February 8, 2012
The latest snowfall, mainly over eastern England, differed from snow events of recent winters. Did you notice, for instance, that the snowflakes were thin needles rather than the hexagonal star-like plates? Snowflakes come in a variety of shapes, depending on the temperature at their genesis and where they were formed. Stellar dendrites (starry and plantlike) – the most popular form of snowflake – are grown in temperatures from about freezing to – 4°C. Needles, on the other hand, crystallise in temperatures around -5°C and descend from mid-level clouds (e.g. Altocumulus). At -5.5°C, hollow columns are formed and at -12°C flakes start forming again. The best part is, no-one knows exactly why.
The snow was deep (around 18cm) in my neck of the woods and took an imprint well. Unfortunately, because it descended throughout the night, by dawn it had obscured the activity of most of the nocturnal animals that bothered to venture out.
A pheasant, however, had been roosting in the big tree above the gateway in the photograph and it’s descent in the morning was beautifully captured by the snow. The fan and sweep of the cock bird’s tail is perfectly preserved, as is the random meander away. The only thing missing is the racket he makes, but I’ve heard that often enough, thanks.
Diurnal creatures – birds, squirrels and the odd fox left their mark on the first day but after a night of lying snow the ground the following morning was criss-crossed with trails. The fox trots in deeper snow with his body at an angle in a peculiar form of dressage, so that his tracks form a single line. If you look carefully you can see where the sweep of a foot joins up alternate tracks on the left and the right.
The back foot of each side lands in the spot where the front foot of the same side fell. At my place of work, a visitor wondered ‘what one-legged animal’ had made such trail.
The fox steps daintily, as always, while the low-slung badger goes through seven inches of snow like a snow-plough. Look closely and you can see the longer heel of the badger’s hindfoot as it too lands where the front paw was a moment before.
There is so much study in just one night’s activity, I have spent entire days from first light to dusk following the trails of animals and birds. This hunting fox is a typical example of recapturing the previous night’s play.
Why hunting? Because of the slow gait, frequent pauses and points where it turns around sniffing for food under the snow.
How can I tell what it is doing? Look carefully at the snow and notice the soft imprint of a nose.
December 11, 2011
Recent nights have brought forth two stunning lunar haloes.
The one on the10th December was one of the most intense I have ever seen and it surrounded the full moon. Naturally, the one two days previously could not match it as the moon was two days less full.
In both cases a weather front was involved. On the 8th a front that brought severe gales and torrential rain had recently passed through and the Cirrostratus was trailing behind. On the 10th the Cirrostratus was a precursor of rain the following morning, even though the night had started intensely frosty.
Such 22 degree radius haloes are formed by moonlight, in this case, but more often sunlight, passing through hexagonal ice crystals in cold high Cirrus or Cirrostratus cloud. The tiny ice crystals are tumbling randomly in the cloud but there are enough of them with their axes roughly perpendicular to the direction of the light so that when light rays enter these prisms through a side face and leave through another tilted 60 degrees to the first they are refracted 22° or more. The little glints, all connected up, form a ring and that is why the halo starts at that distance from the sun or moon and is diffuse but bright beyond that radius with a darker hole within – albeit one with a bright light source! No sparkles from the refracted light are turned into the middle – there are just direct rays from the light source itself.
Two people see the glints from different but suitably orientated crystals to each other, so your halo was not the same as mine. What’s more, a halo only exists if something is there to see it. It is the result of a collection of light rays travelling in particular directions that can only be captured by a receiving lens into which the rays converge. That lens may be in an eye or in a camera – but if a lens is not present, neither is the halo…
December 1, 2010
It’s a popular misconception that squirrels hibernate. What would be the point of all that food caching in the autumn if the squirrel then goes and sleeps through the winter? If it is really cold, like at the moment, the animal can stay snug and warm in its drey and venture out only when it is hungry, should it so choose. That might mean a couple of days without putting in an appearance.
Squirrels are good animals to track in the snow. Their footprints are easy to recognise, if snow conditions are kind – and blowing or fresh-falling snow, like many of us are currently experiencing , are not helpful. I was lucky enough to chance upon these very fresh. Squirrel hind feet usually land ahead of the front feet because of the bounding hop that the animal employs to get round. Their soles are naked (unlike ,say, a stoat or a fox, which have hairy pads), so toes tend to be distinct, as are their lumpy pads. The squirrel has no ‘thumb’, just a fleshy lump, and thus forefoot tracks show only four toes while the back show five. The three middle toes of the hindfoot are all of equal length.
