Tuesday, March 20, 2007

Changing Seasons

March is a period of transition on the Farallones. The typical southwesterly winds which bring in those impressive winter storms gradually shift around to the north, often blowing with a vengeance and driving the process of upwelling that makes the Gulf of the Farallones one of the most productive areas in the world. This change in the weather coincides with dramatic changes in the wildlife dominating the island. The elephant seal breeding season has come to a close. The last pups have weaned from their mothers and the cows and bulls have finally returned to the water after spending the last several months on land. There they will spend most of their time feeding and recuperating from the trials of the breeding season, regaining their energy reserves and putting on a nice thick layer of blubber.

March is also the time when the seabirds return to take over the island and set up for their own breeding efforts. Experienced birds will return to their former breeding territories, court mates, and begin nest building while younger birds will come back for the first time to try to fight for a spot of their own.

These changes of course also trigger a period of transition for the small human population on the island. On March 10th, the winter elephant seal research crew departed the island to be replaced by the seabird crew. Over the next six months we will dedicate ourselves to studying the population trends, survival, diet, and reproductive success of the 12 species of seabirds which call these rocky islands home. Western Gulls, Common Murres and Brandt’s Cormorants cover the surface of the island during the summer months.

Cassin’s Auklets, Rhinoceros Auklets, Pigeon Guillemots, Tufted Puffins, Ashy and Leach’s Storm-petrels rule the underworld. They make their nests underground in dirt burrows or rocky crevices. Pelagic Cormorants dot the cliff sides with their nests while Double-crested Cormorants prefer to stick together in one small colony on the very top of a particular hill called Maintop. Black Oystercatchers, our only breeding shorebird, fill the remaining space around the perimeter of the island.
More than a quarter million seabirds breed on the Farallones each year, including the world’s largest breeding colony of Western Gulls with almost 20,000 birds, and the largest colony of Common Murres in California with more than 210,000 birds last year!

Biologists from PRBO have been conducting research on the Farallones since 1967. The long-term datasets that we have compiled on seabird populations, reproductive success, phenology (timing of reproductive events such as egg laying) and diet has revealed some dramatic changes over the last 40 years and has allowed us to use seabirds to learn about both natural and human caused changes in the marine environment.

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