Sir David Attenborough has warned that cats are killing huge numbers of birds in British gardens.

The TV naturalist said cat owners should buy bell collars for their pets to help stop the deaths.

Sir David, 87, features the robin on the Christmas Day edition of Radio 4 programme Tweet Of The Day.

He told the Radio Times that cats and the cold winter weather, when frozen ground makes it difficult to find food, are the biggest problems faced by birds.

"Cats kill an extraordinarily high number of birds in British gardens," the broadcaster said.

Asked whether cat owners should buy bell collars for their pets at Christmas, he replied: "That would be good for the robins, yes."

The presenter also warned that scientists should not attempt to bring back species such as the woolly mammoth.

TV presenter Alice Roberts recently urged society to "grapple with" the issue of bringing Ice Age animals back from the dead after Japanese scientists extracted the bone marrow from woolly mammoth remains with a view to resurrecting the creature.

But Sir David, who encounters extinct animals in a new Sky documentary using special effects, said he was not keen on the idea.

"I think it could conceivably happen, but to what end? It'd be a nice intellectual triumph for the scientists, but where's the poor thing going to live?

"Where's it going to find a mate? What's it going to do? We've got quite enough problems saving the species we've got without bringing old ones back," he said.

Sir David also suggested that he had mixed feelings about the approach, taken by conservationists, of focusing on the danger of particular species dying out.

"It's a mistake that conservationists have made (to focus on species such as this). But it's a useful mistake. It made sense to concentrate on the disappearance of species that we care about, the charismatic species, in order to make people aware of what mankind is doing," he said.

"It's very easy to say 'The giant panda's disappearing'. What you should be saying is that the ecosystem of which the giant panda is only a part is disappearing.

"Because the world wouldn't change hugely if we lost the panda. But if we see the disappearance of the bamboo forests on which the panda depends, that will disrupt the whole natural pattern of things."