Category Archives: Natural History

Owl Box for Gunnersbury Triangle

3 March 2015 Ian Alexander

It was a very rainy workday, and with only two of us around we wondered what to do. It was time for an indoor project that we’d been putting off … make an owl box. Tawny Owls might seem surprising citydwellers, but they are around in the leafier suburbs and larger parks.

We looked at the RSPB website for instructions, calculated the measurements of all six faces of the box on a sheet of paper, and studied the bits of plywood we had available. Just whiz along with the circular saw, screw it all together and we’ll be done.

It took a little longer. To cut the wood, we needed to be outside. Where it was raining. The wood got wet and it was hopeless trying to draw lines in pencil or biro. Felt pen worked, sort of, but gave us thicker smudgier lines. We drew, went outside, held and sawed, dusted down, came inside, made another cup of tea, drew again, went outside.

Finally we had a forlorn pile of long, dirty, improbably shaped bits. They seemed nothing like a nestbox. Let’s finish it next time, said Netty, sounding a lot less keen than she had at the start. Let’s get it done, I said. It’ll not take long now. We were a bit cold. We screwed the front to the sides, which were the thickest parts. Suddenly it had a shape. We took the extraordinarily long back and screwed it to the sides. A box. A very long box. We pushed the base into the hole. It wobbled. We pushed it down the very long hole with an umbrella and got some screws in. It was all done save the lid, which needed waterproofing with some roofing felt, and attaching with a rubbery damp-course hinge.

The next time was dry, and we took the box outside. It seemed enormous, and Netty had fixed on a long bit of dead branch as an owl-perch, but it went in a wheelbarrow and we set off with drill, ropes, and a ladder to the chosen Oak, a tall straight tree off the beaten track.

We managed to get a rope over a branch and haul the box up. Only, how to fix it and get the rope down again? We let it down, threw a thin plastic rope over the branch as well, hauled the box up, tied the thin rope onto the top of the box, and stood back. The box was up, but definitely dangling. We could easily fix some screws into the stub at the base of the box, but how to do the same for the stub at the top? We moved the ladder around the tree to find a way to reach. With the ladder in the easiest place, the box was directly above our heads. We tried it every which way, we couldn’t reach. We put the ladder back where it was. With two of us holding the ladder and one on the top rung, it was just possible. Trying to tie knots or fix a screw with one hand … is quite tricky. We were very pleased when it was done. We’ll be delighted if a family of owls takes up residence. Or even some jackdaws.

Natural History

How to Tell WhoDunnit: Pigeons Killed by Sparrowhawk, Fox

23 February 2015 Ian Alexander

Pigeon plucked by Sparrowhawk — Scene of Crime in London Wildlife Trust’s Gunnersbury Triangle Local Nature Reserve

OK, you see a blizzard of feathers, the entire mortal remains of a Wood Pigeon that once proudly flew the woods, jauntily sailing away from a mere human. Who did it – Sparrowhawk or Fox? You might think it impossible, given that both eat most of their quarry, leaving little but bloodied feathers.

The Guilty Party?
Sparrowhawk in Gunnersbury Triangle

The Culprit?
Red Fox in Gunnersbury Triangle

But you’d be wrong. Each leaves distinctive clues in the debris of their dastardly deeds.

How would one tell if the brutal murder was the Butler with Carving Knife in Pantry, or Doctor with Stethoscope Hose in Library? (with apologies to Cluedo) Or rather, Sparrowhawk with Beak and Claw in Mid-air Murder, or Fox with Teeth in Ambush from Shrubbery? Here’s how to be a wildlife detective …

Sparrowhawk with Beak and Claw in Mid-air Murder

The Sparrowhawk has no teeth; and it doesn’t like to eat feathers. So, it grips each one, and boldly plucks it from the dead prey, leaving whole feathers – the shaft tapering to a point that was once inside the bird’s skin – neatly removed, each in one piece.

