If your teacher has trouble keeping track of your class on school trips, imagine what it's like trying to count tens of thousands of identical puffins!
That's what animal experts are trying to do as they start counting the puffin population on the Farne Islands, off the Northumberland coast.
It's not easy. The seabirds don't like staying still, they all look really similar and some even live underground!
The count happens every five years to try to keep track of their numbers.
The last few surveys have seen the puffin population increase, but no-one knows what will happen this year as about 800 puffin nests were washed away last year during heavy rains.
Their teeth point backwards
They're only about 30cms tall
A baby puffin is called a puffling
Their bills can hold lots of fish
The last survey, in 2003, recorded up to 55,000 breeding pairs of puffins, which are also known as the clowns of the sky. The latest results are expected in the summer.
Farne Island's head warden David Steel said: "By counting the population we can see if they are doing well or doing badly and then examine the reasons behind that."