Record numbers of rare birds are breeding in Sussex, newly released figures have revealed.

Statistics released by the Rare Birds Breeding Panel (RBBP) show that birds which once would only visit the county are now staying to nest.

The Little Egret, which until 1996 had never bred in Sussex, now has 17 breeding pairs at six sites.

The Firecrest population in Sussex has increased, going from 23 breeding pairs in 2005 to 64.

The most likely reason for the increase in rare birds in the county is climate change and milder winters.

Ten years ago there were fewer than ten breeding pairs of the Cetti’s Warbler.

The latest figures show there are now 48 pairs.

Dartford Warblers have more than doubled their numbers from 48 in 1996 to a minimum of 106.

Birds that prefer milder weather can find food in Sussex, encouraging them to stay or migrate here rather than staying on the continent.

The Little Egret, which looks like a small heron, eats frogs, shrimps and tadpoles from rivers and wetlands.

Mark Hollings, secretary of the RBBP who analysed the data, said: “It needs to feed from still, usually fresh water and if it’s very cold it can’t access the food, which hides at the bottom of the pool.

“It’s more accessible if the weather is milder and they have started to breed here.”

Mild weather is also important for very small birds such as the firecrest which would freeze in cold weather.

Mr Hollings said: “The firecrest particularly likes places such as Brighton and Bournemouth along the coast. Its success is in some way due to the maturation of coniferous plants in the area in which it lives.”

Adrian Thomas, from the RSPB, said: “As the new birds become increasingly established here we will have to see these as native species.”

However, the milder winters are having a negative impact on some birds which have bred here successfully in the past.

Birds such as the Serin are declining in Sussex and the UK. The Wryneck is now extinct as a breeding species in the south east.

Ornithologists are keen to get a clearer picture of what is happening to birds in the country.

A nationwide survey has now begun by the British Ornithological Trust. They are being supported by the Sussex Ornithological Society who are also conducting a bird atlas in Sussex.

Data is being collected between winter 2007 and July 2011 and the results are expected to be published in 2014.

The RBBP figures are based on 2006 numbers, which are the latest to be released from the organisation.

They bring together information from all over Britain for the 2006 breeding season.

The delay in releasing the figures is partly due to protecting the vulnerable birds and their nests and the difficulty in collecting figures from across the country.