Welcome to the American Ornithological Society 2018 Annual Conference. We are pleased to have you join us at the lovely Hilton El Conquistador Resort in Tucson, AZ.
Migratory birds must time stopover with availability of local resources. Here we investigate the effect of resource mismatch during stopover for two long-distance migrant shorebirds that share similar nonbreeding, breeding, and migratory sites but differ in their foraging strategy. We predicted that a passive foraging strategy would make species more sensitive to effects of mismatch, while an active foraging strategy could help buffer against changing local conditions. We estimated arrival times, start of mass gain, and rate of mass gain for a passive forager, the red knot (Calidris canutus rufa), and an active forager, ruddy turnstone (Arenaria interpres) during spring stopover in Delaware Bay, USA. We estimated the effect of availability of horseshoe crab eggs—a key prey item—on annual variation in the timing and rate of mass gain over 20 years. Red knot experienced more annual variation in both the start day and rate of mass gain than ruddy turnstone. In cooler years, horseshoe crabs spawned later and red knot started to gain mass later. Delayed mass gain was associated with an increased rate of mass gain; birds were able to increase mass gain to avoid delayed departure from the stopover site. Ruddy turnstone experienced little annual variation in onset of mass gain and were not influenced by the availability of horseshoe crab eggs. An active, generalist foraging strategy may buffer ruddy turnstone against variation in local conditions during migration. If local cooling trends continue, phenological mismatch between bird arrival and horseshoe crab spawn could become more severe.
