DAVIS, Calif. -- Despite heroic rescue efforts by people in the wake of oil spills, few birds cleaned and released back into the wild survive more than one or two years, according to a new report published by researchers at the University of California, Davis.
The new results support a growing body of evidence indicating that rehabilitation techniques have not been effective in returning healthy birds to the wild, says Dan Anderson, a UC Davis professor of wildlife, fish and conservation biology and co-author of the paper.
The findings may lead to improved techniques for removing oil from birds and for handling and rehabilitating them. The work also may stimulate the development of better strategies for releasing rehabilitated birds back into the wild. Another possible outcome is rethinking the worthiness and cost-effectiveness of wildlife spill cleanups or redirecting resources to protection or population restoration.
"Is there life after oil spills?" asks Dan Anderson. "We're saying it's not working too well the way it's been done."
The study is published Oct. 25 in the international journal Marine Pollution Bulletin by Anderson, researcher Franklin Gress and avian sciences researcher Michael Fry.
Using a combination of radio signals and special color markings, Anderson and his colleagues tracked 112 California brown pelicans that were cared for and released after oil spills in 1990 and 1991 off the coast of Southern California.
Two years after the 1990 spill, only 8 of the 91 (9 percent) rehabilitated pelicans could still be accounted for on the California coast compared to 10 of the 19 (53 percent) unexposed pelicans in the control group. The researchers found similar results for the fewer pelicans exposed to the 1991 spill. Tracking of all the birds ended in 1992.
The researchers could not determine the fate of every pelican, but extensive searches for the birds and known deaths and survival data on a known sample of losses make investigators confident in their conclusion that rehabilitated birds had a lower survival rate, they report.
In the two years following rehabilitation, only one bird among all the oil-exposed brown pelicans showed any activity in breeding colonies, and that bird only lingered a few days there. This surprised researchers, who predicted normal breeding behavior based on normal body weights and restored plumage upon release and hints of normal mating behavior in captivity before release. Wild control pelicans showed normal breeding activities in both years.
"Oil causes more problems than we ever imagined," Anderson says.
Other studies, including some conducted by Fry, show that ingested petroleum products cause a number of physiological disruptions in birds and mammals, including anemia, immunosuppression, additional stress-related phenomena such as endocrine dysfunction, reductions in nutritional status, and internal lesions. The UC Davis study was not designed to separate the toxic effects of oil from the stress effects of handling the birds, which could also contribute to a lower survival rate.
Anderson's study corroborates a paper published this spring in the international bird research journal Ibis by Oregon ornithologist Brian Sharp. He reported an average life expectancy of 9.6 days for rehabilitated common murres.
Earlier studies report that, for the first year or two after exposure, oil-dosed birds suffer reduced breeding success for one or two years, lower adult attentiveness to or even abandoning the nest, and a higher death rate.
Anderson isn't ready yet to throw in the towel on individual bird cleanup efforts. "We need as many tools as possible to restore individuals and populations after oil spills," he says.
Since the pelican study, Anderson and his UC Davis coworkers have duplicated their results working with coots under more controlled conditions. Work is continuing that will attempt to identify the mechanisms that cause bird impairments observed in the field studies.
"Cleanup efforts are demanded by the public; people will not just leave animals out there to die," says veterinarian Dr. Jonna Mazet, UC Davis-based director of the statewide Oiled Wildlife Care Network, a legislated program funded by state Fish and Game. "We want to protect and care for wildlife in the most professional manner possible. Advances in rehabilitation have been made since 1991. Research like this is giving us insight into what we can do to improve our efforts."
Anderson's study was funded by the U.S. Dept. of the Interior, Minerals Management Service, and the California Dept. of Fish and Game, Office of Oil Spill Prevention and Response.