In the snow they usually move with a purpose, and that is to find food. This one was travelling fast with distances between bounds of over a metre (twice its body and tail length combined). It then slowed and hopped to a particular spot where it dug down and retrieved a buried hazel nut. It is possible to see the impression of the nut in the soil because the squirrel lifts it with its teeth, not by scooping it up with its fingers.
But how did it find it under the snow?
It was long believed that squirrels sniffed out their scatter-hoarded nuts. They have a good sense of smell and it can be quite apparent on observing a squirrel under normal foraging conditions that they are using their noses to find hidden food. Conversely, it has long been known that hoarding birds like the Jay, which have no sense of smell, have an area of the brain especially to remember where they hid stuff. We have a small ability in that area but bird and rodent have to remember thousands of spots over the winter and following spring. Part of the bird’s brain (the hippocampus) actually expands in the autumn to accommodate all the extra data it will need to pack in, but because the squirrel’s brain does not obviously do this, scientists have been reluctant to acknowledge that squirrels have a similar ability.
Several times over the years, in lying snow I have seen clear circumstantial evidence that the squirrel carries a map of its treasures in its head. Trails leading unerringly to a spot in a wood or field and then a single dig, with the tell-tale impression of a nut in the hole, sometimes with a split shell resting on top of the snow, indicating success. The depth of snow seems to rule out sense of smell being used in this case – and there are no ‘snuffle’ marks or nose impressions leading up to the spot.
Science has finally caught up with common sense. Researchers in University of California, Berkeley have concluded that as well as their sense of smell, ”They use information from the environment, such as the relative position of trees and buildings, and they triangulate, relying on the angles and distances between these distant landmarks and their caches.”
The multi-talented squirrel is understandably a bit paranoid about his neighbours stealing his food. If it were all in one spot he could lose it in one go, which is why he scatter-hoards it. Some pilfering does go on, with another squirrel’s nut sniffed out by chance, here and there – but definitely not in the snow.
March 5, 2010
Over recent days there have been a variety of transient atmospheric phenomena, fleeting lights in the daytime sky. They are mostly associated with thin high cloud, Cirrus, Cirrocumulus and Cirrostratus and their various species – yes, clouds have species! As these clouds are mostly composed of minute ice crystals when the sun shines through them, depending on the shape and angle of those crystals, they may act as tiny prisms refracting the light and splitting them into rainbow colours.
To see them, first you have to be aware that conditions are right for them to occur. Sunshine is a precondition, plus any amount of the aforementioned cloud to make it hazy. Then you have to look for them. Unlike ordinary rainbows which occur opposite the sun, most of these other effects occur in the direction of the sun. We rarely look that way, with good reason – it can permanently damage your eyes. So wear good sunglasses, position yourself with something between you to screen the sun, such as a tree, or shield it with a hand or a book.
The commonest phenomenon is the 22° halo. An outstretched hand at arm’s length should cover the sun with the thumb, while the tip of the little finger rests on the circumference of the ring. This won’t be enough to shield your eyes though. For most of this day’s observing I stood in the shadow of our chimney stack. The 22° halo sometimes has additions – extra rings or arcs associated with it, some of which are very rare, and for that reason plus its sheer beauty it is always worth photographing, in my opinion.
Commonly associated with halos are sundogs – there is one faintly visible in the halo photo and a second taken at sunrise on the following day.
Apparently, these are formed by light refracting through crystals that are shaped differently from those that create halos. The two together tells of a mix of crystals in the high atmosphere and also extends the possibilities of what light shows may be seen. Sundogs sometimes have a white outer extension. The right hand sundog from the sunrise display began to stretch some distance and was very intense.
This was the beginning of a parhelic circle (par – through, helic from Greek helios – sun). Occasionally a white line may encircle the whole sky, passing through the sun. I have observed this only twice and it is quite a surprising sight, I can assure you!
The final crystal induced effect was a circumzenithal arc (circum – around, zenith – sun’s highest point in the sky). It happened when the sun was low and occurs quite a distance from the sun. It resembles an upside down rainbow with the centre of the bow sunwards and red on the lower surface. Although the colours can be intense it is difficult to photograph, in my experience.
The particular conditions that brought about these effects – a collision between cool and warm air masses – also created a different optical phenomenon – irisation or iridescent cloud. Newly condensing cloud, also at fairly high altitude, may be formed of super-cooled water droplets rather than ice crystals. These refract light differently and produce beautiful pastel hues close to the sun – sometimes too close for comfort. I was lucky with the position of the chimney stack and I mostly let my camera do the looking. Wearing sunglasses will allow you to observe this effect more often. The same thing occurred next morning but the light was too intense to photograph though I saw it clearly through my shades.
