Monday, November 06, 2017

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.