Recreational activities in protected areas can influence wildlife and acoustic environments, yet methods for simultaneously monitoring human activity and biodiversity responses remain limited. We used passive acoustic monitoring to assess whether anthropogenic sounds were associated with reduced bird acoustic detections at Alpine climbing sites located in protected areas in north-western Italy. Ten autonomous recording units were deployed at climbing sites within the Maritime Alps Protected Areas, recording 10-min segments hourly from April to June 2025 and yielding 15,701 recordings. Automated bird detection was performed using BirdNET, with species-specific confidence thresholds derived from manual validation. Anthropogenic sound categories, including engine noise, human voices, and non-vocal human sounds, were fully manually validated. Recordings containing more engine or human noise were associated with significantly lower detected bird species richness. In a within-recording analysis, bird detection rates declined significantly more following the onset of real anthropogenic sound events than around pseudo-breakpoints assigned to undisturbed control recordings, across all three temporal windows tested (30, 60, and 120 s). These results suggest that anthropogenic sound at climbing sites is associated with measurable reductions in bird acoustic detections. Passive acoustic monitoring offers a practical tool for tracking local anthropogenic acoustic activity and biodiversity indicators in protected mountain areas used for outdoor recreation.