A handful of web sites are listed below that may be useful for digging deeper into particular topics or for keeping up-to-date on recent product developments.  See also the forums listed in the next section (A.2, below).  If you find an especially useful site not listed here, please contact me so I can include it in the next update.

http://en.wikipedia.org/wiki/Digital_photography

http://www.birdsasart.com

http://www.digiscoped.com/

http://www.birds.cornell.edu/AllAboutBirds/bp/

http://www.luminous-landscape.com

http://www.cambridgeincolour.com/tutorials.htm

http://photo.net/learn/nature/

http://digital-photography-school.com/

http://www.completedigitalphotography.com/

http://www.robgalbraith.com/bins/index.asp

http://naturephotography.fredhurteau.com/ToolsIndex.htm

http://www.birds.com

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A.2 Forums

Some forums are better than others, and for different reasons.  To keep up-to-date on new cameras and lenses, I regularly scan the Canon/Nikon forums at dpreview.com and fredmiranda.com.  For posting your images with minimal chance of harsh and unfair criticism, birdforum.net and flickr are generally good places to start, though it's easy for your photos to get overlooked in the vast sea of images that get posted daily to these and other sites.  Note that some sites place what some may consider unreasonable restrictions on file size (e.g., 200kb, 800 pixels), forcing you to reduce the quality of your images via more aggressive compression, cropping, or downsampling, which in turn invites criticism from the more ignorant viewers (e.g., complaining that your image is too small, cropped too close, or too noisy due to file compression).  Some forums also have a higher ratio of obnoxious and opinionated commenters, including in some cases even the moderators themselves.  Some forums charge a fee for image hosting, while others permit you to link to photos you've hosted elsewhere; other forums charge a fee simply for registration.  If you find a good site not listed here, please submit it for inclusion in the next update.

http://www.birdforum.net

http://www.dpreview.com/forums/

http://www.fredmiranda.com/forum/

http://www.luminous-landscape.com/forum/

http://www.cambridgeincolour.com/forums/

http://photography-on-the.net/forum/index.php

http://www.naturescapes.net/phpBB3/index.php

http://www.birdphotographers.net/forums/forum.php