Perhaps few people would argue that a vanishing population of unique native foxes should be protected at all costs from non-native predators. But what if the predators were golden eagles?

That is the dilemma outlined in the Nov. 28 issue of the journal Science by a UC Davis conservation biologist and two colleagues. "This exemplifies how solving conservation problems is often more complex than redressing its primary cause," writes Rosie Woodroffe with co-authors Franck Courchamp of the University Paris-Sud and Gary Roemer of New Mexico State University.

In this case, the species at risk is the island fox (Urocyon littoralis), a candidate for listing under the U.S. Endangered Species Act. The fox evolved in isolation in California's Channel Islands, which lie roughly 25 miles off the state's southern coast. Ten years ago, golden eagles (Aquila chrysaetos) from the mainland began breeding in the islands. Golden eagles are not considered endangered or threatened but are protected by federal laws.

Although the eagles preyed mainly on feral pigs, they also killed many island foxes. Soon the fox subspecies on San Miguel and Santa Rosa islands became extinct in the wild, with the last few animals taken into captivity. On Santa Cruz Island, 1,500 foxes were reduced to just 65.

Deeply concerned, wildlife managers opted to remove both the eagles and the feral pigs, which damage native plants. All but a few wily eagles have been relocated; pig hunting was to begin soon. Then Woodroffe and her colleagues analyzed the fox preservation plan with a mathematical model; the Science article tells their conclusion: "Eagle predation on foxes increases as pig availability declines."

In that case, if the Santa Cruz Island foxes are to be saved, they conclude, both the pigs and the remaining eagles must be removed -- "by any and all means." For eagles that evade traps, that could mean shooting.

Woodroffe is familiar with conservation issues that are emotionally, politically and legally challenging: She is a member of a scientific committee that earlier this month said the controversial practice of killing wild badgers in England to prevent tuberculosis in cattle may cause more disease, not less.