Birds: teal's last in, rest shot, flying! (9)

'birds' is the definition.
(throstle is a kind of bird)

'teal's last in rest shot flying' is the wordplay.
'last' says to take the final letters.
'in' indicates putting letters inside.
'flying' is an anagram indicator (letters fly around into new positions).
The last letter of 'teal' is 'l'.
'rest'+'shot'='restshot'
'restshot' anagrammed gives 'throstes'.
'l' placed within 'throstes' is 'THROSTLES'.