If You Are Interested In The Bird...
here's the current source code for it:
http://necros.quaddicted.com/temp/ne_bird(18.12.11).qc
you'll also need this model:
http://necros.quaddicted.com/temp/raven.mdl (that's the h2 raven model with an ugly new skin)
should be almost plug and playable. probably just need to declare a few extra entity fields.
also, this is totally a WIP... that code is probably pretty wasteful atm and there is a lot of unimplemented stuff.
i eventually want to give them real goals like eating (diving for fish in the ocean), hunting (flying in a local area over water) and resting (standing on the ground wandering around) as well as making them sort 'stubborn' so they'll form up in distinct groups and tend to stay with their own group, instead of forming one giant flock 100% of the time.
they don't land on their own, but if they hit the ground in a way to set their on_ground flag, they will sit around for a little while before flying again. there's supposed to be some extra stuff here that's not implemented, but standing birds should try to move together if other standing birds are near, and should be more likely to wait on the ground if they have company or fly sooner if they are lonely.
to use birds, just put some creature_bird entities in and then make some bird_anchorPoint entities in areas you'd like birds to loiter around. they'll move to the different anchor points randomly.