Exotic immigrants heading this way

A NEW wave of immigrants, exotic and colourful, is about to take up residence in Britain - in trees, on lakes and in reedbeds.

The newcomers are the increasing number of bird species that ornithologists believe are poised to extend their breeding range from the Continent to the British Isles.

They range from the unmissable, such as the spoonbill - now regularly seen in East Anglian wetlands sweeping its strange-shaped beak through the shallows to pick up crustacea - to the easily missed, such as the tiny greenish warbler, hopping about in the treetops, whose presence has been detected by its song.

They and several other species are expected to start nesting here before the turn of the century, for reasons ranging from climate change to pressure of population, says the British Trust for Ornithology (BTO).

Top of the list are little egrets, small pure-white herons from the Mediterranean, extremely rare until the 1960s, but which in recent years have been flying in from the Continent in unprecedented numbers, with at least 250 arriving this August.

They breed regularly in France and have raised young in the Netherlands. ''They're forming flocks in southern estuaries - surely they will start to breed here soon if they're not doing so already,' said Chris Mead of the BTO.

Spoonbills, another spectacular white species, have been spotted carrying nest material, so there are high hopes that they will soon breed in Britain. They already do just across the North Sea in the Netherlands.

But first their UK population may have to expand to the point where they form flocks - that is probably needed to stimulate breeding.

Some smaller birds are expanding their range towards us from northern Europe. The scarlet rosefinch has been moving swiftly westward along the shores of the southern Baltic, and last year three pairs bred in England for the first time. The species is expected to establish itself now. In their second year the males, previously fairly drab, explode into a beautiful carmine plumage.

From Scandinavia the greenish warbler is heading towards us, a tiny 'leaf-warbler' so small it can feed on the outermost twigs of trees and bushes without bending them over. Singing males have been heard proclaiming their territories in the spring and breeding is expected to follow soon. The bluethroat, which looks like a large robin with a blue breast, is making similar progress towards us.

Among water birds, the red-necked grebe, a regular winter visitor, seems to be trying to set up house in Britain from Denmark, while the ring-billed gull, a North American species, is heading towards us across the Atlantic in increasing numbers.

If it starts to nest it will be the first recorded case of a North American bird starting to breed in Britain in modern times.

One of the main reasons for these movements is that birds, like almost all other creatures, always tend to disperse their populations. They are rather better at it than most. Some individuals are always trying to push into new territory, and changes in climate, favourable winds and a string of wild winters can help. They may find an empty niche to exploit.

It has been suggested that the movements of birds may be harbingers of climate change, but there is no firm evidence. It seems that bird populations are commonly waxing and waning through the years.

TWITCHERS and birders unite. Today is World Birdwatch Day, involving more than 90 countries around the globe, with more than 120 birdwatching events taking place in the UK from Orkney to Jersey.