Anacapa Island Conservation

By Eilene Lyon

The highlight of our recent vacation trip to Channel Islands National Park, off the coast of southern California, was a day spent at Anacapa Island. Anacapa consists of three islets about 11 miles from Santa Barbara.

Landing on East Anacapa was adventurous. The zodiacs transporting us from the National Geographic Venture had to navigate into a narrow, sloshing cove, continually pushing the bow into a ladder to unload passengers, as the bow rose and dipped with the waves.

After ascending the ladder, we had to climb about 130 steps to reach the top of the cliffs. The odor of bird guano could be a bit overpowering if you were downwind. Brown pelicans, western gulls, and cormorants seemed perched on every cliff-top and every cranny from there down to the water. On the southern shoreline, California sea lions congregate in large numbers.

The islands are considered “wilderness,” though East Anacapa has a lighthouse and several other buildings. A trail circumnavigates the upper portion of the island, and there is a campground as well. November is a dormant period for much of the vegetation, though the native ice plant was blooming. There is also non-native ice plant that the park is working to eradicate.

One of the biggest conservation problems on Anacapa involved the non-native black rat (Rattus rattus). Rats have populated 90% of the worlds islands and are believed to have caused 50-60% of all bird and reptile extinctions since 1600.

They may have first come ashore on Anacapa in 1853 with the wreck of the steamship Winfield Scott (no human lives were lost in this gold-rush era event). Or they might have arrived when the lighthouse was built, or when sheep ranching was active on the island. The rats impacted rare bird species, such as the Scripps’s murrulet (Synthliboramphus scrippsi), by eating eggs. They also preyed on the native side-blotched lizards and Anacapa deer mice (Peromyscus maniculatus anacapae).

In the 1980s and 1990s, studies began to evaluate and plan for rat eradication. Due to the steep cliffs, aerial spreading of rat poison would be required. This method had been used in New Zealand, but never in the United States. Before implementing the baiting, plans and procedures had to be established to protect the native deer mouse population and birds, including songbirds, seabirds, and raptors. (Details of the procedures can be found in the source documents and web sites.)

There were animal rights organizations and individuals opposed to the rat-poisoning project. Their lawsuit to stop the eradication did not succeed. East Anacapa was baited in December 2001, and the other two islands were done in November 2002. Deer mice had been captured and contained prior to both events and were reintroduced (nowhere did I find an estimate of how many mice and rats died during the poisoning phase).

Most raptors were relocated to the mainland, but peregrine falcons were held and released back on the islands after the threat of incidental poisoning had passed. One hundred songbirds, particularly rufous-crowned sparrows (Aimophila ruficaps obscura) were found in post-poisoning surveys, though this is not the total incidental kill; some birds were likely scavenged or simply not found. Gulls were probably affected more than other seabirds. After the project, a number of dead gulls washed up on the Santa Barbara shore.

As for the benefits to native populations: side-blotched lizard populations increased, deer mouse populations soon achieved a density similar to pre-project surveys, and murrelet nest success increased dramatically. Overall, nesting bird populations increased and species began arriving that had not previously been observed on the islands.

But did the eradication project get rid of all the rats? Theoretically, one mating pair of rats could produce a population of 5,000 in just one year. Yikes! Ten years after the eradication, researchers found no evidence that rats still inhabited the island.

A big question mark popped up while we hiked around, though. On the path to the lighthouse, I spied two dead rodents. One was a deer mouse. The other was not.

Mentioning it later to some of the ship’s crew, they asked if I had taken a photograph. The significance of the find had escaped me at the moment, and I had not. (I did not learn about the rat eradication project until that evening.) Fortunately, one of the photography instructors leading a group around the island also spotted the dead rodents and did get photos.

Stay tuned!

Sources:

Howald, Gregg R. et al. “Eradication of Black Rats from Anacapa Island: Biological and Social Considerations.” 2005 https://sbbotanicgarden.org/wp-content/uploads/2022/09/Howald-et-al-2005-black-rat-eradication-Anacapa.pdf

https://www.nps.gov/chis/learn/nature/restoring-anacapa-island-sea-bird-habitat.htm

https://milliontrees.me/2022/03/01/when-the-killings-done-maybe-never/