One of Britain's rarest birds has made a return to London - but it seems to be feeding on one of Britain's rarest mammals.

The bittern has made a second appearance at the London Wetland Centre on the bank of the River Thames in Barnes, south-west London.

The bad news is that they seem to be attracted by a meal of one of the water voles, another rare British species.

The bitterns, extremely elusive members of the heron family, arrived at the centre over the weekend.

In nature there is always a winner and a loser and I would not want to be a water vole right now." Wetland Centre spokesman Martin Senior

They are thought to be the same birds which stayed there for around six weeks in January - the first bitterns reported in the capital for nearly 100 years.

They are likely to have flown over from Europe and wardens are hoping they have chosen the site as their winter home.

Only about 20 males are thought to be left in the UK, as their reed bed habitats have disappeared in recent years.

One likely attraction of the reserve is the abundant supply of water voles which were re-introduced last year and have been breeding successfully.

The creatures, on which Kenneth Grahame based his character Mr Rat in the Wind in the Willows, have disappeared from most of Britain's waterways.

Martin Senior, spokesman for the Wetland Centre said: "We are delighted that the bittern have returned again.

"But in nature there is always a winner and a loser and I would not want to be a water vole right now."