Bewick's swans' arrival at Slimbridge heralds start of winter

The first Bewick's swans have arrived at a nature reserve in Gloucestershire, heralding the start of this year's winter.

At least five of the birds have arrived at the Wildfowl and Wetlands Trust (WWT) at Slimbridge.

Every winter the swans fly about 3,500 km (2,000 miles) on their annual migration from Arctic Russia to seek out comparatively warmer weather.

Bewick's are the UK's rarest swans, with numbers in decline since 1995.

They have unique yellow and black beak patterns so experts can identify individual returning birds, and each bird is given a name.

The Bewick's have been studied at Slimbridge for more than 50 years, with more than 10,000 swans being recorded - making it one of the longest single species studies ever researched.

A breeding pair, named Primero and Piquet, were the first to arrive at the end of last week and at least three other Bewick's have now joined them.

Numbers in north-western Europe have decreased from about 29,000 in 1995 to about 20,000 recorded in 2015, and conservationists are still trying to confirm the reasons for the decline.

The swans' arrival in the UK is traditionally seen as the start of winter.