Four endangered subspecies of fox on the northern Channel Islands off the California coast have recovered so well over the past 11 years that the Fish and Wildlife Service is announcing Wednesday that it is starting to consider taking them off the endangered list.

Study and discussion of their status will take about a year, but if the agency does decide to delist the foxes, the decision will signify the fastest recovery ever of a mammal under the endangered species act, said Robert D. McMorran, the lead biologist in the Ventura office of the service.

“It has been a fantastic success,” said Christina Boser, a California islands ecologist with the Nature Conservancy, which owns most of one of the islands and is participating in the announcement with the agency and the Catalina Island Conservancy and the National Park Service.

All of the groups own or run parts of the four islands where the foxes went into a catastrophic decline, and all joined in the recovery planning and work.