Some text from the Cornell website: "The Wrentit’s characteristic bouncing-ball song is a classic sound of coastal scrub and chaparral along the West Coast. Seeing a Wrentit is a challenge as they sneak around inside shrubs, rarely making an appearance. Males and females sing at all hours of the day, all year long, most often hidden from view. With patience, a brownish-gray bird with a piercing white eye might pop out of the shrubs, cock its long tail off to the side, and sing. Wrentits rarely travel far from their territories, so you can enjoy their presence year-round."
Here are my pics from San Diego, CA.