The team counts every single bird on the island using a pair of binoculars and a notepad.
Researchers have been counting them in the same way since the 1980s, so they can compare more than 40 years of puffin population data.
The 1.13 sq m (2.92 sq km) island is broken up into seven sections, and the team works against the clock and the elements to make sure they have counted every puffin.
If they start the count too early in the season, most of the birds will not yet have returned from their migration, too late and they will be settled on eggs in their burrows.
There are no shops on the island, so the researchers must bring their own food supplies with them whilst they stay there for a few months for the count, but they can catch a short boat ride back to the mainland if they need to.