Bird migration like this is truly one of nature's spectacles. This video from BBC Earth Unplugged captures a massive flock of starlings, some 70,000 strong, as they move across the UK. The hypnotic, undulating way these birds move is known as a "murmuration." Each bird mimics the movement pattern of the bird directly nearby, rippling out to the whole flock. It's mesmerizing, but experts also say it's an effective defense mechanism.