Rotterdam zoo Blijdorp, which was given charge of 51 stolen puffin eggs seized from smugglers at Schiphol airport, has managed to hatch 42 of them.

The eggs were part of a collection of 79 eggs found in the luggage of three German nationals who had travelled from Iceland to Schiphol airport three months ago. Grown puffins can fetch thousands of euros on the black market.

The process of hatching the chicks was “very labour intensive”, zoo spokesman Erwin Zwart told broadcaster NOS. “The first one hatched after just four days and then it was one after another in the weeks that followed. Normally, they would be cared for by their mothers but it was up to us.”

The zoo has experience hatching puffins and already has a puffin colony but was hard put to find enough incubators for them all, Zwart said. “But now the big hatching cupboards are a jolly cacophony of chattering puffballs,” he said.

Puffins are an internationally protected species which only hatch one egg a year. Their survival is threatened by overfishing, pollution and rats and cats in their habitat.

The puffins are healthy but will not be released into the wild because they don’t have the skills to survive, the zoo said. Once they are strong enough, they will go to other zoos and participate in international breeding programmes.

The smugglers, who were also carrying an incubator to keep the eggs warm, were fined €7,500 each earlier this month.

Only five of the 28 duck eggs in the smuggled collection hatched.