This video says about itself:
Plain-Tailed Wrens‘ Songs
7 November 2011
Long-married human couples may finish each others’ sentences, but the plain-tailed wrens of the Andes take things a step further. Male and female wrens sing intimate duets in which they alternate syllables so quickly it sounds like a single bird is singing. New research shows that the brains of both the male and female wrens actually process the entire duet, not just each bird’s own contribution.
Dr. Fortune plays some examples of plain-tailed wrens’ songs.
This video about plain-tailed wrens says about itself:
3 November 2011
And this video is the sequel.
Plain-tailed wrens are not the only wrens singing duets. So do other wren species, especially in tropical countries; eg, band-backed wrens.