Rats are cool. How about birds?

Edit: I should read the Stickies, and I should start my own question threads.

I'm pretty sure this isn't specific to land faring creatures according to the official rules, and certain that it's not specific to land faring creatures in the current version of the module.

The logical explanation? Perhaps the thumping of the wings creature's wings creates sufficient vibrations for it to be detected.

Of course, floating creatures are another matter altogether.

If it doesn't make any sense, a wizard did it.