I'd heard that Australia's Lyrebirds are good mimics of the other birdcalls and sounds in their environment, but you really have to hear their impersonation of camera shutters (and car alarms, chainsaws…) to believe them:
Their wikipedia page carries this great anecdote:
During the early 1930s, a male lyrebird, called “James”, formed a close bond of friendship with a human being, Mrs. Wilkinson, after she had been offering food to him over a period of time. James would perform his courtship dance for her on one of his mounds which he had constructed in her backyard — and he would also put on his display for a wider audience, but only when Mrs. Wilkinson was one of those present. On one such occasion, James' performance lasted for forty-three minutes, and included steps to a courtship dance accompanied by his own tune — and also included imitating perfectly the calls of an Australian Magpie, and a young magpie being fed by a parent-bird, a Eastern Whipbird, a Bellbird, a complete laughing-song of a Kookaburra, two Kookaburras laughing in unison, a Yellow-tailed Black-cockatoo, a Gang-gang Cockatoo, an Eastern Rosella, a Pied Butcherbird, a Wattle-bird, a Grey Shrike-thrush, a Thornbill, a White-browed Scrubwren, a Striated Pardalote, a Starling, a Yellow Robin, a Golden Whistler, a flock of parrots whistling in flight, the Crimson Rosella, several other birds whose notes his audience were not able to identify, and the song of honey-eaters (tiny birds with tiny voices), that gather in numbers and “cheep” and twitter in a multitudinous sweet whispering. In order to mimic the honeyeaters' singing faithfully, James was obliged to subdue his powerful voice to the faintest pianissimo, but he contrived, nevertheless, to make each individual note of the soft chorus audibly distinct. Also included in James' performance was his perfect mimicry of the sounds made by a rock-crusher at work, a hydraulic ram, and the tooting of motor-horns.