▁ol iv ace us , ▁also ▁known ▁as ▁the ▁o live ▁grass ▁mouse ▁or ▁o live ▁ak od ont , ▁is ▁a ▁species ▁of ▁rod ent ▁in ▁the ▁genus ▁Ab ro th rix ▁of ▁family ▁C ric et idae . ▁It ▁is ▁found ▁from ▁northern ▁Chile ▁into ▁southern ▁Chile ▁and ▁Argentina , ▁including ▁the ▁islands ▁of ▁T ierra ▁del ▁Fu ego . ▁It ▁is ▁pr one ▁to ▁large ▁sw ings ▁in ▁population ▁size . ▁ ▁Tax onomy ▁Ab ro th rix ▁ol iv ace us ▁has ▁had ▁a ▁complex ▁history ▁in ▁both ▁of ▁the ▁gener a ▁Ak odon ▁and ▁Ab ro th rix , ▁and ▁includes ▁at ▁least ▁ 2 7 ▁syn onym s . ▁A ▁few , ▁including ▁mark ham i , ▁m ans o ensis , ▁and ▁x anth or hin us ▁have ▁been ▁viewed ▁as ▁valid ▁species ▁until ▁recent ▁years , ▁and ▁several ▁sub species ▁are ▁still ▁recognized , ▁including ▁Ab ro th rix ▁ol iv ace us ▁mark ham i . ▁ ▁Description ▁The ▁o live ▁grass ▁mouse ▁is ▁a ▁small ▁rod ent ▁with ▁a ▁total ▁length ▁of ▁about ▁. ▁The ▁upper ▁parts ▁are ▁grey ish - b rown , ▁sometimes ▁slightly ▁yellow ish ▁around ▁the ▁sn out , ▁and ▁the ▁under parts ▁are ▁pale ▁to ▁mid - gre y . ▁ ▁Distribution ▁and ▁habitat ▁This ▁species ▁is ▁found ▁in ▁northern ▁and ▁central ▁Chile ▁and ▁the ▁western most ▁fr ing es ▁of ▁Argentina , ▁southern ▁Chile ▁and ▁Pat ag onia , ▁including ▁the ▁larger ▁off sh ore ▁islands ▁and