Although this link deals mostly with chickens, it is one of the most comprehensive poultry health sites available on the internet. In Mississippi, poultry is the #1 agricultural product, so their "U" has devoted a lot of time studying it. There are a dozen other Ag schools around the country, where if you search for info on poultry health, they all link to this site! Go down to "Diseases and Pests of Poultry" and click. It will open up about 10 links to choose from (some are the same thing, just organized differently, ie symptoms vs body part). All in all, I think it is the best single source available for poultry health issues.
http://www.poultry.msstate.edu/extension/ Hope that many of you can benefit from this extensive info.