The Irish government legally protected Ballygilgan as a national nature reserve in 1986, specifically to preserve the overwintering barnacle geese whose numbers had been falling alarmingly through the 1970s. The cause was familiar - habitat loss, disturbance, hunting on the migration route - and the response was simple: set aside the land they actually used, and keep them safe on it. The strategy worked. The flock now numbers consistently around 3,000 birds, Ireland's largest mainland gathering of the species, managed by the National Parks & Wildlife Service. It is one of those quiet conservation successes that doesn't generate headlines because the result is the absence of disaster.

Barnacle geese are unmistakable up close - a sharp black-and-white plumage, white face, black neck and breast, grey wings. They are mid-sized geese, smaller than the more familiar greylag. The Irish population breeds in the high Arctic, on the cliffs and steep coasts of east Greenland, where the goslings famously launch themselves off ledges hundreds of feet above the ground within days of hatching, bouncing down the slopes to reach the feeding grounds below. By autumn the survivors fly south, across the Atlantic, to spend the dark months on the comparatively gentle pastures of western Ireland and Scotland. Ballygilgan is one of a handful of sites where they reliably congregate. They arrive in October. They leave in April. The cycle has been running for thousands of years.

The geese are the main attraction but they are very far from the only birds at Ballygilgan. Through the winter the wet pastures and the seasonal pond host teal and wigeon ducks, pintails, shovelers, redshanks, greenshanks, bar-tailed godwits, golden plovers, lapwings, and dunlins. At the eastern end of the reserve, oats and linseed have been planted in a small cereal patch specifically to feed the smaller seed-eaters - chaffinches, bramblings, greenfinches, goldfinches, buntings. The whole reserve functions as a small refuelling station for the migrating bird life of the north Atlantic flyway. In summer, with the geese gone, the pasture is grazed by sheep and cattle to keep the sward at the height the returning birds will need.

The reserve sits beside the Lissadell estate, which carries its own freight of Irish history - it was the childhood home of the revolutionary Constance Markievicz and her sister, the poet and suffragist Eva Gore-Booth, both of whom W. B. Yeats memorialised in his poem "In Memory of Eva Gore-Booth and Con Markievicz." The Goose Field and the great house share the same north Sligo light, the same Atlantic weather, the same view across to Benbulbin in the south and out to the open ocean in the west. It is a quiet corner of the country, easy to drive past without realising what you've passed. The geese know it's there. They have known for a very long time.