Annual variation in the benefits of a nesting association between Red Phalaropes (Phalaropus fulicarius) and Sabine's Gulls (Xema sabini)

By nesting near aggressive birds, timid species can reap the benefits of aggressive nest defense while avoiding the costs. Red Phalaropes (Phalaropus fulicarius; hereafter "phalaropes") typically nest in grass-sedge marshes, but nests have also been noted in rocky coastal habitats. We studied the reproductive ecology of phalaropes at East Bay, Southampton Island, Nunavut, to determine whether their use of coastal nest areas reflected a protective nesting association with an aggressive larid, the Sabine's Gull (Xema sabini; hereafter "gull"). From 2000 to 2002, we found and monitored 29 phalarope nests with gull nests nearby (<= 150 m away) and 26 without gulls nearby. Coastal phalarope nests were nearer to gull nests than expected by chance. No habitat differences were detected between coastal areas with and without gull nests, but only three phalarope nests were found in coastal areas without gull nests. Thermistor probes inserted in phalarope nests revealed that incubators with gulls nearby behaved less cryptically, taking more frequent and longer incubation recesses. In human-approach experiments, phalaropes with gulls nearby flushed earlier than those without gulls. In 2000 and 2001, hatch success was 17-20% higher for phalaropes with gulls nearby, but these nests had lower success rates than those without nearby gulls in 2002. These gulls are able to defend their nests from avian predators only; in 2002, arctic foxes (Alopex lagopus) were abundant, and their primary prey, collared lemmings (Dicrostonyx torquatus), were scarce. We suggest that phalaropes select coastal areas near gulls, but that this association is beneficial to phalaropes only in years when egg predation by arctic foxes is low.