Another Life: Was it for this the wild geese spread the grey wing on every tide?

No sound lends autumn a more thrilling voice than the bonding clamour of a flock of geese deciding where to land. Some migrants among the 50,000 geese that Ireland feeds in winter are already here, but October brings peak arrival, as flocks from the Arctic glide down to estuaries, bogs and wetlands the length of the island.

Differences among them span five species, from brents to barnacles, but one of the iconic, migrant and Yeatsian "wild geese" of Ireland gained its scientific identity only in 1948. That was when Peter Scott and Christopher Dalgety, British ornithologists, shot an unfamiliar goose on the Wexford slobs. With dark-grey plumage and long orange bill, it was distinguished as Anser albifrons flavirostris, a subspecies of Europe's greater white-fronted goose. (The "white front" is the forehead above the bill; flavirostris means "golden beak".)

What had been, for many, just “the bog goose”, long a traditional quarry of Ireland’s rural hunters, is now Europe’s rarest goose. It breeds in summer in just one area of tundra in west Greenland and is faithful to certain wintering grounds in Ireland and western Scotland.

In earlier centuries it fed in winter on the starch-rich underground stolons of plants such as sedge and bog cotton, on peatland that was rarely frozen hard. Many small flocks still use the bogs in this way, but as undisturbed peatland diminished, and farming offered richer grazing, the birds moved increasingly to grassland. As better feeding helped reproductive success, this long-lived species returned faithfully to some 80 wintering grounds in Ireland and Scotland.

About half of the whole population are protected and closely studied at their stronghold on the cultivated fields of the Wexford slobs, feeding on barley stubble and potatoes and roosting at night on the harbour’s sandbanks. Here they have numbered up to 10,000, while most of Ireland’s remaining rural flocks number fewer than 100 birds.

After a steady decline of the white-front, hunting bans were introduced throughout their range, including – if belatedly, in 2006 – their Iceland staging post, where about 3,000 geese were being shot every autumn. Protection in Ireland and Britain let their total numbers double by the late 1900s, to more than 35,000. Their steady decline since has puzzled ornithologists.

The current drop in reproduction to fewer than 20,000 birds has triggered special concern from AEWA, an international agreement on the conservation of African-Eurasian migratory waterbirds. A "single species action plan" (online at iti.ms/2dh4qRV) urges more restraint from disturbing the geese on their wintering grounds.

This must apply especially to Irish wetland sites where flocks are at most risk of extinction, dwindling to fewer than 50 birds. In 26 traditional Irish sites listed in AEWA research, many are on western blanket bog, but eight midwest lakes and estuaries, along with the Blasket Islands, are thought to have lost their geese already. Some goose families may have moved to Wexford, keeping numbers there still relatively stable.

The need for even closer monitoring has brought a special appeal to the 350 volunteers who regularly survey wetland birds in winter for BirdWatch Ireland and the National Parks and Wildlife Service. It comes from two leading researchers for AEWA, Alyn Walsh, warden of the NPWS Wexford reserve, and Tony Fox, an expert on the white-front's social dynamics in the UK and Greenland.

In the current newsletter for volunteers (I-Webs News at birdwatchireland.ie), they review possible reasons for the crisis in white-front reproduction. "Goose in trouble as Atlantic warms" is the heading on their article, telling how change in surface sea temperatures since the 1990s has pushed weather depressions up to western Greenland in April and May, just before the geese reach their individual nesting grounds.

After the long migration north the females need to graze, to build up fat for laying and incubating their eggs, but arrive to find the tundra deep in snow. “Reproductive success is the key to saving the population,” write Walsh and Fox, “yet it seems the climate is against the geese.”

With white-fronts denied them (against much resistance) after the 1980s, Ireland’s hunters were left with tightly limited access to another quarry of long tradition, the big greylag goose, Anser anser. As a winter migrant from Iceland it arrives in cackling hundreds to feed on cereal stubble in coastal fields from Co Donegal to Co Waterford.

There are also, however, increasing numbers of feral greylags, gone wild originally from domesticated farm stock and breeding across Ireland. There are reports of 28 flocks, including some of more than 100 birds, in Mayo, Galway and Donegal. Hunting pressure on Iceland’s wild population is severe, so shooting of greylags in Ireland is permitted only between September 1st and October 15th, before the Iceland birds arrive, and later (October 16th to January 31st) at wetlands in Wexford and Cork where no ringed birds from Iceland have yet been confirmed.

Michael Viney's Reflections on Another Life, a selection of columns from the past four decades, is available from irishtimes.com/irishtimesbooks