Three subspecies of island fox that nearly became extinct in California two decades ago have recovered so fully that federal officials today announced their removal from protection under the Endangered Species Act, providing a powerful success story for legislation many detractors call flawed.

The foxes had fallen from about 4,000 on three of the Channel Islands—Santa Cruz, Santa Rosa and San Miguel—in 1994 to fewer than 100 by 1999, due in part to a proliferation of nonnative feral pigs that attracted legions of predatory...