Maximizing detection probability to optimize nocturnal bird surveys in large areas

Aim
Our specific objectives were to (1) estimate probabilities of detection of each species, after taking into account survey-specific covariates, and (2) investigate the influence of site-specific covariates on owl and nightjar abundance, integrating effects of imperfect detection.
Innovation
We conceived a survey protocol to estimate probabilities of detection and estimates of abundance of owls and nightjars in a large area, the Basque Country, northern Spain.
Main Conclusions
Our results show that detection probability was strongly influenced by playback broadcast and by observer experience. Date irregularly affected species according to their reproductive periods, and we also found that vocal activity gradually diminished proportionally to the hour after sunset. Tawny owl (Strix aluco) was the most abundant and widely distributed species. Its abundance was positively related to forest areas (mainly pine timber forests) and decreased in large urban and agricultural areas. Open space ...