Why do geese travel in a group is this adaptation a behavioral or physical?

I've been told by people who have degrees in Veternary Science that it is instinct for geese to travel in groups. I happen to disagree.

Considering that they have been hunted for hundreds of years, I think they realized they had to stay together for their own safety.

Geese and especially ducks are not stupid. If you observe them long enough you will see that they reason and respond to situations.