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

Abstract

Predators that hunt by sight should be constrained by light levels. This problem should be especially acute in aerial predators such as common poorwills (Phalaenoptilus nuttallii: Caprimulgidae), which capture small insects at night. The purpose of our study was to test the hypothesis that poorwills are constrained to catching larger insect taxa due to limitations of visual orientation under low light. We assessed diet by analysing poorwill faecal samples collected at nest and roost sites in the Cypress Hills of Saskatchewan where prey density is relatively low. Coleopterans (44% and 39% in 1991 and 1992, respectively) and lepidopterans (46% and 55%) dominated the diet, yet these two insect orders were rare in light‐suction trap (22% lepidopterans and 1% coleopterans) and sticky trap samples (11% lepidopterans and 2% coleopterans). Based on measurements of femur length, all consumed coleopterans were > 5 mm long, even though 57% of those available were < 5 mm. Our results suggest that poorwills are constrained to taking prey above a certain size, but above this threshold, particular prey types and larger sizes may be selected. Selection for coleopterans may reflect the need to acquire polyunsaturated fat to facilitate the use of torpor.

DNA diet profiles with high‐resolution animal tracking data reveal levels of prey selection relative to habitat choice in a crepuscular insectivorous bird

“…Although it is widely recognized that Coleopterans are a common food item for nightjars, Lepidopterans are known to be more energy rich in comparison (Bayne & Brigham, 1995). The number of Coleopterans found in our study is low when compared F I G U R E 4 Preference plot for nightjars in Bosland and Thetford, comparing the observed interaction frequencies (dots) to the 95% confidence intervals from the null model (vertical dashed lines).…”

“…Although it is widely recognized that Coleopterans are a common food item for nightjars, Lepidopterans are known to be more energy rich in comparison (Bayne & Brigham, 1995). The number of Coleopterans found in our study is low when compared with traditional previous morphology‐based studies (38% (Cramp et al., 1985); 20% (Schlegel, 1967); 5%–18% (Sierro et al., 2001), but similar (2% of fecal pellets) to that found in Thetford Forest (Sharps et al., 2015).…”

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

“…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).…”

Notes on the Incubation, Brooding, and Provisioning Behavior of Chuck-will's-widows

“…Although we did not videotape Chuck-will's-widows at dawn, Sprunt (1954) noted that they forage most often at both dusk and dawn. Nightjars are visual predators, and their foraging behavior may be constrained by light levels (Mills 1986, Bayne andBrigham 1995). Furthermore, the greatest amount of insect biomass may be available at dusk and dawn (Jetz et al 2003).…”