Help - Blurry Captures

[Fotografer]

I am getting frustrated. I have been working hard at eagles and waterfowl but not getting quality tack sharp images. I am using a Canon Xti with a new Sigma 100 - 400 F4/5.6. It seems to be autofocus issues but I cannot nail it down. Maybe it is just lighting?</p>
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<p>This eagle was taken on an overcast day</p>
<p><img src="http://i404.photobucket.com/albums/pp124/jstafford_photos/IMG_7314trimmed.jpg" border="0" alt="" /></p>
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<p>This was on a bright day</p>
<p><img src="http://i404.photobucket.com/albums/pp124/jstafford_photos/IMG_7163trimmed.jpg" border="0" alt="" /></p>
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<p>Same as it flew out of the tree, note the glow</p>
<p><img src="http://i404.photobucket.com/albums/pp124/jstafford_photos/IMG_7169.jpg" border="0" alt="" /></p>
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<p>This was better as it came back around</p>
<p><img src="http://i404.photobucket.com/albums/pp124/jstafford_photos/IMG_7196trimmed.jpg" border="0" alt="" /></p>
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<p>A goose on the same outing that is much better</p>
<p><img src="http://i404.photobucket.com/albums/pp124/jstafford_photos/IMG_7214trimmed.jpg" border="0" alt="" /></p>
<p>&n