Zoo shots. I expected better, but are these any good?

I took a ton of photos at the Atlanta Zoo the other day, and I expected all of them to be excellent (yeah, right), but even though I knew I'd have many bad ones, it seemed to me that most were bad.

Oh well, here are a few that I'm fairly happy with, although they are not razor sharp.

Would a tripod make a big difference? Should I consider one? These are taken from a Rebel XS and a 100-400 F/4.5-5.6 L USM IS). Great camera and lens, but not so great photographer.

How many of you would use a tripod in these situations?

Keep in mind that each photo was sharpened beyond reasonably to make them work.

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

HTTP response: 404 | MIME changed to 'image/gif' | Byte size: ZERO | PHOTOBUCKET ERROR IMAGE

Gator, Pandas and Child look good. The rest look as if you're fighting some serious back lighting.

The subject exposures are good but the backgrounds and rim lighting are very blown out.

ETA: Shooting very long glass (400mm) takes practice and even then you'll get your share of misses if you are falling below 1/500 on the shutter speed.

If I had the option I would most likely use a tripod, obviously it's not absolutely needed for all situations, but it usually doesn't hurt. I only checked the first image for the exif, and it was not there so having no idea what your settings were, especially shutter speed, it would be difficult to estimate how much a tripod may have helped. Good lighting and fast shutter speeds with the least amount of movement will yield the best results. I don't see any bad motion blurr, but just a small amount can soften the image. Some lens filters will also degrade the image, so if you are using a filter you might try shooting without to see if that makes you any happier.