aggression

All pet owners will happily explain to you their dog or cat's character traits -- probably in far more detail than you ever wanted to know. But the idea of animal personality is not one that's been formally studied all that much.

A new study has classed a species of bird into groups of more and less aggressive males. Researchers gauged the response of male collared flycatchers to female birds, to a strange object, and to other males. They found that each type of individual displayed consistent behavior in each of these situations.