From 1993 to 1999 the National Park Service monitored the population of Island Fox on San Miguel Island. Each summer, foxes were trapped and tagged. When each fox is first captured, it is implanted with a device about the size of a grain of rice called a passive integrated transponder tag, or "PIT" tag. The tag gives each fox a permanent, unique number that can be read with a special scanner and allows scientists to monitor individual foxes over the years.

The Warning

Park biologists estimated there to be over 400 foxes on San Miguel in 1994, but by 1995, an alarming decline had begun. With each passing year, fewer foxes were trapped in the monitoring grids. At the same time, rangers and visitors reported seeing fewer live foxes and more fox skeletons and carcasses. By 1998, the San Miguel population was down to a few dozen. Similar declines occurred simultaneously in the island fox populations on neighboring Santa Rosa and Santa Cruz Islands.

In fall 1998, National Park Service biologists initiated a radiotelemetry study of island foxes on San Miguel Island to determine causes of mortality. Of 15 radiocollared foxes tracked from 1998 to 1999, 5 were believed to be killed by golden eagles and 2 died of other causes. This confirmed the results of an earlier study on Santa Cruz Island where golden eagle predation was identified as the cause of death for 21 of 29 fox carcasses. This level of golden eagle predation is considered by scientists to be unnatural because golden eagles were never known from the Channel Island before the 1990's.