Foraging Behavior of Ospreys in Northwestern California
ABSTRACT
Fishing success of Ospreys (Pandion haliaetus) at South Humboldt Bay, California, was determined during spring and summer, 1972. Five hundred twenty-three of the 639 observed fishing efforts (82 percent) were successful. Fifty-six percent of the fishing efforts required only one dive. The mean length of time spent foraging for each successful fishing effort was 11.8 minutes. The highest fishing success occurred during the fledging period, and lowest during incubation, 86 and 79 percent, respectively. Successful fishing efforts were highest on the outgoing tide early in the breeding season. Fishing success on outgoing tides decreased as the season progressed, and increased (59 percent) on the incoming tide. Successful fishing efforts were the same (43 percent) on both incoming and outgoing tides during the brooding period.
