`This bear is not miserable - official'

London Zoo has had to erect signs to reassure worried visitors that a depressed looking bear is perfectly happy.

Lanka, a 14-year-old sloth bear from South Asia, has been displaying worrying behaviour since her move to London from Warsaw Zoo three months ago.

She rocks from side to side in a motion that some animal experts have described as a classic sign of boredom.

But keepers have moved to dispel the worries of people viewing this strange spectacle by putting up signs around her two acre enclosure.

The sign states: "You may have noticed that the female sloth bear sometimes displays an abnormal `rocking' behaviour in front of doors. The keepers are trying to cure this with a wide variety of behavioural enrichment ideas".