These Arctic Wolf cubs still with the brown fur so they can remain difficult to see in their underground burrow have started to emerge to the delight of zoo visitors.

The four cubs are the first to be born after a seven-year pause in new arrivals at the world's oldest zoo located in the Austrian capital Vienna.

That changed with the arrival of a female wolf who arrived at Schonbrunn Zoo in 2017 from the Knuthenborg Safari Park in Denmark, and then after that two male wolves from the Monde Sauvage Safari Park in Belgium turned up last year.

The four cubs were born at the end of April in a low-lying burrow and were raised there by their mother.

Animal keeper Paul Wagner said: ‘At first, wolf puppies closed their eyes and are completely helpless. They need the protection of the cave and the care of the mother. Meanwhile, you can often watch the four little ones playing, drinking and exploring. In addition, they gain their first social experiences with the pack.'

They rarely retreat to the building to sleep and are suckled for about three months before slowly moving over to the diet of meat.

Zoo Director Stephan Hering-Hagenbeck said: ‘The breeding success confirms that the composition of the pack fits.'

He said that the Arctic wolf inhabits the northern regions of North America and Greenland and added: ‘The brown-colored juveniles are difficult for enemies to spot in the burrows. Later, they get the bright white fur which in their snow-covered homeland makes them almost invisible to prey.'