Radio Collars Protect Island Foxes

courtesy of Kevin Schafer

Island foxes are making a strong recovery across the Channel Islands, but the need to monitor their populations continues.
 
This past year, in 2013, three radio-collared island foxes were killed by golden eagle predation. Two foxes were killed by a golden eagle on San Miguel Island and one on Santa Cruz Island. Biologists do not know if the island foxes were killed by the same golden eagle or by two different golden eagles. The distance between the islands can be easily managed by a single large eagle. However, in the past, golden eagles have often preyed on island foxes in a specific area when they have been successful.

As the populations of island foxes have increased, the cost of radio-collaring all adults has become prohibitive. Radio-tracking collars now cost $300 each. A representative number of island foxes are radio-collared on each island–approximately 5% to 11% of individual island foxes on each of the northern islands. 

golden eagle at Denali Nat'l Park, courtesy of NPS

For each radio-collared island fox killed by a golden eagle, there is the possibility of several non-collared foxes being impacted as well. Island foxes are well camouflaged for their habitat. When an island fox without a radio collar is killed by a golden eagle it is difficult to know the incident happened, little alone to find the fox's remains. 

Because radio-tracking collars give off a specific signal when a fox is no longer living, radio collars are vital tools for locating individual island foxes and responding quickly to determine why that animal has died. Island Fox CSI

On Santa Catalina Island this past year biologists were on the look out for stowaway raccoons carrying disease. But in 2013 they encountered a new invader–a northern opossum that hitchhiked on a private boat and made its way onto the island. Introduced animals pose a serious disease threat to island foxes. Canine distemper 

Radio-tracking collars are the island foxes' best defense against unexpected threats. To-date Friends of the Island Fox supporters have funded 96 radio collars. 

The Foxy Ladies of El Segundo Ladies Golf Club

$300 Helps protect island foxes. Who has funded radio-tracking collars? 

• Classes of school children
• Zoo keepers
• Zoo docents from across the country
• A Baseball team
• People giving a radio collar sponsorship in honor of someone special
• And Private individuals Like You

Join with other people to help fund radio collars for island foxes. 

Channel Island Foxes and Golden Eagles in 2013

NPS photo of a golden eagle in Denali N.P.

Between February and March of 2013, a threat to island foxes on the northern Channel Islands returned - a golden eagle.

Golden eagles migrate north from Mexico and the lower 48 U.S. states up into Canada and Alaska annually. Sometimes this means they fly over the Channel Islands. Historically, golden eagles have not lived on the Channel Islands for two primary reasons:

1. Golden eagles are mammal specialists. Their chosen diet consists primarily of mammals about the size of a football. The Channel Islands, prior to European settlement, did not have adequate food resources for this large predator to successfully live and breed.
2. Bald eagles historically thrived on the Channel Islands because they prey on fish, sea birds and carrion. Similar in size, bald eagles are highly territorial and dissuaded the golden eagles,  from spending extended amounts of time in the island ecosystem.

Why Did Golden Eagles Become a Threat to Island Foxes?

Beginning in 1843*, the islands were transformed into ranches. The surrounding ocean was the perfect fence.  Domestic animals (pigs, sheep, goats, rabbits (on Santa Barbara Island) and even cattle) were introduced and then allowed to go wild or feral. Mule deer and elk were also introduced on Santa Rosa Island for paid hunting trips. The young of these species, plus entrails left behind from hunting, attracted golden eagles to the northern islands.

By the mid 1950s bald eagles on became extinct on the Channel Islands because of DDT in the marine ecosystem. Without the bald eagle to drive it away, the golden eagle took up residence on the northern islands. Between 1994 and 2000, golden eagles nearly ate all of the island foxes on San Miguel, Santa Rosa and Santa Cruz Island. Island fox decline.

Positive Conservation Steps

island foxes during captive breeding, NPS

While the island foxes were protected in captive breeding facilities on the islands (2000-2008) conservation efforts helped restore balance on the islands:

• ~40 golden eagles were captured and relocated to northern California
• Bald eagles were reintroduced to Santa Cruz and Santa Catalina Islands. In 2006 they began reproducing naturally. The recovering bald eagle population is helping to stop golden eagles from recolonizing  the islands.
• Feral pigs, sheep and goats were removed and by 2012 introduced deer and elk were removed from Santa Rosa Island

Golden Eagles in 2013

On February 26, 2013 a group of bird watchers spotted a golden eagle at the Saticoy Spreading Ponds in Ventura. During this same time period, two island foxes on San Miguel Island were preyed upon by a golden eagle and a golden eagle was also seen on Santa Rosa Island.

