Parents of many species of seabird carry back whole prey items to feed their chick at the colony.
Researchers can use binoculars, telescopes, or take photos of these “bill-loads” and identify the species, number and size of prey delivered. 
This information can tell us a lot about what food is locally available, and how well the chicks are being fed.
This sounds fairly easy, but you can imagine how hard it is to get a good look at a puffin flying at top-speed, or a murre parent that refuses to look in your direction!
Yumi Arimitsu is a researcher working with the Alaska Science Center, and she specializes in the small fish that seabirds eat (forage fish).
Yumi and colleagues recently put together this great guide to teach seabird researchers how to successfully identify prey items held in the bill.