I agree with LCARS, nice to see something a little different in the zoo photography line. C&C per req:
1. Since I'm always saying that you should have subjects looking toward you, I probably shouldn't like this one, but I rather do. I think the pensive sort of look in his (her?) face is rather good, and makes for an interesting and unique image. It might be worth trying to tone down the background a little though, as it is rather bright.
2. This one is a take it now or it's gone forever sort of image, so it's hard to say much about it, but the bright highlights and distracting background do take away from what otherwise would have been a really neat capture. Watch your focus, as the eyes are a little soft here.
3. I wonder if he flosses every day? Again, neat, but I would have prefered to see more 'gator. His skin is a bit dark, and I think perhaps metering for that would have helped.
4. Hmmmm... interesting, but I'm afraid I'm not getting a lot from this image. I think the under-exposed subject and blown background are working against each other. If you're camera is able to spot-meter, this would have been the time to use it.
5. Soooooo close; once again just missed focus by that >< much! It's a shame because this is a really neat image; to me, his (her?) face has very human qualities.
Overall, nice shots! I think two things to really concentrate on are: Getting your focus correct, and trying different exposure/metering modes to become more adept at dealing with scenes such as #4.
Just my $00.02 worth - your mileage may vary.
~John
Ps. I see nothing wrong with your watermark. It's small, unpretentious and doesn't block out large portions of the image.