Fox Foto Friday - Counting Island Foxes

Capture cages and ID microchips are key in counting island foxes across the Channel Islands. Camera trap images, like this one, may help provide additional information on island fox behavior. This fox is alone, appears healthy, and shows no sign of injury from interactions with other island foxes. It's also wearing something important around its neck.

What Do Brown Boobies Have To Do With Island Foxes?

Have you heard that a seabird called the brown booby (Sula leucogaster) has recently been found nesting on Santa Barbara Island for the first time? 

brown booby beneath western gull; Santa Barbara Island, CA

If you did, you might not have connected this news to island foxes. Brown boobies have historically been residents of Baja and Mexican coastlines. They typically feed on fish species found in warmer waters and are considered a tropical and subtropical species. Channel Islands National Park reports that brown boobies have been gradually moving north since the 1990s. Their occurrence on the Channel Islands coincides with documentation of warmer ocean temperatures along California's coast. The fact that these southern birds are attempting to nest here for the first time is evidence of a healthy marine ecosystem, but also changing local climate. Similarly, our brown pelicans (Pelecanus occidentalis), which were previously only known to nest in California, have been ranging further north. They have attempted to nest along Washington's Columbia River and in the past few years have become summer regulars in southern British Columbia, Canada.

Strong-flying birds have the ability to relocate as temperatures change. Island foxes and the other terrestrial plants and animals of the Channel Islands do not have that option. They will have to adapt to changes in their environment to survive. There are some reports of island foxes breeding and having pups earlier on the southern Channel Islands then documented in the past. Lightening storms brought fire to Santa Cruz this summer and extended drought has challenged some island fox populations.

While the brown boobies are a native coastal species, they have only been occasional visitors to the Channel Islands in the past. Brown boobies are diving seabirds larger than our commonly seen western gull (Larus occidentalis). They are exciting to see, but will their northern movement have an impact on other native species? (video of brown boobies on Santa Barbara Island in 2015 via TheEarthMinute.com)

Are there other, small and less observable species, that are also relocating to the Channel Islands? Will climate roamers bring beneficial diversity or new parasites and disease? 

In this time of global change, monitoring island foxes and their island ecosystem is vital to the species' long-term survival.

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.