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.
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| 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.
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| 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.
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| 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
