Scott Sillett, researcher at the Smithsonian Migratory Bird Center, received a $20,000 grant from The Nature Conservancy (TNC) to study the endemic and declining Oreothlypis celata sordida, a subspecies of the orange-crowned warbler, on the California Channel Islands (Santa Catalina and Santa Cruz).
The project will compare the population biology of warblers between the two islands, with particular focus on the response of warblers to the islands' understory vegetation.
The picture below shows orange-crowned warbler habitat on Catalina Island. Note the lush vegetation on the ground due to the lack of feral pigs—the warblers often build their nests on the ground where the vegetation provides camouflage from predators.
Feral pigs and goats were removed from Catalina several years ago. As a result, the understory on Catalina is regenerating and warblers reach incredible population densities in some moist canyons on the island.
Although cows and sheep have been removed from Santa Cruz, about three to four thousand feral pigs remain and the forest understory is severely degraded. The Nature Conservancy initiated a feral pig removal program in March 2005.
We will collect one season of warbler data on Santa Cruz this year, prior to pig eradication (TNC won't be removing pigs from study areas until after the warbler breeding season).
Warbler demography, habitat selection, and behavior will be compared to data from Catalina as well as data we collect in subsequent years on Santa Cruz as the understory recovers.