East Coast warbler, landed in Inverness, likely “misoriented”

Paul Hurtado
Groups of birders flocked to Second Valley in Inverness in September hoping to catch a glimpse  of a single Blackburnian warbler, who likely confused its cardinal directions.  
10/12/2017

Streaks of black line the orange face and breast of the Blackburnian warbler, an East Coast species that somehow wound up in the alder trees above an Inverness creek this September. Renée Cormier, an avian ecologist for Point Blue Conservation Science, first spotted one with a research associate and a flock of interns near the Second Valley tennis court. “There are a lot of vagrant, or out-of-range, migratory birds that wind up in Point Reyes, though typically birders head out to the Point—to Chimney Rock or the lighthouse—to look for them,” Ms. Cormier said. Word of the sighting got around, and ever since, birders have visited Vision Road, hoping to spot the warbler and other rare species that have appeared in the drainage this fall. Ms. Cormier said that although they’re not particularly rare on the East Coast, typically just one of the warblers is spotted on Point Reyes every couple of years. The species, the only warbler with an orange throat, summers in the northeastern United States and eastern Canada, migrates south along the eastern edge of the Rockies through the Midwest and makes its way to Central and South America for the winter. About five inches long with an eight-inch wingspan, it breeds in boreal and mixed forests, and especially in spruce and hemlock trees. It prefers feeding on caterpillars, particularly those of spruce budworms. The individual spotted in Inverness stayed for about a week before setting off again. “One of the great things about birding in West Marin in the fall is that you get to enjoy the regular migrant species and the more abundant, common species. And then sometimes you get a surprise,” said David Wimpfheimer, who has been birding in West Marin for over 30 years. He said that other less-common species have also popped up this fall, including the northern parula and the prairie and Tennessee warblers. “Sometimes migratory birds travel in small flocks, but other times they are alone, and it’s usually at night, when there is less turbulence and fewer predators, and so it’s almost random where they happen to end up at daybreak. They are usually looking for a place where there is food and trees to rest in,” Mr. Wimpheimer said. According to an essay written for Bay Nature magazine written by birder and West Marin resident Carolyn Longstreth, vagrancy was first identified along the California coast in the late 1800s and is now considered a worldwide phenomenon. In 1967, researchers at Southeast Farallon Island began to trap and band all species, including the unusual birds. Records from the island now reveal that about 4 percent of all fall migrants caught were vagrants. Ms. Longstreth wrote that researchers once believed that the birds were disoriented, but now consider vagrants to be “misoriented”— consistently oriented, but in the wrong direction. She cites Dave DeSante, a retired ornithologist with the Institute for Bird Populations, who conducted experiments with vagrant blackpoll warblers on Southeast Farallon Island and theorized that these birds have a defective sense of direction, called “mirror-image misorientation.” If a species’ normal route is 40 degrees east of due south, a misoriented bird such as this September’s Blackburnian warbler orients 40 degrees west of due south and keeps going, eventually reaching the coast of California.