Listening to a lot of public radio programming over the last couple of days and have had so many reminders of why I am so fascinated and way of birds. (Yes, wary of those reptilian bastards - they know too much.)
Off the top of my head, the main reasons for wariness: birds not only see a totally different range of colors, but also the electromagnetic field - but only out of the right eye. Remarkable in general, just weird when particular to only one eye. And they can also hear earthworms dig.
Check out the episode of 'On Point' with Tom Ashbrook and the English ornithologist Tim Birkhead.