Yellow-rumped Warbler

Habitat:

During breeding season in mature coniferous and mixed coniferous-deciduous woodlands (such as in patches of aspen, birch, or willow). During winter, in open areas with fruiting shrubs or scattered trees, such as parks, streamside woodlands, open pine and pine-oak forest, dunes (where bayberries are common), and residential areas.

Notes:

This I believe is an immature Myrtle (regional subspecies). It had just noticed some yummy gnats swarming overhead.