California condors are one of those valuable species that clean up after the rest of us, eating flesh and even bone from carrion. Since their near-extinction 30 years ago, owing largely to lead poisoning from bullet fragments in the meat they consume, the population has been slowly rehabilitated. During the 1980s, the 22 condors remaining in the wild were relocated to zoos in a last attempt to increase their numbers. Efforts to reintroduce the condors to their natural habitat began in California in 1992 and in Arizona in 1996. To date, the population has risen to a total of 285 birds, including 69 birds in the wild in California, and condor pairs have started to produce nestlings. But a new problem, discovered by a team of scientists led by ornithologist Allan Mee, may threaten the condors' fragile reestablishment.
During a postdoctoral fellowship with the San Diego Zoo's Millennium Field Program in Conservation Science, Mee studied breeding attempts in the reintroduced condor population in the Los Padres National Forest in Southern California. The research, published in June in Bird Conservation International, finds that condors are bringing unprecedented amounts of human trash to their nestlings. "We had no idea that junk ingestion would be a problem," Mee says. But condor chicks are dying as a result.
Adult condors seem to be able to regurgitate most trash that they ingest. Not so for nestlings. The junk they eat lodges in their crops and gizzards, severely impairing the absorption of nutrients and, in some cases, causing life-threatening metal toxicity. Two of the nine Los Padres chicks that hatched between 2001 and 2005 died as a direct result of junk ingestion, and several others died of junk-related complications.
Everything from metal springs and glass fragments to bits of electrical wiring and cloth has been found in the crops and gizzards of the deceased chicks, as well as in condor nests. The body of one nestling contained a veritable trash pile: 30 metal items, 54 glass, 28 pieces of plastic and 2 miscellaneous items—a total of 200.5 grams of junk. Another contained 193.5 grams, and several others held 60 grams or more.
Although scientists noted anthropogenic junk at condor nests as early as 1922, it has not been shown to be a serious problem before now. Why should reintroduced condors have a greater propensity for bringing home junk? The answer, as one might expect, is complex. To reduce the risk of lead poisoning from bullet-killed carcasses, wildlife managers feed condors every three days at designated feeding sites. The Southern California site is located just two miles from the nearest condor nest.
"It's kind of created an outdoor zoo syndrome," says Mee. "The birds are waiting for the next handout. They have a lot of time on their hands" (wings, that is). As the Los Padres relocation site is located almost within sight of Los Angeles, directly adjacent to an oil field, there's plenty of junk around to catch a condor's eye. And not only are the bored birds picking up more trash, they are feeding their nestlings less often than did condors in the 1980s.
The reintroduced population in Arizona has had much less trouble with trash. "Most nests located in the Grand Canyon are far from provisioned feeding sites—up to 50 miles, as the condor flies," Mee notes. Greater travel time to the provisioned site means the birds have little time to spend picking up junk. Furthermore, there's simply less of it to find than in Southern California. "To get trash in Arizona, condors have to search for it," he says.
Condors in Arizona also have better and more diverse wild food sources, including elk and bighorn sheep. Though this makes the population more susceptible to poisoning from lead bullets, the overall effect is positive: Reintroduced condors in Arizona can relearn natural foraging patterns, while their California cousins don't seem to be catching on.
Christine Kreuder Johnson, an assistant professor at the University of California, Davis, Wildlife Health Center, has studied the effects of lead ingestion on condors and believes the new findings are significant. "This brings to light a serious challenge facing the reintroduced Southern California condor population," she says. "The quantity and variety of junk fed to the nestlings in this report is unusual for a free-ranging species. The toxicity potential for many of these items is of particular concern."
Mee sees two essential approaches to the problem: "manipulating the population" by bringing nestlings in for surgery and by physically removing trash from nests, and long-term, holistic efforts to ensure that condor populations can be self-sufficient. For the longer term, lead poisoning remains a crucial issue. If lead bullets could be phased out of the condor ranges in favor of copper bullets, Mee says, provisioned feedings could be reduced, encouraging the birds to relearn the foraging habits of their wild-raised ancestors. Johnson agrees: "It seems unlikely that this reintroduced population will develop normal foraging behavior as long as the birds are heavily dependent on supplemental feeding to avoid lead exposure."
A volunteer program of the Arizona Game and Fish Department that provided hunters with non-lead rifle ammunition resulted in a 40 percent drop in condor lead-exposure rates in 2005; the department is optimistic about recruiting even more participants in future years. A bill that would ban the use of lead bullets in condor habitats is currently working its way through the California State Senate. The legislation was passed by the California State Assembly in May, and supporters are hopeful that it will be approved by the State Senate as well.
In the meantime, conservation scientists are trying some other innovative methods. Mee worries that even if condors are able to feed on wild animal carcasses, they may have formed a search image for human trash. Michael Mace, curator of birds at the San Diego Wild Animal Park, has been working with one pair of repeat offenders. After the pair's chicks died three years in a row, U.S. Fish and Wildlife Service biologists brought the birds to the Wild Animal Park. The condors were exposed to junk that was wired to deliver mild electric shocks; they soon learned not to pick it up. The pair reared a chick successfully in captivity and were re-released this year; Mace and others are waiting to see whether the aversion training will have a lasting effect. But until condors can be reliably divested of their junk-eating habits, retraining junk-tossing humans may be the best bet for the California condor's survival.—Anna Lena Phillips
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