What does all this mean to bushcrafters? Well, it is always good to improve your powers of observation and your awareness of Nature. On the day that most of these phenomena occurred, it was evident to me from watching, that the clouds aloft were moving in the opposite direction from the wind and clouds near ground level. The upper air was moving in from the SW and therefore likely to be warm and moist originally. The lower wind was a chilly ENE, a cold air mass undercutting the warm and forcing it upwards where it cooled, showing an incredible mix of lively Cirrus formations and very long aircraft condensation trails, indicating that it was unstable. Something similar can be created by the approach of a warm front, but in this case the nearest front was halted over Ireland so the weather did not deteriorate further. It was worth keeping an eye on all the same. The atmospheric phenomena I witnessed can portend a change and with the warming of the Northern Hemisphere as Spring approaches there will be further collisions between warm and cold air masses over the British Isles which will bring about further opportunities to observe lights in the sky.
Although halos and sundogs have been known of for thousands of years (Pliny the Elder wrote about them in his Natural History from the 1st Century) a number of explorers and observers of Nature, notably William Edward Parry in 1820, Tobias Lowitz in 1790 and Gerald E Owen in 1935 were the first to see and record the rarer arcs and related phenomena. Some managed to have arcs named after them. While today it is a subject of proper scientific study the amateur observer still has a role to play.
February 16, 2010
With snowfall in this country there is often a limited window of opportunity to make the most of your tracking skills before a thaw sets in again. If you are tied to a daily job (I am lucky enough to be self-employed) you also need it to snow at the weekend! Still, it is worth persevering for a large amount of experience will come your way in a short space of time. There is more snow to come for many parts, so make the most of it.
Good snow, perfect tracking snow – settling all day to a depth of say 10cm and not freezing hard, nor melting at all at night when most creatures are active or all the next day while you are out in it – not only reveals exciting little details but also the big picture of what is about and where they go. The later in the season it falls, the more activity you are likely to encounter; the early winter lethargy of many animals will have passed and fat reserves run down, so food will take higher priority. Badgers, for instance, begin to move around more as pregnant females make space for themselves, perhaps evicting some other sows and younger boars from the sett in the process. Much seasonal activity is dictated by day length and that inexorably gets greater as we move towards spring.
The most recent snowfall (here in my part of Kent) spoke volumes. As I stepped out of my door I immediately learned that we have a Wood Mouse (or possibly the closely related Yellow-necked Mouse) or two, using our coal bunker as a thoroughfare. The curious cloven-hoof-like tracks of a mouse hopping in snow can be quite a puzzle if you have never encountered them before. In February 1855 large numbers appeared in the snows of rural Devon and were not generally understood for what they were. They caused such a stir that some folks thought they were the footprints of Satan himself and the incident was reported in The Times!
A close look, in most cases, will reveal the imprint of the tail. That said, a little while later, in the woods I found a hopping mouse trail with no tail drag. (see photos below) That trail also followed the mouse’s outward line on the return journey, making a confusion of prints that needed unpicking.
The direction of movement is indicated by the wider gap. This is made by the hindfeet landing ahead of the forefeet. A Rabbit (inset) shows something similar but greatly scaled up.
Bear in mind that two way trails are common with many mammals. A small creature like a mouse or rabbit will have a learned route that they can flee down in moments of danger without a thought or hesitation, so ingrained that they know where every obstacle is for an instant manoeuvre.(It has been shown by experiment that for a while they still jump over objects that have been removed.) Other animals follow scent trails that they have laid down, Badger and Fox, for instance, but the Fox also has excellent vision and may follow his own trail by sight.
Here is an example of where a Fox has struck out over a rather wide open area but has stuck almost exactly to the trail it had left previously. You can see that in places the animal deviates from line slightly (probably to investigate a scent) but otherwise holds it tight. These tracks led to (and from) a spot where there had been a lot going on. I thought it may have been hunting activity but there was absolutely no sign of prey, just indications of more than one Fox. Then I realised it was play, probably between dog fox and vixen as the mating season is only just coming to an end. Aside from a patch where one animal had rolled in the snow, there was a beautiful example of a four-footed pounce, with a brush mark, something that a Fox usually does when catching mice or voles.
I didn’t get very far in four hours, there was so much to see. More woods and a river nearby but not the time on this occasion. Probably the most strangely beautiful sight of the day was the double imprint of a Blackbird that had inadvertently landed in deep snow and floundered, leaving the impressions of fanned wings and tail, feet and even chin and beak.