3 Kinds of Radio Tracking Collars to Monitor Island Foxes

Look who received a GPS tracking collar that you helped fund!

 

This young female island fox lives at the tip top of Santa Rosa Island in Channel Islands National Park. The GPS collar she's wearing was refurbished with donations to Friends of the Island Fox. The movements of this fox, documented by her collar, will help tell the story of her life: Where and how large is her territory? What resources can she access? Combined with dietary info, it will reveal how she is interacting with the island ecosystem.

 

VHF Collars - The Original 

As island fox populations recovered from near extinction on four islands, individuals released back into the wild were collared with VHF radio-tracking collars to monitor their survival. (video of Senior Biologist for Channel Islands Park tells the story of island fox collapse of 1998–2000) VHF collars provide the location of an individual island fox at a specific moment. Biologists in the field are able to use hand-held antennae to triangulate the island fox's location. If a radio-collared island fox stops moving for 6–8 hours, the collar has a sensor that changes the signal from a "live-animal" beep to a possible "mortality" beep. This allows the quick retrieval of island fox bodies so the cause of death can be determined and steps can be taken to protect the island's entire island fox population.

In 2026, FIF's goal is to raise funds to refurbish 15 VHF radio collars for San Miguel Island. Cost to refurbish a VHF collar: $220  

 

GPS Collars - More Info/Bigger Price 

Initially, GPS tracking collars were too large for female island foxes to wear. Today, modern GPS and battery technology provides for a smaller collar with less weight that can be worn by both male and female island foxes. GPS vs VHF collars

GPS collars document an individual island fox's location several times a day for months to a year. This data can now be downloaded remotely to allow researchers to track movement patterns, territory size, and overlap with other collared individuals without having much of an impact on wild island fox behavior. These collars include VHF capabilities and sometimes have additional abilities, like accelerometers that document movement patterns over 24 hours. 

A new GPS collar for an island fox can cost $2400. GPS collars used in prior research projects for island foxes and San Joaquin kit foxes can be refurbished at a much reduced cost.

In 2026, FIF's goal is to raise funds to refurbish 12 GPS tracking collars for Santa Rosa Island. Cost to refurbish a GPS collar: $500

Island fox with new Digipeater collar in 2025

Digipeater Collars - New Technology and New Strategy

Digipeater collars include VHF capabilities, but they interact with a series of antennae stations. An island fox within signal view of the antennae is automatically check-in and reported as alive and well. Digipeater collars don't record precise movement like GPS collars, but they monitor island fox survival while reducing staffing hours in the field. More on digipeater collars and system

Sustainable monitoring of island fox survival requires reducing costs. FIF is assisting with the transition to monitoring island foxes on Santa Cruz Island with the Digipeater system.

FIF has already raised funds for 15 new Digipeater collars in 2026. Now our goal is to raise funds for 3 additional antennae stations ($2000 each). 

 

No matter the type of tracking collar, protecting island foxes requires monitoring! Tracking collars provide the best opportunity to monitor island foxes while they live their wild lives. 

FIF Research Grant Expands Investigation of Link Between Island Fox Genetics and Health

Friends of the Island Fox happily announces that the 2025 Research Grant was awarded to Kimberly Schoenberger to expand her investigation of connections between island fox genetics and health: Transcriptomics of the Channel Island Fox (Urocyon littoralis) through RNA-seq.

Schoenberger is a Ph.D. candidate at the University of Southern California and works with the Natural History Museum of Los Angeles County. This second year of grant support will fund RNA genetic sequencing of an additional 40 foxes from across all six Channel Islands. 

The initial 48 island foxes were all adults who had never been vaccinated. (First year of study) This second group includes juveniles and adults that had been previously vaccinated.

Health checks have revealed that San Nicolas Island foxes have similar ear mite infestation to Catalina Island foxes, but the foxes on San Nic do not develop microbial monocultures or cancerous tumors in their ears. Genetically influenced immune-system response may offer insight into why some island populations face health threats that others do not. Similar ear mite infestation with reduced microbial diversity has been found on San Clemente Island and the population there has faced survival declines in the last three years. (More on microbiome and connection to cancer in Catalina Island fox).

Examination of an island fox's ear canal with an otoscope

Schoenberger's RNA research may also provide noninvasive ways to detect dangerous amounts of internal parasites in island foxes. Examination of immune transcriptomes in dogs has shown that  increases in specific interleukins signal the presence of intestinal worms. Currently island foxes are challenged by intestinal parasites, especially spirocerca on San Nicolas Island, an ancanthocephalin on San Miguel Island, and possibly a new parasite on Santa Rosa Island.

