Nature 2014 October

Roaming in the Chiltern Gloaming

A few weeks ago we had a less than usual visitor, as twilight (aka gloaming) fell, roaming in our garden – a grey heron. It was a juvenile, distinguished by its hunchback profile and stubby grey bill, contrasted with the adroit stance and blood-orange rapier of the adult bird. When not flying overhead, we most frequently view herons at the water’s edge, riverbank, canal tow-path, through reeds or in open water, standing statuesque.

With no pond nearby, remaining motionless and allowing the prey come to within reach was not an option. Instead, this youngster contented itself with scouting for food in the long grass and beneath shrubs. Several minutes passed while it stalked its hidden prey. I’ve never had the opportunity to observe a heron at close quarters. The way this bird moved had remarkable similarities to that of a chameleon. It is interesting how these two very different animals have adopted a similar approach to finding food. Given that their chosen meal is fast-moving, they have developed a similar strategy which maximises their chances of success.

Slow, very slow, deliberate movements are interposed with a jerky swaying of the whole body, aimed at concealing that a predator is hunting down its next meal. Once in position their final movement, be it with a stiletto bill, or an elastic sticky tongue, is lightning fast. In the case of the heron the wilderness in our garden would provide rich pickings, including mice, voles, beetles, frogs and toads. Eventually it ended its roaming as dusk fell and flew off languidly. There are few animals that can be considered predators of herons. In theBritish Isles, the heron is effectively the top of the food chain. However, there is one bizarre example of the heron being taken advantage of. Some of the most reliable foods of the heron are small freshwater fish such as the stickleback. Sticklebacks forage for much of their food from the detritus that falls to the bottom of rivers. Within this muck are nutritious items such as small insects and eggs which have been deposited in large quantities.

The fish will indiscriminately consume these and unwittingly swallow eggs of tapeworms, many of which are parasitic on fish, but in some cases subsequently need to parasitize birds. In one case the chosen bird is a heron. Having been ingested by the stickleback the tapeworm hatches and grows in the stomach of the fish. Once it reaches a certain size it needs more sustenance than is available from the fish. Perhaps it induces the fish to behave differently by making it feed from near the surface of the water and in so doing the stickleback becomes susceptible to being caught by the heron. Once inside the heron the tapeworm attaches itself to the wall of the digestive tract of the bird, grows rapidly and produces eggs which are subsequently excreted by the bird, fall into water and sink into the detritus. It is worth contemplating how this complicated association between a tapeworm, a fish and a heron evolved!

I am sure many of us have experienced the reaction of friends and relatives who, when visiting here for the first time, express how surprised they are at the remoteness of the Hilltop Villages. Much of this feeling comes from the scattered plantations of beech woods, which these days have replaced the ancient oak woodlands which once covered nearly all of the Chilterns. Today there are just small vestiges of these once magnificent forests that were progressively but very gradually cleared over several thousand years. But what might be considered remote today is nothing compared to the remoteness of these hills in past millennia.

The earliest humans appeared around 400,000 years ago and there has been evidence, from stone axes found, which indicates they were roaming across the Chilterns. This was a time when the truly prehistoric wild animals roamed southern Britain, like woolly rhinoceros, mammoths, cave bears, and the giant Irish elk.

However, several glaciations have dramatically changed the Chiltern landscape and the forests first appeared around 12,000 years ago. They were originally pinewoods, replaced 8,000 years ago by birch woods (as the climate continued to warm) and eventually mixed elm oak and beech woodland from 7,000 years ago. This was a true ‘wildwood’, a habitat we cannot find in the British Isles today, but would not have been too dissimilar to that still found in the remotest parts of Canada and New Zealand. By this time the giant mammals such as wild ox, arctic fox, bison, wild horse, wolf and wolverine were already in decline, very rare or already absent from these parts.

To understand what large mammals were around in these primordial forests, good references are fossil bones and later the tools developed by humans. Some of the best evidence of the variety of wild animals encountered by man comes from the flint tools developed, with different shapes for each task or specific animal. From this we know there were brown bears, beavers, wild boars, deer, otters, pine martins and, familiar to us, badgers.

It is generally agreed that farming arrived around here between 6-4,000 years ago with wild cattle and horses being domesticated soon after. This was the start of the gradual retreat of the second wave of wild animals, most of which had probably disappeared from these hills some 3-2,000 years ago. Climate change has always played a role, whether man or naturally driven and both will continue alongside other impacts by man to influence our landscape, habitats and wildlife. Enjoy roaming in the Chilterns gloaming while you can!

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