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. 

 

How Do Biologists Capture Island Foxes?

Meet guest blogger, FIF Board Member, Jessica Sanchez. 

Sanchez is a wildlife veterinarian and epidemiologist who's been working with Channel Island foxes since 2006. She started her career managing the captive breeding and wild fox monitoring program on Santa Cruz Island. For her master's degree, she researched social interactions among island foxes, and modeled vaccination and monitoring methods to prevent and detect disease outbreaks. She is currently a consulting veterinarian for island foxes across the Channel Islands, providing medical care and advising on biosecurity and fox health research.

Every year, island managers and biologists conduct island-wide capture of wild island foxes to monitor the population size, reproduction, and health of individuals. This is done using the same locations every year, so direct comparisons can be made and trends identified. (counting island foxes)

The first step is finding a safe location to place a box trap–somewhere with flat ground, so it won't roll. It has to be out of the direct sun and wind, away from water with no risk of flooding, and where we can use vegetation to cover and disguise the capture device.

 

We capture foxes using wire, humane, live box traps; the very same ones used to capture feral cats. There is a "treadle plate" at the back that is attached to the door with a stiff wire. When the animal steps on the treadle, the door closes behind them.

We disguise the wire bottom by covering it lightly with grass or other vegetation. This also provides a comfortable bed for the fox to spend the night. We attract the fox with a small cup of fox-safe food at the very back, past the treadle. The fox must enter far enough to trigger the door and close it behind itself. An aromatic scent is also spread on a branch above the box trap–this scent travels longer distances than the smell of the food and attracts the fox to the area.

We cover the box trap with vegetation so the island fox is shaded and protected from any other animals that might come poking around. Then, we leave it overnight and return to check it first thing in the morning.

Sometimes, animals will try to get to the bait without going inside. This trap was disturbed by ravens! Ravens are extremely smart and will learn that the brightly colored "flagging" we put on trees to mark locations means there is an easy meal nearby.

If a fox is in the box trap, we first weigh both the trap and the fox. Once the fox is released, we subtract the weight of just the trap to calculate the fox's weight. An adult island fox will weigh between 1.5–3 kg, or 3–6 lbs, with foxes being slightly different sizes on different islands (largest on Santa Catalina, smallest on Santa Cruz).

We carefully remove the fox from the trap, being sure not to get their tail caught in the door!

The first thing we do once we have the fox in hand is scan it for a microchip tag, just like the ones used in dogs and cats. This tells us that the fox has been previously caught. The microchips are small implants, the size of a grain of rice, and are inserted under the skin near the shoulder blades using a needle.

The microchip provides lifelong identification of an individual so we can track its history–the locations it was captured, its age, any injuries, whether it had offspring, vaccines administered, any blood test results, and radio-collar frequencies.  - Jessica Sanchez

See F257's multi-year story.

The microchip can also alert the biologist that the captured fox has already had a health check that year. If so, it is immediately released.

 

If not, the island fox will receive a full health check. Follow as Jessica provides an island fox with a Health Check Part 2 - body condition. 

Health Check Part 3 - Preventative care 

Other species encountered during health checks

Fox Foto Friday - Where's M152?

Remember this face from last year? M152 is a male fox on the eastern side of Santa Rosa Island. 

This year he was not counted during the annual count and health checks in his area. But don't fear... M152 is doing well. We know he is still in his territory and going about his daily life because he is wearing a radio-tracking collar.

This demonstrates the importance of having two ways to monitor island foxes. 

Annual counts and health checks allow biologists to check the health and well-being of individual animals while they have them in-hand. This provides a snapshot of the population's health as a group at a specific time.

Radio-tracking collars enable the monitoring of individual foxes throughout the year. Their movements in an area can be tracked and if something happens to them, their radio collar reports to  biologists.

M152 did not come into a capture cage this year. Perhaps he was finding plenty of food because of the normal rainfall this spring and saw no reason to enter a capture cage. Perhaps when he came across a capture cage, another fox was already in it.

