They call it the Devil Bird, but that's not the only thing interesting about seeing it at San Francisco's Lake Merced:

The birds, known scientifically as Quiscalus mexicanus, have in recent decades expanded their range from Texas and parts south of there to Northern California, most likely because of human-caused changes in their habitat. The first sighting in California was along the Colorado River in 1964. The birds have since colonized much of urban Southern California and parts of the San Joaquin Valley. Great-tailed grackles have been seen in the Bay Area before. A pair of them gained fame in 1986 when they dive-bombed workers attempting to cut down their nesting tree.

(photo by Gary Kramer/USFWS)