Every Island Fox Has a Story - Results from 2026 Island Fox Necropsy Workshop

 

At the Island Fox Necropsy Workshop in May, veterinary pathologist Leslie Woods, retired from UC Davis, led a group of island fox biologists, researchers, and others through the steps of an island fox necropsy (or autopsy) to understand the cause of the animals’ death. More about the Necropsy Workshop

Six island foxes from four islands were necropsied. Each tells a different and important story.

Parasitologist, Dr. Childress holds sample of parasites collected from island fox.

 

An island fox hit by a car is a snapshot of island fox health. For an island fox from San Nicolas Island, the immediate cause of death was car strike and a fractured skull. Further evaluation, however, revealed lungworm and that intestinal parasites (Spirocerca lupi) had traveled out of the fox’s intestines and through the blood vessels to other parts of his body. Even before its encounter with a vehicle, this island fox was critically ill. Previously, Spirocerca intestinal worms were considered a background health issue, incidental and typically not deadly. In 2026, however, nearly all island foxes on San Nicolas Island are infested with this worm and the average fox has a greater  amount of its intestine impacted. These worms can cause internal bleeding and infection. Across the islands, Spirocerca has become a more frequent cause of death for island foxes. The prevalence of this canine parasite is another reason people should not take pet dogs to the Channel Islands.

 

A San Clemente Island fox was discovered to have a swollen paw and inflammation around a rear leg bone. The necropsy revealed its forelegs were filled with cactus spines under the skin (see photo above). While this may have brought pain to the fox, the primary cause of death was kidney failure. Kidney or renal failure is a common cause of death for island foxes, yet the reason remains unknown. More research is needed to understand if there is a virus or bacterial connection or if something else makes island foxes vulnerable to kidney disease.

A Catalina Island fox was also found to have cactus spines in its tissues, but its cause of death was related to atrophy of its rear limb muscles which compromised its mobility and led to starvation. The cactus spines were not in the muscle. The cause of the muscle atrophy in this older fox remains unknown.

A second Catalina fox, a female in her prime, died of bacterial septicemia. Bacterial infection overwhelmed her heart and kidneys. Unfortunately, the initial source of the infection remains undetermined.

Despite concerted efforts to reduce island fox access to D3 rodenticide on San Clemente Island, another island fox accessed the material and was inadvertently poisoned. Knowing that rodenticide poisoning is still happening helps land managers make changes to protect other island foxes.

FIF President Mike Watling prepares protective gear

Friends of the Island Fox President Mike Watling and Treasurer Keri Dearborn helped necropsy a Santa Cruz Island fox. This 4-year-old male fox was the first fox mortality detected with the new digipeater collar system on Santa Cruz Island. Biologists were alerted through the automated system and the fox's body was found within 14 hours of his death.

Photos are taken throughout the necropsy to provide maximum information

His teeth showed hard wear for his 4 years. The good news was he appeared healthy, with no internal parasite problems or signs of disease, but this fox suffered an extreme abdominal trauma that caused internal organs to be pushed outside of his body. He was found up on a hillside a great distance from the road and there was no evidence to suggest car strike.

Did he fall from a cliffside or a tree? There were no other signs of physical trauma. Was he kicked or struck? He was in an area with few people. Was the weakness of his abdominal wall a genetic symptom that has yet to be identified? We don't know, but across the islands, everyone will be watching for similar unusual physical issues.

At the 2026 Necropsy Workshop, no new disease threats were identified. These necropsied island foxes provided important scientific information for the health of all island fox populations:

• Renal failure is a chronic island fox health problem; more research is needed to understand why. 
• Intestinal parasites and lungworm are growing concerns for all islands. 
• Prickly pear cactus spines may be more dangerous to island foxes than previously known. In the foxes examined, there was no walling off of the spines by the fox's immune system. Other island foxes have recently been found with plant matter that has migrated through their tissues into the lungs, causing death. Does greater investigation need to take place before prickly pear cactus is used in island restoration projects? 
• Investigation of viruses, fox immune systems, and thinking outside of the box on genetic vulnerabilities are needed going forward.  

Thank you to the Fresno Chaffee Zoo Wildlife Conservation Fund for a grant supporting island fox necropsies and pathology.

For more about the participating organizations in the 2026 Island Fox Necropsy Workshop 

Learning from an Island Fox's Death - Island Fox Necropsy Workshop 2026

Attendees viewing samples of parasites found in island foxes.

 

When an island fox dies, understanding the cause of death is important. Was the cause a disease that could threaten an entire island? Was the cause a human impact that could be avoided? Did a healthy appearing island fox meet with a sudden death that captured the actual state of its health like a photograph fixed in time? Was the cause of death unusual and greater understanding is needed?

In May, Friends of the Island Fox and the Santa Barbara Zoo hosted our second Island Fox Necropsy Workshop. Over the course of the day, six island foxes that died under different circumstances were examined. Physical specimens from various organs and parts of their bodies were collected and labeled for further evaluation at the California Animal Health and Food Safety Lab.

Veterinary pathologist Leslie Woods retired from UC Davis led the workshop with the assistance of parasitologist Dr. Jasmine Childress from the University of Wisconsin, and veterinary epidemiologist Dr. Jessica Sanchez from Utah State University and her graduate student veterinarian Kelsey Rayment.

