What is Island Fox Density?

 

Density is a term used in biology to express the number of individual living things in a given area. Biologists use a defined area size–ie. a square meter, square kilometer or square hectare–to quantify density. 

A square kilometer is equivalent to the footprint of Disneyland in southern California and a square hectare is equivalent to a professional baseball field.

Understanding how many island foxes are living in a square kilometer is part of the calculation for estimating the size of an island-wide population.

At the recent Island Fox Conservation Working Group Meeting, land managers reported on the island fox density for their islands. There was a noticeable difference between northern and southern islands.

Northern islands are reporting considerably higher island fox density. The causes for this are not completely clear. Northern islands may benefit from less extreme weather–higher average rainfall and more moderate summer temperatures–which support diverse prey and plant food for island foxes. Northern islands also have fewer impacts from humans; Catalina Island and the two Navy islands, San Clemente and San Miguel, have roads and cars that cause the highest percentage of fatalities for island foxes. 

High density, however, can have a downside. Catalina Island has been stable for the past 10 years with a density around 9 foxes per sq km. The island with the highest density in 2023–14 foxes per sq km–was also the smallest, San Miguel Island. When density increases, individual island fox territory decreases. A smaller territory means a smaller area to find food. High density can push some individuals into habitats with fewer quality resources. San Miguel's resources are less diverse than the larger islands and there are fewer options for foxes when drought or other weather extremes occur.

 

When island foxes are living closer to each other, the possibility of disease moving rapidly through a population also becomes heightened. Parasites can spread more easily.

Understanding population density is important for calculating risks to populations and making informed conservation decisions. 

What Questions Do You Have For Island Fox Experts?

Next week 

the Island Fox Conservation Working Group 

meets for its 

25th Annual Meeting !

It's a time to celebrate the biologists, land managers, researchers, technicians, veterinarians, ecologists, government agencies, academic institutions, and conservation organizations that all came together to formulate a plan and take action to save island foxes from extinction and shepherd their recovery. 

It is also a time to ask questions of the folks that were on the ground trying to discern why island foxes were disappearing on the northern islands in the late 1990s.

And how was it discovered that canine distemper virus was killing island foxes on Catalina Island in the south?

How were the Catalina Island foxes saved from high levels of cancer?

What do we still need to find out about island foxes to protect them into the future?

Friends of the Island Fox 

is looking for your questions

Thursday May 18, we'll be posing your questions to the people of the Island Fox Working Group and videoing their answers.

Send your questions to info@islandfox.org

2021 Update For FIF Donors

Tuesday May 18, 2021 Friends of the Island Fox Board members participated in the annual Island Fox Conservation Working Group meeting (via a virtual space hosted by the Santa Barbara Zoo).

We thought we'd try something new and share the FIF Update with you so you could see exactly where your donations have gone this past fiscal year and where we are focusing our efforts right now.

 

We can't say it enough "Radio collars, radio collars, radio collars!" This season's radio collars and vaccinations will be shipping out in the next few weeks, along with the bill. 

Your donations help fund these vital efforts to protect island foxes.

Biologists, researchers and pathologists from across the Channel Islands also reported on island fox status and health. 

The news is good and FIF will post a summary of the Working Group Meeting next week.

Working Together to Save Channel Island Foxes

The success of Channel Island fox recovery is rooted in cooperation among a broad group of government agencies, public and private conservation groups, scientists and researchers, and an active local community. Students, from elementary through high school, have played an active role as Island Fox Ambassadors–raising funds for radio tracking collars, ID microchips, and vaccinations.

This month students from the Buena High Enviromental Club (Ventura, CA) received national recognition for their efforts in restoring native plant ecosystems in Channel Islands National Park. The students from Buena High have also been strong supporters of island fox conservation.

Friends of the Island Fox's motto has always been "Working Together to Save the Island Fox." Many endangered species to not have the benefit of people working in collaboration. We have seen the Channel Island fox rebound from the edge of extinction because people working together can facilitate positive change.

photo courtesy of K. Lampkin

Three Cheers for our active young people and Many Thanks to all the people, near and far, who have helped to fund conservation efforts that have worked!

• Fresno Chaffee Zoo Conservation Grant
• Santa Barbara Zoo
• Fort Collins CO Foxes Baseball Team

It all begins with the annual meeting of the Island Fox Working Group in June. Last year we found out about the threat posed to island foxes by trash cans on Santa Catalina. (2014 meeting of the Island Fox Working Group) You helped us respond to this conservation challenge. Any day now we hope to announce we have reached our goal on this effort.

This year drought and biosecurity are on the meeting agenda, both pose threats to stable Channel Island fox populations. Stay tuned for updates from the biologists, veterinarians, and scientists working in the field. 

Channel Island Fox Status Update June 2014

photo courtesy of Dave Graber

photo courtesy of Kevin Schafer

The annual meeting of the Island Fox Conservation Working Group reported that the general status of the six subspecies of Channel Island foxes is GOOD.

All subspecies are maintaining stable populations of over 300 individuals. There are no known specific issues that put any of the Channel Island fox subspecies in eminent threat of extinction. Each island, however, faces its own concerns and challenges. 

