I have a single WP install that has accumulated a mix of content, large subjects of which I want to separate into something resembling their own blogs. Example:

Among the pages and posts on myblog are large numbers pertaining to birds. But every post on birds is mixed in by publication date with the other posts on myblog. I want to:

1. Create a virtual (or should it be a truly separate?) birds blog at myblog/birds, with its own front page.
2. Segregate birds content from the other content at myblog, so that birds posts don't show up in the root myblog post lists, nor do tags or categories for birds show up in the root blog's tag clouds or category lists.
3. But: inbound links to the old birds page and post permalinks still (ultimately) reach them at their new /birds subdirectory.

I can see features that produce some but not all of this functionality (e.g., use an archive page and ensure all birds posts share the top-level birds category; or create a separate WP install and migrate all birds pages and content to it...) but I don't want to start down a road only to learn after much hacking that I can't accomplish all three of the objectives above.