Miraculous time-keepers
THERE CAN be few more rewarding presents than a cylindrical plastic bird feeder and a packet of the goldfinch’s favourite Nyjer seeds. Every morning, at 8.30, a dozen or more of these enchanting birds descend from the heavens to take up position on the branches of a nearby camellia bush. Then, all in a rush, they head for the feeder – there is only room for three at any one time and in their squabbling for a perch, the flashing gold of those hovering wings is a truly wondrous sight.
Their early morning punctuality is most intriguing, contradicting the common notion that the perception of time must be a uniquely human attribute. We are certainly inveterate time travellers, continually moving back and forwards from the present, recalling the immediate and distant past, anticipating and planning for the future. This mental time travel is denied our fellow creatures, who must, one would imagine, be stuck forever in the present – but apparently not. Rather, the accuracy of their perception of time can be much superior to our own, as when dogs, it is reported, head off to the railway station to meet their owners on return from work, their timing far more reliable than the trains themselves.
There is, predictably, considerably more to this uncanny timekeeping than is immediately apparent, first hinted at by pioneering investigations into the navigating skills of migrating birds. In 1949 German ornithologist Gustav Kramer inferred from observing the orientation of caged starlings during the periods of their annual spring and autumn migration that they take their bearings in relation to the position of the sun.
This avian ‘sun compass’, it turned out, is not fixed (as might be supposed) on the changing altitude of the sun as it traverses from east to west but rather the point on the horizon directly beneath it – known as the azimuth. This poses a major navigational challenge, for while the azimuth moves by just eight degrees an hour in the early morning and evening, at noon it can shift by as much as 55 degrees. Thus, Kramer proposed, the migrating starlings must possess a highly sensitive internal clock allowing them to maintain a constant direction by continually calibrating the changing tempo of the movement of the azimuth – slow at dawn and dusk, rapid at midday – against the time of day.
This masterful chronometry is paralleled in a rather different way by the foraging honey bee when communicating to its fellows the direction – and distance – of the rich source of nectar from which she has just returned, heavy laden. Those instructions, as all know, are conveyed through the waggle dance, its meaning famously decoded by the late Professor Karl von Frisch of Munich University. The dance consists of two semi-circles; the returning forager first runs in a straight line for a short distance, vigorously waggling its abdomen from side to side, turns left, and makes a semi-circle back to its original starting point. It then reruns the straight-line course, but this time turns right to make another semicircle back to the beginning.
Following decades of measuring the angle and direction of these dances, von Frisch found there to be a direct correlation between the time the bees spent on those straight-line runs waggling their abdomens and the distance to the source of the nectar – if it took two seconds the nectar was two thousand metres away; three seconds, three thousand metres. No other creature possesses the same unique ability to transmit with such precision one type of information (distance) in terms of another (time).
The ramifications of accurate timekeeping in the natural world are clearly considerable – one further truly astonishing incidence concerns the noisy sun-loving cicadas that ‘fill the air with their tremendous song so the whole earth vibrates in response to their music’ (E L Grant Watson). The cicadas lay their fertilised eggs beneath the bark of trees, which, having matured into larvae, then jump to the ground, burrowing into the soil to a depth of ten feet or more. There they will reside in darkness, cut off from the outside world, surviving by sucking the sap of roots, for either thirteen or seventeen years (depending on the species). Then they emerge synchronously, millions of them, shed their carapaces, stretch their wings and for the next few weeks make the best of their brief sojourn in the sun. The immense difficulty of keeping track of time when underground is well illustrated by the experience of a young caving enthusiast, Michel Siffre, who in 1962 volunteered to spend sixty days in the caves of the Alpes Maritimes. He emerged thinking that just 35 days had elapsed. How the cicada knows to the day that seventeen years have passed, no one can tell.