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.

Climate and Island Foxes

Santa Catalina Island

Across the six islands that are home to island foxes (Habitat), pairs like Tani and Tiptu are breeding and finding an appropriate den site. Island fox pups are typically born in late April.

Like all wild animals, island fox reproduction is impacted by the amount of local resources–food, water and territory. As endangered populations of island foxes have recovered, there have been several years where female foxes have had large litters of pups. Typically two pups are born in a litter, but when resources are abundant there can be as many as five pups.

Because the recovering endangered populations were small, there was little competition for territory and food. In the mid-2000s, it was not unusual for island foxes on San Miguel to have litters of three to five pups. With large litters of offspring the San Miguel Island population, that had nearly gone extinct in 2000 when there were only 15 surviving individuals, was able to exponentially increase each year.  Graph

But severe climate can greatly reduce the resources available to island foxes. 2007 was the driest year on record in southern California since National Weather Service records began in 1878; less than four inches of rain fell. The lack of rainfall reduced the plant foods on the islands which reduced the deer mice, insects and bird life. Without winter rains, the Catalina cherry, native currants, toyon and other fruit producing plants produced less fruit for the foxes to eat. Less food, meant fewer island fox pups were born or survived. The winter seasons of 2008 - 2011 averaged approximately 12 inches of rain, the low side of normal, but still enough that Channel Island wildlife flourished.
 

This winter season is showing early signs of drought. As mid-March approaches the Los Angeles area has received less than six inches of rain. This year if spring rains do not arrive, we may see fewer island foxes born and fewer that will survive. Climate fluctuations act to moderate animal and plant populations, but climate change means greater weather extremes. Drought in 2012 could make it more difficult for young island foxes like Tani to successfully reproduce and could slow down the recovery of endangered island foxes.