I know one of their construction folks came over to get into the duct sytem. (They're renovating, which explains the open duct). I called the emergency clinic here and they suggested a humane trap and some tuna fish, and the fire department if he can't get out on his own. Yikes. So we're all thinking along the same lines. Thanks so much for your quick reply. It 's a big help to know there are others out there to touch on who can think through something like this.

I told my parents that there's also the possibility that he's not in the duct at all, that he found some really obscure place to hide, because he couldn't go outside and he's not used to being inside. I left my cat at my best friend's house one year and she thought she lost my cat for a couple of days -- turned out Sophie had ripped a hole into their box spring and holed up in there all that time. I can understand that kind of behavior, given the circumstances. Of course, the vent could be one of those great places to hide.... I'm hoping the little guy will reappear on his own -- probably when everything calms down again. It sounds like they're being pretty loud and freaked out about this, which I'm sure isn't helping the situation. Still, they need to check the vents and I'm glad they're moving on that.

Thanks again -- I'll post the outcome when I know it.