  
Island Fox Update 2014 pdf, a specific island-by-island summary

• San Miguel Island - 577 (low of 15 in the year 2000). Population recovered with over 500 individuals since 2010. Concern: New threat from parasites.
• Santa Rosa Island - 894 (low of 15 in the year 2000). Population steadily increasing.
• Santa Cruz Island - 1,085 (low of 62 in the year 2002). Population recovered and stable with over 1,000 individuals since 2009.
• Santa Catalina Island - 1,852 (low of 103 in the year 2000). Population recovered and stable with over 1,000 individuals since 2010. Concern: Climate change impacts and high risk for introduced disease.
• San Clemente Island - 1,002 (not Endangered). Population stable. Concern: New disease threat connected to mineral particulates in the air.
• San Nicolas Island - 350 (not Endangered). Population high, but declining. Concern: Cause of decline currently unknown, see below.

Concerns:

As populations reach the carrying capacity on some islands, there are new challenges to island fox survival. Continued drought appears to be impacting prey and plant species on some islands, which in turn impacts the island fox. Not only are resources reduced, there may be new threats posed by parasites. (Spiny-headed worm on San Miguel Island).

raccoon stowaway on Catalina Express, Dec. 2013
photo courtesy of Ciara Virdan

Introduced disease remains a threat to all island foxes, especially on islands visited by people. Dogs, cats, and introduced species, like raccoons, are all avenues for disease to be transported to isolated and disease-naive island foxes.

 Canine distemper virus (CDV) caused the population collapse of island foxes on Santa Catalina in 1998-2000. Vaccination against CDV is part of protecting island foxes on all six islands. Island foxes, and many other wild species, are unable to withstand the standard CDV vaccine given to dogs and depend on a vaccine produced by Merial, the corporation that makes Frontline and other veterinary products. Unfortunately, there has been no production of the vaccine this year. If the vaccine is not available by fall counting and health checks, island foxes may go unprotected for the 2014-2015 year.

On San Nicholas Island where the fox population has been high and stable for years, annual monitoring has revealed a trend toward decline that is currently unexplained. A group of island foxes on San Nicolas Island will be radio collared in the fall during annual counting to help biologists determine the cause for the decline. (For more specifics see Island Fox Update 2014 pdf above)

Positive Notes:

While there are concerns regarding San Miguel and San Nicolas, island foxes are doing well. Working with U.C. Davis and veterinary pathologists, National Park biologists hope to determine the specific reasons behind the appearance of new parasites on San Miguel Island and the long-term threat they pose to the island fox population.

Monitoring with radio collars on San Nicolas Island will enable biologists to locate individual island foxes that die in a timely manner. Necropsies performed on these animals will help provide information regarding cause of death.

The most positive note of all is that the Island Fox Conservation Recovery Group continues to meet. Nothing is more important for the continued recovery of the island fox than bringing this group of people together who can share their expertise, their experience, and their creative solutions. Friends of the Island Fox thanks all of our donors who made this annual meeting possible!

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. 

Annual Meeting of Island Fox Conservation Working Group

photo courtesy of Channel Islands National Park

 Every year biologists, veterinarians, researchers, educators, private individuals, government officials and land managers involved with Channel Island foxes meet in June to share information. As the four endangered subspecies have approached population recovery, funding for this important annual meeting has weakened. 

This year the June 2014 meeting of 

the Island Fox Conservation Working Group 

is being hosted by Friends of the Island Fox!

Through the generous donations of private individuals and community organizations, FIF is making sure this important networking and sharing of scientific information continues. Thank you to all of our island fox supporters. You have made a huge difference for the continued success of endangered island fox recovery.

When the Working Group meets next week there will be specific updates on each island fox subspecies. (Six different subspecies). 

Representatives from Channel Islands National Park, the U.S. Fish & Wildlife Service (USFWS), Institute for Wildlife Studies, Catalina Island Conservancy, United States Navy, The Nature Conservancy, University of California at Davis School of Veterinary Medicine, Santa Barbara Zoo, Smithsonian Institute, Channel Islands Park Foundation and Friends of the Island Fox will present reports and discuss issues pertaining to island foxes.

Island fox having teeth checked during Health Check, NPS

Some of the Report Topics:

• Pathology from island foxes that died over the past year
• The future of a representative mainland zoo population
• Amyloidosis in island foxes (a build up of proteins that can cause health problems)
• Modeling the risk of epidemic disease for island foxes
• What new genetic information reveals about the evolutionary history of the island fox
• Procedures to de-list eligible island fox subspecies from the Endangered Species List

Proposed Issues for Discussion:

• Agency plans for detecting and mitigating golden eagle predation
• Fine tuning the epidemic response plan regarding sentinel fox mortalities
• Impact of a new parasite detected in San Miguel Island foxes
• Storage and utilization of island fox biological samples (obtained from island foxes during health checks and from necropsy of deceased foxes)
• Decision tree for treating injured wild island foxes

You can see the important items that will be addressed and information that will be shared. The greatest successes for endangered species come when people sit down together and share their expertise and ideas for solutions. 

Thank you again to all of our island fox friends that helped to continue this important meeting.