According to the Mass Audubon Breeding Bird Atlas, the Warbling Vireo is the most drab and unassuming in appearance.  It more than makes up for this, though, with its effervescent and melodious song.  Warbling Vireos can be heard singing throughout the breeding season in Massachusetts, and their breeding range within the state has expanded considerably.   Warbling Vireos seldom appear in Massachusetts before May, but most of them arrive within the first two weeks of that month.  Pairs may arrive already attached, but they quickly find each other even if they arrive singly.  Males sing constantly throughout the breeding season.  They make take a brief hiatus while the dependent fledglings are being raised, but will pick up again during the late summer.  The pattern of the Warbling Vireo’s rollicking, whistled song is sometimes remembered by the amusing mnemonic, “If I could see one, I would seize one, and would squeeze one, till it squirts!” or some similar variant.  Most of the nest-building is done by the female, who locates a suitable forked branch high in a deciduous tree.