What is the length of tunnels puffins dig in the Farne Islands?
If that's the current number of tunnels at any one time, it can be right, it depends if they dig a new nest every year. 

Farne islands has mostly horned puffins with rainbow beaks as opposed to tufted puffins which have an different beak, the former makes nest around 1 meter and the latter up to 2.75 meters, 

Puffins lay one egg per year, there are 30-50,000 pairs of them on Farne islands, that's about 40km of new tunnels every year. 

Every five years the trust carries out a larger audit, the last being in 2013, when puffin numbers on the islands were strong, at just under 40,000 pairs.

That was an increase on the 2008 figure when a stormy summer hit numbers hard from a high of more than 50,000 down to 36,000 breeding pairs.