Prey selection in relation to insect availability by the common poorwill (Phalaenoptilus nuttallii)

In the Okanagan Valley, British Columbia, the two major insect orders present in poorwill diet in 1989 were Coleoptera (47% by volume) and Lepidoptera (49%), which comprised only 15 and 3%, respectively, of the insects sampled using sticky traps. All coleopterans eaten were longer than 6.7mm (excluding the head) whereas 76% of the coleopterans caught on sticky traps were <6.7mm long. There was no evidence to support the prediction, based on optimal foraging theory, that poorwills would broaden their diet to include other insect taxa or size classes during 1990, when wet conditions likely depressed prey availability and foraging opportunities. There was no difference in the proportions of various taxa consumed or the size of coleopterans eaten between 1989 and 1990. The apparent prey selection by poorwills may result passively from the constraints imposed by detecting prey under conditions of low light. -from Authors