A cardinal to me doesn't really portray a mean, aggressive or tough bird...
Funny article from espn.com
http://sports.espn.go.com/nfl/news/story?id=1977191
A few quotes from the article:
"The old Cardinal logo was a roundhead bird derisively referred to as a 'parakeet.'"
"The outline is in black," Michael Bidwill said. "We've made the beak much more predatory and much more aggressive. The face is much more streamlined. It's faster looking. The eye has been described as mean, we'll say tough. We've taken tail feathers and given them speed, as well."
"The cardinal is a small bird, but it can be a very aggressive bird. That's the idea." - Dennis Green