A severe icy winter naturally poses problems for roosting birds. Most seek shelter overnight in dense bushes or with larger species, in tall trees.

The smaller the bird the more rapidly they lost body heat so tiny species such as goldcrests suffer. Wrens (pictured) have been known to roost en-mass all snuggled up in nest boxes.

There is one species namely the pied wagtail that congregates in large numbers in well lit and comparatively warm town centres . Real 'townies' indeed.

In Wimbledon town centre stand four tall plane trees the most sheltered of which plays host to dozens, even hundreds of the birds as dusk falls. They arrive in numbers from outlying areas and noisily jostle one another for the best positions. They all face one way into any breeze and looking up, we can see their white breasts  reflecting street lights looking like little tennis balls among the branches.

The roost has been in use for many years but this winter the number of wagtails using it has increased dramatically.

Most commuters hurrying to and from the station don't even seem to notice the birds.

Most wagtails disperse shortly after dawn but a few hang around all day, running jauntily along the station precinct, tails wagging furiously and uttering their 'chiswick' contact calls as they pick up crumbs dropped by passers-by.