Below is Michael Walter's latest report:
Blean Woods has a new tourist attraction – a waterfall! But before you pack your camera and book a river trip to see this wonder, I should warn you that the waterfall is about four feet high, on a “river” of similar width. The stream that runs through the wood rises just south of Dunkirk in a network of farm ditches, eventually being honoured with the name of Sarre Penn as it flows to the north of Canterbury, and past Sarre, its fate being to end life as it began it, in an array of ditches, but this time in the marshes around Plucks Gutter. In its passage through the reserve, the stream behaves in a largely natural manner, twisting into loops that finally get cut off as miniature oxbows, and dams are an intrinsic feature of such undisturbed systems, whether the result of beaver activity or, as in this case, due to a build-up of debris washed down in winter floods. The initiator of this waterfall was a cluster of field maple stems leaning heavily across the stream. The species is itself significant, as field maple is just about the rarest tree on the reserve because, being a lover of alkaline soils, it cannot get established on the acidic clay and gravels found at Blean, but just as the Egyptian fields are fertilised by silt deposited by the annual flood of the Nile, so the very gentle valley through Blean Woods is enriched with minerals from further upstream. Hanging low over the stream, the maple trunks snagged a log, which then trapped another one: branches were next to get caught up, and as the mesh grew ever tighter so twigs, leaves, and finally even silt was snared to create an impressively watertight dam, the water backing up some 200 yards, and flooding the nearby visitor trail. Where it gushes over the dam its impact on hitting the stream bed has carved out a hollow, the displaced material being redeposited in a hump a few feet further along. Similar gouged dips are strung out the length of the stream, the results of earlier blockages, and are now a vital feature of the aquatic ecosystem as, when the stream dries up each summer, these holes survive as water-filled sumps teeming with fish and aquatic larvae. All this because a log washed down in a flood became entangled in a tree that dared to lean too low across the stream.
Below: The waterfall with impounded “lake” behind
The waterfall
Bird survey work began again in early March, giving me a chance to pay more attention to what is going on in the wood. I wasn’t to be disappointed this morning when I was startled by a whitish bird flying up ahead of me; it disappeared into an oak uttering the call of a nuthatch! Unfortunately, the view was a brief one, and my binoculars were steamed up at the time, but the bird appeared to be off-white below and weak coffee-coloured above. This is typical of a leucistic bird – one that lacks the cells that manufacture the black pigment, melanin, that is needed to create many of the darker colours in all bird plumages. Unlike albinos, which lack all pigments, leucistic birds can produce some colours; hence the nuthatch’s beige appearance. Albino and leucistic birds are rarer than might be expected, partly because their conspicuousness renders them far more susceptible to predation, partly because the melanin present in normal plumage helps to strengthen the feathers and ensure they are in good condition.
Final Note from Sue Parker : A Google search under ‘leucistic nuthatch’ will reveal plenty of photos and articles for anyone interested. Unfortunately all the photos are copyright so I am not able to reproduce any of them here.