Bird Flu...Hum.. I am planning on adding chickens this spring as the easiest way to add a ready source of protein. Last year I replaced some flowers with vegetables and hope to expand that this year. My chickens will be laying hens of heritage varieties as I can see myself getting too attached to ever butcher them! I though about the bird flu angle a lot. But it seems that avian flu is primarily spread by migrating water fowl and is not in the songbird population. I am not near any waterfowl flyways and my toney neighborhood does not have any other farm animals for miles. I live in what was once farmland and my little patch of ground is still zoned agricultural although I am now surrounded by MacMansions. Hopefully I will be able to vacinate my chickens against avian flu as a precaution; I understand that chicken vacines have been developed.
In Europe, the order is vaccinate them and to keep them in a totally enclosed house or pen (with side and overhead chickenwire) so they can't mix with the free rangers.  Lots of complaints about building the required structures.
I have to have wire pens with mesh overhead anyway, because I have two pair of hawks nesting in my woods......
Two thoughts on this...
Having actually kept chickens for a few years, they seem to react in enclosed spaces much like rats and humans-- they start tearing at each other's feathers and generally exhibit stress due to crowding.  Our chickens, (circa 1997-2000), were free range during the day, were absolutely healthy and produced eggs too large to fit in a carton.  Our rooster seemed to keep them all safe in a habitat that included dogs, coyotes, feral cats and snakes.  (They also all had names and distinct personalities).
OTOH...all the avian flu sites I keep up with report today of confirmed cases as far north in the EU as the Baltic Sea.  I have no idea if the vaccine that the Asian countries are using is effective or not, at this point, but I would think that sooner or later federal action/local hysteria would demand that you cull.  I think it's pretty iffy right now.