Foraging associations between Bonaparte’s Gulls ( Chroicocephalus philadelphia ) and Common Loons ( Gavia immer )

We quantified multispecies foraging associations (MSFAs) between Common Loons (Gavia immer) and migrating Bonaparte’s Gulls (Chroicocephalus philadelphia) during 25–27 March 2026 at Lake Jocassee, South Carolina, USA. From 10:00–16:00 h EST each day, two teams in separate boats searched different areas of the lake for MSFAs. When an association was detected, observers approached the group and quantified its composition, behavioral characteristics, and duration. We documented 10 MSFAs, involving a mean (±SE) of 13.4 ± 2.8 Common Loons and 26.4 ± 4.7 Bonaparte’s Gulls, with associations lasting 21.6 ± 2.5 min. During these foraging events, loons formed groups and dove synchronously, driving forage fish toward the surface, where Bonaparte’s Gulls captured prey by plunging into the water. In all 10 MSFAs, loons initiated the association and gulls subsequently joined the foraging group. The number of gulls was positively correlated with loon group size (r = 0.88). Although MSFAs are well documented in marine environments, they are less frequently reported from freshwater systems. Our observations document repeated multispecies foraging associations between pursuit-diving Common Loons and migrating Bonaparte’s Gulls in a freshwater environment.