Michael Walters latest update:

We have two relatively common small raptors – the kestrel and sparrowhawk – but with different fortunes and lifestyles.  While the sparrowhawk has made a welcome comeback from near-extinction following the grim decades of persistent pesticide application to our farmland, the kestrel, formerly easily our commonest bird of prey, has declined by around 30% in the past 25 years.  Their hunting techniques differ radically:  the sparrowhawk will typically fly fast and low in the hope of surprising small birds and then giving chase, or patiently perch quietly within the wood until an unsuspecting bird passes, its fate determined by whether it is athletic enough to outstrip the cheetah-like burst of speed of its pursuer.  The kestrel, in stark contrast, is a bird of open habitats with few trees, turning into the wind to hover for seconds at a time, its penetrating gaze scanning the vegetation below for the least movement.  So, unsurprisingly, extensive woodland is totally unsuited to the kestrel’s modus operandi, but I do see them from time to time in Blean Woods, as the tree cover is by no means solid.  The most likely place to see one is the 12-hectare heath, a large area with just a scattering of mature trees and extensive swards of grass, heather and gorse or broom scrub, and that is where one appeared this afternoon while I was checking the goats.  So far as I am aware, they have never attempted to breed on the reserve, but the introduction of a large open-fronted nestbox on the heath margin might conceivably prove sufficient incentive for a pair to take up territory.

 

Work continues on blocking up streams and ditches to help the reserve retain its water for longer.  The main stream flows through a shallow valley from south west to north east.  In the past it has been free to wander to left and right along its narrow floodplain, but more recently, perhaps 1-200 years ago, stretches of the stream were straightened in a bid to make the wood drier, and so facilitate extraction of timber in the boggy winter months.  In the process all the interesting wiggly bits were cut off, leaving them high and dry.  These truncated meanders survive as ghostly impressions in the ground, and the current rewetting project is taking advantage of their presence by encouraging water to overflow the stream banks behind the new dams, and spill onto the graceful curves of the old meanders.  But why did the stream wiggle its way down the valley in the first place?  Actually, with such a shallow gradient, it would be a small miracle if it did flow in a straight line.  The least resistance, such as a fallen branch, will encourage the water to deviate to one side, and once the slightest of bends has been created, nature does the rest, as countless ‘O’ level and GCSE geography students have learnt.  On meeting a change of course, the flow on the outer edge of the bend moves more quickly, supplying it with more energy to scour the crumbling bank, while the water on the inner edge of the curve slows down, enabling it to deposit a little of its load of transported silt.  So one bank on the bend is gnawed away while on the opposite bank a shallow shoal of silt and stone builds up, further deflecting the water towards the eroding bank.  In this way some dramatic and remarkably graceful curves can slowly develop until, in some cases, the loop curves back on itself, the stream breaks through the narrow neck of land, straightening its course and leaving a classic arc of an oxbow pool to one side.

 

Life may seem a bit grim right now, but I’m writing this on 16th December, so in just six days’ time the days will be getting longer, and then before we know it the snowdrops will be out, and I’ll be on the lookout for early-flowering hazel and primroses.  Meanwhile, I would like to wish you all a Happy Christmas!

 

Michael Walter

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