I had domestic geese at one time and I never saw the gander sit on the eggs. He guards the nest. But unlike Canada Geese, who mate for life, there's only one gander in a gaggle of geese. He guards them all. And will attack anyone he sees or interferes with the goose sitting on the nest. The most dangerous thing you can do with geese is to approach a goose with goslings. If she doesn't know you well, she and all the rest of the geese,gander and all, will chase you. Their beaks are strong enough to snap a finger and if you get hit humoorus (sic, I think) of the wing it's strong enough to break your arm or the lower part of your leg.