International Fox Day - "The Unflinching Island Fox"

Reflections by Kris Chatari, FIF Board Secretary 

September 17 is International Fox Day. What better day to pay homage to all foxes, then by sharing my experiences with the absolutely unflinching Channel Island fox. 

I have had the honor and privilege to work side-by-side with my daughter, Dr. Jessica Sanchez, on Santa Cruz Island for a week during each of the past several years as she administers health checks and vaccinations to the foxes. Dr. Sanchez is a wildlife veterinarian who began her career in the early 2000’s working at the island fox captive breeding pens and is a member at large on FIF’s board of directors.

So, what do I mean by “unflinching?”  Let me explain.  It is very exciting to be checking a trapline grid and get the signal that there is a fox in the trap. (Island foxes are captured in safe capture cages) 

The first task is to get a weight of the trap with the fox in it.  

Next, the fox is scanned for a PIT tag number to determine if it is already in the fox database.  If no tag is found, that means we have just caught a brand-new fox, and the adrenaline starts to rise!  This fox’s health check has just taken a detour.  It is first given a PIT tag which contains a unique ID number. This involves placing a microchip the size of a grain of rice under the skin between the shoulder blades.  

PIT or Passive Integrated Transponder tags

Unbelievably, the fox does not flinch.  

Next, it is necessary to draw blood for purposes of DNA and disease surveillance research.  By this time, the fox has a cute green mask over its eyes and is laying on its back in the lap of the biologist/veterinarian.  Typically, if it is not a pup of the year, up to 10 ccs of blood can be collected.  Guess what?  The fox does not flinch during this process. 

 

Next comes the basics of the health check:  checking its eyes, assigning it an age class by viewing the back molars, combing it for parasites, assessing its general body condition, and noting whether it has any signs of reproduction that year.  

Then comes a major health component.  Each fox that is determined eligible (new pups of the year are excluded) are given two vaccinations:  a canine distemper (CDV) vaccine administered intramuscularly in the hind leg; after which the fox is turned to the other side and a rabies vaccine is administered subcutaneously.  You guessed it – neither prick elicits any noticeable flinch from the fox patient.

 

As I securely hold the fox next to my chest, its green mask is removed before release, and the REAL flinch test is about to occur.  As a whisker is plucked from each side of the fox’s face with a pair of tweezers, I am flinching on the inside with anticipation. Using stable isotope technology, a whisker can tell the secrets of what that individual fox has been eating for the last six months. But other than a moment of tautness, there is zero fox flinch. 

The average island fox only tips the scale at 3-5 pounds.  But it is the apex predator on each of the six islands on which it lives, and is not about to show any sign of being anything less than ferocious!  When the fox is finally released, it typically runs about 20 yards away, turns and stares you down, and then lifts its leg as if to say “thanks, but no thanks, piss on you!”

 

"Date with a Fox" on Island Fox Health Checks

 Join Friends of the Island Fox for:

 "Date with a Fox"

Tuesday, Feb. 10, 2026

6:30 pm PT 

with Jessica Sanchez, DVM

Island Fox Health Checks: From Exam to Research 

• How are wild island foxes handled during annual health checks?
• What data determines a healthy island fox?
• What measures are taken to safeguard island fox health into the future?
•  How do island foxes contribute to ongoing research investigating their health, diet, and relationship to island ecology?

In this online Zoom program, FIF Board member and wildlife veterinarian Jessica Sanchez will take us through the steps of an island fox health check. She'll detail why each step is important and give the inside scoop on what a day performing health checks is really like. See the program video below:  

 

Island Fox Gets a Health Check - Part 3

Welcome guest blogger Jessica Sanchez, wildlife veterinarian and FIF Board Member. She's explained how island foxes are captured annually in Part 1 and shown how a fox's body condition is evaluated in Part 2. But an island fox health check includes additional health measures.

We check the foxes for ectoparasites such as ticks, fleas, mites, and lice. We comb their fur to find fleas, and pay special attention to their ears, armpits, and belly area–where lice and ticks are often found. 

Ticks are collected so we can identify the species and test them for viruses or bacteria they might be carrying. Since ticks can feed on multiple hosts in their lifetime, testing the ticks tells us about what diseases the island spotted skunks, deermice, and other island species might be exposed to as well. 

