Tuesday, June 01, 2021

2021 Island Fox Status Update

All island fox populations are healthy and stable, but biosecurity and the potential of deepening drought raises concerns.

That is the update from the Island Fox Conservation Working Group meeting held May 18, 2021, which reports on the status of island foxes across the islands. The following information is taken from FIF notes taken at the meeting. Population numbers reported here are official estimates from each land manager as calculated from the 2020 counting period. (How are island foxes counted)

Overview: COVID-19 restrictions impacted human travel to the islands, but all islands were able to implement protocols to keep biologists and island foxes safe. Annual counting was delayed on some islands and research was halted temporarily, but all efforts were able to resume.

Following a year of normal rainfall in 2019, 2020's lower rainfall levels resulted in island fox populations on San Miguel, Santa Cruz, and Santa Catalina Islands adjusting downward within expected normal levels. Reduced resources, resulted in fewer pups being born, but adult survivorship remained high and the estimated number of foxes per square kilometer, or fox density, remained high (Miguel 7.4 foxes per km squared, Cruz 9.4, and Catalina 9.3). 

The major threats to island foxes in 2021 are:

  • biosecurity: the threat of introduced viruses, disease, or nonnative animal species
  • climate change impacts: increasing regional temperatures, decreasing rainfall, and prolonged drought, which reduces food resources, increases wildfire threats, and promotes parasites
  • parasites: ticks, fleas, tick-borne diseases and intestinal parasites on some islands

How is Friends of the Island Fox helping Island Foxes? -video update

Greatest Concern

Santa Catalina Island foxes continue to maintain a stable population and fox density is high. However, an outbreak of canine distemper virus is currently impacting wild raccoons on the adjacent mainland. In 2020, a raccoon roamed Catalina's interior for several weeks until it was caught. The Catalina Island Conservancy reminded everyone that if distemper arrives on the island again, the high fox density could facilitate the rapid transmission of this fatal virus. FIF is currently raising funding to support the vaccination of 300–350 island foxes on Catalina Island. This is vital to protecting a core population and reducing opportunities for the virus to spread.

 FIF help support testing for disease antibodies in island foxes in 2020. This effort revealed an increasing prevalence of Adenovirus and Coronavirus on Catalina, fortunately neither virus appears to be causing mortalities. The increase, however, reminded everyone of how canine distemper virus would also spread if foxes were not vaccinated.

Tick below island fox eye
Though no tick-borne disease has yet been found among Catalina Island foxes, 48% have evidence of ticks and fleas. Studying tick-borne illness continues to be important for foxes and people. 

Interactions with people are greatest on Catalina and 75% of island fox deaths on this island were related to people–car strikes, attacks by pet dogs, etc. If drought conditions persist, parasites are expected to increase and foxes may be more attracted to human-inhabited areas.


San Miguel Island foxes have returned to stability, but they are a naturally small population. Renewed drought could cause declines as it did from 2015–2018. Research continues to search for the vector species that is being consumed by island foxes and leads to fatalities from an intestinal parasite. Channel Islands National Park continues to watch this population closely. (In the graph below the Green line shows even years, the population estimate in 2019 was 453.)


The two other smaller islands San Nicolas and San Clemente remain stable. In fact, San Clemente experienced a localized rain event that occurred at the perfect time in spring 2020. Plant life and deermice thrived and the island fox population boomed (see Blue line in graph below). Human impacts–car strike, entrapment in man-made structures, toxic waste, and improperly deployed rodenticide remain the greatest threat to these island foxes.

Santa Cruz Island foxes remain close to carrying capacity for their habitat and naturally adjusted downward in a lower rain year. Adult foxes had a 93.1% probablity of surviving in 2020. Study of tick-borne disease continues. Biosecurity is a concern for this second most visited island. The Nature Conservancy is analyzing boater activity around the island and determining the most critical areas to deploy biosecurity cameras to watch for nonnative species making their way onto the island. This may be important technology looking forward.


Santa Rosa Island foxes
are believed to have increased in 2020 and have yet to reach a carrying capacity plateau. (Pink line in graph above.) The estimated population now exceeds all other islands and the density is estimated at 11.3 foxes per km squared. The high number of foxes on this island may increase survival challenges for island foxes as drought impacts heighten. Another thought is that prior range-size data may no longer accurately represent this island. The last time data on range size was studied on Santa Rosa was 2009–10, when fox density was much lower. Friends of the Island Fox would like to support a GPS/telemetry collar investigation of island fox range size on Santa Rosa Island to update the understanding of range size in a dense population. This data is vital to accurate population estimates and understanding of how disease might move through this population.

*Note graphs show population estimates from even years. Population graphs with data from all years show greater fluctuation. 2019 was a record high population year for Santa Cruz and Santa Catalina Islands, these two populations adjusted downward in 2020. 

Researchers also gave updates on island fox diet and microbiome investigations. FIF will report on this in the coming weeks.