Fox with Teeth, Ambush in Shrubbery

The Fox, however, wastes no time on single feathers, biting off and spitting out fluffy mouthfuls as quickly as he can. They may be bloodied, as below, when the skin gets torn, but the feathers generally have broken shafts.

Pigeon feathers bitten off by Fox, detail

The overall effect is still a blizzard of feathers, all that remains of the ex-Pigeon. But, though the Pigeon is no more, its traces indicate quite clearly whodiddit.

Now you know.

Sentimentality

There is a sad little postscript to this tale. Near both murder sites was a scatter of bird-seed. Some kind, well-meaning person, perhaps lonely, perhaps seeking friendship, had put out some food for the pigeons to eat in the cold weather.

Well-meaning, but unwise. The pigeons became accustomed to feeding on the ground … in poor light … without looking about them too much … and fell victim to two keen, hungry, unsentimental predators.

Natural History, Natural Patterns, Nature Reserves

Winter Colour and Light at Thursley Common

18 February 2015 Ian Alexander

Panorama of Thursley Common bog pools (full image is 7330 x 2245)

On a gloriously sunny, still winter’s day, Thursley Common looked wonderful. There were few signs of wildlife – a Crow or two, some Stonechats hawking for flies from the tops of small bushes – but wide horizons, quiet, a sense of space and freedom.

Swirly patterns with beetle holes in dead pine

Some dead pines displayed magnificent natural patterns, the product of bare wood drilled by Longhorn Beetle larvae and exposed to the elements.

Spiralling orange patterns on softening dead pine — Turbulent orange patterns on softening dead pine

We visited Thursley’s thousand-year-old church – the north side of the choir has two small narrow Saxon windows, walled in for centuries. The church, of St Michael and All Angels, was wisely sited by the Saxons on a ridge of the Greensand, high and dry above the boggy moorland.

We enjoyed the modern glass doors engraved with a Tree of Life which turned out to be a Silver Birch. Among the animals praising God in the glasswork are a soaring, singing Woodlark; a perched Nightingale; a Lizard, a Purple Emperor butterfly, a Common Blue butterfly, and a selection of dragonflies: clearly the local fauna.

Conservation, Natural History, Nature Reserves

Quick, Fix Those Nestboxes! The Natural History of Nestbox Damage

11 February 2015 Ian Alexander

Fixing anti-squirrel plates to nestboxes

Quick! Spring is in the air, the Dunnocks are passionately singing their tuneless songs, the Great Tits are yelling Zi-Za-Zi-Za-Zi-Za endlessly, the Greenfinches are wheezing out their odd song (‘Zheee’), it’s time to fix those nestboxes. Most of those in the Gunnersbury Triangle had been “hammered” by Tits or Woodpeckers, or gnawed by squirrels. And a few had been rather roughly drilled by humans. So the warden decided that all of them should be given anti-squirrel plates; all, that is, except the Robin boxes, which have a wide rectangular opening in the front.

A few of the boxes seemed to have been attacked by squirrels. This one has what could be toothmarks and signs of extensive tearing of the wood outwards at a shallow angle, which looks like gnawing rather than hammering. It isn’t obvious why the basically herbivorous Grey Squirrel should do this.

This box, on the other hand, seems to have been hammered at a sharp angle to the surface, whether by the Tits themselves (they certainly do this sometimes) or by Greater Spotted Woodpeckers preying on nests – although they mainly eat insects and seeds, they do take eggs and chicks when the opportunity arrives.

At least 4 of the nestboxes had substantial and reasonably fresh remnants of nests inside; this older one contained two long-addled tit eggs (just one shown here; it was 16 mm long) with a mixture of moss and down as insulation.

Tegenaria, the Giant House Spider, at home in a very messy nestbox

Finally, one very old nestbox, carefully engineered with beading around the hinged lid complete with little brass hooks, contained a Giant House Spider, Tegenaria, a lot of beetle pupae, and what could be Gypsy Moth pupae as well. The box was a messy tangle of thick sticky cobweb, and the spider was distinctly reluctant to leave, seeming to want to stand and fight off any intruder.

