Species vs. Species

Shrike conservation threatened foxes on a California island

Because loggerhead shrikes on San Clemente Island are critically endangered, the foxes that prey on their nestlings should be controlled. Right? Wrong. The problem is that the foxes are also at-risk. A new analysis shows that instead of pitting the shrike against the fox, both species could have been protected with an ecosystem-wide conservation plan.

“This endangered species conflict might have been avoided through a more balanced ecosystem approach,” say Gary Roemer of New Mexico State University in Las Cruces and Robert Wayne of the University of California at Los Angeles in the October issue of Conservation Biology. Roemer is also the World Conservation Union (IUCN) island fox coordinator.

The San Clemente loggerhead shrike is one of the most endangered birds in the world, with about 50 in the wild in 2003. Until this year, the shrike’s federal recovery program included controlling all its predators – even the San Clemente island fox, which is listed as threatened in California. The fox has declined by about 60% in the last decade and was down to about 400 in the year 2000.

In 1999, foxes were killed to protect the shrike. After that, foxes in shrike nesting areas were inadvertently caught in traps set for feral cats or held in captivity during the breeding season. Either way, these foxes were not breeding and so were not bolstering the population. In 2000, more than a tenth of the foxes were held in captivity during the breeding season. In 2003, fox control efforts finally stopped.

Besides having hurt the foxes, the shrike recovery program does not do enough to help the birds. While the feral goats and pigs that degraded the island’s habitat have been eradicated, there has been little habitat restoration. Consequently, there are not enough shrubs, which provide foraging perches for the shrikes, and too many non-native grasses, which are taller and denser than native grasses and so presumably make it harder for the shrikes to hunt insects.

The shrike recovery program costs a lot – $2.3 million in 1999 – and Roemer and Wayne suggest a way to benefit both the birds and the foxes without spending any more. The answer is simple: shift the money that was spent on controlling the foxes to restoring the island’s habitat. “Such efforts may actually allow for species co-existence,” say the researchers.

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CONTACT:
Gary Roemer: 505-646-3394, groemer@nmsu.edu
Robert Wayne: 310-206-0334, rwayne@protos.lifesci.ucla.edu