i have been wondering this for sometime now but what are the birds for in here? i keep shooting the ones i find in hope of some achivement or award or something does anyone know what they are for?

Clutter. That's the only reason they're there. Much like the junk items they serve no real purpose (although with OWB installed a lot of junk items now have a purpose).

They're just there for flavour. Kinda like how rabbits run around in Skyrim.

Lord Death Perk

Target practice.

It's an omen that Randall Flagg walks the earth.

Crows are the eyes of the Legion. How else did they know I killed everyone in Nipton? I killed the Legion, their dogs, the Powdergangers, the guy who won the lottery, the scorpions. The only thing I didn't kill were the crows.

The Legion started with the Blackfoot. What have black feet? Crows. What does Caesar have decorating the top of his clothing? Black feathers, what have black feathers? Crows. What does the Legion do to people that stand in their way? They murder them. What do you call a large gathering of crows? A murder of crows.

Do I need to say anything else?

They add atmosphere in an attempt to make the world more believable.

Are you a conspirancy theorist?