 

Researchers like Kimberly Schoenberger are vital to healthy island fox populations. Insight from her work will help inform land managers and protect island foxes into the future. 

Your donations make FIF's support for research possible. 

Vaccinating Island Foxes is an Annual Need

 

Companion dogs are vaccinated against canine distemper annually and so are island foxes.

This Since June biologists have been out in the field across the Channel Islands vaccinating island foxes against rabies and canine distemper virus. The vaccine being administered across 4 islands was provided by donors like you. Who's helping fund vaccinations?

Did you know?

• Canine distemper virus (CDV) is a dog version of the measles virus. It's highly contagious like measles, entering the body through the respiratory system. New research suggests that measles from humans was transferred to dogs 500 years ago during the Spanish colonization of South America. 

 

• Distemper spreads rapidly through wildlife populations. CDV infects dogs, foxes, wolves, and coyotes, but also raccoons, ferrets, and skunks. The virus is especially deadly to African and Asian species of big cats (lions, leopards, tigers, etc.)

 

• CDV is so lethal to island foxes, they can't withstand the vaccine created for domestic dogs. Island foxes are treated with a dead-virus vaccine that is made in small batches, by one company, and is used by a short list of endangered species: black-footed ferret, giant panda, Iberian lynx, African wild dog, African lion, all tiger species, and other large cats.

 

•  A new study from Penn State University has found evidence that canine distemper virus is influencing grey wolf evolution. A gene mutation, CPD103, creates a black coat in grey wolves. This mutation also makes the lungs less susceptible to the introduction of disease. Black-colored grey wolves are less likely to become infected with CDV. In areas where CDV occurs in high rates, entire wolf populations become darker in color, because the lighter colored individuals are lost to the disease. Read more about this study.

 

Health efforts for rare wildlife go hand-in-hand with research. FIF raises funds to vaccinate island foxes and to investigate important health research.

"Date with a Fox" - Sylvie's Story

Do you remember this island fox?

In the Fall of 2023 this young female island fox was found injured on San Nicolas Island. Her story demonstrates the power of people working together toward a positive goal. Federal and state governmental agencies, biologists, zoos, private individuals, and Friends of the Island Fox donors, all came together to give this island fox a second chance.

See the virtual program  

Date with a Fox - Sylvie's Story

Tuesday, Nov. 11, 2025

Link to a Japanese translation of this video program - courtesy of Takao Ono

We heard from the team that found Sylvie and made all of the necessary connections to facilitate her transfer to the mainland.

Francesca Ferrara, Natural Resource Specialist, Naval Base Ventura County

Robyn Powers, consulting biologist, SWCA Environmental Consulting 

V.P. of Animal Care and Health at the Santa Barbara Zoo, veterinarian Julie Barnes detailed the medical efforts that were needed to treat Sylvie's injured foot. You'll see the results from the orthopedic surgery that donors like you helped to pay for.

How is Sylvie today? 

 

Living Desert Animal Care Curator, Heather Down, updates us on Sylvie's recovery. 

FIF is Thankful for donors like you that helped to make this successful story possible.  

Celebrating 20 Years of Island Fox Conservation and Looking to the Future

Pat Meyer meets Jane Goodall in 2006

 

Friends of the Island Fox (FIF) was founded in 2005, when Channel Island foxes were critically endangered on four islands.

See a short history of the organization presented during our August "Date with a Fox" on-line program and hear from FIF Board member Justin Purnell about a fieldwork study program for high school students that provides a personal experience with the island ecosystem.

 

Friends of the Island Fox is partnering with the Field Studies Cooperative to provide more students with this life-changing opportunity. 

 

New Technology for Monitoring Island Foxes

Monitoring island fox survival is vital to protecting the vulnerable and small populations on six separate Channel Islands. (Current island fox status)

 

Checking for the individual radio signals from 50–60 individual island foxes across an entire island every two weeks, can require many staff hours. Reducing staffing hours would make island-fox monitoring less expensive?

Enter a new technology referred to as "Digipeater." The collar pictured above is one of the 10 new Digipeater radio collars funded by FIF and fitted on Santa Cruz Island foxes this summer. While the collar size is similar to VHF radio-tracking collars, the new collars weigh slightly less and have an additional ability: they interact with stationary digital repeating antennae in the field. 

