Vole relative (7)
I believe the answer is:
lemming
'vole relative' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lemming that I've seen before include "Rodent that follows others headlong over a cliff" , "Supposedly suicidal animal" , "Rodent related to the vole" , "Rodent renowned for mass migration" , "One misjudges landing" .)