Environmental correlates of Freckled Nightjar ( Caprimulgus tristigma ) activity in a seasonal, subtropical habitat

We examined environmental correlates of activity in the Freckled Nightjar (Caprimulgus tristigma), a nocturnal aerial insectivore that is resident year-round in the colder and drier parts of southern Africa. Specifically, we tested the prediction that air temperature (T _a), in addition to light availability, is a significant correlate of Freckled Nightjar activity. We found that aerial insect density varied by over three orders of magnitude (from <1.0 to 117.1 insects 1,000 m⁻³) during the course of the study, and was strongly and positively related to T _a. Nightjar activity was also significantly temperature-dependent, with a cessation of activity at T _a < 12°C. Consistent with previous studies, we found that activity levels were strongly related to ambient light, with markedly reduced activity levels on dark nights. The average number of Freckled Nightjars encountered per 14.6-km transect was 1.95 ± 2.44 nightjars transect⁻¹ during nights near full moon, but only 0.17 ± 0.61 nightjars transect⁻¹ around new moon. Our study reveals that caprimulgid activity can be significantly influenced by temperature as well as ambient light.