Has it happened to you, goes an article in a French bird magazine, that you were sitting quietly in a park when you thought you saw a small bird fly towards a tree trunk just in front of you - and then suddenly vanish? Were you imagining things? There are no branches on the trunk, no holes where the bird might have vanished into and yet you see nothing of it. But the bird is there, a treecreeper hanging on to the bark, his claws a little parted. Holding himself up by his strong tail, and with his head not moving, he is invisible. But just wait. Don't move and then you will see him as he turns his head and shows a white breast, and, like a mouse, he will be creeping up and round the trunk. He has a curved beak, long for his size and is probing cracks for insects or larvae or whatever. His length is given as 12.5 cms, i.e. shorter than a robin. While he looks brownish from a distance, he is, in fact, streaked with russet or buff. Here in Ireland there is a tree with a straight trunk on a river bank beside a cottage. From the windows you may see a treecreeper silhouetted against the water behind. He is the certhia familiaris, very like the bird described in the French magazine, the certhia brachydachtyla. It's hard to separate the two, says the authoritative Birds of Britain and Europe by Heinzel, Fitter and Parslow. The French magazine shows big photographs of the bird set against the trunks of two different trees which give a well-streaked impression while, looking down on a bird apparently in flight, the camera reveals an altogether more colourful creature than he seems from eye level. Cabot tells us that while the species is widely scattered across Ireland, with 45,000 pairs, there has been a noticeable reduction in recent years in Co Wexford, north Cork and in the Midlands. These eyes have never seen a close view of the bird with total wingspread, but the pictures mentioned above give an altogether unexpected glamour to the apparently modest treecreeper. They nest in cracks in the tree and, says Cabot, "prove very difficult to entice into a net box." Remember, if you see what you think is a mouse on a tree-trunk, it's probably not. By the way, in the city the underparts may be grimy in colour, but in the country a good white.