The rain is torrential as I arrive at the London Wetland Centre on a September afternoon. Close by me and around the trees and lakeside statue of the late, great naturalist Sir Peter Scott speed clouds of house martins, jinking and zipping low over the water snapping up hatching flies.

There must be up to a hundred birds here and Sir Peter, whose inspiration it was to create the Centre would be as thrilled as I am to see so many birds revelling in his dream habitat.

The martins have come in from miles around to take advantage of this ideal feeding station. They can also be seen above the round pond in Kensington Gardens on wet days such as this.

Of our four streamlined swept-back wing lookalike species, swifts are the first to leave our shores in the second week of August followed by swallows in September,then sand martins and finally house martins which linger on until October.

On summer days,swallows hunt low,martins occupy the middle air while swifts fly high,each species exploiting its own special hunting niche.However,on wet days all may follow insect prey at low level.

The white upper rump of the house martin is diagnostic,the tail is shorter and less forked and wings are broader and less angled than those of swallows.

In fact to my mind, the house martin is a most attractive little dumpling of a bird that should be with us well into October.