Oiled Wildlife Care Network

photo: Western gull with implanted antenna
Western gull with a radio transmitter. Research is providing important answers about post-release survival of oiled birds.

Post-Release Studies

How long do rehabilitated oiled animals survive after release, and do they return to normal biological function?

Several reports in the literature suggest that oiled and rehabilitated animals survive for only days, not months or years. Other reports show examples of birds surviving decades after being cared for during an oil spill event. Post-release survival is a critical knowledge gap in understanding the overall effects of oil in wildlife.

To address this issue, beginning in 1995, the OWCN has conducted specific studies on the post-release survival of rehabilitated oiled wildlife, and now strives, when possible, to conduct such projects on every spill in California. Post-release studies are collaborative efforts between the OWCN and appropriate experts, with funding coming from a reserve within the OWCN budget. This research is crucial not only to determine that treated animals survive and return to normal after release, but also that protocols are improved based upon the success of the animals in their natural environment.

Overview of Studies

To date, three post-release projects on oiled seabirds have been initiated by the OWCN: one following Western gulls after the Torch/Platform Irene spill off the central coast in 1997, one evaluating common murres after the 1999 Stuyvesant oil spill in northern California, and one tracking surf scoters affected during the Cosco Busan oil spill in San Francisco Bay in 2007. Each project used radiotelemetry devices attached to rehabilitated and control birds and followed animals after release. In each study, findings suggested that overall success (as determined by survival) was better than determined prior to the development of the OWCN and other spill response organizations around the world.

In addition to these intensive studies, all birds released after an oil spill are individually identified with a federal leg band. This enables others to report sightings of rehabilitated birds in the wild.

Results of Studies

  • A post-release study of birds following the Cosco Busan oil spill is in progress.
  • Golightly, RT, SH Newman, EN Craig, HR Carter and JAK Mazet. 2002. Survival and behavior of Western Gulls following exposure to oil and rehabilitation. Wildlife Society Bulletin 30(2): 539-546.
  • Newman, SH, RT Golightly, EN Craig, HR Carter and C Kreuder. 2004. The effects of petroleum exposure and rehabilitation on post-release survival, behavior and blood indices: A Common Murre (Uria aalge) case study following the Stuyvesant petroleum spill. Final Report. Oiled Wildlife Care Network, Wildlife Health Center, School of Veterinary Medicine, University of California, 1 Shields Ave, Davis CA  95616. 46 pp. Download here.