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

Philina A English,David J Green,Joseph J Nocera

doi:10.1002/ece3.4077

Philina A English, David J Green + Show 1 more

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https://doi.org/10.1002/ece3.4077

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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.

Highlights

Studies of reproductive phenology in seasonal environments often focus on an organism’s ability to track food availability (Beaugrand, Brander, Alistair Lindley, Souissi, & Reid, 2003; Malick, Cox, Mueter, & Peterman, 2015; Pearce-Higgins, Yalden, & Whittingham, 2005; Visser, van Noordwijk, Tinbergen, & Lessells, 1998)
We predict that whip- poor-wills will suffer fitness costs if they cannot track both food and lunar cycle, but that an inability to track food availability will have greater fitness consequences than an inability to track the lunar cycle
We modeled daily survival rates (Dinsmore, White, & Knopf, 2002) using the Program MARK version 8.0 (White & Burnham, 1999) and calculated the cumulative expected survival, separately for a 20-day incubation period and a 15-day prefledging period over the 3 years of our study

Summary

| INTRODUCTION

Studies of reproductive phenology in seasonal environments often focus on an organism’s ability to track food availability (Beaugrand, Brander, Alistair Lindley, Souissi, & Reid, 2003; Malick, Cox, Mueter, & Peterman, 2015; Pearce-Higgins, Yalden, & Whittingham, 2005; Visser, van Noordwijk, Tinbergen, & Lessells, 1998). The strength of selection for a match between demand and availability will depend on the relative magnitude and duration of a seasonal peak in resource abundance (Durant et al, 2005; Vatka, Rytkönen, & Orell, 2014), but the outcome can be constrained by a species’. Despite the synchronization between timing of reproduction and the availability of moonlight being expected to maximize fitness (Figure 1a,b), nightjars do not always time their reproduction to match the lunar cycle (Brigham & Barclay, 1992) This mismatch between reproductive phenology and moonlight could arise when other resources, like prey abundance (Figure 1c), or temporal constraints (Figure 1d) are more important. We use estimates of daily nest (egg or chick) survival and annual productivity to assess the fitness consequences of matching reproduction to availability of both food and moonlight for a population of whip-poor-wills. We predict that whip- poor-wills will suffer fitness costs (lower daily nest survival and per pair productivity) if they cannot track both food and lunar cycle, but that an inability to track food availability will have greater fitness consequences than an inability to track the lunar cycle

| MATERIAL AND METHODS

Findings

| DISCUSSION