Nightjars may adjust breeding phenology to compensate for mismatches between moths and moonlight

Abstract

Phenology match–mismatch usually refers to the extent of an organism's ability to match reproduction with peaks in food availability, but when mismatch occurs, it may indicate a response to another selective pressure. We assess the value of matching reproductive timing to multiple selective pressures for a migratory lunarphilic aerial insectivore bird, the whip‐poor‐will (Antrostomus vociferus). We hypothesize that a whip‐poor‐will's response to shifts in local phenology may be constrained by long annual migrations and a foraging mode that is dependent on both benign weather and the availability of moonlight. To test this, we monitored daily nest survival and overall reproductive success relative to food availability and moon phase in the northern part of whip‐poor‐will's breeding range. We found that moth abundance, and potentially temperature and moonlight, may all have a positive influence on daily chick survival rates and that the lowest chick survival rates for the period between hatching and fledging occurred when hatch was mismatched with both moths and moonlight. However, rather than breeding too late for peak moth abundance, the average first brood hatch date actually preceded the peak moth abundance and occurred during a period with slightly higher available moonlight than the period of peak food abundance. As a result, a low individual survival rate was partially compensated for by initiating more nesting attempts. This suggests that nightjars were able to adjust their breeding phenology in such a way that the costs of mismatch with food supply were at least partially balanced by a longer breeding season.

Comprehensive estimation of spatial and temporal migratory connectivity across the annual cycle to direct conservation efforts

“…In North America, we found moderate (r M = 0.3-0.4) spatial connectivity north of the Gulf of Mexico during both migrations, which could affect breeding populations through threats like vehicle collisions in areas of high road density (Camacho 2013). We similarly found moderate fall and spring temporal connectivity in North America, suggesting population-specific breeding ground departure and arrival timing that could lead to differential population trends via threats like differential changes in aerial insect phenology (English et al 2018). Finally, we found a strong peak in spatial connectivity at 44°N during spring migration.…”

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

“…Nightjars typically hawk prey from below in steep flight while the prey is silhouetted against the bright sky (Alexander & Cresswell, 1990; Camacho, 2014; Evens et al., 2018; Jackson, 2003). As such, activity patterns, foraging ecology or flight behavior of moths (Merckx et al., 2012), or different attractions to light (Merckx & Slade, 2014) are probably influencing the interactions between nightjars and their prey (English et al., 2018).…”

Remote estimation of overwintering home ranges in an elusive, migratory nocturnal bird

“…One important caveat to our findings, however, is that while we assume the timing of our location points coincides with foraging activity, some locations may be nocturnal roost/resting locations. This may be especially of note on nights with little to no moonlight, which we did not account for, as this appears to drive foraging activity on the breeding grounds (English et al, ).…”

“…We expect that birds use the structural aspects of habitat as a cue for food resources (structural-cues hypothesis; Smith & Shugart, 1987). Whip-poor-wills during breeding appear to time their breeding phenology with flying insect abundance, which may also limit nest survival (English, Nocera, & Green, 2018); thus, exploring relationships between food resources and overwintering land cover are warranted.…”