Outfoxing conservation threats on Santa Cruz Island
The Nature Conservancy's work has had extraordinary outcomes — but there's still work ahead (including outfoxing invasive ants), says Conservancy scientist Scott Morrison.
Thu, Jun 17, 2010 at 04:53 PM
Santa Cruz Island fox. (Photo: Ian Shive)
Santa Cruz Island is many things to many people. An escape into a California of yesteryear. An iconic U.S. national park.
For me, it is the quintessential example of science in practice, of the extraordinary conservation outcomes that can come from the hard work of a lot of people with a shared and ambitious long-term vision.
When The Nature Conservancy first invested in the island in the late 1970s, the island was on the brink of ecological collapse. Overgrazing by sheep had turned an island once rich in oak and ironwood into a barren expanse of grass and dirt.
A decade later, most of the sheep were gone. And the island staged a remarkable recovery: Native scrublands and pine forest rebounded.
But in the 1990s, the endemic island fox suddenly stopped being so common. In fact, it almost disappeared altogether.
Turns out, golden eagles, which were not native to the island, had colonized it — an invasion made possible because the island was overrun with feral pigs that provided an abundance of food. Predation of foxes by golden eagles was enough to drive the foxes to near extinction. Today, the Santa Cruz Island fox is listed as a federally endangered species.
The strategy to recover the fox was many-pronged. A captive breeding program was established to help augment the population. Golden eagles were captured and relocated to the mainland. And the non-native pigs that subsidized the golden eagle population were removed.
And in addition, bald eagles were reintroduced. Bald eagles had been eliminated from the island a half century ago, due to pesticide contamination of their food supply. An effort to reestablish the birds to the Channel Islands culminated with the bald eagles (at last!) again nesting on Santa Cruz Island in 2006.
An additional advantage of having bald eagles back on the island was that they might help defend it from golden eagles. Unlike the golden eagles that devastated the fox populations, bald eagles eat mostly fish and carrion. And bald eagles basically don’t like having golden eagles around.
Where are we now? Better on all fronts. The sheep and pigs are gone. The fox captive breeding program has been shuttered, because we now have 10 times more foxes than we did just 8 years ago. Golden eagles no longer breed on the island. But bald eagles do: We now have 4 breeding pairs on the island.
Does this mean that our work is “done”?
No. There’s still much to do to enhance the resiliency of the island. We need to tackle weeds — and there is an introduced ant species on the island that is of great concern to Conservancy scientists. We also need to continue to monitor the ecological changes underway.
Just the other day, for example, a bald eagle brought a fox into its nest as food for its young. Is that a cause for alarm? No. An occasional fox being taken by eagles (though perhaps unfortunate) is not a problem. What matters is how many foxes get taken and how fast.
On the California islands, foxes coexisted with bald eagles for millennia. Hunters specialized on fox-like prey, like golden eagles, are what foxes have a hard time surviving with. Golden eagles have clearly demonstrated their ability to depredate foxes faster than they can reproduce.
So as we enter our fourth decade of adaptive management on Santa Cruz Island, we do so attentive to the threats to the unique plants and animals of this extraordinary place. We keep an especially vigilant finger on the pulse of the foxes: We regularly monitor over 70 radio-collared foxes across the island, so that if there’s a population problem like a disease or a spike in predation, we’ll know it in time to do something about it.
That science-based approach has brought about incredible and inspirational conservation outcomes. And it’s that approach that has me so looking forward to what unfolds in the decades ahead.
— Text by Scott Morrison, Cool Green Science Blog