As the terns arrive, the geese leave

IT’S changing-of-the-guard time on the Dublin coast this month.

As the celebrity birds of the winter months, the Brent geese, prepare to depart for the Arctic, Sandwich terns are winging their way from Africa.

They should arrive here just after St Patrick’s Day. Both birds will be present into April, the loud kik-kik-kik calls of the terns mingling with the purring rruk-rruk of the Brent flocks. It’s a magical time.

The Brent has become Dublin’s most conspicuous bird, visiting open ground even in built-up areas. Flocks, sometimes hundreds strong, fly over the city.

If, like American states, each Irish county had an official bird, Dublin’s would surely be the Brent.

The name comes from an old German word, ‘brunnen’, meaning ‘burnt’; the bird resembles a charred log: black, grey and white.

The smallest Irish goose, not much bigger than a duck, frequents estuaries and the seashore.

The favourite food is zostera, a grass which grows on mud-flats, and the green algae which thrive in nutrient-rich waters.

Brent don’t venture inland, but, in recent years, they have taken to visiting parks, golf links and sports pitches close to the coast.

Their little bills can’t deal with long grass, but are ideal for grasping closely-cropped shoots.

Brent breed all over the high Arctic, the Irish contingent nesting on some of the most remote islands of Canada. Having grown up in uninhabited areas, Brent are not fearful of people, which is why they so readily enter cities.

Goose populations have their ups and downs.

Although their flesh is unpalatable, Brent were hunted.

Then the zostera beds were decimated by a mysterious disease.

Goose numbers declined, and, in 1950, Robert Ruttledge estimated that there were only about 5,000 left. With a moratorium on shooting, the population began to recover.

By 1960, we had 12,000 birds and Olivia Crowe, in Ireland’s Wetlands and their Waterbirds, gives a figure of 20,000 for the 1990s. According to the Irish Brent Goose Research Group, there may be up to 40,000 Brents in Ireland nowadays.

On arrival here, in autumn, the geese congregate in Strangford Lough, dispersing to locations around the coast.

Before leaving for the Arctic, in spring, many geese return to Strangford, where the flocks combine prior to migration.

They face one of the longest journeys of any wildfowl species. Bathurst Island, the stronghold of Irish Brent, is 4,000km away as the crow flies.

But geese don’t fly in a straight line like the proverbial crow; their first port of call is western Iceland, 850km from here.

They will spend a few weeks there fattening up for the next, and most gruelling, part of the trip, the crossing of the Denmark Strain, the Greenland icecap, and the Davis Strait, to reach Baffin Island off the coast of mainland Canada.

Ironically, global warming may be helping our Brent.

If spring is late in the Arctic, the permafrost sucks the heat from eggs, food is scarce, and few young fledge.

Until recently, good and bad breeding seasons alternated.

Now, the permafrost is thawing earlier and conditions are more favourable for raising young than they were even a decade or two ago.

The flocks returning to Ireland in recent years have a high proportion of young birds.

Strangford is also the prime destination for Sandwich terns; the largest Irish breeding colonies are there.

Named after a town in Kent, the Sandwich tern, like the Brent goose, travels a long way to breed.

Some terns spend the winter off the southern tip of Africa or even in the Indian Ocean, but most of them prefer the African coast, between Senegal and Ghana, 5,000km from Ireland.

Travel for terns is a more leisurely affair than it is for geese.

These light birds don’t fly fast, but they’re as much at home in the air as on the ground.

In-flight meals are available virtually on demand; terns catch fish, opportunistically, as they travel. Seabirds tend to be noisy at their breeding colonies, but are silent at all other times.

Terns, for reasons known only to themselves, are an exception to the rule. They are vocal throughout the year.

The noisiest of all is the Sandwich tern, whose call is the characteristic sound of summer along the coast where I live.