Laura Erickson's For the Birds

I’ve only seen this species once, in Hungary in 2014. But it has an entry in the Guinness Book of World Records for mimicking more bird songs and calls than any other bird:

Most birds mimicked by a bird. The marsh warbler (Acrocephalus palustris) is capable of imitating the songs of up to 80 other species of birds, most of them African birds heard in the warbler’s winter home. Song is necessary for mate attraction and selection as well as being an important means of marking territory.