All in all, what might have seemed a mundane bit of metalwork turned out to be a day full of interesting natural history. (But the metalwork was fun, too.)

Natural History

The Natural History of Humans and Sea Shells

9 February 2015 Ian Alexander

In an earlier post, Archaeology: Human Natural History, I wrote about some of the wonderfully rich history that can be gleaned from a walk along the bed of the River Thames at low tide. I delighted in the pottery and pipe-bowls, as I do still.

But today, on a gloriously sunny, still and almost warm day with the tide right out, and the Egyptian Geese honking stridently and flying about — three pairs, and an equally loud loner — my walk along the river produced unexpected and equally delightful results.

Along with a nice potshard of Maling ware (it says “S” “MAL” and half an “H”) , I found an enormous toe-bone of a horse, 95 mm long. It fits snugly in my hand; it’s roughly the size and shape of a pistol grip, and as heavy. It was a proximal phalanx – the sequence is distal (hoof bone) – medial – proximal as you go up the leg. Now, today, one can barely imagine throwing a horse bone into a river. But in the days before public health officers and EU safety regulations, it was nothing strange. For a start, London was full of horses, both fine beasts for gentlemen to ride, or to pull their carriages; and small, tired, sometimes broken-down nags that pulled the rag-and-bone man’s recycling cart, and everything in between. For another thing, people ate horsemeat, as they do today (in decreasing amounts) all across the continent of Europe. If you were poor in Victorian London, horse stew must have been a rich, warm, nutritious and welcome dish: even if the horse had died of old age.

In the soft light, a set of old wooden steps, the timbers worn and scoured by thousands of tides carrying currents of mud, sand, shell and even shingle, were quite beautiful in their natural simplicity, revealing the structure and fibres of the once-thick and rectangular treads.

On the sand a little way further were scatters of Oysters and Cockles, with some other kinds of clam for good measure.

Now at first sight there is nothing very surprising about finding shells in a tidal river: sea shells, sea water. But these are fully marine species: they need salt. And are they not suspiciously fresh? Indeed, they are still articulated. Someone, having enjoyed an excellent seafood dinner, has still, this year, happily thrown out their shells onto the river bed, just as their ancestors did before them through the centuries. The fresh pottery fragments indicate that broken cups, plates (and indeed also pub glasses and bottles) similarly continue to find their way into the the river’s archaeology, just as they have for centuries, if not millennia. The river of life flows on; man’s natural history, his interaction with wild-caught or farmed animals (from horses to horse mussels, perhaps) leaves behind its small detritus of bone and shell, from one generation to the next.

What will the archaeologists of 2,000 years hence make of our generation, our few varves in some long sequence of layers of lake-mud? It is a curious reflection. In the sixties we hoped that it wouldn’t be a plutonium-iridium layer for them to puzzle over. Let’s again hope that it won’t be that.

Conservation, Natural History, Nature Reserves, Wildlife

Animal Tracks in the Snow

3 February 2015 Ian Alexander

Animal tracks: Fox, Crow, and Squirrel prints on a snowy boardwalk

Today we woke to a snow-covered city, just a light dusting; and as often with snow, the weather was appreciably warmer than before the snow arrived.

Down at the nature reserve, the paths were empty of human footprints, but thickly sprinkled with animal tracks. Here some crows had walked to and fro across the path; there, a fox had jogged along the trail. But better was to come: the boardwalk across the pond was interlaced with tracks. On the left, a fox had gone the length of the boardwalk. In the centre, a crow had walked unsteadily along, the same way as me; and it, or another, had walked more rapidly back. On the right, more birds’ footprints: and the four-feet-together group of a squirrel, the smaller front prints clearly showing the marks of the sharp claws.

