Secrets of the Goldeneye

Out there, towards the centre of the sheet, is a drake goldeneye, accompanied by three females. They are diving repeatedly, actively feeding. As he emerges the drake looks brilliant in the January sunshine, an essay in black and white.

Of all the species of wildfowl which come to spend the winter with us, the goldeneye is one of the most striking and distinctive. The plumage of the drake is not really black and white, but snowy white and the darkest glossy green or purple, depending on the angle of the sun.

At this range, though, the head looks black, with a large white spot below and just in front of the eye. This, and the elegant black and white pattern on the back and wings, lets you identify him at a great distance out on the water, even when your binoculars are being jostled by an east wind which numbs gloved fingers and makes the eyes stream.

The forehead of the goldeneye has a characteristically steep profile which enables you to pick out the females and immature birds – with drab grey bodies and chocolate brown heads – from the coots, pochards, and tufted ducks.

As would be expected, these drabber birds, or “morillons”, usually outnumber the males. At its height in midwinter, the local population consists of no more than about a dozen birds, if that.

Looking back over twenty years of records on index cards, the assorted localities, numbers, and dates make for confusing reading. An evening with a pocket calculator and a tablet of graph paper is scarcely more enlightening. Statistical analysis, the calculation of means and probabilities and standard deviation, is time-consuming and prone to error.

But the naturalist now has a new ally: the microcomputer. Even a relatively humble model, obtainable in any high street, makes short work of the statistics. With a carefully designed program and carefully entered data, the real wizardry of the computer takes over and magic begins to emerge.

The records, hundreds of them laboriously culled over many notebooks and many winters, are transformed into a volatile set of electronic signals which the program manipulates at incredible speed. In a few moments we can abstract any given group of records – for locality, date, number, sex ratio – or put them back, or give them special weighting for greater observer coverage, or less. Touch a key and the graph illuminates the screen. Touch another and the figures appear.

January is shown to be the peak month for goldeneye in the Colne Valley between Rickmansworth and Uxbridge. Total birds and average record size both reach their maximum – except at Stocker’s Lake, where there is a unique and unexpected fall. Why, and where do the birds go?

Press another few keys. Yes: that’s where they go. A little way down the valley to the giant Broadwater gravel pit at Denham. The graph here shows a sudden and untypical rise in January. Press more keys. The rise at Broadwater corresponds almost exactly to the fall at Stocker’s Lake. But why?

The answer probably has something to do with the goldeneyes’ food: the molluscs and crustacea they find in the mud on the lake floor.

Either there is a preferred prey animal at Stocker’s Lake which is harder for them to find in January, or some special delicacy at Broadwater which becomes numerous in that month. Or else it is a simple matter of ice cover. Broadwater, being so much bigger, will be slower to freeze and will do so less often. Already the computer is beginning to suggest lines of approach to the problem: it wants more data, on the weather, on water temperatures, on the goldeneyes’ diet.

The machine reveals things previously known only to the goldeneyes themselves. Hidden deep in the figures are trends and patterns which a lifetime of casual observation would never uncover. They are real and constant from year to year, and must somehow be of service to the species in its struggle for survival. Similar, but slightly different, patterns emerge for closely related species. As the relationship grows more distant, so the patterns become more dissimilar. Goldeneye resembles teal, because both are ducks; but teal resembles mallard more, because teal and mallard are very near in evolutionary terms and have much the same way of life.

Here by the shore at Broadwater, despite your thick coat and woollens, you begin to shiver. The wind is dashing real waves, bigger than many at the seaside, against the crumbling soil of the bank. The goldeneye are impervious to the waves, impervious to the cold. Look – the drake has just surfaced.

How are his preferences and tastes programmed in the living chip behind that high, triangular forehead? And where in his memory are the myriad bits of navigational data that will guide him and his followers home in spring, a thousand miles and more to the rivers and forests of Russia and Scandinavia? Over what aeons of time was that machine code written?

A mystery. It’s all a mystery. There: he has dived again.

(Introduction to these pieces; see all)