Multiple times a day, receivers on the antenna scan for fox-collar signals. When a signal is picked up, it's relayed from one antennae to another until it reaches a base station. The base station transmits information directly to biologists. A biologist doesn't have to be in the field to know that all collared island foxes are active and well.

If an island fox goes for a number of days without being picked up by the automated system, biologists can go into the field looking for the signal from that specific fox.

 

The U.S. Navy on San Clement Island has been using Digipeaters for several years. Last summer during a wildfire that burned across a third of the island, biologists were restricted from going into the field. As the low-burning wildfire spread, the Digipeaters continued to collect status information on island foxes. From a safe location biologists could detect island fox activity and survival. No collared island foxes died in the wildfire. 

 

This Santa Cruz Island fox was fitted with a "Digipeater" collar in July. Her new collar reports in daily and requires less in-person labor. It's a win-win for monitoring island foxes.

These collars are possible, because of donors like you. 

Digipeater collars are $350 each and are made locally in Southern California. 

Island Fox Status Update 2025

In 2024, island foxes remained healthy. Normal rainfall levels led to population balancing; high density populations decreased in number and low density populations increased. San Clemente Island, however, realized a third consecutive year of population decline. Concern for these island foxes grows because a specific cause for the decline remains unknown.

island fox on San Clemente Island

The following is an update across the Channel Islands from notes compiled by Friends of the Island Fox at the Island Fox Conservation Working Group Meeting May 15, 2025 hosted at the Santa Barbara Zoo (hybrid meeting).

Reported population numbers are the official estimates submitted by the land managers and calculated by them from island foxes captured for health checks June 2024–January 2025. (How island foxes are captured and given health checks) 

Overview: While food and shelter resources for island foxes were good across the islands in 2024, dry conditions were more prevalent on San Clemente Island and a wildfire burned a third of the island. Monitoring systems documented island foxes surviving the fire, but it is possible the fire contributed to the low number of pups documented. Weather extremes are becoming more frequent across the islands. 

Fox Density: Because island size, weather, and habitat varies from island to island, comparing island fox density can be more informative than comparing population sizes. Fox density reflects the number of island foxes found within a square kilometer (per sq km). (More on density).

A density of 8–12 island foxes per sq km, is the fairly high density of individual animals typically found across the Channel Islands. When a density rises above this range, as San Miguel Island did in 2023 (see graphic above), it is not surprising when the population adjusts down the following year, especially if weather conditions are not optimum for growing native fruit and supplying large amounts of insect and rodent prey.

The two smallest islands with island foxes, San Miguel and San Nicolas, remain most stable when their population density is around 8 island foxes per sq km. Food resources on these smaller islands are never as plentiful as on the larger islands. While the population number decline on San Miguel may seem concerning, the downward adjustment in density creates a more sustainable population. 

The larger islands, Santa Rosa, Santa Catalina, and Santa Cruz provide greater biodiversity of resources and can maintain higher island fox population densities. Densities over 12 foxes per sq km, however, can mean that some island foxes are pushed to very small territories with lower quality resources. Drought, flooding, or the introduction of disease, often has a greater negative impact when foxes are living in high density.

The density graphic above also shows how thin the island fox density was on San Clemente Island in 2023 and 2024. Everyone is watching this island closely and investigating leads on the causes. 

Pup on Northern Islands in August 2024

 

In 2025, the leading threats to island foxes are:

• reduced funding for Federal lands: Monitoring island foxes requires staffing. Reductions in Federal funding for National Park staffing, especially biologists, and unknown budgetary cuts affecting U.S. Navy base environmental efforts threatens island fox health checks and monitoring in 2025. Across Federal lands health checks began early in hopes of completing them before funding cuts were enacted. The ability to continue monitoring on Santa Rosa, San Miguel, San Clemente, and San Nicolas Islands remains in jeopardy for 2026 and into the future. 
• biosecurity: Annual vaccination of island foxes for the deadly canine distemper virus remains a priority. If health checks are discontinued on Federal lands, there will be no annual opportunity for vaccination. Additionally, canine adenovirus (dog flu) has swept across several islands and may be impacting pup survival.
• climate change: Weather extremes not only influence island fox health and resources, they also impact island fox monitoring. The heavy rains of 2023 limited access to Santa Cruz Island and the data collected that year led to a false representation of an upward spike in population numbers. Quality monitoring requires consistency in data collection. Monitoring data in 2024 revealed a stable population on Santa Cruz–mitigating the spike. This highlights the importance of annually collected data to provide the most accurate depiction of island fox population trends across the islands.    

island fox having teeth examined during a health check

 

Greatest Concern: We know how quickly an entire population of island foxes can be impacted by disease, resource loss, or an introduced threat. Quality monitoring is the cornerstone of island fox recovery success. Millions of dollars invested in island fox recovery could be swept away to save a few $100,000 in annual monitoring costs. 

