Migrant rook eggs picked up (5)
I believe the answer is:
Here is my best explanation:
'migrant' is the definition.
'rook eggs picked up' is the subsidiary indication.
I cannot really understand how this works, but
'rook' could be 'r' (abbreviation in chess) and 'r' is present in the answer.
'up' could be 'over' and 'over' is present in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
(Other definitions for rover that I've seen before include "Old scout", "Nomad", "Itinerant person", "gypsy", "pirate ship", "Wanderer, rolling stone", "A vagrant", "one in Bristol, one in Doncaster, perhaps", "rambler" and "Pirate; dog's name".)