Maximizing detection probability for effective large-scale nocturnal bird monitoring

Aim Our specific objectives were to (a) estimate detection probabilities of nocturnal bird species, after taking into account survey‐specific covariates, and (b) 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 species were less common. Barn owls (Tyto alba), little owls (Athene noctua), Eurasian scops owls (Otus scops) and long‐eared owls (Asio otus) avoided forest areas, but showed different responses to agriculture, grass‐fields, scrub and urban areas. Finally, European nightjar (Caprimulgus europaeus) was moderately frequent, and its abundance was favoured by scrub areas and, weakly, by eucalyptus patches, whereas it was negatively affected by large forest areas. We have shown that it is fundamental to consider the effects of survey‐specific covariates in the methodology design and analytical development. Our results also indicate some ecological adaptations and population changes in the nocturnal bird community following an increase in urbanization and in the extent of timber plantations, and also the simplification of natural habitats.