On a Birch branch above the anthill meadow, a Green Woodpecker hammered in search of food. Down by the ‘mangrove swamp’, a Jay screeched harshly, either for us or for a fox. Near the picnic meadow, a Sparrowhawk flew from its high perch, wheeled above the treetops, dived rapidly out of sight.

We carried tools and a ladder to visit the nestboxes and take down all that needed repairs. While I held the ladder, a party of four Long-Tailed Tits blew by, crossing from one Birch to the next one at a time. One of the boxes contained not just a mossy nest (like three others) but two old addled eggs, probably of Great Tit. While we struggled to prise off a somewhat too well attached box for maintenance, a Robin perched nearby, in hope of eating any grubs we might have disturbed. Several boxes had had their openings enlarged by much hammering by Blue Tits or Great Tits: nobody knows why they might do this, as it increases the threat to their nests from predators. We will make aluminium plates for the fronts of all the Tit boxes (the ones with circular holes): the Robin boxes just have a wide rectangular opening, which they definitely prefer. Inside one of the boxes was a mass of woodlice in the moss; another had a plump dead Noble False Widow Spider (Steatoda nobilis) inside.

Love of Nature, Natural History, Nature Reserves, Wetlands, Wildlife

Bullfinch! Winter Walk Hits Target

2 February 2015 Ian Alexander

Winter has definitely set in. The spinach beet in my garden was all frozen, the air at -3 Celsius and the ground presumably rather colder under a clear night sky. Fearing it might all be lost, I picked some and went out to see what there might be today down at Wraysbury Lakes.

Almost the first thing I saw was a bulky little finch high in a waterside willow. It called ‘deu’ quite loudly, fidgeted about and flew before I could focus on it. Still, there was no doubt it was a Bullfinch: the call, its shape, its solitary habits, and its shyness all pointing the same way. It is never an easy bird to see, even where it is resident (it is regularly ringed at Wraysbury). Leafless trees and the rising energy of the coming breeding season provide one of the few opportunities to catch a glimpse of this less well known finch.

At first sight there seemed to be no birds out on the lake. Finding a small illicit patch cleared by a fisherman I set up the telescope and looked about. A Pochard or two; some Tufted Duck and Coot; a male Goldeneye… but the Smew and Goosander of a week or two ago were nowhere to be seen. The old truth is that you never know what you’ll see: but it’s often a delightful surprise, and almost always energizing to be out in nature.

I walked on and looked about again: some rather white ducks caught my eye in the distance. Two male Goldeneye, each with a female in tow. The males threw their heads forward a few times, pretended to preen; one threw his head back and forth, then lowered his head and stretched it out and in. His female swam after him, her head resting on her back as if she were asleep! But she was certainly watching the display, and swimming to keep up a few lengths behind.

A loud squawk betrayed a Heron; it flapped out of cover at the end of the lake and landed on the bank behind the ducks. A few Mallard panicked from the water below me; a Moorhen briefly took flight.

Away from the lake, a few Robin and Dunnock hopped in and out of the bushes. A solitary Fieldfare or two gave their chack-chack call from the hawthorns, watchful and flighty. Another Bullfinch calling, this time atop a bare hawthorn bush – or maybe the same bird, half a mile on – and again I couldn’t get binoculars on to it, despite my stealthiest movements: it had surely seen me at once, and just took a few seconds to decide when to flee.

A Kestrel hovered beyond the tall poplars: no Buzzards or Red Kites today, but really the Kestrel feels almost more special than them, its numbers declining across Britain.

A few Jackdaws, Carrion Crows and Wood Pigeons on the horses’ hill; some Fieldfares in the trees, with a single Redwing; a Stock Dove flying low.

Natural History, Nature Reserves, Wildlife

A Bright Winter’s Walk in Richmond Park

30 January 2015 Ian Alexander

In Scotland, the male of the Red Deer is called simply a Stag, all other male deer (presumably Roe in that country) being known as Bucks. Down here, with Sika and other species about, it may be wise to name the species explicitly. There are signs up warning of the impending cull, so now may be the best time of year to see fine large stags resting quietly, the rut over.

