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Human disturbance was indirectly responsible for lowered nesting success. Observations from a blind showed that after an investigator left an island, herring gulls (Larus argentatus) and great black-backed gulls (Larus marinus) returned much sooner than common eiders (Somateria mollissima). Before common eiders returned, nests were highly vulnerable to predation by gulls. When the island was revisited one or more times on the same day, after setting nets or banding common eiders, many newly destroyed nests were evident. Gulls were seen flying back to the island as soon as workers left, and they no doubt destroyed many nests before the common eiders returned. Human disturbance did not appear to directly cause much nest desertion. A few clutches apparently were lost because of overexposure to heat when nests were checked on hot, sunny days. Overheating occurred when many common eiders were flushed from their nests for 2 hours or more. Goose Island, with more than twice as many visits, had 27% nest success--about two-thirds that for East Goose Rock (40%); the difference significant (P < 0.01).