|Least Bell's Vireo. April 20, 2014. Mission Trails Park, San Diego, California. Greg Gillson.|
They usually are harder to actually see, singing their quick buzzy song while hidden in dense willow tangles in a few stream bottoms in southern California. Their stronghold is Camp Pendleton, the marine corps base north of Oceanside, California.
It's rather a plain bird, grayish-green with a slight hint of an eyering and a single wingbar. The heavy hook-tipped bill helps visually separate vireos from warblers.