It began with the Hudson Bay blanket my grandmother sent me my first term at university. I wrote to her about the first snowfall, describing the exotic world of icicles and snow banks, the novelty of sleeping in socks and sweaters. Two weeks later, a thick wool blanket arrived, white with four stripes in green, red, yellow and indigo.

‘The English settlers used these blankets to trade with the Indians in exchange for beaver pelts,’ she wrote, ‘but the blankets aren’t made in Hudson’s Bay, but in England, and the point system yours is a four point doesn’t refer to its value in pelts as commonly believed, but to its size and thickness.’ She enclosed a map of Canada. Written beneath the words Hudson’s Bay, in her blue-black ink, was ‘breeding ground for snow geese’.

My Hudson Bay blanket kept me warm for the next four years. It also reignited my passion for snow geese, a passion that had begun in my childhood when I once saw them flying over the Delta and heading up the Mississippi River, their highway up north. Their appearance seemed as carefully planned as a homecoming parade. They arrived on time, in formations of Vs, in such vast numbers that, after half an hour, it felt more like an eclipse than a migratory miracle.

Reverence for snow geese was instilled in me on that day. I was told that they mate for life and are devoted parents, who stay with their offspring on the first migration south, keep together during the winter, and return to the breeding ground in Hudson Bay en famille, the male leading the family in flight, ‘unlike ducks, where the female takes the lead’.

Then, life moved on. I gave my Hudson Bay blanket to a nephew, along with a tear-stained copy of Paul Gallico’s The Snow Goose and my copy of Water Birds of North America. A few years ago, however, in a nostalgic moment, I bought a linocut of snow geese by Robert Gillmor, and last spring, on a visit to Cornwall, I stayed up all night reading a book called The Snow Geese by William Fiennes.

The writer follows the snow geese on their migration north, starting in Texas and travelling all the way to Foxe Land north of Hudson’s Bay. Travel book and naturalist’s guide, it’s also a meditation on ‘home’ its importance, not only to humans, but to many other species.

Missing from The Snow Geese was the botanist Robert Jefferies. Like Mr Fiennes, Prof Jefferies was born in England, and, like the writer, he became fascinated by snow geese. In 1975, Prof Jefferies left the University of East Anglia to spend a year as visiting professor at the University of Toronto. He then spent the next 30 years in Canada, studying nesting snow geese at Hudson Bay. One of the earliest scientists to record the exploding population of snow geese, Prof Jefferies traced the change to farmers in the South, who were cultivating more and more land and no longer ploughing fields in autumn, thus providing the geese with ample meals of wheat, soybeans and maize.

The well-fed birds were in better shape for their long journey and for breeding. However, once the for-aging birds reached the arctic regions, they were stripping the vegetation of the salt marshes, causing seawater to seep into the marshes, which in turn increased the reflectivity to the sun, making the temperatures to rise. The snow geese were contributing to global warming.

Prof Jefferies’ discovery won him a Nobel Prize he was part of the UN panel on Climate Change that shared the prize with Al Gore in 2007. Before he died last week of a cerebral haemorrhage, Prof Jefferies revealed how increased use of fertilisers was having the same effect on salt marshes in Europe. His work on snow geese says more about humans than the birds he loved. On this farm, we’ve just completed our harvest, a whole month earlier than we did when I arrived here in 1986. Call it the message of the snow geese.

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