 

Smaller Islands

Because of the amount of years tracked, the graph above shows population estimates for even years only. While smaller populations can be more volatile, San Nicolas and San Miguel Islands remain stable. 

San Miguel Island (lime green line): The downward adjustment of the population from an estimated 525 individual island foxes to 322 reflects a rebalancing to a more sustainable population density. Trends suggest the resources on the island can support 300–450 foxes. Pup numbers were typical in 2024 and individual health appeared good.

San Nicolas Island (pink line): The population remained stable. General health remained good and pup numbers increased. Forty percent of the population shows antibodies for exposure to adenovirus. Ear mites are prevalent. In 2025 foxes receiving health checks will be treated with a topical intervention, following protocols developed on Catalina Island. The hope is to reduce ear mite infestation and increase overall health.

San Clemente Island (blue line): Adult survival dropped from an 89% chance of surviving the year to 69%, and only 7 pups were documented in 2024. Investigations continue into pup survival, the impacts of adenovirus (exposure now prevalent in 80% of the population), and the quality of food resources. The wildfire may have also contributed to population decline. Car strikes add an additional threat to survival. Providing necropsies of individuals killed by vehicles may be vital to identifying health concerns that have gone undetected. 

Larger Islands

Because of the amount of years tracked, the graph above shows population estimates for even years only. As all of these islands hover at carrying capacity, their populations remain stable.

Santa Catalina Island (red line): This population increased slightly in 2024. Treating island foxes for ear mites has reduced cancerous tumors and increased overall health. Introduced adenovirus, corona, herpes, and parvo viruses all continue to decline. Biosecurity threats are greatest to this island, but no raccoons or other invasive species were detected on the island in 2024. The greatest threats to island foxes on this island are people and their pets. Eighteen island foxes were killed by cars and two were attacked by dogs. Rodenticide and unintended poisoning is a growing threat on all human-inhabited islands.

Santa Rosa Island (pink line with black centers): This island currently has the greatest island fox density–13.2 island foxes per sq km. As the density has increased, adult annual survival has declined slightly to a 72% chance of surviving the year. How this high density impacts available resources and fox territory is under investigation this summer with a group of known individual foxes wearing GPS tracking collars and being monitored for diet and health.

Santa Cruz Island (black line): This island continues to have the largest island fox population. As expected, the estimate of over 4,000 individuals in 2023 was an anomaly created by not being able to count foxes at historic counting locations because of stormy weather and flooding. Returning to count in the historic spots in 2024 resulted in a scientifically supportable and healthy population estimate of 3,086. 

Your donations help fund vaccinations and radio collars for monitoring island foxes. 

As July and August unfold, biologists are in the field vaccinating island foxes and fitting them with radio-tracking collars funded by Friends of the Island Fox.

Healthy island foxes depend on people like you supporting conservation efforts. 

 

Vaccinating Island Foxes Takes a Community

 $15,322 of vaccine is headed into the field to protect island foxes!

Donors like you made this possible! 

courtesy M. Navarro, NPS

Why do island foxes need to be vaccinated annually?

Canine distemper virus (CDV) caused a catastrophic decline of Santa Catalina Island foxes 26 years ago. Evolving in isolation on their islands, island foxes haven't developed immunity to typical canine diseases. To protect populations, each year at least 100 island foxes are vaccinated on each island against this deadly dog disease and rabies. On Catalina the goal is to vaccinate 350 island foxes, because the threat of introduced disease is so much higher for this population.

Island foxes are so susceptible to CDV that they can not tolerate the vaccine commonly given to dogs. They must be vaccinated with a special dead-virus vaccine that is produced in small batches and only provides protection for less than a year.

That means island foxes need to be vaccinated annually and the effort is one of the more expensive measures taken to protect their health each year.

This year's 650 vaccinations were supported by:

• Island Fox Ambassador Schools & Projects
• Local organizations 
• Recycling 4 Island Foxes & the Planet
• USU Recycles 4 Island Foxes
• 2024 FIF Island Trip participants 
• Private donors
• a grant from the Fresno Chaffee Zoo Wildlife Conservation Fund

How do you vaccinate an island fox? 

