Breeding biology of chuck-will's-widows: Incubation, brooding, and provisioning behavior and characteristics of nest sites.

摘要

Chuck-will's-widows (Antrostomus carolinensis) are cryptically colored grounding-nesting nightars that breed throughout much of the eastern United States, primarily in mixed-forest habitat. Because of their cryptic plumage and nocturnal habits, little is known about their behavior, particularly their breeding and nesting behavior. Thus, my objectives were to: (1) quantify patterns of incubation behavior (e.g., on bouts vs. off bouts) and the respective roles of males and females, (2) quantify the brooding and provisioning behavior of males and females, and, (3) compare the characteristics of nest sites and randomly selected unused sites to determine those features important in nest site selection.;My study was conducted at the Richard and Lucile Durrell Edge of Appalachia Preserve in Adams County, Ohio. During the breeding seasons of 2011 and 2012, I located six Chuck-will's-widow nests. All clutches consisted of two eggs laid on either leaf litter (N = 4) or bare ground (N = 2). Females were observed incubating more often (N = 12 observations at four nests) than males (N = 3 observations at two nests). Additionally, during 16 visits to five nests, females were flushed from nests more often (N = 14, or 87.5% of visits) than males (N = 2). Overall, the mean duration of incubation on-bouts was 442.1 min (N = 94). Incubation bouts of females were longer (mean = 274.5 min, N = 12 at four nests) than those of males (mean = 7.7 min, N = 3 at two nests). Females incubated eggs both during the day and at night whereas males were only observed incubating eggs at dusk.;Most incubation off-bouts occurred at dawn (N = 45 at six nests) and dusk (N = 48 at six nests) and averaged 35.0 min in duration (N = 104). Nightjars are visually oriented crepuscular and nocturnal insectivores so eggs are likely left unattended at dusk and dawn so adults can forage. Off-bouts were shorter in duration during the middle (days 10 -- 15) and late (days 16-21) stages of incubation than early in incubation (days 4 -- 9). Changes in nest attentiveness may be related to the increased reproductive value of eggs as the incubation period progresses. Both males and females provisioned young, with eight observed visits by males and three by females. At dusk, feeding rates were highest (P = 0.0026) during the hour immediately after sunset and declined thereafter. Chuck-will's-widows may actively forage during the period after sunset because prey availability is higher and light levels are sufficient for effective foraging.;Most characteristics of nest sites and randomly selected unused sites were similar, but nest sites had less canopy cover (mean = 70.8%) than unused sites (mean = 92.4%). Nest sites in areas with less canopy cover may have increased light levels and thus may provide better foraging habitat for Chuck-will's-widows. In addition, a more open canopy may make it easier for adults flying to and from nest sites. Chuck-will's-widows have high aspect ratio wings and so may prefer more open canopies above nest sites to make it easier to visit and leave nests under low light conditions.