Why woodcock commute: testing the foraging-benefit and predation-risk hypotheses

Moving between sites is a common behavior employed by prey in order to balance trade-offs associated with acquiring resources and avoiding predators. At dusk during summer, American woodcock frequently fly from diurnal coverts in forests to nocturnal roost fields. We tested 2 hypotheses, the foraging-benefit hypothesis and predation-risk hypothesis, to determine the benefit gained by woodcock that commute. We used telemetry to identify the diurnal coverts and nocturnal roost fields used by woodcock in Rhode Island, USA, during 2 summers. At each site, we measured the availability and diversity of woodcock prey, soil properties, and mammalian predator activity. Earthworms were 3–4 times more abundant at diurnal coverts than nocturnal roost fields. The richness and diversity of woodcock foods was greater at diurnal coverts during 2011 but similar between sites during 2012. Soil moisture content was about 1.5 times greater at diurnal coverts, whereas other soil properties were similar between sites. At night, mammalian predators visited diurnal coverts more frequently than nocturnal roost fields for 73% of the woodcock we monitored during 2011. During 2012, the number of days until initial predator visit was 1.8 times greater at nocturnal roost fields. Our results provide the first empirical support for the predation-risk hypothesis. During summer, woodcock fly from diurnal coverts to nocturnal roost fields to avoid predators and not to feed.