Are Grapes Toxic to Island Foxes and Gray Foxes?

Recently, this question was posed to Friends of the Island Fox by a wildlife sanctuary that cares for gray foxes. Because gray foxes are wide-spread and considered common, little scientific research has evaluated their daily behavior, including diet. Island foxes, however, have been through periods of captive breeding when they faced near-extinction and there is a growing library of research on their diet and health.

Since island foxes are recently descended from gray foxes, it stands to reason that the two species would have similar responses to toxins. We reached out to the veterinarian members of the Island Fox Working Group and discovered there is no authoritative answer.

Tartaric acid in grapes can be toxic to domestic dogs, damaging kidney function. Since island foxes and gray foxes are part of the canine family it's reasonable to extrapolate that grapes could be toxic to foxes as well. Inquiries to toxicologists and a range of references uncovered no reputable sources that confirmed or denied that grapes are toxic to foxes (or any wild canid). "In the absence of evidence," says wildlife veterinarian and FIF Board member Jessica Sanchez, "it seems reasonable to err on the side of assuming things toxic to dogs will be toxic to foxes." Therefore, grapes, cocoa, and coffee are all substances that should be kept away from gray foxes and island foxes.

island fox in a fig tree

 

Do wild gray foxes sometimes eat grapes? Yes, one scientific paper, from the last century, reported wild grapes were found in 9.5% of gray fox stomachs. What is unknown is the comparative level of tartaric acid between wild and domestic grapes and whether or not eating grapes impaired kidney function in the wild foxes.

 

Ironically, in classical Greek and Roman literature, foxes were depicted as raiding vineyards to eat grapes. In Aesop's fables, a fox's craving for sweet grapes turns to disdain when his goal becomes unreachable. Aesop's fox, however, is a red fox and not a close relative of the gray fox and the island fox.

gray fox in a Camarillo backyard

 

Still, there are anecdotes in Lyndal Laughrin's 1980 paper "Populations and Status of the Island Fox" that recount how the number of island foxes on Santa Cruz Island in 1918 was so great, they "were destroying the grapes in the vineyards." Whether or not the foxes fared well after consuming the grapes, is not reported.

toyon berries are eaten by island foxes

 

Gray foxes and island foxes are omnivorous. Native fruit can make up more than 50% of an island fox's diet. How do island foxes process toxins found in some of the fruit they eat? Answering these questions for island foxes would also help us understand gray foxes better, and maybe other canines, too.

Friends of the Island Fox supports island fox research

Applications for the FIF 2024 Research Grant 

will be accepted through June 30, 2024  

(Thank you to J. Sanchez DVM and J. Barnes DVM for their investigation of this question.)

Fox Foto Friday - Injured Island Fox Back on Her Feet

This young female island fox was discovered during capturing of island foxes for counting and health checks with a broken rear leg. Her story is one of multiple agencies, institutions, and a community of people working together to help her survive.

Friends of the Island Fox and donors like you helped raise the $1,900 to pay for her specialized orthopedic surgery. Following her orthopedic evaluation on March 15, Julie Barnes, V.P. of Animal Care and Health at the Santa Barbara Zoo, reported that "the fracture is healing really well and no longer needs bandaging." 

March 28th and she is standing solidly on all four legs!

All island foxes are under the jurisdiction of the California Dept. of Fish & Wildlife (CDFW). Removing an individual from its island habitat is a major decision because once an island fox comes off of its island of origin, it can not be returned. Because island foxes evolved in isolation on the Channel Islands, they are very susceptible to diseases from the mainland. Canine distemper virus is lethal to them and nearly caused extinction on Catalina Island in 1998. Today, a minimum of 100 island foxes are vaccinated against distemper on each island annually. (Help FIF vaccinate foxes)

 

To protect the wild population, the injured female island fox can not return to San Nicholas Island. The CDFW has approved The Living Desert Zoo and Gardens in Palm Springs as her new home. The Living Desert is an American Zoo Association accredited zoo and has cared for other island foxes in the past. She will be moving to her new home March 30th.

Currently, there are six island foxes living in zoos on the mainland. The CDFW requires that each facility only have males or females, since no island foxes can be bred on the mainland for release on the islands.

If you can't travel to the Channel Islands, you can see island foxes at:

The Santa Barbara Zoo

Brothers, Lewis and Clark, were abandoned by their parents as pups during a drought year on San Clemente Island. The Santa Barbara Zoo leads the zoo community's efforts toward island foxes and hosts the annual Island Fox Conservation Working Group Meeting.

