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 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 favored 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 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.

**研究目标**：本研究的具体目标为：(1) 在纳入调查特异性协变量（covariate）的前提下，估算各物种的检测概率（detection probability）；(2) 探究生境特异性协变量对鸮形目（owl）与夜鹰类（nightjar）种群丰度的影响，并整合不完全检测（imperfect detection）效应。
**研究创新**：本研究设计了一套标准化调查方案，用于估算西班牙北部巴斯克地区大范围尺度下鸮形目与夜鹰类的检测概率及种群丰度。
**主要结论**：研究结果显示，物种的检测概率显著受鸣声回放（playback broadcast）与观察者经验的影响；调查日期会依据物种的繁殖周期对其检测概率产生不规则影响，同时研究还发现鸟类的鸣唱活跃度会随日落后时长的增加呈比例逐渐降低。灰林鸮（Tawny owl, *Strix aluco*）是种群丰度最高、分布最广泛的物种，其丰度与森林生境（主要为针叶用材林）呈正相关，而在大型城市与农业区域中丰度会降低。开阔生境物种的种群丰度相对较低。仓鸮（Barn owl, *Tyto alba*）、纵纹腹小鸮（little owl, *Athene noctua*）、欧亚红角鸮（Eurasian scops owl, *Otus scops*）与长耳鸮（long-eared owl, *Asio otus*）均回避森林生境，但对农业、草地、灌丛与城市生境表现出各异的响应模式。最后，欧洲夜鹰（European nightjar, *Caprimulgus europaeus*）的出现频率中等，其种群丰度受灌丛生境的正向促进，受桉树斑块的影响较弱，而大型森林区域则会对其丰度产生负向影响。本研究证实，在方法学设计与分析流程中纳入调查特异性协变量的影响是至关重要的。研究结果同时表明，随着城市化进程加快、用材林种植面积扩张以及自然生境简化，夜行性鸟类群落已出现生态适应性调整与种群数量变化。