Overcrowding at Little Skellig — an island in Ireland’s southwest corner — have led gannets to move along the southern coast to Great Saltee Island, County Wexford. Gannets, one of the biggest and heaviest seabirds in the North Atlantic, mate for life. Pairs may be together for up to 20 years and return to the same nest each breeding season. Their nests are just a mound of rotten vegetation, lined afresh each year with new seaweed, grasses, and feathers.