M152 is a pretty wily fox. We think he is approximately 5–6 years old. In that time he's only been captured twice: in 2014 and last year in 2018. ID micro-chips make is possible for each island fox to be tracked as an individual.

We're sorry that the biologists didn't have a chance to weigh him, check his health, and take a whisker sample this summer. It would have been great to compare to his last health check.

But other foxes did get examined and their stories are important too.

Fox Foto Friday - Time for Health Checks!

Across the Channel Islands, island foxes are being counted and given health checks. This island fox on Santa Cruz Island also received a refurbished radio-tracking collar funded by Friends of the Island Fox. See her as she is released.

For the next three years this radio collar will tell biologists that this island fox is up and moving around in its environment. It will also give off a mortality signal to alert biologists if something should happen to this individual island fox. Rapid response to mortalities enables a quick response to disease or threats to other island foxes. 

What are the current threats to island foxes in 2019?

Fox Foto Friday - Counting Island Foxes

Capture cages and ID microchips are key in counting island foxes across the Channel Islands. Camera trap images, like this one, may help provide additional information on island fox behavior. This fox is alone, appears healthy, and shows no sign of injury from interactions with other island foxes. It's also wearing something important around its neck.

What Do Island-Fox Biologists Do?

Each autumn, field biologists work hard and long hours checking the status of Channel Island foxes. What do island-fox biologists do during the course of an autumn day?

Here are excerpts from some personal accounts from Santa Barbara Zoo Animal Care staff who elected to spend a week providing 64 volunteer hours assisting National Park Service biologists in Channel Islands National Park.

Scott Daugherty (on San Miguel Island):
Our job was to place radio tracking collars on some foxes and collect biological data, so the Park Service could get an accurate count of how many foxes were on the island, and could make observations about how well the whole population was surviving. This is all accomplished by dedicated individuals, trained to trap and handle the endangered foxes safely...

capture cage hidden under a shrub

One thing that I didn’t realize before actually getting out to the island was just how much work it is to participate in these kinds of studies. Just getting to the traps was almost half an hour of hard hiking, and the traps themselves were set 250 meters apart, making each day a minimum of 5 miles of tough terrain, nearly all of it off trail. Each morning, we would get up before sunrise, and hike out to our trapping grid by first light. Each of our 18 traps needed to be checked and reset, and most foxes that were caught needed to get a full work up...

The conditions on San Miguel can be harsh, with regular winds gusting at 30 mph, and the temperature fluctuating from a warm 75˚F during the day to close to freezing over night. Like the California condor, the Channel Island fox recovery is one of the great successes of conservation study and education, and I am extremely proud to be able to participate.

photo courtesy of NPS

Damian Lechner (on Santa Rosa Island):
In September, I went out to Santa Rosa Island to meet up with Angela from the National Park Service.  We set up 3 grids of traps, each consisting of 12 traps. ....  I was shown how to handle the Foxes and [spotted] Skunks that we trapped, check for parasites, record broken teeth, vaccinate the foxes, micro chip, collect blood and urine samples, collect weights, and take whisker samples. 

island fox having teeth checked; photo courtesy of CIC

(To minimize stress to these wild animals, the goal is to complete all data collection and health maintenance tasks in 12 minutes or less.)

After arriving back at the cabin around noon, we processed the blood and urine that we collected and restocked our kits for the following day.  We continued this for the rest of the week then we collected the traps and hiked out with them on our backpacks.  I learned a lot that week, helped to save Island Species and hiked countless miles.  I’m very appreciative for the opportunity given to me to contribute to this project and hope to go out to the Island again next year.

A huge Thank You to the island-fox Field Biologists for all they do on behalf of Channel Island foxes. Vaccinating island foxes against canine distemper and rabies is vital to their future survival. You can help this effort. FIF is trying to raise funds to protect 500 island foxes.

Our thanks also to the Santa Barbara Zoo and their Animal Care staff who care for Channel Island foxes on the mainland and put in countless volunteer hours to assist the National Park. Thank you also to the Santa Barbara Zoo for sharing the personal accounts of their staff.
 

