The Common Guillemot — Uria Troile (Linnæus)
In its habits, food, and actions this species closely resembles the Razorbill, and they are usually found breeding on the same cliffs. The numbers at a colony can only be reckoned in countless thousands, the birds sitting crowded together as close as possible.
This species lays its egg on the bare open ledges and never seeks the nooks and recesses made use of by the Razorbill. The eggs are very pear-shaped, a wise provision which prevents their rolling off the narrow ledges on which they are laid. In colour they are most variable; the commonest variety is greenish in ground colour with brown or black streaks and markings; cream varieties somewhat resembling those of the Razorbill are not uncommon, but they may always be distinguished by the yellowish white lining membrane, whereas in the Razorbill the membrane is greenish.
The young bird when first hatched is covered with iron-grey down on those parts of the body which are brown in the summer dress of the adult. The under parts are white and there are a few bits of white down on the head.
In its habits and moults it resembles the young Razorbill.
In summer the adult has the upper parts, chin, and throat dark brown, and the rest of the body white. The black bill is long, pointed, and sharp, and not flattened as in the Razorbill. At the autumnal moult the brown on the chin, throat, and back of the head is replaced by white, and in this and the other allied species all the flight feathers are moulted at the same time. Length 18 in.; wing 7·5 in.
There is a curious variety of this bird known as the Ringed or Bridled Guillemot, which may be distinguished in summer by having a narrow white ring round the eye which stretches backwards for a short distance along the feather crease behind it.