Why do some birds mimic the sounds of other species?

Based on the title, I was hoping for an explanation. Instead the article is a collection of "maybe it's this?" points.

It's still great that Cornell Lab provide resources like this. Another project of theirs, BirdNET [0], is fantastic for identifying bird song.

[0] https://birdnet.cornell.edu/

Here's the one that blows my mind:

  https://www.youtube.com/watch?v=mSB71jNq-yQ

Search YT for 'lyre bird imitating chainsaw' for a choice of vids.

Sometimes it's just fascinating thinking about the evolution of why some birds mimic - for instance one could spend a lifetime every time a flock [1] Sulphur crested cockatoos that have decided to roost and feed nearby listening to them screech for hours and not hear any other variation of trying to mimic other bird species - but infrequently I and others will note a few when perhaps they've noted us, try to imitate phrases of those well meaning folks who set out bird feeding stations for them.

But I consider myself blessed that about 35 years ago when certainly there was a larger amount of birds species as well as general bird population, one year (unsure of season) I witnessed one particular nondescript brown bird about the same size as a magpie that had an amazing range of bird differing bird calls. I could recognise about half I thought at the time, and over a few days wondered what it's own call was. More often it made an incredibly raspy call, that was similar to both the (nocturnal) native possum and (nocturnal) flying fox species that inhabit the region. Since it could mimic so well, and the rasp was quite distinct to me from either possum and flying fox, I eventually assumed that the raspy call was its own. Why blessed - I witnessed something clever on the birds part, being chased out of a tree by another small flock of similar sized birds, it looped up high above, coming down imitating a whistling kite [2] with the flock scattering leaving the shady tree all for its own ... well ____ me, down the rabbit hole and it solves a 35 + personal mystery where when I tried to identify the bird and was made to feel stupid by those I asked for perhaps not being familiar with what either a possum or flying fox sound like and of course told I was mistaken in what I'd observed. Most likely what I'd seen was a spotted bowerbird [3] ... I haven't to my knowledge seen once since in all that time and I used to bush walk around the tropical scrub at least once a month up until a few years ago -- now less frequent.

[1] https://en.wikipedia.org/wiki/Sulphur-crested_cockatoo [2] https://en.wikipedia.org/wiki/Whistling_kite [3] https://en.wikipedia.org/wiki/Spotted_bowerbird

> When approached by humans or other potential threats, males at bowers and females at nests often mimic the calls of predatory birds such as the wedge-tailed eagle (Aquila audax), blue-winged kookaburra (Dacelo leachii), grey-crowned babbler (Pomatostomus temporalis), grey butcherbird (Cracticus torquatus), pied butcherbird (Cracticus nigrogularis), Australian magpie (Gymnorhina tibicen), Australian raven (Corvus coronoides), apostlebird (Struthidea cinerea) and honeyeaters (Meliphagidae spp.) among others

Edit for clarity