I don't know whether this is a bug or a feature, but it seems like a bug.
When frogs attack moslings, they will call for the Moose/Goose to fall from the sky, but the Moose/Goose never attacks the frogs.
This results in the frogs simply murdering the moslings while the Moose just stands there... Watching.
Go to goose nest with moslings, spawn a frog, let frog attack moslings.