Country & Coast: The master builder in a dinner jacket and shirt

I was reminded of this when I came across a small flock of house martins collecting mud from the edges of puddles along our back lane. As most of us know, they mix it with plant fibre and saliva, and use it to construct their amazing nests that cling to the walls of houses or outbuildings. They hang below the eaves as if threatening to fall at any moment. Indeed, some do fall – it's defective materials, the owners would say. Or sloppy workmanship.

We tend to take this skill for granted but, remembering that a house martin's plumage is a dark blue-black on its upper parts with pure white beneath, how does it manage to collect mud and construct a nest without soiling its smart clothing?

It's like a bricklayer or garage mechanic working in his dinner jacket and white dress shirt.

The house martin's building work is achieved by its beak alone – collecting the mud, carrying it, preparing it, placing it in the right place and finishing off to ensure the structure doesn't fall down. Perhaps that old man mentioned earlier was correct in calling them

house builders?

Swallows also collect mud to build their nests but their under-parts are a soft buff colour that might disguise any faint stains. They have red chins and long, forked tails, and so they differ from house martins whose tails are short but forked.

The easiest way to distinguish a house martin from a swallow is to look for the white rump. That is very clear in flight – remember, it belongs to house martins. Of the swallow tribe, neither swifts, swallows or sand martins can boast such an identifiable feature.

Furthermore, swallows' nests do not cling to walls or hang beneath the eaves. They are usually supported by a ledge, beam or shelf of some kind, often in an open barn, garage or porch .

Each year, our local house martins seem to arrive later than most of their colleagues, certainly long after swifts

and swallows. It may be that the martins who remain in the south of England arrive there as early as April or May, while here in the North we don't see them until late summer or even into September.

There have been occasions when our resident house martins have not arrived until September, whereupon they have promptly started to build their nests.

Such a late start always makes me wonder whether any youngsters will be too late to migrate. But they never are, although I must admit I cannot say whether or not they do reach their winter homes.

But I am sure they will be sparklingly clean upon arrival.

CW 14/8/10