Another Life: Will our swans desert us if Irish winters keep getting warmer?

Between the worst of the storms a score of whooper swans left the shelter of their lake beneath the land cliff and let the wind lift them north along the shore to graze grass at the edge of the strand below me. The flicker of their wings gleamed as brightly as the surf.

Floods from the mountain had raised the lake so that, even when upending, the last of the pondweed was beyond their beaks. The grass of the pasture, pooled with rain, was short and salty but fresh and sweet. From time to time a bird would lose its balance in a gust and have to sit to go on feeding, the feathers ruffling on its back. The pasture covers layers of old sand, but a scoop of this is good for swans, as grist for the gizzard.

One afternoon they were joined by almost 50 barnacle geese, taking refuge from Frehil, the twin-humped islet offshore. Geese peck a lot faster than swans, but there was room and food for everybody.

Between pondweeds and salty grass, our whoopers, from Iceland, at least have a natural diet, fertilised only by rabbits and sheep. Most of their species, Europe wide, now feed routinely on farmland. The change in behaviour is historically recent, noted first in Britain in the 1940s, as wartime arable farming extended into wild wetland areas.

In Northern Ireland, which has about 1,500 whoopers on Lough Neagh and 1,000 on Lough Foyle, the lakes provide safe roosts at night, with a daily commute to fertilised, reseeded grass. The switch has also been to winter cereals and oilseed rape, or fields with potatoes or other root crops. In Scotland the birds have been seen feeding on seedling oilseed rape by moonlight, a most unusual departure from the birds’ normal rhythms.

At Wexford Wildfowl Reserve up to 600 whoopers regularly feed on surrounding grassland, and some 800 have been grazing where they could in the flooded Shannon callows and fields along the River Suck.

They are some of the 10,000 or so Iceland swans that migrate to the Republic, with another 4,500 to the North. In midwinter, whoopers (Cygnus cygnus) substantially outnumber the 9,000 or so resident mutes (Cygnus olor).

Wetland censuses have shown the continuing decline – perhaps to an imminent absence – of the migrant Bewick's swans (Cygnus columbianus). In 2010 these were down to 160 in Ireland, most in the Republic and perhaps half at the Wexford reserve. Yet once they were reckoned the most abundant of Ireland's visiting swans.

Bewick's, named in 1830s England for the wildlife wood engraver Thomas Bewick, is the smallest of the three northern swans. Graceful and rather gooselike, it has more black than yellow on its bill, compared with the whooper. It also feels the cold more than bigger swans, which explains fluctuations in numbers escaping winters on the Russian tundra.

The big decline in Ireland began after the mid-1980s, when some 2,300 Bewick’s swans were estimated; a decade later the number had halved. As European winters have eased, most of the birds move no farther than to the west of the Continent and, in Britain, to the Slimbridge wildfowl reserve, where barley is scattered free.

If warming winters keep birds nearer their breeding grounds, could the whoopers, too, desert Ireland, in a migratory change shaped over thousands of years?

Iceland already shares in the great Arctic thawing, the island rising measurably as the weight of glaciers melts away. But climate change will not affect winter darkness, unless the swans find something to graze on by Northern Lights.

Meanwhile, as the storms subsided, any calm, mild morning since New Year’s Day has had me listening to early birdsong: song thrush, blackbird and robin. What these delicious melodies portend of spring’s advance I can only guess at. But the breeding season of songbirds will now have to reckon with burning upland gorse in spring and the slashing of roadside hedges in late summer.

Final submissions for and against changing the limits on cutting and burning dates had been with Minister for Arts, Heritage and the Gaeltacht Heather Humphreys for almost a year. The day before Christmas Eve, and a month or so ahead of the election, she granted, in "pilot measures", much of what the Irish Farmers' Association had been urging: hill-scrub burning extended to March and hedge cutting allowed in August. As an "alarmed and perplexed" BirdWatch Ireland pointed out, most submissions to the Minister had opposed such changes, following conservation policies in the rest of these islands.

So upland wildfires will soon come a bit later, when gorse is drier and burns stonechats’ nests faster, scorching the hills for the rain to run off faster. And late-breeding birds like the yellowhammer may have to get a move on, or choose the right side of the hedge.

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