Roost site selection of dunlin (Calidris alpina) on Arcata Bay, Humboldt Bay, Humboldt County, California

I examined the relationship between nonbreeding dunlin (Calidris alpina) roost use on Arcata Bay and energy balance (proximity hypothesis), predation, and predation risk. Individuals used roosts that were closer to their last foraging locations than roosts that were known to them and roosts that were available to the population. These findings are similar to findings on temperate and tropical bays as well as those derived from models. Predation danger and predation avoidance, two complementary factors included in the predation risk analysis, influenced dunlin roost use at high tide. Individuals were likely to abandon their roost during the observation period if the initial flock size was high. Conversely, they did not return to the roost the following day if the number of attacks sustained at the roost was low and if the final flock size from the previous day was low. Individuals consistently selected roosts that had higher initial flock sizes as well as higher numbers of attacks, successful attacks, and predators present. These results suggest that individuals are making daily decisions regarding their roost use and basing those decisions on the need to minimize energy as well as reduce their predation risk.