Neotoma cinerea

from WordNet (r) 3.0 (2006)

Neotoma cinerea
    n 1: any of several bushy-tailed rodents of the genus Neotoma of
         western North America; hoards food and other objects [syn:
         {packrat}, {pack rat}, {trade rat}, {bushytail woodrat},
         {Neotoma cinerea}]

from The Collaborative International Dictionary of English v.0.48

packrat \packrat\, pack rat \pack rat\n.
   1. Any of several bushy-tailed rodents of the genus {Neotoma}
      of western North America, especially {Neotoma cinerea},
      which hoard food and other objects in their nests.

   Syn: trade rat, bushytail woodrat, {Neotoma cinerea}.
        [WordNet 1.5]

   2. A person who habitually saves items, even those unlikely
      to be useful. [Informal]
      [PJC]