Channel Island Fox Update 2016

photo courtesy of Anita Machlis

The annual meeting of the Island Fox Conservation Working Group in 2016 reported that the general status of five subspecies of California's Channel Island foxes is GOOD and STABLE. Concern for the San Nicolas Island fox continues.

2016 was a busy year for island foxes. Three subspecies were removed from the Endangered Species list and one was downlisted to Threatened status. The following update includes the population numbers from fall of 2015. (Land managers are currently compiling the fall 2016 data to present their official 2016 population numbers at the Annual Meeting in May 2017.)

San Nicolas Island

Drought impacts were a major concern in 2015-2016, however island foxes on San Miguel and San Nicolas Islands were more severely impacted. These two islands have the least amount of native plant diversity, leaving the highly omnivorous island foxes more dependent on introduced ice plant and the introduced snails and earwigs that live within it. (Island fox diet study) Continued years of drought dramatically reduced introduced species, greatly impacting the island foxes on these two islands. The situation on San Miguel and San Nicolas Islands, however, continue to be different from each other. This is the challenge of protecting island foxes.

photo courtesy of Paul Bronstein

Island Fox Update 2016 a specific island-by-island summary pdf

• San Miguel Island ~ 382 foxes (low of 15 in the year 2000). Population numbers were revised in late 2016 going back to 2008. The population has recovered from extinction threat and slightly increased in number from 2014. Concern: Drought impact on food resources and increase in life-threatening parasites. (see Island Fox Update 2016 above)
• Santa Rosa Island ~ 1,256 foxes (low of 15 in the year 2000). The population has recovered from extinction threat and, despite the drought, continues to thrive and increase. Concern: An unusual and fatal parasite, Leptospira, may have been introduced via sea lions. Further investigation is needed to determine the extent of threat to island foxes. 
  (see Island Fox Update 2016 above)
• Santa Cruz Island ~ 2,170 foxes (low of ~ 80 in the year 2002). The population has recovered from extinction threat and is very robust. The increased number of older animals in the population combined with carrying capacity and drought may have caused a drop from the 2014 population high of ~ 2,700. Plant diversity on this island provides island foxes with diverse resources and drought has not been a threat. Concern: Golden eagle predation occurred again in 2016, but was limited. Biosecurity–introduced disease–remains a threat.

  

  native plant restoration efforts in 2016 on Santa Cruz Island

• Santa Catalina Island ~ 1,812 foxes (low of ~ 103 in the year 2000).
  The population has recovered from extinction threat, but continued threats connected with large numbers of people visiting the island prompted the USFWS to maintain a Threatened status for this island fox subspecies. Concern: Biosecurity–introduced disease–poses a constant threat to Santa Catalina Island. Serology testing is an especially important conservation effort looking for early evidence of disease introduction. Even human trash poses threats to these island foxes. 

  

  photo courtesy of Melissa Baffa
  

   
• San Clemente Island ~ 888 foxes (Not Endangered; adults only). Island foxes remain robust on this island, though the drought may have depressed survival in 2015. Concern: Island fox survival may have decreased in areas with less native plant diversity and therefore fewer food resources. The Navy has begun native plant restoration projects, but the effort is still in the early stages. The rainy season of 2016 may have positively impacted this effort. Island fox pups, abandoned by parents on this island, are the few individuals currently found in California zoos.
• San Nicolas Island ~ 260 foxes (Not Endangered; adults only). In 2012, San Nicolas Island had the greatest density of foxes anywhere in the world and a population estimated at over 600 individuals. Since that year the population has declined and stabilized at ~ 250 individuals. Concern: The native plant diversity of this island was severely impacted in the last century. San Nicolas has the least biodiversity of native plant species. Island foxes became dependent on introduced plant species that died off during the years of consecutive drought. Island foxes have shown signs of emaciation and severe parasite infestation, either or both of these impacts may be a cause for decline. More on drought impacts as reported in 2016. The Navy has begun native plant restoration projects and the rainy season of 2016 may have positively impacted this effort. 
 

In addition to drought and disease impacts, there are concerns regarding the lack of genetic diversity in the San Nicolas Island fox population. To-date there is no evidence that the San Nicolas population suffers from genetic anomalies that could negatively impact their reproduction or survival. However a lack of genetic diversity can also impact how a species or subspecies is able to respond to disease challenges. Genetics and Disease Immunity Research. 

Everyone is watching the San Nicolas Island fox population and trying to establish why they have declined and whether or not their numbers improved in 2016. 

Keep informed of the status of the San Nicolas Island fox by subscribing to the FIF bimonthly newsletter SUBSCRIBE

Channel Island Fox Status Update 2015

photo courtesy of M. Solomon

The annual meeting of the Island Fox Conservation Working Group in 2015 reported that the general status of the six subspecies of California's Channel Island foxes is GOOD.

However, four of six islands saw dips or declines in population in 2014. The historic drought and its impacts on food resources is believed to be the cause. Biologists on Santa Catalina have documented a direct connection between rainfall levels and island fox reproduction. Years with drought-level precipitation result in reduced plant food and prey, thereby causing fewer island fox pups to be born or to survive. The extent of drought impact varies significantly by island.

