Sentence:  The voices of male <WSD>vireos</WSD> are a constant in the spring woodland, providing background music to the longer, prettier songs of tanagers and thrushes. <WSD>Vireos</WSD> tend to sing in bursts interrupted by short or long pauses. 
Meaning of the word marked with <WSD> tags:  Any of a number of small insectivorous passerine birds, of the genus "Vireo", that have grey-green plumage.