Peak rates upset flyers (9)

I believe the answer is:

parakeets

I'm a little stuck... Click here to teach me more about this clue!

'flyers' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how one could define the other.

'peak rates upset' is the wordplay.
'upset' is an anagram indicator.
'peak'+'rates'='peakrates'
'peakrates' anagrammed gives 'PARAKEETS'.

Can you help me to learn more?

(Other definitions for parakeets that I've seen before include "Birds" , "Peak rates (anag.)" .)

I've seen this clue in The Independent and The Telegraph.

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