timber harvesting and is becoming widely adopted in Amazonia. Understanding how biodiversity will respond to RIL demands assessments that include interactions among initial site conditions, specific harvest techniques, and responses of species that can be compared across varied forest types and regions. We assessed the short-term effects of RIL on 10 avian species in logged and unlogged portions of two concessions in Acre State, Brazil. We performed 460 point-count surveys and estimated variation in occupancy using a removal model that accounts for imperfect detection. Species were selected to include birds with contrasting expected responses to logging activities. We also conducted vegetation assessments at bird sampling locations, paying particular attention to bamboo (Guadua spp.) structure and distribution due to its dominance in forests of the region and high importance as a habitat component for Amazonian birds. Occupancy of four species varied between RIL and unlogged areas and was highly influenced by the percentage of bamboo present. Overall, bird responses to logging was greater where percent cover of bamboo was highest and, for two species, elevated occupancy was closely associated with elevated bamboo density. Bamboo dominance did not differ between logged and unlogged areas; our analysis indicated that this may have resulted from avoidance of bamboo stands by logging crews. This potential behavior, in turn, insured that bamboo refuges were maintained within logged areas, aiding species otherwise negatively affected by logging. Our work suggested how important logger behavior can be in influencing the structure of wildlife habitat under RIL management and that bird responses to logging, both positive and negative, are strongly influenced by local forest conditions.