Barnacle Goose
Branta leucopsi
Gé ghiúrain
Almost all of Ireland's wintering Barnacle Geese are found in islands on the west and north coasts, to which they migrate from arctic Greenland each year. The most striking of geese to be seen in Ireland, its grey, black and white patterns of plumage make identification straightforward. In flight, extensive grey patches show on the wings and the flock calls with a noisy yelping. The main habitat is on low, grassy islands but flocks also commute to coastal fields on the mainland.

Brent Goose
Branta bernicla
Cadha
The Brent Goose is the smallest of Ireland's geese, being not much larger than a Mallard Duck. The pale-bellied form (the form occurring in Ireland) is greyish on the belly and flanks. Brent Geese have small white markings on the sides of the neck and the bill is very small. The young have pale edges to some of the feathers on the back. Flocks of Brents call with a low 'gurgling' noise both on the ground and in the air. They feed on eel grass and other marine plants on coastal mudflats, their primary habitat.

From the Appletree Press title: Birds of Ireland.
Also from Appletree: Animals of Ireland.