The Collaborative International Dictionary of English v.0.48:

Birdseed \Bird"seed`\, n.
   Canary seed, hemp, millet or other small seeds used for
   feeding caged birds.
   [1913 Webster]

WordNet (r) 3.0 (2006):

birdseed
    n 1: food given to birds; usually mixed seeds [syn: bird feed,
         bird food, birdseed]