Richmond's splendid anthills — Richmond’s splendid anthills

I was welcomed to the park by a flock of Jackdaws chattering in the trees. Down in the valley, last year’s grass stalks are whitening, the fine big anthills well outlined in the low winter sunlight.

A Stonechat was perched on a slender stalk, level with the tops of the grass; there cannot be much in the way of insect food to catch just now.

On the Pen Ponds, there were remarkably few waterfowl of any kind, but the lower pond had half-a-dozen Pochard. the males handsomely rufous-headed, a pair of Wigeon, the male with a conspicuous white wing-bar, and tucked in a corner under the willows a pair of Egyptian Geese, taking to the water and protesting with short dry honks when molested by a dog.

Walking back up the hill, a Kestrel hovered briefly, rested in a tree giving a good view of his spotted breast and back. Two herds of Red Deer, one at the base of the hill, one at the top, both with all ages and both sexes together, grazed silently. In the muddiest places, footprints of men, dogs and deer clustered together.

Environment, Love of Nature, Natural History

Unquestionably Globally Warmer

18 January 2015 Ian Alexander

“We have a clear signal that our climate is changing, and when you look at the evidence it’s because of human activities. The evidence is so strong I don’t know why we are arguing any more”.

So said Don Wuebbles of the University of Illinois. He pointed out that the world has just had the hottest year for 1,700 years, very probably for 5,000 years.

NOAA 1880-2014 global average temperature anomaly: recent decades, and especially the most recent twenty years, have been the warmest since records began. Global warming is under way

Thirteen of the fifteen warmest years ever recorded in Britain have been since 2000: the others were just before then. 2014 had the hottest summer for 350 years (when local records began). There is no doubt that we are experiencing climate change in these islands.

Around the world, the pattern is as clear as crystal: rapid, global warming, especially strong in the furthest northern climes, as in Alaska. There, the warming is drastic. Permafrost, which stores enormous reserves of carbon locked away in frozen peat, is melting: and the fossilized plant material, exposed to the air for the first time in millennia, is starting to oxidize. There is nothing to stop all the rest of it melting away.

Actually, the story up in the far north is more frightening than that. The warmer it becomes, the more three different positive feedback cycles collaborate to speed up global warming even more.

First, as mentioned, the permafrost is melting. That releases carbon to the air, as the greenhouse gas carbon dioxide, which accelerates the warming and melting.
Second, as the ice vanishes, the albedo (reflectivity) of the once-frozen north goes down dramatically, from icy white (reflecting most of the sunlight that hits it) to muddy brown or black (hardly reflecting anything). The ground absorbs more sunlight, so it becomes warmer, accelerating the melting and oxidation of carbon; and it directly contributes to having a warmer planet.
Thirdly, as the lakes and pools lose their ice cover, enormous amounts of methane hydrates, chilly masses of carbon-rich material in the icy mud, collapse and release streams of bubbles of methane gas, a far more potent greenhouse gas than carbon dioxide. If it were to be burnt, carbon dioxide would be released; unburnt, it accelerates global warming still more rapidly.

Back in Britain, everyone noticed that the weather in late 2014 was exceptionally warm. October and November in my childhood were leafless windy months with what seemed to be incessant grey skies and driving rain that churned football pitches into cold greasy mud. This time around, it was possible to work outside in shirtsleeves to the end of November. The change? Out of all recognition. It was a wholly new climate.

But the weather is not the climate. Britain is now in winter’s grip. Scotland shivers down to -15 Celsius. Here, under clear blue skies, the Birch trees glitter in the nearly horizontal sunlight. A greater spotted woodpecker, calling “Chik!” loudly, flies into the canopy of a Birch, clings to the elegant white trunk, the few remaining triangular leaves shining a rich yellow. The woodpecker bounds off, its wings whirring in short bursts.

