Depth of Field is how wide the area in front of and behind the spot you've focused on that will look in focus. Remember, if you're focused on one spot, things in front of it or behind it will look blurry because they're not in focus. When you use digital zoom, like you did on the second shot, you'll get an even shallower DoF. At 15 ft, it'll be less than an inch. So making sure your camera is focused on the right point is extremely important. Extended zoom lengths also make your picture-taking extremely vulnerable to camera shake. The rule of thumb for hand-holding is 1/focal length; which is for 35 mm film; you'd use the SX10's equivalent focal length to find that in the second picture, you should be at 1/1500 sec. IS will give you maybe 3 stops, so around 1/350 second; you were at 1/100 sec., so you probably are seeing some camera shake. Using a tripod with the SX10 won't do you a lot when shooting birds; you need to press the shutter directly, which causes camera shake. And using the self-timer to minimize that problem means you'll usually miss them.
The other thing to remember about birds is that even when they're sitting still, they're not sitting still. There's yet another reason to use as fast a shutter speed as you can.
I've done a few bird shots with my SX10. These are probably in about the same situation you were in, except they were hand-held. But notice I made sure the birds were centered, where the focus zone was.
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