That was a scientific article, which was quite insightful to how evolution works...in summary: Flightless birds can carry around the extra weight, so grow big

That was a scientific article, which was quite insightful to how evolution works...in summary: Flightless birds can carry around the extra weight, so grow big penises to impress mates, while flying birds can't afford the weight and so must result to colorful feathers to impress mates.