The Common Yellowthroat is well-named. This bird sports a yellow throat and is common over much of North America. Because of the male's black mask, Erika and I often call him the Zorro Bird. Other times we say, "There's a Witchity-witchity-witchity Bird" after its distinctive call. Common Yellowthroats are often found in marshy or grassy wetlands. They usually respond well to birders' squeaking noises and come close to investigate.
Females, like in the photograph below, are intrinsically more difficult to identify. All are greenish above and mostly yellow below and have a slight chestnut wash on their forehead (this bird seems to have more brown on the head than normal.
Yellowthroat pairs are almost always monogamous, at least within a single season. The female, however, is completely unfaithful to her mate and will copulate with other males. These guys often hang around a mated pair's territory on the chance they will "get lucky." (Guzy, Michael J. and Gary Ritchison. 1999. Common Yellowthroat (Geothlypis trichas), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/448)