Bird vocal activity is affected by endogenous and exogenous factors. Owl surveys are mainly based on the detection of nocturnal calls, and therefore, the impact of exogenous factors on owls’ vocal activity may have consequences in conservation planning and behavioural studies. However, our current knowledge about the impact of climatic factors and the moon phase on owl calling behaviour is very limited, especially in the Neotropics. We used autonomous recording units to evaluate the effect of air temperature, rainfall, relative air humidity, and percent of the moon illuminated on the vocal occurrence (active/inactive) of the Ferruginous pygmy-owl (Glaucidium brasilianum) over three consecutive moon cycles in the Brazilian Pantanal. Vocal activity was positively associated with the percent of the moon illuminated, with 75% of the nights on which the species was vocally active having a moon illumination percentage higher than 77%. The vocal activity of the species was negatively associated with the nocturnal air temperature, with more vocal activity observed on cooler nights. Relative air humidity and daily rainfall were not associated with the vocal activity of the Ferruginous pygmy-owl. Our study improves the knowledge about the impact of exogenous factors on the calling behaviour of Neotropical owls. We conclude that future surveys aiming to detect the Ferruginous pygmy-owl should be carried out on nights with a high percent of moon illumination (>75%) and nights with low average temperature (< 18 °C).

中文翻译：

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铁质侏儒猫头鹰 (Glaucidium brasilianum) 的声音活动与月相和夜间温度密切相关

鸟类发声活动受内源性和外源性因素的影响。猫头鹰调查主要基于夜间呼叫的检测，因此，外源因素对猫头鹰声音活动的影响可能会对保护计划和行为研究产生影响。然而，我们目前对气候因素和月相对猫头鹰叫声行为影响的了解非常有限，尤其是在新热带地区。我们使用自主记录单元来评估气温、降雨量、相对空气湿度和被照亮的月亮百分比对铁质侏儒猫头鹰 (Glaucidium brasilianum) 在连续三个月亮周期中的声音发生（活跃/不活跃）的影响巴西潘塔纳尔湿地。声音活动与被照亮的月亮的百分比呈正相关，有 75% 的夜晚声音活跃，月亮光照百分比高于 77%。该物种的声音活动与夜间气温呈负相关，在较冷的夜晚观察到更多的声音活动。相对空气湿度和每日降雨量与铁质侏儒猫头鹰的声音活动无关。我们的研究提高了关于外源因素对新热带猫头鹰呼叫行为影响的认识。我们得出的结论是，未来旨在检测铁质侏儒猫头鹰的调查应该在月亮照度高 (>75%) 的夜晚和平均温度低 (<18°C) 的夜晚进行。该物种的声音活动与夜间气温呈负相关，在较冷的夜晚观察到更多的声音活动。相对空气湿度和每日降雨量与铁质侏儒猫头鹰的声音活动无关。我们的研究提高了关于外源因素对新热带猫头鹰呼叫行为影响的认识。我们得出的结论是，未来旨在检测铁质侏儒猫头鹰的调查应该在月亮照度高 (>75%) 的夜晚和平均温度低 (<18°C) 的夜晚进行。该物种的声音活动与夜间气温呈负相关，在较冷的夜晚观察到更多的声音活动。相对空气湿度和每日降雨量与铁质侏儒猫头鹰的声音活动无关。我们的研究提高了关于外源因素对新热带猫头鹰呼叫行为影响的认识。我们得出的结论是，未来旨在检测铁质侏儒猫头鹰的调查应该在月亮照度高 (>75%) 的夜晚和平均温度低 (<18°C) 的夜晚进行。我们的研究提高了有关外源因素对新热带猫头鹰呼叫行为影响的认识。我们得出的结论是，未来旨在检测铁质侏儒猫头鹰的调查应该在月亮照度高 (>75%) 的夜晚和平均温度低 (<18°C) 的夜晚进行。我们的研究提高了关于外源因素对新热带猫头鹰呼叫行为影响的认识。我们得出的结论是，未来旨在检测铁质侏儒猫头鹰的调查应该在月亮照度高 (>75%) 的夜晚和平均温度低 (<18°C) 的夜晚进行。