A PIERCING whistle whipped across this wood by Tillicoultry, so I crept towards the source of the sound and soon spotted the nuthatch slowing working its way up a tree trunk.

What a marvellous little bird it was. About the size of a plump sparrow, the attractive plumage is a mix of slate-grey, buff and chestnut.

It is the wonderful piercing song that really catches the attention; a liquid-flowing repertoire fit for any choir, featuring an incredible range of ringing notes including one melody that is similar to a boy whistling.

The poet John Clare described the song as a "long and loud continued noise" that "often stops the speed of men and boys".

The nuthatch is similar to a small dumpy woodpecker, but unlike a woodpecker it can crawl down a tree trunk headfirst, its sharp grasping claws providing perfect grip and its long bill ideal for searching the nooks and crannies of the bark for insects.

But what is even more astonishing is that until a few decades ago the nuthatch had only been sparingly recorded in Scotland, despite being a relatively common breeding bird in England.

Then, in the late 1980s something remarkable happened. The number of records increased and the first breeding occurred in the Scottish Borders.

The nuthatch has spread rapidly since and is now well established in many southern and central parts of Scotland, and moving into Perthshire, Dundee and Angus.

The nuthatch has most interesting nesting behaviour. It likes to breed in holes in tree trunks or branches, but if the hole is too big, it will plaster the edges with mud thus reducing the size of the entrance so that the bird can just squeeze in.

This helps reduce predation of nestlings and prevents other larger bird species from using the hole for their own nesting purposes, given that there is often competition for such sites.

As well as invertebrates, the nuthatch is fond of nuts and seeds, which it often fixes into a crevice in the bark and hammers away until it extracts the kernel.

The name nuthatch can be traced back to the old English 'notehache', which is derived from 'nut' and 'hack'. Another delightful country name is 'mud stopper', a reference to its mud plastering activities.