Influence of localized artificial light on calling activity of Common Poorwill ( Phalaenoptilus nuttallii )

The presence of localized artificial light at night (or ALAN) drastically changes the landscape for organisms by providing areas of darkness and light within an area that was once only dark. This change can influence the behaviors of organisms in many ways. One such behavior is bird song. Many studies have examined how ALAN influences diurnal bird song, but few have examined its influence on nocturnal birds. We examined the influence of lunar illumination and localized artificial light on the calling behavior of the nocturnal Common Poorwill (Phalaenoptilus nuttallii; hereafter poorwills). To do so, we erected artificial light stations in poorwill territories and then conducted point count surveys at these stations to count poorwill calls with the lights turned on and off. We hypothesized that artificial light would have a similar effect to lunar illumination, and we would see an increase in calling when the lights were on. However, the results we obtained were mixed. We found there was no significant effect of artificial light on calling rate and, as expected, a strong positive effect of moonlight. Surprisingly, however, there was a negative effect of the interaction between moonlight and artificial light, with birds calling less when artificial light was on during nights with high lunar illumination. One possible reason for this result is increased visibility leading to increased predation risk under high levels of ambient illumination.