The Effect of Food Supplementation on the Territorial Behaviour of a Nocturnal Bird: The Common Poorwill (Phalaenoptilus Nuttallii)

Abstract

When animals have more energy available to them, they should be able to spend more time on other activities such as territory defense because they are able to spend less time searching for food. Most studies examining this relationship have been on diurnal organisms where the time available for these activities is quite long. In contrast, the focus of my study is on a visual-hunting nocturnal species where the time available each day is much shorter because of the constraints imposed by reductions in ambient light. I examined the influence of food availability on the territorial behaviour of the insectivorous Common Poorwill (Phalaenoptilus nuttallii; hereafter poorwills). To do this, I erected artificial lights to attract and concentrate insect prey and therefore increase the ease of foraging. I then conducted point count surveys at stations with and without concentrated prey sources and assessed the vocal territorial behaviour of poorwills at these stations. The aim of my project was to determine whether increased prey availability would lead to increased territorial behaviour and to determine the influence of predation risk on this relationship. I hypothesised that increased prey availability would lead to increased territory defense, leading to the expectation of more calls detected at stations where the prey was concentrated. In addition, I expected to find a decrease in territorial behaviour when I detected the presence of predators. My results were mixed, with no influence of the concentrated food source alone on calling activity. However the visibility of moonlight was highly influential, with increased calling activity on nights when the moon was visible. In addition, there was a negative influence of the interaction between moonlight and food supplementation on calling behaviour—meaning that when the moon was visible and the light on, the birds called less. There was no influence of predator presence on calling activity, most likely due to the low predator density at my field site. From these results I conclude that poorwills exhibit more territorial behaviour on moonlit nights however I did not see any effects of the artificial lights .