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.

Fox Foto Friday - It's Research

 It's Research For Fox Sake!

 

This is an up close image of tiny bits of island fox whisker in a mini aluminum specimen holder. The micro-sample of whisker is on it's way to a mass spectrometer for analysis. Find out more about Juliann Schamel's research project with FIF.

The deadline to apply for FIF's 2020 Research Grant is August 31, 2020. 

Grant Application information

We're looking for research to support!

Island Fox Whiskers Go to the Lab

Schamel with island fox pup

FIF Research Grant recipient Juliann Schamel has been collecting island fox whiskers to study the diet of island foxes through stable isotope analysis. Her research project is in conjunction with Dr. Seth Newsome and the Center for Stable Isotopes at the University of New Mexico.

Juliann says "Once I learned how stable isotope ecology works and what we could learn about island fox ecology from this method...I was hooked. The invisible chemical world can reveal fascinating connections within food webs and beyond." More on stable isotopes

"This year, with the support of Friends of the Island Fox and [another conservation fund], we are able to investigate a variety of conservation-geared questions about island fox diet on San Miguel and Santa Rosa Islands. We are looking into how diet differs among habitats on the islands, among demographic groups, and between island fox and island skunk. We are also assessing if and how fox diet has changed over time (2010–present) in response to things like density changes in the fox population and rainfall (drought conditions). This last question may have important implications for the ecology of the acanthocephalan worm, a novel parasite that appeared in the San Miguel Island fox in 2012 (at the beginning of the drought) and has spread through the fox population."

The spiny-headed worm, a species of Acanthocephala, has been implicated in the low population numbers on San Miguel in recent years. Parasite threatening San Miguel Island Fox.

"By using whisker samples that are linked to a known individual with a known history within the island fox monitoring program," Schamel says, "we are able to track the diet of individuals over time to see if and how their diet may have fluctuated during the drought or as they moved to a new habitat."

A number of whisker specimens were collected this winter, including in the beach/dune habitat on Miguel and Rosa where island foxes are not typically counted. This will provide data on dietary resources in the marine adjacent habitat that has not been collected before. Schamel says "I am very excited to run these samples!"

Collected whisker samples are sorted, inventoried, and cataloged. Once they are cleaned, rinsed, and dried, each individual whisker is placed in vial.

Newsome and his lab manager at UNM use a razor and tweezers to divide each whisker into sub-samples: 0.2mg (weighed precisely with a micro-scale).

Schamel explains these sub-samples are fed into "the mass spectrometer, which consumes the samples and spits out data on carbon and nitrogen isotope ratios." The ratios are compared to a library of food resources and their known isotope ratios. "The FIF funding is actually paying the mass spectrometer for its time."

Schamel in the field on Santa Rosa Island.

So far ~100 island fox samples from Santa Rosa have been analyzed from a variety of habitats. In addition ~200 island fox whisker samples from San Miguel have been analyzed from 2010–2012, before the drought. Schamel will be at UNM this spring working on samples from 2014–2016. "There are many samples from the same individuals across this time frame, which will be exciting to see!"

Juliann Schamel hopes to present preliminary data at the 2019 Island Fox Conservation Working Group Meeting in May. 

Research like Juliann Schamel's is vital to understanding island fox health and long-term survival.  This research is only possible with donations from people like you.

Applications for the 2019 Friends of the Island Fox Research Grant will be available on islandfox.org on April 15, 2019.

Island Fox M152 Has a History

Island Fox M152

Each island fox counted across the Channel Islands during summer/fall monitoring is a documented individual. They each receive a microchip tag (or PIT tag) like your dog or cat. Why is that important? Why does FIF help fund ID microchips?

When island fox M152 received his radio collar this fall, he already had a documented history.

- He was first captured in 2014, when he was a young adult (estimated 1-2 years old). Island foxes live to be 8-12 years old in the wild. M152 is an adult male in his prime.

- He was living in the same area four years ago, which tells us that he is an adult male with an established territory in this location. Seven pups were seen in this same area in 2018. There is a good possibility that M152 is their father or grandfather. DNA comparison of blood samples could document their relationship. A blood sample was taken from M152.

M152's territory includes hillsides and coastal beaches, lucky fox

- 2014 was a drought year and M152 weighed 4.5 lbs (he was considered "thin"). In 2018 he had beefed up to 4.9 lbs (a weight considered "healthy"). A half pound might not seem like much of a difference, but when you are tiny that's almost 10% of your body weight.

island fox chin whiskers

- What has made the difference in M152's weight? Is he just eating better this year or is he eating a different diet than in 2014? Four years ago, a whisker sample was taken from M152. This year a whisker sample was collected again. Friends of the Island Fox has funded a Research Grant to evaluate these whisker samples. Whiskers record what the fox has been eating over a four to six month period. Isotopes from the food items, prey or plant matter, are laid down in the whisker as it grows out. M152 may help us learn what an island fox needs to eat to be healthy and successfully parent pups.