California Living Museum, Bakersfield

Two sisters, from San Clemente Island, were also abandoned by their parents as pups during a drought year. They are in an enclosure with a female gray fox. The only place where you can see these two species side-by-side.

The San Diego Zoo Safari Park
Is home to Sage, a female island fox from Catalina Island, who was separated from her parents by people as a pup, resulting in chronic health issues. She was unable to be released back into the wild and requires regular veterinary care. 

The little San Nicolas Island fox joins her five cousins as ambassadors for their wild relatives. They tell a story of how human actions can be detrimental or positive for island foxes.

The San Nicolas Island fox has a second chance because people like you came to her aid.

FIF Research Grant Application 2024

Friends of the Island Fox is currently taking applications 

through June 30 for the 

FIF 2024 Research Grant

Download Application

From the complex relationship between island foxes and island spotted skunks, to diet, microbiome impacts on health, and changing territory sizes, research projects are revealing the complexities of the Channel Island ecosystem and the role of island foxes in island ecology.

In 2024, Friends of the Island Fox is offering up to $7,000 in support to research projects benefiting greater understanding of the island fox and the Channel Island ecosystem.

 

Last year's grant recipients are using wildlife cameras to quantify island spotted skunk populations and investigating the impact of individual island fox behavior on the island ecosystem.

It's Science, for Fox Sake! And we encourage all applicants to apply.

 

2023 grant recipient, D. Thomaier

Past Research Grant Recipients and Projects

Grant Recipients are asked to provide public updates on their work - "Date with a Fox" programs, hear from the researchers

Published science on island foxes and island spotted skunks

 

 

Your Donations Help Fund this Important Science!

FIF 2023 Research Grant to Investigate Individual Island Fox Impact

FIF awarded a second Research Grant in 2023 to Juliann Schamel, NPS biologist and graduate student in Ecology and Conservation at University of Aberdeen, Scotland...

Juliann Schamel in the field with island fox

 

and Dr. Alexandria DeCandia, biology professor at Georgetown University...

Dr. Alexandria DeCandia

 

for their project: From Microbes to Habitats: How Individual Fox Foraging Behavior Cascades Through an Ecosystem.

Schamel and De Candia are combining their respective work in stable isotope diet analysis and microbiome research to investigate the specific interconnections between 15 male island foxes and the island ecosystem. The team says, "Recent research has revealed that the island fox displays a high level of individual specialization, from their diet, to activity patterns, to the germination rate of scat-dispersed native seeds." This work builds on stable isotope diet analysis that Schamel presented at the Channel Island Symposium that demonstrated that diet specialization is occurring on Santa Rosa Island. 

GPS radio collar deployed on Santa Rosa Island

The 15 island foxes to be studied were part of a territory range investigation monitoring island fox movement with GPS radio collars by FIF 2021 Research Grant recipient Katie Elder. The final collection of data occurred in December 2023 when the island foxes were recaptured and their GPS collars removed.

Combining specific daily movement data (over the course of a year) with stable isotope diet data from individual whisker samples and microbiome swabs of gut microfloral offers a unique window into the lives of these individual island foxes. 

Microbiome sample swabs

 

It's easy to assume that island foxes, as a species, have a specifically defined relationship with plants and animals in the island ecosystem. However, Schamel's island fox dietary data has revealed a great deal of individualism in dietary choice, especially when resources are abundant. Some island foxes are eating beach foods, some are fruit specialists, others prey predominantly on deer mice.

Island fox whisker sample being collected

 

This investigation will try to reveal "a more holistic understanding of island foxes," DeCandia says. "[H]ost-associated microbes are critical to ... digestion and immunity,... By linking gut microbial communities with individual diet, movement, and activity patterns, we can begin to untangle the eco-evolutionary factors shaping these island hosts, their microbes, and the ecosystem in which they live."

Comparing microbiome of island fox and island spotted skunk, A. DeCandia

 

Friends of the Island Fox is proud to invest in this cutting-edge, multidisciplinary scientific investigation that brings together academic and governmental organizations and investigators. Whisker samples will be processed and analyzed by Julianne Schamel and Seth Newsome at the Center for Stable Isotopes at the University of New Mexico. DNA from microbiome swabs will be extracted by Alexandria DeCandia at the Center for Conservation Genomics at the Smithsonian's National Zoo and Conservation Biology Institute. Undergraduate researchers at Georgetown University, University of New Mexico, and California State University Channel Islands will actively participate in sample collection, laboratory preparation, data analysis and interpretation, and co-authorship of findings. 