The cold weather, like the increasingly violent storms that brought down two trees in the reserve last week, is part of the warming pattern too. The atmosphere has more energy than before: warmer air masses meet cold ones with a higher difference in temperature, releasing more powerful storms than we ever used to see. Winters can be colder, wetter, and windier as a result: more trees fall; more valleys flood. It may not feel warmer, but this is a direct consequence of climate change. Feel like denying it? Look at the evidence. It’s all around you.

Environment, Natural History

Lichens in London’s Streets: Local Pollution Down

10 January 2015 Ian Alexander

Crustose and Foliose lichens on a street tree in West London

Amidst the grim news of habitat loss and species in retreat or going extinct, it is pleasant to be able to observe a small conservation success story. Lichens, which had almost disappeared from Britain’s cities by 1970 – I was there, and I remember looking about in Hyde Park with some disappointment – are creeping back into London’s streets, and (I don’t doubt) streets all over Britain.

Back in 1970, if you wanted to see a lichen in Britain, you basically had to travel westwards, to Cornwall, Wales, the Lake District, or the Highlands and Islands. Those places had what lichens need: good rocky habitat, or old forest trees; and one special ingredient: clean air. For, we had unintentionally discovered, lichens are sensitive indicators of air quality.

Or, to put it bluntly, air pollution. Tiny concentrations of sulphur dioxide gas are enough to kill all the lichens in an area. Britain today has rather few volcanoes belching out clouds of dangerous sulphurous gases. The sulphur came from fossil fuels, mainly coal. When it was burnt, the sulphur was oxidised to sulphur dioxide (SO₂) , and when mixed with rainwater, it fell as sulphurous acid (H₂SO₃). Where did it fall? Initially it just trickled out of small chimneys, of homes and factories, polluting the cities and creating “London fog” – in reality, a poisonous yellow photochemical smog, a witches’ brew of sulphur and nitrogen oxides.

This problem was interestingly addressed by the Tall Chimneys policy. The smoke was carried up much higher than before, so Britain’s prevailing Westerlies blew the stuff much further afield. The concentration of noxious gases around our factories fell satisfactorily; London’s romantic Dickensian “fogs” disappeared. The gases travelled across the North Sea, causing acid rain in Scandinavia, and depriving Stockholm and the beautiful clean-looking pine forests and islands of its Archipelago of their lichens. I know, I looked for them in 1986, and I remember finding one small colony in a morning’s walk.

Back to here and now. Nearly all our coal mines have closed, and with them most of the shipyards and steelmakers too. Houses are heated by clean natural gas – nearly pure methane. Houses are no longer blackened by smoke; a shirt worn in the city for a day does not have a black collar in the evening. And lichens are creeping back into the streets.

In the photograph, you can see at least four species of lichen. There are the large rounded colonies of crustose lichens in the centre, with olive-disked apothecia (fruiting bodies containing masses of spores) rimmed with white. There are small grey foliose (leafy) lichens of the kind I still call “Parmelia“. There is a much larger, greyer “Parmelia”. And there are many small colonies of an orange foliose lichen, probably the Common Orange Lichen, Xanthoria parietina. Perhaps there are more. (If you are a lichen expert, I’d love to know what they all are. Do contact me.)

Apparently there are now 17 urban lichens, up from, well, one rather tough species – Lecanora conizaeoides. It’s a tiny, rather flat grey species, and it alone can tolerate a moderate dose of sulphur dioxide; at least, it could be found in sheltered places even in London, even in 1970, away from the worst of the smog.

Is this a conservation success? The Tall Chimneys were a health measure; the death of Coal was mainly an economic matter. Still, it’s nice to see the lichens coming back. Perhaps in a few decades’ time (lichens are rather slow-growing) we may see big yellow splashes of lichen on roofs, walls and trees in every street. Let’s hope so.

ObsessedByNature