The Science of Counting Island Foxes

courtesy of National Park Service

In 2000 when there were only 15 island foxes surviving in captive breeding pens on San Miguel, you could count them easily on your fingers.

Today all Channel Island foxes across the six islands where they live are back in the wild. (A few rescued individuals from San Clemente Island can be seen in mainland zoos.) The recovery of the endangered island fox on San Miguel, Santa Rosa, Santa Cruz and Santa Catalina Islands has been record-breaking and the days of counting all of the physical island foxes are long gone.
 

courtesy of National Park Service

The process of counting foxes on each island begins in the fall with special capture cages.

These cages are set up either at the cross sections of grids or along a string depending on the island and its topography (More on strings and grids)

Cages in an area are set out over the course of a specific number of nights and checked each morning. On Catalina, each string is run for four consecutive nights; after that, typically the majority of individuals would be foxes that had already been captured on previous nights. Each island fox is identifiable because it has a Passive Identification Transponder (PIT) microchip. An island fox caught for the first time receives a PIT tag. From that point on the PIT tag allows it to be recognized as a specific individual. It can take weeks for biologists to evaluate each island.

Over the course of all the capture nights, the number of individual island foxes, their gender, ages and location caught are documented. Island foxes are quite territorial, therefore it is unlikely that a fox caught in one area of the island would be found on a different area of the island during the month of counting. (If it is, that is important too.)

The data is input into a modeling program for analysis. Different programs may be used on different islands and over the years land managers may change which program they use. The modeling program calculates the density of island foxes in specific habitats across the island and estimates a total island population.

Sometimes, however, it takes a human brain to see complexity in the numbers. On two islands where recovery has been robust over the past few years, San Miguel and Santa Catalina, the estimated population numbers appear to be higher in 2013 than they were in 2012.

But observations on both islands conclude that drought may have reduced births and did cause starvation in a number of pups last summer, prior to counting. How could the population number increase while the number of surviving pups decreased significantly?

Biologists Calvin Duncan and Julie King from the Catalina Island Conservancy explain that on Catalina they caught a greater number of adult island foxes that had not been counted for a number of years. Young animals are more likely to be curious and challenged with finding food; they venture into capture cages more readily. Once an animal is in the cage, no other can be caught that night. This year, on the fourth night of capturing, they were still finding a high percentage of animals that had not been caught on previous nights.

courtesy of Kevin Schafer

The increase in the population number for Catalina is warranted because of the number of unique individual animals that were counted. But rather than an increase in the population, the number represents a refinement of the estimate toward greater accuracy.

On both San Miguel and Santa Catalina Islands, island fox numbers have surpassed historic population figures. Both islands may have reached carrying capacity, or the number of individual animals that can find the territory and food resources necessary for a healthy life. As the drought continues this summer, there may be further impacts not only on pups, but also on older individuals.

Counting island foxes provides an important picture of island fox recovery, but observations throughout the year, health checks, blood tests, data collected from radio-collared island foxes and necropsies is vitally important to understanding the whole recovery picture.

Counting Channel Island Foxes

How do you count a population of small animals across an island, when they are so well camouflaged?

How long did it take you to find the island fox?   photo courtesy of M. Jakubowski

Each July to December, across the six Channel Islands where island foxes live, biologists put out special capture cages to catch individual animals. These wire box-traps have a door that snaps shut when the fox steps on a trigger plate at the rear of the box.

The number of cages put out each night and the manner in which they are arranged differs between islands and land managers. Tim Coonan, senior biologist for Channel Islands National Park explains that on Santa Rosa and San Miguel "Traps are deployed in small grids." These grids typically are stretched over rolling hills. The grid pattern may be two traps by six traps wide or three traps by six traps wide. The capture-trap locations are spaced approximately 250 meters apart with the capture cages usually under bushes or scrub. The cage is covered with  burlap to further protect the fox from the elements.

Cages are baited with fragrant substances particularly interesting to island foxes. Each cage has food and water. The grid of cages is checked each morning. Foxes in the cages are first scanned for their microchip ID. Biologist Calvin Duncan explains why this is important.