Metabarcoding Reveals the Genetic Fingerprints of Prey in Scat

 

Scat samples from island spotted skunks and island foxes were collected last December on Santa Cruz Island. The samples were part of a trial research project to determine if a conservation working dog, Moose, could accurately locate and identify island spotted skunk scat. Meet Moose; How accurate was Moose?

A total of 15 island spotted skunk scats were compared to island fox scats using metabarcoding. 

Metabarcoding is a process that takes a general biological sample and sifts out short sections of DNA and matches them to known strands of DNA representing different species. Using this process, a sample of pond water can provide a list of species that have been in that pond. In the Florida Everglades biologists are using metabarcoding to locate invasive pythons. The pythons shed DNA into the environment and metabarcoding can identify their presence.

 

In a scat sample, metabarcoding can help identify food items that an animal has eaten, especially when that prey may not leave exoskeletons, seeds, fur, or bones visible in the scat. (Scat & fox diet)

If island foxes and island spotted skunks are competing for the same food resources, the growing number of island foxes could have a population-limiting impact on the smaller species, the island spotted skunks. (Island foxes and island spotted skunks)

The preliminary results are very interesting.

There was an overlap in some prey species. Both island foxes and island spotted skunks were consistently consuming Jerusalem crickets in the fall of 2024. This large insect is an important food resource for both species. 

Jerusalem cricket

Deer mice appeared to be more important in the diets of island foxes than island spotted skunks. Both species also preyed on katydids, millipedes, and crane fly (most likely the larva which can be large and pump in the fall). For these three arthropods, island foxes were more likely to include them in their diet than island spotted skunks.

 

There were also a large number of prey items that were unique to either foxes or skunks.

Island foxes were frequently eating ground beetles and earwigs, which skunks were not eating. They were eating faster-moving diurnal species like: grasshoppers, song birds and quail. They were consuming fly and moth species that were different from those consumed by the skunks. Island foxes were also occasionally consuming snails. While snails might seem a slow-moving, nocturnal prey, their DNA did not show up in the skunk scat. 

Island spotted skunks were also consuming unique prey species. Several moth species were detected and more than a third of skunk scats revealed moth DNA. Island spotted skunks are strictly nocturnal and it's not a surprise that nocturnal species like moths and field crickets would be prey. Surprisingly, petrel DNA, a sea bird, was also found in about a third of the scats. These are small marine birds nesting in sea caves on the islands. Slender salamanders, a small terrestrial species most likely found in moist canyon soils were a common food source, while weevils and butterflies (possibly overwintering chrysalis) were occasionally eaten.  

While this was a preliminary study over a short amount of time with a small sample size, it suggests that, at least in the fall, there is not a lot of overlap in resource use between island foxes and island spotted skunks. We don’t know how many different island foxes or island spotted skunks are represented by the scat samples and more data is definitely needed.

The scat samples are currently being evaluated for plant DNA.

A Nose for Identifying a Species

Last December, Friends of the Island Fox worked with The Nature Conservancy and Working Dogs 4 Conservation on a project to see if a specially trained dog could track down island spotted skunk dens and scat. (See Moose the conservation working dog)

courtesy of TNC and WD4C

 

In the initial project, Moose used his specially trained nose to locate 11 scat samples. Two scat samples were also found by humans. The samples were sent to the Genetics Lab at UC Davis and Friends of the Island Fox helped fund the genetic testing of the samples. How well did Moose do identifying island spotted skunk scat from island fox scat?

Moose: 9 out of the 11 scats came from island spotted skunks. 1 sample was too degraded for DNA analysis (it might have been skunk) and 1 sample was island fox scat. 90% accurate!

Humans: 1 of the 2 scats came from an island spotted skunk, the other was island fox. 50% accurate!

 

Obviously, Moose is better than humans at detecting island spotted skunk scat.

island fox scat

The next questions: 

• Is there enough quality DNA in a scat sample to determine the identity of an individual island spotted skunk?
• It would cost $7,000 to develop island spotted skunk genetic markers to determine individuals. Can enough scat be located to establish a population estimate and would it be fiscally feasible to count the population this way?

 

The other information obtained from the scat samples pertains to diet. Island spotted skunk scat was compared with island fox scat. Stay tuned for more on metabarcoding.

Why do we need to count island spotted skunks?