It was only natural that once it was late that Eagle didn't wander around outside. He had bad night vision.

And it was only natural that he thought Aqua shouldn't wander around. Firstly, she was a sea otter, and he was fairly certain that her night vision wasn't better than his. He wouldn't have been able to sleep thinking of her wandering around by herself. So he had asked her to stay for the night.

He can't exactly make her sleep on the ground, he prepares a bed for himself on the floor so she can take his couch.