A person who is more energetic and active during the day than at night. The opposite of a "night owl." My husband is a real day lark—he has boundless energy as long as the sun is up, but after it sets, he crashes. I'm sure she's up with the sun—she's always been a day lark. Because I would have to be at work at 5:30 AM, I became something of a day lark over the years.