In June 1970 two Dutch students, Jan den Held and Marcel Groenendaal, decided it would be an interesting use of their summer vacation to count all the tens of thousands of seabirds on the Isle of Noss National Nature Reserve in Shetland. No-one asked them to do it and no-one paid them. It was a huge undertaking but they and four friends produced a more detailed estimate than any previous study of the16 different species on the great sea cliffs of...