Prey Selection by Common Nighthawks (Chordeiles minor) Across Seasons and Fire Management Regimes

Common Nighthawks (Chordeiles minor, hereafter nighthawks) belong to the aerial insectivore guild, which is rapidly declining in part because of changes in insect prey bases. To understand the ability of nighthawks to accommodate fluctuating prey communities, it is necessary to understand their degree of diet specialization, how specialization changes throughout the annual cycle, and the effects of land management practices on prey availability and nighthawk habitat use. We examined prey selection by breeding and non-breeding nighthawks by collecting fecal samples during two breeding seasons in Florida, USA, and two non-breeding seasons in Corrientes Province, Argentina. We used DNA metabarcoding to identify insect prey in nighthawk fecal samples, and we coupled fecal sampling with aerial insect sampling to assess prey selection. In Florida, we sampled birds and insects across an array of forest plots with different fire return intervals to assess how fire frequency and recency affect prey availability. We found that breeding nighthawks have less diverse diets and preferentially feed on fewer insect orders than they do in the non-breeding season, despite no difference in the diversity of available prey. This suggests that breeding nighthawks are more selective, and thus could be more vulnerable to changes in prey availability, than non-breeding nighthawks. On the breeding grounds, we found that frequent fire positively affects the abundances of nesting nighthawks, but only for the first year after burning. We also found that fire frequency and recency have variable effects on nighthawk prey, but prey abundance does not affect nesting or foraging nighthawk abundance. We demonstrate that effective conservation of nighthawks and other aerial insectivores requires measuring prey preference at multiple periods of the annual cycle, especially for migratory species, to allow for focused conservation at local scales. Moreover, our findings regarding the effects of fire on nesting and foraging nighthawks are in line with studies conducted in Alberta, Canada, suggesting that consistent management strategies may be used for this species throughout its breeding range.

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