 

 

We take a look in the fox's ears using an otoscope, just like the doctor uses to examine your ear canal. On Santa Catalina Island, where ear mites introduced by feral cats have been associated with ear tumors, foxes are treated with a topical medication to kill ear mites and reduce inflammation in the ear canal.

We collect blood from the jugular vein. This is used to test for exposure to disease, genetic analyses, and to look at other health parameters like liver and kidney function.

One of the most important steps is to administer vaccinations. A subset of the population is vaccinated every year for rabies and canine distemper virus. Neither disease is currently found on the Channel Islands, but we vaccinate as a preventative measure after the Santa Catalina Island foxes almost went extinct due to the introduction of canine distemper in 1999–2000. Vaccinations ensure that if there is ever an outbreak of either disease, at least the vaccinated foxes will survive to repopulate the island. (FIF's efforts to provide vaccine for island foxes in 2023)

A subset of foxes also gets radio collared. 

 

These collars are small, less than 5% of their body weight, and do not interfere with the foxes going about their daily life. Collars serve multiple purposes, allowing us to track the size and location of home ranges, monitor survival, and find dead animals quickly so their carcasses can be sent for necropsy ASAP to identify the cause of death. 

Most of the radio collared foxes are unvaccinated "sentinels," meaning if a disease outbreak occurs, they are not protected and may get sick, but their deaths will be detected via the change in their collar signal so we can recover the bodies for necropsy. Without collared animals, we would not know foxes were dying and would not be able to find the carcasses to get more information about the cause. Monitoring mortalities also gives us information on trends in other causes of death, such as internal parasites or being hit by cars, so we can address those threats as well.

Foxes are released after their workups and immediately run off! - Jessica Sanchez

 

In Part 4, Jessica details what happens when an island spotted skunk is unexpectedly caught during island fox health checks.

An Island Fox Gets a Health Check - Part 2

Welcome guest blogger Jessica Sanchez, wildlife veterinarian and FIF Board Member. In Part 1, she explained how island foxes are captured annually. Now, she'll take us through an island fox health check.

As biologists and veterinarians, we carefully remove the fox from the box trap, being sure not to get their tail caught in the door!

Island foxes are blindfolded to help keep them calm and reduce stress. Foxes do not have any natural predators on the Channel Islands so they are very brave, but they can still be stressed from handling by humans. Exams are quick and we do our best to be quiet and efficient. Island foxes are not sedated, so they can be released immediately and return to life as normal ASAP.

The health exam begins with an examination of teeth.

We open their mouths very gently so we can see the upper premolars. The wear on these teeth allows us to classify each animal into an "age class." Age classes range from 0 (pups born that year) to 4 (very old foxes with worn teeth). The pups also have serration on their incisors that have not yet worn smooth. Although age classes are not an exact age–and can vary by island, diet, and habitat (rougher food and sand wear teeth faster)–they give us a semi-standardized guide for assessing how old the population is overall. (more on using teeth to age island foxes)

We can also identify the pups of the year (less than a year old) by their appearance. They start out darkly colored and slowly transition to their adult gray/rufous/white. By the time we catch them during the summer/fall season, they look like mini-adults but with a rounder, fluffier shape.

Reproduction can be assessed in the females by examining their abdomens. A female who has not had pups that year will have white fur on her belly, with no mammary/nipple development (left, below). A female nursing pups will have the hair licked away from her nipples, the surrounding hair will be stained red from the saliva of the puppies, and her mammary tissue will be large and well developed from producing milk (right, below).

We do a thorough exam, assessing body condition and checking for any injuries. We check each foot to make sure they have no injuries to their claws, which are semi-retractable. Island foxes and grey foxes are unique among canids in that they can rotate their wrists, allowing them to grip and climb trees. (more on the island fox's ancestor, the grey fox)

Foxes often have grass awns or other debris stuck in their eyes, so we clean these out and remove any gunk that has accumulated. - Jessica Sanchez

In Health Check Part 3 - Jessica will detail the specific health measures taken for island foxes.

Part 4 - Other species encountered during health checks

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

Radio Collars Going On Island Foxes!

Radio-tracking collars are the primary way that island fox survival is monitored across the Channel Islands.

 

12 new radio collars and 21 refurbished radio collars funded by your donations are going on island foxes RIGHT NOW on Catalina Island.

 

Across Catalina Island wildlife biologists are giving island foxes health checks. Weighing them, checking their ears, 

teeth, 

and overall condition.

