Look around you.

True...

Birds, Haruna, and Wo-Class

But Haruna-chan, it has to be warm.

The Mr. Birdies' friends are all waiting to cross the ocean with them.

But we're Mr. Birdies' friends too!

...but it's natural for the Mr. Birdies to cross the ocean with their friends and spend the winter somewhere warm with plenty of food.

They'll come back when it turns spring, so we have to be sure and let them move.