Friends of the Island Fox funds ID microchips, blood testing, 

and new island-fox research. 

You are the important partner in all of these efforts. 

When you donate to Friends of the Island Fox you are helping

 M152 and his pups have a safer future.

FIF Research Grant to Investigate Island Fox Diet Through Whiskers

photo courtesy of P. Bronstein

Island foxes have lots of long black whiskers. These specialized hairs hold important information on diet that could inform decisions on island fox conservation.

Friends of the Island Fox is happy to announce: 

Juliann Schamel is the recipient of the first FIF Research Grant

Schamel is a Biological Science Technician at Channel Islands National Park and the $5,000 grant will help fund research on "The Channel Island Food Web–A Decade of Dietary Resource Use in Channel Island Fox: Implications for Reproduction, Recruitment, and Resilience in a Changing Climate."

It's a big title reflecting the broad range of important data that may be revealed. 

Schamel's work will build on important past research.

island fox scat (or poop)

In 2009, researchers collected island fox scat samples to look at seasonal diet across all six islands. Their 2014 paper revealed diet varied from island to island and included a higher frequency of insects and fruit than expected. They cautioned that islands with poor native plant diversity offered fewer food options for island foxes in the event of drought. 

photo courtesy of P. Bronstein

Just as the science warned, during the consecutive years of the recent drought, island foxes were challenged to find enough food on San Miguel and San Nicolas Islands. Decline of San Nicolas Island fox. During this time a new parasite entered the San Miguel Island fox's diet causing fox deaths.

While scat successfully reveals visual items, (insect exoskeletons, cactus fruit skin and seeds), it may not visually capture everything in the fox's diet. Also, scat data is limited to recording diet in an individual over a short time period, a few days.

In 2010, building on work done on the San Joaquin kit fox, a small sample of island fox whiskers were investigated using stable isotope analysis. 

You are what you eat. Food items (prey and plant) have their own isotope fingerprint. Carbon and nitrogen isotopes consumed by the fox are laid down in the hair shaft documenting an individual's diet over months. 

Since 2010, biologists have been gathering whisker samples from individual island foxes during health checks on the northern islands. These samples have been cataloged by year and with individual fox identification. 

FIF is excited to support Schamel's research using whiskers because it has the potential to:

• Compare diet between successful mothers and unsuccessful mothers
• Discover dietary differences between coastal living island foxes and interior living foxes
• Document changes in diet over the past 9 years, through the drought and as the fox populations have grown
• Possibly reveal prey items that are a vector for the intestinal parasite on San Miguel Island which has caused fox deaths

Whiskers are amazing! Not only do they offer an opportunity to invest in greater knowledge about the secret lives of island foxes, whiskers grow back and their collection is non-invasive. 

FIF will be bringing you more on Juliann Schamel and her research as her work progresses.

Thank you to all of the 2018 grant applicants for sharing your research goals with FIF. There is so much more to learn about island fox health, behavior, and interactions with other species.

Application for the 2019 Research Grant

will be available April 15, 2019

Re-examining Island Fox Diet

What do island foxes eat?

Island fox scat with native fruit seeds

It is a common question and examining island fox scat (or poop) has provided some of the best answers. In 2009 a year-long study examined island fox scat over four seasons and across the six islands where they live. New Findings on Island Fox Diet.

The findings from this study, however, were done before multi-year drought impacted vegetation across California and on several islands. Have island foxes shifted their diet to other foods to make-up for the decreased availability of some plant foods or prey species?

Island fox scat with insect exoskeleton remnants

In 2009, island fox populations were recovering on four islands from near extinction and their population numbers were still relatively low. Most fox pairs could establish a territory in an area with abundant resources. Now that the populations have recovered, are island foxes eating a more diverse diet to meet their food needs? Are beetles and insects still the most frequently eaten prey? Have island foxes in marginal territories started to consume other food items? 

In addition to scat, whisker samples can provide evidence of what an island fox has eaten over several months. Whiskers are specialized hairs that grow over an extended amount of time. Trimming an inch or two off the end of a whisker, can provide researchers with information on what a specific individual fox has been eating. Isotopes laid down in the hair shaft document the kinds of proteins and plant matter consumed.

 While we don't think of island foxes eating marine animals, during a limited test study, one individual island fox was found to have isotope markers that signaled it was eating marine proteins, fish or crustaceans. Was this individual unusual?

Research on island fox diet is an on-going project. Biologists in the field counting island foxes on the northern islands were taking whisker samples this year.

Whether it is scat or whisker samples, it is time to add a new chapter to research on island fox diet.