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

Abstract

We determined the diet of common poorwills (Phalaenoptilus nuttallii) by analysing fecal samples collected from roost and nest sites in the Okanagan Valley of British Columbia. The two major insect orders present in the 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 in 1989. Based on the femur length of coleopterans consumed, all coleopterans eaten were longer than 6.7 mm (excluding the head), whereas 76% of the coleopterans caught on sticky traps were less than 6.7 mm long. We found 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. Acknowledging the bias of our insect sampling regime, we conclude that the apparent prey selection by poorwills results passively from the constraints imposed by detecting prey under conditions of low light.

Feeding ecology of the bat Eptesicus fuscus: ‘preferred’ prey abundance as one factor influencing prey selection and diet breadth

“…Twenty-two beetles ranging in body length from 2.4 to 28.1 mm were taken from light traps and used to develop the regression function for the relationship between claw Claw length described a significant amount of the variation in body length (r 2 = 0.74, F 1,21 = 56.80, P < 0.05), a result comparable to previous studies (e.g. Aldridge & Rautenbach, 1987; r 2 = 0.75; see also Csada, Brigham & Pittendrigh, 1992). Eighty-five beetle claws were extracted from the guano samples collected between 28 April and 30 June to determine the size of beetles eaten during the prematernity and maternity periods (Fig.…”

“…Aldridge & Rautenbach, 1987; r 2 = 0.75; see also Csada, Brigham & Pittendrigh, 1992). Eighty-five beetle claws were extracted from the guano samples collected between 28 April and 30 June to determine the size of beetles eaten during the prematernity and maternity periods (Fig.…”

“…Thus specializing on beetles in spring could be advantageous for pregnant females that frequently use torpor (Grinevitch et al, 1995). It is noteworthy that two nocturnal aerial insectivorous birds, C. minor and the common poorwill Phalaenoptilus nuttallii, commonly prey on beetles despite apparently low beetle abundance (Brigham, 1990;Csada et al, 1992;Bayne & Brigham, 1995;Todd, Poulin & Brigham, 1998). Although C. minor seems to use torpor rarely (Firman, Brigham & Barclay, 1993), P. nuttallii uses torpor frequently in spring (Brigham, 1992).…”

Prey selection and foraging constraints in common poorwills (Phalaenoptilus nuttallii: Aves: Caprimulgidae)

“…This makes for a natural comparison of prey selection by this species at the two locations. Csada, Brigham & Pittendrigh (1992) found that poorwills in the Okanagan selected lepidopterans (moths) and coleopterans (beetles) from the insects available. Further, poorwills only ate the largest beetles, suggesting that the birds preferred them.…”

Reproduction constrains the use of daily torpor by free‐ranging common poorwills (Phalaenoptilus nuttallii) (Aves: Caprimulgidae)

“…Only moths, beetles and flies were considered in the analysis since these groups constitute > 95% of the diet (Csada, Brigham & Pittendrigh, 1992;Bayne & Brigham, 1994).…”