- By eggedit
February 2, 2015
I clamber up a steep slope of crumbly rock, sculpted over centuries by the wind into fantastic mini spires and castles. We are in the rain shadow section of Robinson Crusoe Island, Chile, and the landscape is a desert, with barren white and brown rock and hardly a plant in sight. Every few feet a tunnel disappears into the soft rocks—tunnels of Pink-footed Shearwaters, a seabird related to albatrosses. I unwind an infra-red camera on the end of a long, flexible hose, and snake it down one of the tunnels. The image of what the camera sees is sent to the video goggles I wear that make me look like some futuristic space explorer.
The tunnel goes down and down—the entire six-foot long hose of the camera fits down the tunnel without reaching the end, so I hold the end of the camera and stick my arm in up to my shoulder to gain another few feet. Still too long. Pink-footed Shearwaters like their burrows deep, and with the soft sandy soil here they can dig and dig all they like. I try the next burrow over, and at the end of the tunnel I spy a bird—long, hooked bill, elegantly shaped head. I mark down AD, for adulto (Spanish for adult), in my notebook. Jessie and I are working in a colony of Pink-footed Shearwaters on Robinson Crusoe Island, in the Juan Fernández Islands of Chile. Our job is to identify and mark a sample of burrows to determine the occupancy rate, hatching success, and chick survival of the Pink-footed Shearwaters (known as Fardelas Blancas in Chile) in this colony. This particular colony, called Tierra Blanca for its white volcanic soil that gives it a moonscape appearance, is one of several major colonies of Pink-footed Shearwaters on the Juan Fernández Islands. Approximately 720 breeding pairs raise their chicks in Tierra Blanca, out of around 5,000 total pairs on Robinson Crusoe Island. The species only breeds on three islands worldwide—Robinson Crusoe and Isla Santa Clara, both in the Juan Fernández Islands, and Isla Mocha, an island further south and much nearer to the coast in Chile.
Pink-footed Shearwaters have attracted international attention lately, due largely to their status as a threatened species and also in part because they make impressive migrations during the austral winter (i.e., the summer in the U.S.A.). They depart Chile and head north, cross the waters of many countries on their way—Peru, Ecuador, several Central American countries, Mexico, and finally arrive on the west coast of the United States. They make the journey in order to forage in the highly productive waters of the California Current and heavily utilize areas from Baja, Mexico up to British Columbia, Canada. They can regularly be seen in the summer off the coast of California. Thus, these birds that look like mini-albatrosses are citizens of the world, even though by birthright they are Chilean. The global breeding population of Pink-footed Shearwaters is estimated to be around 28,000 pairs. This number is not too worrisome, but not exactly high enough for comfort, either, especially considering the multitude of threats the birds face on land and at sea. On the Juan Fernández Islands, the birds have to contend with a host of introduced mammalian predators; with introduced European Rabbits that exclude them from burrow sites; with cows that trample their burrows; and with habitat modification from introduced grazers, such as loss of plant cover to stabilize the soil in their colonies.
Relatively little is known about the direct threats at sea, but there are indications that the birds are caught fairly frequently by fishing vessels as bycatch. The term “bycatch” refers to animals that are unintentionally hooked during fishing, along with the target species. Birds caught as bycatch may die immediately, or are sometimes released to the water if they are still alive, though they may die of injuries later.
Oikonos has been working in the Juan Fernández Islands (JFI) since 2001 on conservation of Pink-footed Shearwaters and other threatened seabirds, endangered landbirds and native ecosystems. Happily, there are many simple steps that can improve the situation at the breeding colonies. On Isla Santa Clara, one of the islands in the JFI archipelago, Oikonos worked with the Chilean National Park system to remove the introduced rabbits in 2003. Three years after the rabbit eradication, the number of nesting Pink-footed Shearwaters on Santa Clara had increased by almost 40%, and native plants (many of which are critically endangered themselves) have begun to re-establish themselves slowly. On Robinson Crusoe Island, Oikonos constructed a cattle exclusion fence around a shearwater colony to prevent burrow trampling. Once again, this resulted in a double benefit for both shearwaters and native plants.
Which brings us back to Jessie and me sweating up the steep slope of the Tierra Blanca colony on Robinson Crusoe. The data we are collecting will be important because there are tentative plans to install a predator-exclusion fence around the colony, to protect the shearwaters from introduced cats, rats, dogs, and coatimundis (a sort of South American version of the raccoon). We also are quantifying the plant cover in the colony (close to zero!), because if a fence goes up, introduced rabbits could be hunted out of the enclosed area as well, potentially resulting in recovery of the threatened native vegetation. Fences, of course, do not fix the ultimate problem for the shearwaters, which is that there are introduced, non-native mammalian predators and competitors on their breeding islands. Removing the non-native mammals completely would be a better fix for the birds, but Robinson Crusoe Island is inhabited by around 800 people as well, making complete removal of any predator complicated.
For example, shearwaters fall easy prey to feral and domestic cats, because the birds are awkward and naïve on land. Many island residents cherish their pet cats, however, and complete removal of cats from the island is not an option for the foreseeable future. Currently, Oikonos and Island Conservation run a free spay and neuter program for pet cats and dogs, to help control the populations of strays. In addition, there is an adopt-a-kitten program, in which stray island kittens can be adopted by Chileans on the continent, where they will not threaten the fragile island ecosystem. Despite these excellent measures, at least in the short term there will still be cats (and rats, dogs, and coatimundis) on the island, which is why a well-placed predator-proof fence is highly needed.
I pause a moment to observe the shearwater patiently incubating the one egg it will lay this year, thinking about the huge, untiring effort that the parents will put into nurturing and provisioning their single offspring from egg to fledged chick, over four months. I move on to check the next burrow, collecting data that will be one small part of the equally determined effort to conserve these special birds. Ryan Carle