The workshop goal was to teach field biologists how to identify probable causes of death and how to prepare specimens to be sent for further study. The workshop brought together representatives from the Channel Island land managers as well as veterinarians, technicians, and researchers from Cal State Long Beach, UC Riverside, USC, and the University of New Mexico.

The workshop helps researchers connect with how specimens are collected and builds holistic understanding of island fox physiology. Researcher Kimberly Schoenberger (USC) recently published on the brain size of island foxes working from skulls preserved at museums, but this was her first opportunity to directly encounter an island fox brain. Researcher, Eve Rowland (UNM), commented “I had a great experience. I have previous experience preparing specimens for museum collections, but it is pretty different from necropsy. … [I]t was helpful to understand how that process works.”

Dr. Childress shows collected intestinal parasites

 

Participants collected samples of various intestinal parasites and were able to examine and identify them under a microscope. It was a day of biological education, but also camaraderie and network building.

A huge thank you to FIF Board member Dr. Jessica Sanchez for spearheading the event, FIF Secretary Kris Chatari for organizing snacks and breaks, and to our co-hosts at the Santa Barbara Zoo, especially master organizer Nadya Seal and the veterinary team. Thank you also to the San Diego Zoo, UC Davis, and the CA Animal Health and Food Safety Lab for supplies and expertise.

Stay tuned for the findings from 6 island fox necropsies.

Hear directly from Dr. Woods about the importance of necropsy
See Dr. Sanchez give an island fox a health check
Researcher Eve Rowland will be presenting her work at the August 18, 2026 "Date with a Fox"

Endangered Island Foxes Stabilizing But Need to Monitor Continues

courtesy of Kevin Schafer

The annual meeting of the Island Fox Conservation Working Group took place yesterday, hosted by Friends of the Island Fox. 

The good news is that the four endangered populations of island foxes on San Miguel, Santa Rosa, Santa Cruz, and Santa Catalina Islands continue to recover and stabilize. 

Island foxes on the two Navy islands, San Clemente and San Nicolas, are not considered endangered by the U.S. Fish & Wildlife Service (USFWS) and their populations remain stable and at high densities (number of individual animals per square kilometer).

The graph below shows population numbers for San Miguel Island through fall 2013. The population was initially estimated in 1994. Actual individuals were counted when island foxes were in captive breeding pens on the island. Through 2007, the island foxes on San Miguel were gradually returned to the wild. Wild population figures are estimated through an annual catching of individuals and computer extrapolation of that data. More on Counting Island Foxes.

The graph shows how San Miguel's population dropped dramatically due to golden eagle predation at the turn of the century. Fifteen surviving individuals became the founders of the current San Miguel Island fox subspecies; captive breeding by the National Park Service saved this subspecies from extinction.

The population has made an amazing and rapid recovery to a level greater than historically estimated before the crisis. Statistical analysis through fall 2013 calculated that for the fifth year in a row,  individual island foxes on San Miguel have a 90% chance of surviving through the next year and the potential for species extinction is very low.  

Currently the density of island foxes on San Miguel is very high, 10-20 individuals per kilometer in some habitat areas. National Park biologist Tim Coonan believes the data shows the San Miguel Island fox population has fully recovered and has reached the "carrying capacity" for this small island. This means the food and territory resources available on San Miguel can not support continued population increase. The minor population ups and downs since 2010 follow the pattern of a population responding to resource availability. 

Conservation efforts on behalf of the San Miguel Island fox have been very successful. Across Santa Rosa, Santa Cruz and Santa Catalina the stories of population recovery from the brink of extinction are all inspiring.

However, there is an additional cautionary chapter in the San Miguel story. As the island foxes in the National Park have recovered, funding has decreased for their management. The staff that works with the foxes on San Miguel and Santa Rosa has gone from six to three technicians. 

Since the end of 2013 thru May of 2014, seventeen radio-collared island foxes on San Miguel have died from peritonitis caused by a parasitic spiny-headed worm (the exact species is still being determined). This parasite has not been a problem on the Channel Islands before and typically does not cause mortality in canines. The spiny-headed worm is transmitted to the fox through another animal-species host that the fox has eaten.

Today as the biologists, veterinarians, land managers and government officials meet for a second day, they are sharing expertise and ideas about how to respond to this potential threat to the San Miguel Island fox. Over the next few months they will be looking for answers to new questions:

• What prey species is carrying the parasite?
• Have island foxes on San Miguel changed to a prey species that is a vector for this parasite?
• Across San Miguel Island a higher number of island foxes are appearing underweight. Are these foxes infected with the parasite as well?
• Is drought a factor in this problem?
• Is high population density a factor?  
• Why is the number of these parasites so high in individual foxes?
• During the fall count, there appeared to be a very low number of pups on San Miguel. Is this a natural response to high population density and reduced resources? Is the parasite impacting female health and therefore reproduction?
• Is the parasite a possible threat to other Channel Island fox subspecies?

Channel Island foxes are rare creatures. Prior to the near extinctions of 2000, little was known about this endemic California species. If there is one thing that has become obvious over the years, it is that change to the island habitat, either directly by people or indirectly through environmental toxins, climate change, or introduced invasive species, island fox survival requires vigilance. 

The continuity of public support and scientific experts engaged in island fox conservation is vital to maintaining this unique species into the future. Funding the Island Fox Conservation Working Group meeting is an important part of island fox conservation.

Stay tuned for more information from the Working Group meeting.