Primate seized by bird, nimbly from behind (5)
I believe the answer is:
indri
'primate' is the definition.
(I know that indri is a type of lemur)
'seized by bird nimbly from behind' is the wordplay.
'seized by' says the answer is hidden in the clue (the answer has been seized by the clue).
'from behind' is a reversal indicator.
'irdni' can be found hidden inside 'bird nimbly'.
'irdni' in reverse letter order is 'INDRI'.
(Other definitions for indri that I've seen before include "Madagascan mammal" , "Large Madagascan lemur" , "Short-tailed lemur of Madagascar" , "large primate" , "Species of lemur" .)