- Simon Fraser University
- University of New Brunswick
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.
Whip-poor-will diet consists of approximately 60% moths and 40% beetles usually captured on short flights from perches often on, or near, the ground (Cink, Pyle, & Patten, 2017; Garlapow, 2007), and aside from twilight periods around dusk and dawn, foraging activity is dependent on the availability of moonlight (Mills, 1986).
Male whip-poor-wills arrive on their more northern breeding grounds in late April or early May, with females arriving on average more than a week later (English, Mills et al., 2017). Once established, pairs tend to be stable and occupy a general purpose territory for the duration of a breeding season (Cink et al., 2017). First clutches are laid in late May or early June (Peck & James, 1983) and almost always contain two relatively conspicuous eggs laid directly on leaf litter, generally under the shade of trees or tall shrubs (Akresh & King, 2016). The adult's cryptic plumage provides excellent camouflage; consequently, nightjars rarely leave their eggs unattended except for brief foraging periods at dusk and dawn (Troscianko, Wilson-Aggarwal, Stevens, & Spottiswoode, 2016). Males do not usually incubate, although they will visit the nest for brief periods (~5 min) at dusk and dawn (personal observation). Incubation lasts ~20 days (Akresh & King, 2016) and chicks begin perching and making short flights at roughly 16 days of age (Cink et al., 2017). Chicks can hop short distances when only a few days old and will often scatter in opposite directions when disturbed by a predator. This behavior, combined with aggressive distraction displays by the parent, often allows for partial survival of broods (personal observation).
We estimated variation in timing and success of whip-poor-wills breeding in the northern part of their range by finding and monitoring nests over three years. Our study site was Queen's University Biological Station (QUBS; 44.467–44.567°N, 76.333–76.417°W) in eastern Ontario, Canada. QUBS encompasses >3,200 ha of deciduous forest and abandoned farmland in various stages of succession. Both habitats are punctuated by numerous small wetlands, lakes, and ridges topped with small rock barrens. These frequent forest gaps, combined with generally sparse understory vegetation, provide ideal whip-poor-will foraging habitat (English, Nocera, Pond, & Green, 2017).