Song Sparrows (Melospiza melodia)
… are among the first birds to return to their breeding territories and start singing in the spring. While their songs may sound superficially similar to our ears, each male knows up to 20 versions of the basic melody and may improvise broadly on their repertoire. They will repeat a song several times in a row before switching to their next version.
Many of their songs are learned from the males on neighboring territories - a way of ensuring everyone’s talking on the same page, and which helps to establish a friendly neighborhood. The songs are an important part of individual identification - birds can, simply based on song, differentiate between neighbors and strangers; and females have been shown to prefer the songs of their mates over those of neighbors, and the songs of neighbors over those of strangers.
photo by Dan Dzurisin (NDomer73) on Flickr
(via: Peterson Field Guides)