Post-Release Behavior of Surf Scoters (Melanitta perspicillata) Following an Oil Spill: An Experimental Approach to Evaluating Rehabilitation Success

Effectiveness of rehabilitating wildlife following oil spills has been controversial. Impacts include mortality or changes in behavior affecting health or reproduction. Immediately following a bunker fuel oil spill on San Francisco Bay, California, USA, a unique experiment was conducted to examine the movement and foraging behavior of Surf Scoters (Melanitta perspicillata) that had been oiled, captured, cleaned, rehabilitated, and radio-marked. Unoiled Surf Scoters were similarly cleaned, rehabilitated, and radio-marked while other unoiled Surf Scoters were radio-marked as controls. Surf Scoters in the control group had larger home-ranges (46.29 ± 3.23 km2) than either the oiled/rehabilitated (32.58 ± 5.48 km2) or rehabilitated only groups (31.06 ± 3.05 km2); the control group also was more likely to use unsheltered, shallow areas of the bay (66.9 ± 4.3% of locations) than either the oiled/rehabilitated (50.3 ± 5.2%) or rehabilitated only groups (58.2 ± 6.5%). The oiled/rehabilitated group was closer to shore (986 ± 149 m) than rehabilitated (1,894 ± 295 m) or control groups (2,113 ± 227 m). Differences in habitat use, movement patterns, and home range sizes indicated that Surf Scoters held in captivity were more restricted in their movements; therefore, captivity and rehabilitation practices may also influence success of the rehabilitation.