Why do birds bite?

geese bite to keep babys safe also if they feel threatend

(Addition) you've also got to look at the way geese normally behave amongst themselves. Not all bites are intended as an attack. Geese have no hands, and therefore often have to use their mouths the way we use our hands. there are "friendship" nips among geese, and sometimes these geese will give you a playful little nip as well, out of friendship.

Ask youself if the bite really hurt. If a goose wants to hurt you by biting you, it surely can and it will be very painfull. If on the other hand the bite didn't hurt, (perhaps it just startled you) then I assure you that the bite is not intended to hurt.