Meet wildlife biologist Emily Hamblin and hear how she gives health checks to island foxes. "Date with a Fox" program (video recording)

Island foxes also receive vaccinations and have a sample of their blood drawn looking for signs of exposure to other diseases.

Island foxes faced near extinction on four islands twenty-two years ago. One of the causes was introduced canine distemper virus. Island foxes can be vaccinated for this disease, but new diseases arriving on the islands remains one of the greatest threats to this island species. The word for this is "biosecurity." 

Everyone that visits the islands plays a role in biosecurity. See what you can do  

Health Checks for Catalina Island Foxes

biologist checks island fox's teeth

Across Catalina Island biologists are counting island foxes and giving them health checks. Foxes are caught in safe capture cages.

Catalina's population has recovered from the 1998 crisis caused by the introduction of the disease canine distemper. It is natural for populations of wild animals to adjust from year to year. We now know there is a direct connection between rainfall levels and successful island fox reproduction.

The return of drought conditions in 2018 caused an estimated 20% decline in island fox numbers on both Catalina Island and Santa Cruz Island. The Good News is everyone expects 2019's return of normal rainfall levels and a cool spring will bolster plant and animal resources and restrengthen island fox numbers.

We'll be waiting to hear what the biologists find in the field.

island fox receives a distemper vaccination

Lara Brenner, Wildlife Biologist for the Catalina Island Conservancy (CIC), reminds everyone that "Disease is the number one threat to Catalina Island Fox populations." During health checks, biologists monitor fox weight, body condition, and look for "new and emerging health issues."

Catalina is the most visited Channel Island. "Visitors can help protect the Catalina Island fox from disease," Brenner says, "by keeping their pets on a leash when not indoors and by staying up-to-date on your pet's vaccinations." No one wants their pet to pass-on or receive an illness while on vacation.

Wild raccoons are still a possible way for disease to be introduced to any of the islands. Brenner reiterates "Boaters should check their craft for stowaway, non-native animals (like raccoons) that could transmit a fatal disease." 

These simple actions are big steps toward protecting island foxes.

 

Island Fox M152 Has a Health Check

When M152 was fitted with his refurbished radio collar, he also received a health check.

During the health check he wore a special hood. Having his eyes covered makes the health check less stressful and helps the island fox remain calm.

M152 was:
Weighed - to compare his weight with previous years and to provide an overall view of the population across the island. How much did M152 weigh?

Blood Sample - A sample of his blood was taken to look for evidence of exposure to disease. In 2016-2017 blood samples documented adenovirus, commonly called "kennel cough," as it moved across Catalina Island infecting 85% of the island fox population. (See 2018 Update) Fortunately, no island fox deaths were attributed to the virus, but it demonstrated how fast an infectious disease can spread through island foxes. Testing blood samples provides an early warning of dangerous diseases like canine distemper, parvo, and more. It can also indicate whether disease might be influencing low pup survival. Some of M152's blood was also set aside to test for specific white blood cells. A high number of these cells may be evidence of a parasite infection. Some of the blood sample will also be used for DNA studies to determine the familial relationships between individual foxes. How are the pups in M152's territory related to him? All of this is above and beyond simple monitoring. 

Your donations help make this health research possible.

Disease - M152 showed no signs of disease. He appeared healthy.

M152 courtesy of Channel Islands National Park

Whisker Sample - A whisker sample was taken for an important research study on diet funded by Friends of the Island Fox.

Tick Testing - M152 was examined for fleas and ticks. Luckily he was tick free! But not all island foxes are so lucky. 

small red dot is a tick on the fox's ear

Tick-borne disease is a new threat to island foxes. Two infectious diseases carried by ticks have recently been discovered on the Channel Islands: Lyme disease and relapsing fever. Ticks found on island foxes, like the one on the back of an island fox's ear, pictured at right, are being removed and tested for disease. This is important research for island foxes and people. 

How many ticks are carrying disease? How many island foxes are infected? Lyme disease seriously impacts dogs; is it impacting island foxes? The tick is removed and tested to see if it is a disease carrier.

Tick after removal and prepared for testing.

Tick-borne disease is a new threat.

We need your help to fund testing of ticks.  

Removing the tick is also beneficial to the island fox.

Island fox ear after tick is removed.

Island foxes need your help. 

Friends of the Island Fox funds radio collars, 

proactive health testing, and vital research. 

With your continued support, we can hold onto success and keep island foxes like M152 healthy into the future. 

Please donate today.