Endangered Island Foxes Stabilizing But Need to Monitor Continues

courtesy of Kevin Schafer

The annual meeting of the Island Fox Conservation Working Group took place yesterday, hosted by Friends of the Island Fox. 

The good news is that the four endangered populations of island foxes on San Miguel, Santa Rosa, Santa Cruz, and Santa Catalina Islands continue to recover and stabilize. 

Island foxes on the two Navy islands, San Clemente and San Nicolas, are not considered endangered by the U.S. Fish & Wildlife Service (USFWS) and their populations remain stable and at high densities (number of individual animals per square kilometer).

The graph below shows population numbers for San Miguel Island through fall 2013. The population was initially estimated in 1994. Actual individuals were counted when island foxes were in captive breeding pens on the island. Through 2007, the island foxes on San Miguel were gradually returned to the wild. Wild population figures are estimated through an annual catching of individuals and computer extrapolation of that data. More on Counting Island Foxes.

The graph shows how San Miguel's population dropped dramatically due to golden eagle predation at the turn of the century. Fifteen surviving individuals became the founders of the current San Miguel Island fox subspecies; captive breeding by the National Park Service saved this subspecies from extinction.

The population has made an amazing and rapid recovery to a level greater than historically estimated before the crisis. Statistical analysis through fall 2013 calculated that for the fifth year in a row,  individual island foxes on San Miguel have a 90% chance of surviving through the next year and the potential for species extinction is very low.  

Currently the density of island foxes on San Miguel is very high, 10-20 individuals per kilometer in some habitat areas. National Park biologist Tim Coonan believes the data shows the San Miguel Island fox population has fully recovered and has reached the "carrying capacity" for this small island. This means the food and territory resources available on San Miguel can not support continued population increase. The minor population ups and downs since 2010 follow the pattern of a population responding to resource availability. 

Conservation efforts on behalf of the San Miguel Island fox have been very successful. Across Santa Rosa, Santa Cruz and Santa Catalina the stories of population recovery from the brink of extinction are all inspiring.

However, there is an additional cautionary chapter in the San Miguel story. As the island foxes in the National Park have recovered, funding has decreased for their management. The staff that works with the foxes on San Miguel and Santa Rosa has gone from six to three technicians. 

Since the end of 2013 thru May of 2014, seventeen radio-collared island foxes on San Miguel have died from peritonitis caused by a parasitic spiny-headed worm (the exact species is still being determined). This parasite has not been a problem on the Channel Islands before and typically does not cause mortality in canines. The spiny-headed worm is transmitted to the fox through another animal-species host that the fox has eaten.

Today as the biologists, veterinarians, land managers and government officials meet for a second day, they are sharing expertise and ideas about how to respond to this potential threat to the San Miguel Island fox. Over the next few months they will be looking for answers to new questions:

• What prey species is carrying the parasite?
• Have island foxes on San Miguel changed to a prey species that is a vector for this parasite?
• Across San Miguel Island a higher number of island foxes are appearing underweight. Are these foxes infected with the parasite as well?
• Is drought a factor in this problem?
• Is high population density a factor?  
• Why is the number of these parasites so high in individual foxes?
• During the fall count, there appeared to be a very low number of pups on San Miguel. Is this a natural response to high population density and reduced resources? Is the parasite impacting female health and therefore reproduction?
• Is the parasite a possible threat to other Channel Island fox subspecies?

Channel Island foxes are rare creatures. Prior to the near extinctions of 2000, little was known about this endemic California species. If there is one thing that has become obvious over the years, it is that change to the island habitat, either directly by people or indirectly through environmental toxins, climate change, or introduced invasive species, island fox survival requires vigilance. 

The continuity of public support and scientific experts engaged in island fox conservation is vital to maintaining this unique species into the future. Funding the Island Fox Conservation Working Group meeting is an important part of island fox conservation.

Stay tuned for more information from the Working Group meeting.