Larus californicus

You'll be hard-pressed to visit the shores of Mono Lake and not see this very scene: a California gull feasting on brine flies. Mono Lake, just east of Yosemite on the eastern side of the Sierras, is host to the 2nd largest breeding population of California Gulls in the world, just behind Utah's Great Salt Lake. The gulls and their nesting habits are directly responsible for famous conservation efforts that in the 1980's established a minimum lake level, thereby restricting water diversion in Mono County to the City of Los Angeles. In this famous case, siphoning of water from the creeks which feed into the lake was restricted to maintain a level high enough to keep the lake's two islands separated from the mainland, thus ensuring that no coyotes or other predators make their way to the islands' breeding colonies.

This particular gull was employing a sort of catch-all technique, running at a full waddling speed through a thick cloud of flies. It's kind of adorable when they do this.