All but the first and last of the following FAQs (Frequently Asked Questions) and PIPs (Periodic Information Postings) are from Stasya's FAQs and PIPs list, which is the "official" web site for most of these, and is where the most current versions of these FAQs can always be found. I will try to keep these as up-to-date as I can, but for the last word, you should go there first. Or something like that.
How-to: Geese and Raptors by Hawk. -- New! July 13, 1997. Before you read it, let me summarize: It's a guide on giving them oral pleasure, not sexual intercourse. Having sex with a bird can be fatal to the bird, because their organs are too delicate.
The following FAQs and PIPs have been converted into an attractive HTML format by Valadan and are available at Valadan's Stables. Please note that I have made NO modifications to these files, so the site-specific links (such as cgi counters) may try to access his web site directly. Also bear in mind that, due to the effort involved in the HTML conversion, these are not as up-to-date as the text-only FAQs above. However, they are much nicer to look at. :)
The University of Washington has an excellent Sexuality Library resource section, with links to almost every topic you could think of. There was once an extensive (if a bit outdated) zoophilia subdirectory; it was removed due to visitors' objections. Dweebs.