Sedge Wrens are unique in that their songs are improvised, not learned. The variation to their song occurs during the ‘trrrrrrrrrrr’ portion, after the ‘cut-cut-cut’. Amazingly, males have repetoires of upwards of 300 different ‘trrrrrrrrrr’ notes. Each Sedge Wren has, if you will, a “song generator” in its brain. During a male’s first breeding season, it flaunts its best music to nearby females, and uses its unique repertoire for the duration of its life.
Sedge Wrens are nomadic, always searching for suitable breeding habitat. They primarily breed in sedge meadows, which are ephemeral, changing not only from year to year, but also from month to month. All this moving around makes it essentially impossible to settle in and learn neighbouring males’ songs. Imagine the task of bird memorizing and imitating (competing against) two to three hundred variations, only to have the meadow dry up mid-summer, and have the neighbour pack up and fly to a more suitable site?! Improvisation provides each Sedge Wren a “fair shot” at breeding success at *any* site within which they settle. They settle in beside strangers in early June…then perhaps even new neighbours sometime mid July…and give it their best, singing from their own hearts, and from their own unique repertoires!
Information reference/recommended reading: Kroodsma, D.E. 2005. The Singing Life of Birds. The Art and Science of Listening to Birdsong. Houghton Mifflin Co., Boston, MA.