Nature 2011 December

Reading the right signs and navigating Nature’s unmapped highways

In this age of GPS or SatNav, as well as digital maps, and internet-based gadgets be it Streetview or social networking we perhaps take for granted our ancient, inherent but lost or hidden abilities to determine how to find our way from ‘a to b’ or decide when it might be unwise to travel at all.

You may have seen this same theme taken up by a recent TV programme with Alison Steadman and others – All Roads Lead Home – trying to navigate only using nature’s signs. Sadly, TV has a habit of trivializing an otherwise interesting subject. Technology can rule our lives. We all know stories about following a SatNav route and ending down a blind alley when simple observation of the signs around us would have avoided the error of landing up stuck in the mud along Hawridge Lane. In April this year having briefed a team of census collectors on their tasks I was out the next day in Old Hemel High Street with one of the younger crew. Half way through our task I noticed the sky suddenly darken with the arrival of a threatening grey cloud. Pointing at it I ask my colleague if he thought a heavy shower was imminent and should we look for a suitable hostelry to dash for shelter if necessary. He missed my gesticulation towards the sky and instead groped for his iPhone and was checking on the local weather forecast. Having done this he then checked out the pubs in Hemel for a recommendation for one near to us despite there being at least half a dozen within eyeshot. By the time he had finished the heavens had opened.

I’m no Luddite probably a bit of a techno nerd but I’m also struck by the thought that we humans might be suffering a dulling of our natural senses with the inclination to first and always rush to technology to solve our questions rather than also look for the signs around us.

Autumn and Spring are the most significant times of change occurring in the tree-canopy around us. In October and November there is much variation each year in the timing of leaves turning from green to yellow or orange and then brown or red before falling. This is dictated by a combination of max and min temperatures, and day-length or more correctly night-length which changes most rapidly around the equinox and the least amount at the solstice. The tipping-point determining leaf-fall is when there is insufficient light at a given temperature to sustain the production of sugars. The speed of change is always determined by temperature and its change. Thus a longer warmer September and October inevitably followed by a rapid temperature fall in November provided the golden-russet vistas this year. We have all see coastal trees that have been grotesquely sculptured into a distorted shape due to the harsh prevailing winds. However, most trees facing much more modest winds will display more minor distortions to their trunk and branches which are only become visible when the tree is cut down. Observe the tree rings in cross-section and you will sometimes see that one side of the tree will have wider gaps between the rings than the other which can be due to prevailing winds and climatic conditions. Ash seed pods are one of the few fruits of summer’s bounty to remain in situ during the winter. I read that due to prevailing winds these single-winged seeds can oft be seen clearly orientated, pointing towards the south-west, the result of the prevailing north-easterly winds. Following on, mosses and lichens are said to only grow on particular sides of walls. North for mosses and south for lichens. However this is not demonstrating any preference for a particular compass orientation rather the natural consequence of prevailing weather conditions. In the southern hemisphere mosses are found on the south side and mosses on the north side. Furthermore in coastal areas lichens are found in all orientations and ditto for mosses growing in damp woodland and wooded ravines. So be aware they are not always the most reliable of signs.

Unlike less developed societies such as the Inuit, we no longer need to read the signs of migrations in order to survive. With the possible exception of the fishing fleets we no longer depend for our livelihoods on knowledge of the impact of the sun, the moon, the stars and earth’s magnetic field on the influx and outflow across the seasons of animals and birds. Changes to the landscape over much shorter periods, including many examples of more frequent or even daily navigations pass us by unnoticed and as a consequence unquestioned.

Much debate and speculation persists in the scientific world as to the methods by which migration and homing is achieved. Some birds such as Starlings that migrate at night surprisingly utilize the sun to navigate. It is suggested that as the sun sets they orientate themselves and can store a series of readings enabling them to set their course before darkness falls. An alternative method used by other birds travelling by day such as Swallows, utilize the polarization of light coming from the sun. Other birds travelling at night including the Mallard duck and varieties of the Bunting have been found to use star constellations or even individual stars, such as the star Betelgeuse in the constellation of Orion.

Many of our larger butterflies are migrants from the Continent or North Africa. As they are day-flying they use their orientation to the sun and use of polarized light. Moths on the other hand use moon and, remarkably, starlight.

Animals, such as bats use magnetic fields to make longer distance journeys. It is thought that within their brains are small particles of a magnetic mineral called magnetite which react to the magnetic field of the Earth and activate nerves which impact on movements of the limbs. The Common eel which is capable of travelling short distance across land from one river to another will use what we would call scent to identify other sources of water. Fish which live in sea and fresh water e.g. Trout or in estuarine conditions e.g. Eels are driven by changes in salinity when migrating to spawning grounds.

Plants can migrate too, and not only Triffids! Some populations may take hundreds or thousands of years to relocate as climate change impacts. Meanwhile much of pond life is made up of plant life and the vast majority of it is microscopic. On a daily basis these single celled plants migrate towards the top from well-below the surface. As the early day’s light and heat penetrates the deeper areas this kicks off photosynthesis and the oxygen so generated buoys up the organism and it rises towards the surface. Reflecting the daily ritual involved this is known as ‘Diel vertical migration’. Small animals which feed off the plant life will follow the movement of the plant microorganisms and are part of this Diel migration system. Towards dusk as light and temperature falls photosynthesis stalls the organisms return migrating to their lower night-time level. If temperatures or UV light increases to dangerous levels a safety mechanism is triggered and the algae can sink to safer levels. Water plants, such as the insectivorous bladderwort, can move to the surface during the day by inflating their bladders which also are used to capture microscopic animals that live at the surface levels.

Tristan Gooley, who was the mastermind behind the natural science, but not the facile drama, of the television programme mentioned above, has published a book; ‘The Natural Navigator Pocket Guide’. Having just scratched the surface here, I have ordered a copy and hope to return to the subject in the future! Anyhow in the meantime I hope to have stimulated a few readers to take a second look at their surroundings when out and about over the next few months.

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