AGE-RELATED DIFFERENCES IN FORAGING ABILITY AMONG CLAM-DROPPING HERRING GULLS (LARDS ARGENTATUS)

Juvenile birds are generally less efficient foragers than adults, and this can lead to reduced survival or delayed reproduction. Feeding on hard-shelled nuts and mollusks after breaking them open by dropping is particularly challenging. To determine whether juvenile birds are as proficient as adults at this complex foraging task, we compared juvenile and adult Herring Gulls (Larus argentatus) feeding at low tide by dropping clams (Rangia cuneata) at a coastal estuary in Virginia, USA. Juvenile (first-winter) gulls were less successful than adult (2+ years old) birds at finding clams to drop. Moreover, the clams they selected were of a wider range of sizes, more often being difficult to handle or of lower nutritional value. Juveniles did, however, drop clams with the same degree of success as adult birds. Together these results suggest that teaming to find and recognize profitable clams is the developmental bottleneck in this complex behavior.