In many of his wonderful stories such as 'Tarka the otter' and 'Salar the salmon', the great nature writer Henry Williamson makes frequent reference to 'Old Nog'.

We know him better as the grey heron, that tall lanky bird we see standing motionless on the margins of lakes and alongside the Thames or flying overhead uttering his harsh 'kraark' calls, often mobbed by crows as he makes his way to a water body.

A master fisherman, the heron also feeds on frogs, newts, water birds and small mammals. He waits patiently either standing stock still or walks slowly stalking his target, eyes piercing the surface ready to stab his prey with a lightening strike.

Herons hunt alone but if the fishing is good, in company with others of his kind , spaced out like a row of soldiers on parade, or on occasions they can be seen hunched up, necks retracted. I've seen herons catch water voles at the London Wetland Centre and a few years ago also at the centre, a pair of avocets bred for the first time but sadly their fledglings were taken by herons.

I've always thought it rather odd that such a seemingly ungainly bird is capable of perching high in trees and even building nests in such unlikely situations.

Within the past couple of decades small pure white 'herons' have been nesting in Britain but they are in fact little egrets from southern Europe.