Your donations help grow scientific knowledge and the next generation of scientists! 

Applications for FIF's 2024 Research Grant 

will be available March 22

Stable Isotopes Document Decade of Dietary Change in Island Foxes

Juliann Schamel has been researching island fox diet using stable isotopes in whisker samples since 2018. Friends of the Island Fox has supported the processing of whisker samples through several Research Grants. In November of 2023, Schamel presented the following poster of her latest work at the California Islands Symposium.

Using Stable Isotopes to Assess a Decade of Dietary Resource Use in Two Sympatric Island Endemics: The Island Fox and the Island Spotted Skunk (link to complete poster)

Island foxes and island spotted skunks live together on two islands, Santa Rosa and Santa Cruz. When island fox numbers crashed due to predation by golden eagles, island spotted skunk numbers appeared to increase dramatically. In 2011, on Santa Rosa Island, there were still fewer than 90 island foxes in the wild. During annual health checks, whisker samples were collected from both island foxes and island spotted skunks in a northern area of the island and stored for later analysis of what food resources each species was using.

In 2011, island spotted skunks out numbered island foxes in the wild. Stable isotope analysis shows that the skunks and foxes were using different resources. 

J. Schamel, 2023 poster

 

Carbon and nitrogen isotopes travel up the food chain leaving a specific isotope signature for plant and animal resources. Literally, you are what you eat and isotopes from a mammal's diet are laid down chronologically in hair or fur. A single island fox whisker can provide 5–6 months of weekly diet data. On the graph above, native terrestrial plant foods, like manzanita berries, are high in Carbon and low in Nitrogen. A deer mouse is the accumulation of its own, mostly plant diet; it has a mid-range Carbon and Nitrogen signature. In the graph above, the blue data points represent island fox diet and the orange data points represent island spotted skunk diet. 

In 2011, when island fox numbers in the wild were low, their diet tended to be higher on the food chain or trophic level: deer mice, birds and reptiles. The data suggested separate diet niches for island foxes and island spotted skunks. The skunks were eating primarily, lower level prey, like insects, and some plant foods.

J. Schamel, 2023 poster

In 2014, continuing drought influenced wildlife survival; island fox and island spotted skunks were nearly even in number on Santa Rosa Island. Island foxes expanded their diet, including marine resources, and island spotted skunks preyed more on deer mice and higher level prey. The two predators began competing for resources.

J. Schamel, 2023 poster

By 2018, the island fox population had recovered, but island spotted skunks appeared to decline in number. (Counting island spotted skunks) As island fox density increased across the island, they dramatically broadened their diet–from native fruit through a range of prey species. The spotted skunks maintained a more narrow diet, but they were now in constant competition with island foxes. What will this mean for the two species?

Schamel's work also revealed that individual island foxes are becoming specialized in their diet.

J. Schamel, 2023 poster

 

In the graphic above, each circle of data points represents an individual island fox and its diet. Some individuals appear to be specializing in fruit and insects, while others are eating predominately terrestrial prey. How is island fox diet continuing to change?

Save the date of April 30th at 6:30 pm PT 

Juliann Schamel will talk about her work on 

FIF's "Date with a Fox" webinar

sign-up for FIF's e-newsletter to receive an invitation

Measuring out a whisker sample

Whisker samples continue to be collected for both species. 

designed by island biologist, Stacy Baker

When you purchase an island spotted skunk pin, 

you send a sample of island spotted skunk whisker 

to the mass spectrometer to reveal stable isotopes.

You Did It! You Gave An Island Fox a Second Chance!

Thank you to our donors - near and far!

Over the past three days, you've responded with overwhelming support and raised the funds to pay for special orthopedic surgery needed for this young injured island fox. Her story

 

 

Thank you to:

• FIF's long-time donors
• Our Instagram followers
• Our "X" followers especially our "Hijinkai" who love island foxes from afar in Japan

You all have helped to give this island fox a second chance on life.

Injured Island Fox Pup Gets Second Chance

 You can help this young island fox

Friends of the Island Fox is raising funds to pay for her orthopedic surgery

During the annual fall 2023 counting and island fox health checks on San Nicolas Island, biologists discovered this female pup with a recently injured right hind leg. The bones just above her foot, the metatarsal bones, had been fractured and the wound was open.

