The common buzzard was driven to extinction from Ireland in about 1890 and it was not until the 1950s that the breeding of 10 pairs along the Ulster coast - mostly on Rathlin Island - signalled a serious recolonisation from Scotland. There was a set-back when rabbits (the birds' chief prey, along with mice and small birds) were reduced by myxomatosis, but numbers slowly built up until, by the 1980s, the birds were familiar across the North.

It took the Republic's ban on strychnine in 1991 to make the Southern countryside safe for the buzzard's explorations. Today, the South has perhaps 150 pairs, with breeding in five counties as far down as Wicklow, and birds are seen wandering in most of the rest of the island. Seven pairs nesting in north Co Dublin have brought the buzzard's soaring, spiralling flight to the capital's doorstep.

Ireland has added to its birds through natural expansions of species, not all of them ultimately welcome. The island's teeming magpies are reputed to have stemmed from a single flock which arrived in Wexford in 1676. Today, nourished substantially on human leavings, road kills and spring nestlings, there are about 320,000 breeding pairs with some of the highest urban densities in Europe.

The collared dove, with its repetitious hootings from telegraph wires, has also been happy with human neighbours, but its dramatic spread from Europe is recent. Once restricted to Turkey and the Balkans, it erupted westwards in the mid-20th century and reached the Atlantic at Galway in 1961. In a niche with little competition, it raises four or five broods a year, usually in or around towns but also in shelter-belts in the countryside.

Fulmars, the silver-grey, gull-like seabirds gliding on stiff wings at summer cliffs around Ireland, first bred in Mayo in 1911 as part of a dramatic population explosion in the north-east Atlantic. A new food source in fishing industry discards may have helped, but emergence in Iceland of a new genotype in the species is another current theory. Fulmars live for decades and promise to claim any spare space on the nesting ledges round these islands.

Egrets - small herons - are a global family that has more than made up in expansions what it once suffered in declines at the hands of high-society hat manufacturers (who coveted its elegant nuptial plumes). The cattle egret, for example, mainly confined to Africa, arrived on the wind in South America in 1916 and now breeds right up America's Atlantic coast as far as Maine.

In the past few decades the little egret, its whiter-than-white Mediterranean cousin, has spread spectacularly north and west in Europe to colonise the southern coasts of Ireland and Britain. Its first visits may have been "overshoots" as the birds flew from Africa to breed in the south of France. But suddenly, in the 1970s, the egrets increased in number and began to stay for longer and longer.

In the late 1990s, a dozen pairs nested in a grey heron colony in the valley of the Blackwater river in Co Cork. Today there are upwards of 120 pairs and they have even nested in trees on the outskirts of Cork City. Their gleaming shapes are becoming familiar on many muddy estuaries up the east and west coasts, especially in winter, and they seem to have taken up residence on the inlets of north Co Dublin.

The warmer winters of climate change may have played some part in the little egret's invasion, but the ebb and flow of birds can take time to become clear. The Irish breeding population of the blackcap, for example, the "northern nightingale" among the warblers, has been spreading north and west in the island. But the blackcaps increasingly seen at suburban bird-tables on the east coast in winter are migrants from Europe - so far as we know, the Irish birds are still migrating south to the sun.

Photo above: A buzzard: "It took the Republic's ban on strychnine in 1991 to make the southern countryside safe for the buzzard's explorations