Each year the threat posed by golden eagles flies over the endangered island foxes. Radio tracking collars are a primary means of alerting biologists that a golden eagle has killed an island fox. If predation continues, biologists can respond by trying to locate and capture the lingering golden eagle. Microchips under the skin of each island fox help biologists know the age and life history of individual foxes that are the victims of predation. Friends of the Island Fox raises funds to provide radio tracking collars and microchips for endangered Channel island foxes.

As the Channel Island fox populations recover on the northern islands, golden eagles pose less of a long-term threat. A normal population of 500 or more island foxes can withstand the loss of a few individuals to natural predation by golden eagles passing by. As the natural balance of the islands is restored with dense native vegetation, the territorial bald eagle in residence and robust island fox populations, the occasional golden eagle migrating by will become less of a threat.

*"Channel Islands National Park Timeline", Channel Islands National Park

12th Annual Meeting of the Island Fox Recovery Group

Last week biologists and land managers from across the Channel Islands came together to report on the current status of California's endangered island fox.


The news in 2010 is very positive. Conservation efforts are paying off in increased population numbers for all four of the endangered subspecies–San Miguel, Santa Rosa, Santa Cruz and Santa Catalina Islands. But even as there was discussion on the criteria needed to support a possible delisting from endangered status, the importance of monitoring these vulnerable populations was brought home.

In the early months of this year, 11 island foxes on Santa Rosa were killed by an unnatural predator, a golden eagle. A juvenile golden eagle was spotted on several occasions, but to date it has not been caught. The deaths of the endangered animals came to light because of individual island foxes that were radio collared and monitored.

Across the islands radio collars enable biologists to quickly locate a fox that has died. When the animal doesn't move at all for six hours the radio collar changes it signal to a "mortality" pattern. This timely knowledge enables the biologists to immediately find the carcass and begin to determine the cause of death. The sooner the cause of death is understood, the quicker steps can be taken to protect other island foxes.

Radio tracking collars play a vital role in monitoring island foxes and have helped these tiny animals to make an unprecedented recovery for an endangered mammal species. This is why Friends of the Island Fox has worked to raise funds to place radio collars on individual island foxes. (See Radio Collars)

As we distill down our notes from the Annual Conference and verify our information with the island fox biologists, we will be posting an update for each of the 6 subspecies of island foxes.

While there are still challenges ahead for endangered island foxes, population numbers are up and community awareness is growing. Friends of the Island Fox thanks all of you who have played a role in raising funds, educating the public, and working on island fox conservation. You have played an important role in bringing the island fox back from the brink of extinction.

Island Fox Origins and the Truth Behind Eagle Diets

Are you looking for information on the origin of island foxes; how they evolved and their biology? Perhaps you’ve heard people question whether golden eagles were actually preying on island foxes. Answer your questions with information from the primary sources.

Friends of the Island Fox is honored to make information available from top researchers and biologists working with the island fox and the Channel Island ecosystem.


Paul W. Collins, Curator of Vertebrate Zoology at the Santa Barbara Museum of Natural History recently gave two presentations from his accumulated research at an Island Fox Workshop sponsored by the Santa Barbara Museum, Ty Warner Sea Center, Santa Barbara Zoo and Friends of the Island Fox. Both of these presentations are now available through links from the Friends of the Island Fox Educational Research Library.

• Origin, Evolution and Biology of the Island Fox - looks at genetic, morphological, and archeological data regarding island fox origins and the basics of island fox biology, size, behavior, reproduction and diet

• Diet of Bald and Golden Eagles on the Channel Islands - looks at the role eagles played in the decline of island foxes on the Northern Channel Islands and compares the diet of bald and golden eagles on the islands by examining prey remains in nests.

These two slideshow presentations can be found in the Educational Research Library

Under: “Island Fox Fact Sheets & Current Research”

Under: “Links to Research Sources”

Friends of the Island Fox is endeavoring to create the Internet’s most current library of information regarding island foxes. If you are a researcher or biologist and would like us to link to or host your published work relating to the island fox or the Channel Island ecosystem, please contact the Friends of the Island Fox Webmaster at islandfoxnews@gmail.com

Six Islands, Six Different Island Foxes

Island foxes are found on six of the eight Channel Islands off the coast of southern California. (Where does the island fox live? What is an island fox? Experiencing Santa Cruz Island )

A pair of San Clemente island foxes at the Santa Barbara Zoo. (Where can you see an island fox?)