The injury was too severe for treatment on the remote Navy island. According to our friends with the U.S. Navy and the Santa Barbara Zoo: "The cause of the injury could not be determined but her chance for survival without intervention was minimal due [to] the risk of infection and septicemia posed by the open fracture. Releasing her without treatment with such an injury was determined to be both inhumane and life threatening."

island fox in the wild on Santa Cruz Island

Removing an island fox from the island where it lives is a big decision. Having evolved in isolation on their specific islands, once an island fox leaves an island it can not return. The biosecurity risk of introducing disease from the mainland to the wild population is too great.

The young fox was just old enough to be dispersing from her parents. With treatment and several months of observed convalescence, she had a good chance for full recovery. The cost of treatment, however, was being removed from the wild for the rest of her life.

 

The California Department of Fish and Wildlife (CDFW) gave special authorization to transport the state-protected species off of the island and off of the Navy's federal lands into state jurisdiction. She was flown off of San Nicolas Island and transferred to the Santa Barbara Zoo, which has "extensive experience in caring for orphaned and injured island foxes." A pair of brother San Clemente Island foxes who were abandoned by their parents during a drought year, currently live at the Santa Barbara Zoo. (Lewis and Clark)

In consultation with Dr. Steve Klause, a veterinary orthopedic surgeon, the Santa Barbara Zoo veterinary team initiated a conservative treatment plan. While the little fox responded well, the fracture did not initially heal as hoped. 

The Zoo team reached out to Friends of the Island Fox. The little female island fox needed special orthopedic surgical repair for internal fixation of the fracture. Could we help with some of the unexpected costs? 

FIF determined to raise the $1,900 needed.

On December 16, 2023, the little fox had her surgery and Dr. Julie Barnes Vice-President of Animal Care and Health tells us, she is doing well. The island fox still has several months of recuperation before she is fully healed. The Santa Barbara Zoo says "Once fully recovered, the fox will be transferred to a permanent home ... at an Association of Zoos and Aquariums (AZA) accredited facility where she will serve as an ambassador for the species - the first known San Nicolas Island fox to do so!"

Protecting island foxes is a community effort and saving this individual island fox is no different. People from the U.S. Navy, Santa Barbara Zoo, specialist veterinarians, and FIF are all investing in the future of this island fox.

You can HELP Too! 

Join our list of donors supporting this island fox

• Recycling for Island Foxes and the Planet: $200
• school children in Thousand Oaks, CA: $300+
• FIF Instagram followers: $125
• FIF "X" followers, including in Japan: $360
• FIF returning donors: $1,190
  

Unexpected Creatures During Island Fox Counting - Part 4

Welcome guest blogger Jessica Sanchez, wildlife veterinarian and FIF Board Member. She's explained how island foxes are captured annually in Part 1, shown how a fox's body condition is evaluated in Part 2, and demonstrated health procedures preformed on island foxes during an annual health check in Part 3. As she explains, she might be out capturing island foxes, but they aren't the only animals she encounters.

We also catch island spotted skunks, although this has become rarer in recent years.

You know you have caught a skunk even before you get to the trap because...

1. of the smell
2. they ball up all the grass and vegetation in the trap to make a cozy little nest for themselves
   

If you're lucky, they will still be asleep in this nest when you approach the trap the next morning. All of this gives you time to pause and carefully plan your approach to getting them out of the humane box trap. 

Skunks also get a microchip for identification and we take a tiny 2–3mm biopsy of the ear, with a special cartilage snip device, for genetic testing. Then they receive a thorough exam. (similar to island foxes) We try to handle the little skunks carefully so they don't spray us–this is for our benefit and theirs as it can take up to a couple of weeks for skunks to regenerate their spray and they need it to defend themselves. 

Currently, island spotted skunks are not vaccinated, though researchers are investigating options to potentially do so in the future.

Island spotted skunks aren't the only surprise that might be found in a box trap set out for island foxes. See what else Sanchez has found:

 

An island scrub-jay!

The final steps of a long day catching island foxes are to wash off any skunk spray and/or fleas, check yourself for ticks, enjoy a beautiful sunset, and get a good night's sleep before doing it again the next day! - Jessica Sanchez

Part 1 - capturing island foxes

Part 2 - Health Check: body condition

Part 3 - Health Check: veterinary procedures

 

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