As I began an effort to cull all the digital images I had on my hard drive, I noticed a trend in many of those taken with my Sigma lens - most lacked clarity that I was seeing in the images of other photographers and I began to take a hard look at what I was doing incorrectly and asking for insight. There is a saying out there I've seen posted many times over - it isn't the equipment - it's usually the photographer.
What should I have been doing? For one, I was not using good long lens technique!
And with this, I thank the photographers who generously offered advice on how to improve my imaging.
http://www.naturephotographers.net/articles1205/gm1205-1.html
http://www.bestofthetetons.com/2014/02/06/attracting-and-photographing-wintering-back-yard-birds/
http://philipschwarzphotography.wordpress.com/2011/04/10/perches-for-photographing-birds/
http://digital-photography-school.com/backyard-bird-photography-tips
Long Lens Technique:
http://www.naturephotographers.net/ejp0801-1.html
http://www.moosepeterson.com/techtips/longlens.html
http://www.outdoorphotographer.com/how-to/shooting/long-lens-tips-and-techniques.html