[CINC] The Island Foxes

[Barbara Hilburn]

In response to my email sent to Friends of the Island Fox, I received the following reply.  (The chart is the same as the one sent to all of us by Dave Begun.)


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Hi Barbara,

Unfortunately, our office is completely staffed by volunteers and the current status document is in the process of being updated.

I have attached a chart that shows the current official numbers of each of the islands. You will see that while the San Nicolas Island fox number is down from 2008 it is comparable to 2010 (see graph section). It is normal for population numbers to fluctuate. Some of the official numbers for San Nicolas and San Clemente are estimates as complete population surveys on the Navy islands are not always generated annually because these two subspecies are not endangered. The populations on these two islands are quite robust for the available natural resources. Some of the extreme fluctuations in the reported numbers for the Navy islands are an artifact of changes in computer programs that model populations. 

The increase seen in the San Clemente Island foxes is the result of greater population counting and study, rather than a physical doubling of the island fox population. Computer modeling of complete populations using a sample of captured animals is never foolproof and different computer programs result in different population projections. There was a change between 2008 and 2010 in how the total population was estimated on San Clemente.

The San Nicolas Island fox does face challenges from human habitation of the island: automobile traffic is the greatest cause of unnatural mortality on this island, rodenticide and toxic chemicals dumped on the island after WW2 impact some island foxes as well. Feral cats competed with island foxes for the limited prey on the island.  In a move to protect the island foxes, the Navy successfully removed ~50 feral cats in 2009/2010. (Healthy cats were relocated to a rescue facility in San Diego county.) Despite the active military training that occurs on San Nicolas Island, the island foxes are doing well there and the Navy biologists are devoted to seeing this population is protected.

Climate change may be impacting island foxes on San Nicolas Island more than on the northern islands. Low rainfall levels reduce both plant food and prey for the island fox. San Nicolas Island is the driest of the Channel Islands. There are no natural trees, only low scrub, dunes and dry rocky areas. It is natural for island foxes to produce fewer offspring in years of minimal precipitation and some drop in the population may be related to the last three years of average or lower than average rainfall. 

The San Nicolas Island fox population does appear to be less than it was in 2008, but it not considered to be declining. San Nicolas Island is very small and it has the greatest island fox density, more foxes per square kilometer than any other fox species anywhere else in the world. The population in 1994 and in 2008 was at an unsustainable highpoint. The official 2011 population of ~500 is closer to the average steady population number. Official numbers for 2012 will be available in June. 

I hope that I have answered your question. We appreciate your interest in the island fox and hope you will contact us if you have any further questions.

Keri Dearborn, Education Director
Friends of the Island Fox
A Program of the Channel Islands National Park