Monday, 3 September 2012

Great Move North

April and May witness a mass movement of birds north into Europe and North America, and Ireland fully participates in this natural phenomenon.  This migration is largely made up of two elements – the departure of winter visitors to more northerly climes and the arrival of summer visitors from more southerly regions.  Thus thrushes, such as redwing and fieldfare, which were so common throughout the winter have now all but departed.  The throngs of waders (or shorebirds in American parlance) have now mostly left for their breeding grounds to the north.  Ducks and geese will move quickly north as daylight hours increase and breeding grounds lose their snow and ice cover.

Adult Purple Heron by Colm Flynn
At the same time, vast numbers of passerines (small perching birds) move into Ireland to take advantage of longer daylight hours and hugely increased food resources in order to hatch and rear their young.  These are mainly insectivores, which feed on the swarms of flies, midges and other insects that populate Ireland in the warmer months. Whitethroats, chiffchaffs and blackcaps are representative of the warbler family while swallows, martins and swifts occupy the skies. More exotic species such as the cuckoo, flycatchers and wheatears are also seen and the rare crepuscular nightjar may be encountered.

With the warming seas small fish become abundant inshore and this attracts terns such as arctic and sandwich; auks represented by guillemots, razorbills and puffins; gannets and the small but extremely resilient storm petrel.  Ireland is also used as a transit point and feeding station for birds moving further north such as whimbrel, Greenland wheatears and maybe even an osprey or two.

Migration northwards largely stops in late May as the migrants raise their young.  From late August onwards, with the shortening days and dwindling food supplies, the whole process reverses and our summer visitors, augmented by their offspring, head south once more to Africa for the winter.  As the arctic regions become snow-bound thrushes, waders, ducks and geese move back to into Ireland to take advantage of our mainly ice-free conditions and available food supplies.

Migration is not confined to birds as insects and sea mammals also migrate and we will revisit this at a later time.

Over the next few weeks look out for swallows, terns, auks and warblers as well as butterflies such as orange tips, holly blues and green hairstreaks.

At the time of writing a purple heron, an extremely rare visitor to Ireland, has taken up residence at Seafield, Bunmahon. Congratulations to local birder Daniel Wheldon on this excellent find.

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