Each individually identified island fox is counted. This year's pups are counted separately to determine an estimated fertility rate. Pups born in April are old enough to be on their own, but they usually are somewhat smaller than adults and will not yet have received an ID microchip. While in-hand, the island fox receives a health check, vaccinations and an ID microchip or radio tracking collar if needed.

On Catalina Island capture cages are put out along lines called "strings." On mountainous terrain, strings of cages are more practical than grids. On all of the islands, actual numbers of individual island foxes caught during the fall are entered into various population modeling software to determine the best estimate for the total population. After strenuous weeks of counting in the field, it takes months in the office to produce reliable numbers. That is why the number of island foxes counted in the fall becomes official in June of the following year.

These are the official island fox population numbers through fall of 2012.

• San Miguel Island - 540, up from a low of 15 in the year 2000
• Santa Rosa Island - 637, up from a low of 15 in the year 2000
• Santa Cruz Island - 1,354 , up from a low of ~62 in the year 2002
• Santa Catalina Island - 1,502 , up from a low of ~103 in 2000

Notice how Santa Catalina and San Miguel both showed slight population drops last year. Biologists believe this a sign the populations are stabilizing at their natural levels. Drought this year may impact populations as well. Notice too how Santa Rosa is finally showing robust population increase. We hope this population will continue to recover. Whether the numbers are up or down, counting island foxes is the only way we can have the best estimate of population recovery.

How Do You Count Island Foxes?

Across the Channel Islands biologists are setting special enclosure traps to catch island foxes. Each year at the end of summer traps are set-up along specific trails or grids and left open over night. In the evening hours curious or hungry island foxes find their way into the wire mesh traps.

courtesy of Channel Islands National Park

This is how island foxes are counted on each of the Channel Islands. Late summer or early fall is the best season to capture the small foxes because it is late enough in the season that fox pups are no longer nursing and early enough that adult island foxes are not yet preparing to breed for the next batch of offspring.

Before sunrise field biologists head out to check each trap. Frequently if an island fox pup is caught in the cage, biologists report that the parents may be close by, keeping an eye on their youngster. And often island fox parents will leave food, like a dead mouse or two, in front of the cage. This behavior is call "provisioning." Even though the island fox pup is caught in the capture cage, the parents will continue to try and take care of it.

The island fox pup that has been sharing its adventures on Twitter is about to experience an annual Health Check. (See the Twitter box to the right or follow Tani's adventures on FaceBook)


For MORE on an island fox's annual Health Check, LISTEN to biologist Julie King from the Catalina Island Conservancy as she does a health check on an island fox in the wild.

Follow us on @ifoxtweet on Twitter as an island fox pup grows up.

Counting Island Foxes

If you are a fox biologist on the Channel Islands, late summer through early autumn is a busy season. During this short window of time, island fox populations are counted and individual animals receive health check-ups. To get their hands on these pint-sized, but sharp-toothed predators, special box-type traps are put out in specific areas.

In September, Friends of the Island Fox rode along with Julie King, fox biologist for the Catalina Island Conservancy. The day on Santa Catalina Island started very early, because all of the traps on a string must be checked before the day starts to get warm.

Most foxes are captured in the evening or during the night. Even so, the traps are set in shaded spots so that a fox won’t become overheated. Each trap has a covering over the top and grass or hay inside to make it more comfortable

The fox is first identified by its “pit tag.” A scanner responds to the microchip tag and displays the animals identification number.

Endangered island foxes on Santa Catalina, San Miguel, Santa Rosa and Santa Cruz islands are given microchip identification tags like those you would use on your pet dog. The fox in the trap is scanned with the microchip reader to identify it. In this way, the biologist knows when the fox was last caught and whether or not it needs vaccinations, a health check or radio collar maintenance.

If the fox does not have a microchip or pit tag, it will receive one.

If it has already been caught this season and has had its health check, the biologist will release the fox and reset the trap. If not, then the island fox will spend 15-20 minutes with the biologist getting a full health workup.

Join us November 20th for an audio podcast as biologist Julie King does a health check on an island fox.