Bird seed in tray initially (5)
I believe the answer is:
pipit
'bird' is the definition.
(pipit is a kind of bird)
'seed in tray initially' is the wordplay.
'seed' becomes 'pip' (as in a fruit pip).
'initially' suggests taking the first letters.
The initial letters of 'in tray' is 'it'.
'pip'+'it'='PIPIT'
(Other definitions for pipit that I've seen before include "Songbird of rock or meadow" , "Small bird of rock or meadow" , "Bird of meadow, tree, or rock" , "Bird related to wagtail" , "Meadowland bird" .)