Island foxes all have similar lifestyles and habits:

• About the island fox
• Males consistently weigh more than females
• What do island foxes eat? Their favorite food is the deer mouse. (Each island has its own subspecies of deer mouse.)
• Island foxes are good climbers, which allows them to reach bird nests and eggs
• Island fox pups are born in the spring. Island foxes usually have 2-3, but may have as many as 5 pups

But the foxes on each island are slightly different from each other. The differences are great enough that each island has its own subspecies of island fox.

National Park Service biologist Tim Coonan points out that the San Miguel island fox weighs significantly more than the island foxes on the neighboring island of Santa Rosa.

A San Miguel island fox being fitted for a radio collar.

A pair of Santa Rosa island foxes. (Experiencing Santa Rosa Island)













Tail length is a specific physical trait that varies between the different subspecies. Studies show island foxes from different islands have more or less tail vertebra.

In descending order:

1. San Nicolas Island 22 tail vertebra
   
2. Santa Catalina Island 21 tail vertebra
3. San Clemente Island 19 tail vertebra
4. Santa Rosa Island 19 tail vertebra
5. Santa Cruz Island 19 tail vertebra
6. San Miguel Island 15 tail vertebra

Between the shortest-tailed island foxes on San Miguel Island and the longest tailed on San Nicolas Island there is a difference of 7 vertebra. Interestingly, Schoenherr, Feldmeth and Emerson point out in Natural History of the Islands of California (Univ. of California Press 1999) that the island foxes on San Nicolas Island appear to have the least amount of genetic diversity. This suggests the San Nicolas population may be descended from as few as a single pair of foxes.


All of the island fox populations are vulnerable because they live in such limited habitats. Small population numbers mean that a single introduction of a disease, like the canine distemper outbreak on Santa Catalina Island, can threaten an entire island fox population. (Santa Catalina island fox Update) Catastrophic events, like the arrival of an unexpected predator–the golden eagle–can cause near extinction.

The island foxes on San Miguel Island were reduced to only 15 individuals because of predation by golden eagles. This genetic bottleneck means future San Miguel Island foxes will be more genetically alike than they were in the past.

Conservation and research efforts are necessary across the islands to preserve and protect the six subspecies of island foxes.

Donations to Friends of the Island Fox supports conservation and education efforts to Help Save all six subspecies of island fox. See how your donations can make a difference.

Island Fox Research Notes – Hilary Swarts

Hilary in the field on Santa Cruz Island with one of the oldest collared females, A3Y. (Photo by Jessica Sanchez)

“You can kind of see her collar ID colors: Pink, White, Pink, Pink. That's how we identify the foxes photographed by remote cameras. Annoyingly, it doesn't work all the time. This female just got her newly painted collar in mid October.” - Hilary

Research: Circadian temporal activity of the Santa Cruz Island Fox (Urocyon littoralis): A possible newfound anti-predator defense for a naïve, endangered species

Hilary Swarts, a PhD candidate at the University of California at Davis, is studying the behavioral response of the island fox to golden eagles, a predator to which foxes are not adapted. Her theory is that foxes, which are naturally active during the day (diurnal), have possibly changed their behavior in response to predation pressures from golden eagles. Eagles also hunt during the day, so foxes may be responding by being more active at night (nocturnal). Specifically, the research is investigating whether behavior patterns of foxes on Santa Cruz Island have changed in the period since the 1990’s when golden eagles colonized that island. If foxes have changed their behavior, this shift may be a selection- or learning-based response to predation by golden eagles, or it may be a response to reduced fox density.

Hilary’s research will examine several aspects of island fox ecology including reproductive success, changes in population abundance in response to different levels of predation, daytime activity levels in the absence of predation, and will compare measures of daytime activity to the risk of predation. The results from her research will contribute scientifically to the understanding of the effects of invasions on behavioral ecology, while also providing crucial information to resource managers on the risks of golden eagle predation to the Santa Cruz Island fox population.

Hilary Swarts , Ph.D. Candidate
Department of Wildlife, Fish, and Conservation Biology
University of California at Davis


FIF plans to fund future island fox research. You can help with your donation to Friends of the Island Fox, Inc. To donate use the PayPal or Network for Good buttons in the upper right corner.

For more on Santa Cruz Island and the island fox:

• Experiencing Santa Cruz Island
  
• Where Does the Island Fox Live
• What is an Island Fox
• What Do Island Foxes Eat?