Minimal drought impacts on Santa Cruz Island, 2015

 Despite the drought, recovery of the four endangered subspecies of island fox has been very successful and this spring (March 2015), the US Fish and Wildlife Service (USFWS) announced initiation of a status review of the four subspecies. 

Introduced disease continues to threaten all island foxes and a lack of canine distemper virus (CDV) vaccine safe for use in island foxes has been a major concern for two years. The Working Group took urgent steps, and Friends of the Island Fox participated, to determine the effectiveness of a newly available CDV vaccine.
 

courtesy of E. Gotthelf

All island fox subspecies are maintaining stable populations and there are no issues which put any Channel Island fox subspecies in eminent threat of extinction. The continuing drought, however, has more severely impacted island foxes on San Miguel and San Nicolas Islands. As seen in the past, each island faces its own concerns and challenges.


Island Fox Update 2015 pdf a specific island-by-island summary

• San Miguel Island - 520 (low of 15 in the year 2000). Population recovered with over 500 individuals since 2010. Slight population dip. Concern: Threat from new parasites continues, as do drought impacts (see below)
• Santa Rosa Island - 874 (low of 15 in the year 2000). Population recovery stalled by drought, but stable.
• Santa Cruz Island - 1,750* (low of 62 in the year 2002). Population recovered and robust with over 1,000 individuals since 2009. No discernible drought impacts.
• Santa Catalina Island - 1,717 (low of 103 in the year 2000). Population recovered and stable with over 1,000 individuals since 2010. Slight population dip. Concern: Drought impacts and human related impacts, including car strike, and high risk for introduced disease.
• San Clemente Island - 1,230* (not Endangered). Population stable. Concern: Continued fatalities to automobile strike.
• San Nicolas Island - 263* (not Endangered). Population has declined ~41% since 2012 because of drought impacts. Concern: Habitat destruction has left island foxes dependent on non-native plants and prey which have declined dramatically in the drought, see below.

The graph above shows population numbers on even years, therefore the dip from 2013 is not represented. For more detailed graphs see the Island Fox Update document. The numbers represented  are the official 2014 population figures reported at the Island Fox Conservation Working Group Meeting 6/16/15. *Population figures represent adults only.

Concerns:
Healthy plant and animal populations fluctuate normally with available resources. Recovered island fox populations naturally dip when there is not enough food, water, or territory. There is a natural limit to the number of island foxes an island can support, also known as carrying capacity.

Low rainfall has impacted food resources across the Channel Islands. However, islands have not been impacted equally. Some islands appear to have greater natural drought tolerance.

As recently discovered by analyzing island-fox diet, Santa Catalina and Santa Cruz Islands have greater native plant biodiversity than the other smaller islands. Native island vegetation evolved with periods of drought. Native plants are better able to survive and produce fruit vital for the survival of island animals. The greater the native plant biodiversity, the greater the survival options for island foxes.

island fox footprints among ice plant on San Nicolas

The island-fox-diet study pointed out that island foxes on San Miguel and San Nicolas Islands were dependent on plant and invertebrate species which had been introduced to their islands, replacing native plant habitat.  Unfortunately, these introduced plant species, especially, ice plant, and the non-native creatures that live in it–snails and earwigs, have declined dramatically during the last two years of extreme drought. The impact has been greatest on San Nicolas Island where average island-fox weight has declined and the population has dropped 41% since 2012.

Restoring native vegetation is the best long term solution for healthy island fox populations on these two islands. (for more on this topic, see the Island Fox Update 2015 pdf document above)

A secondary impact of the drought has been increased complications with parasites. Changes in diet and decreased general health leave island foxes more vulnerable to internal and external parasites. Here again, each island has its own specific parasite challenges. (See Island Fox Update 2015 pdf for details) (Spiny-headed worm on San Miguel Island first detected in 2013).

Introduced disease continues to pose a threat to all island foxes, especially on islands visited by people. Dogs, cats, and introduced species, like raccoons, are all avenues for disease to be transported to isolated and disease-naive island foxes. Efforts to verify the effectiveness of a new CDV vaccine for island foxes is currently underway.

Positive Notes:

courtesy of D. Mekonnen

There are early anecdotal signs that the small amount of rain this spring and summer may be improving resources on the islands. More island fox pups have been spotted this summer than during the last two summers. However, the official impact on the populations will not be known until counting begins in fall.
  
Monitoring with radio collars continues to provide important information to land managers. Radio collars have helped verify that no golden eagles have returned to eat island foxes on the northern islands. Radio collars were instrumental in determining the cause of island-fox decline on San Nicolas Island. And they continue to provide early warning of disease introduction. Radio monitoring collars will also enable land managers to ethically determine the effectiveness of the new CDV vaccine.

Annual island fox health checks, serology testing, and counting identify threats to island fox survival early, so that actions can be taken to protect island populations.

‘Fox-Saver’ bins on Santa Catalina and the Navy's education outreach on San Clemente are all helping to reduce the number of island foxes hit and killed by cars.

Thank you to the Island Fox Conservation Working Group and all of the important work that has helped island foxes recover from the brink of extinction. Thank you also to the many participants on our June Santa Cruz Island Trip that have allowed us to show you their photographs.