Moonlight, but not cloud cover, predicts the vocal activity of Common Poorwills (<i>Phalaenoptilus nuttallii</i>)

Daily and seasonal variation in light levels as well as meteorological variables can influence vocal behavior in both diurnal and nocturnal avian species. The Common Poorwill ( Phalaenoptilus nuttallii (Audubon, 1844)) is a visually orienting insectivore most active at dusk and dawn as well as during moonlit nights. Cloud cover is known to limit the amount of perceivable lunar light and generally creates a darker environment similar to when moonlight is low or absent. We examined the effect of cloud cover on the calling behaviour of the Common Poorwill while controlling for moonlight to test the prediction that lower light levels would reduce vocal activity. We conducted 291 point count surveys during the 2014 breeding season in southern British Columbia, Canada, starting at the end of civil twilight under various cloud and moonlight conditions. As expected, moonlight was a significant predictor of mean calling rate, but we found that neither cloud cover alone nor the interaction between moonlight and cloud cover was significant. Future studies should examine calling rates near urban centers to gain insight into the impacts of light pollution on nocturnal behaviours.