13 October 2013

Much as I love birds I am no photographer, so it always delights me when friends send me their pictures of birds. An old friend and colleague, Hamish Nicholson, is such a donor and has just sent a number of pictures of sea birds taken on a Norwegian holiday including one which must be familiar to us all: the Great Black Backed Gull.
altThese birds belong to the huge family of Gulls, or Laridae, of which there are 48 species world wide many of which turn up in European coasts with nine in Scotland. It is a common mistake to call them ‘seagulls’ for increasingly gulls are to be seen far inland especially near garbage tips. Two species, the handsome black-headed gull and the common gull, commonly breed on inland waters in Perthshire where in spring time gulleries are raucous with their calls.
In Victorian times these gulleries, particularly of black-headed gulls, were plundered when tens of thousands of eggs were used in the manufacture of patent leather. Today, in more enlightened times, this species is one of our commoner birds and it is hard to believe that the fashion for patent leather nearly rendered them extinct.
In addition gull’s eggs, particularly of the larger species, have featured largely in human diet especially in St Kilda and other western islands. As a boy I remember expeditions to collect lesser black back eggs in Arran.
Two  common species will be familiar to many but are often difficult to tell apart. These are the great and lesser black-backed gulls. When trying to identify similar species it is important to notice where you see them. The ‘great’ rarely leaves marine habitats while the ‘lesser’ is often seen inland, even in Perth, though it should be remembered that the Tay is tidal as far upstream as the Fair City.
As their names imply the ‘great’ is a much larger and heavier bird but size is often hard to judge unless both species are together. A shooting friend of mine tells me he once shot at what he thought was a very high pheasant and a dead starling fell at his feet; so size can be deceptive specially at distance and in poor light. However these two white gulls with black backs can be distinguished by their leg colour, and there is a little jingle which helps memory:
Lesser gulls have Lemon legs.
Little wings and smaller size.
Greater gulls have grey-pink legs
Bigger bills and yellow eyes. 
Great black backs have a bad reputation: like all gulls they are scavengers and carrion eaters and are alleged to kill lambs. This has given rise to many local names such as the Gaelic Arpag, a harpy, or Norse names such as Baakie or Swarbie from Svartbakr (black back) but the adults are handsome, haughty creatures.
Seaside holidays have brought gulls to people’s attention as few other species have done. Gulls are noisy, assertive and aggressive and very communicative especially round their communal nest sites. They are both intensely gregarious but monogamous and territorial and this has lead to a complex form of communication with calls and posturing so that ethologists have been able to translate their body and vocal language into clear messages passing between individuals. This, and their mastery of the air, make them wonderful subjects for study.
Gulls are also long-lived, 30-35 years of life being quite normal for larger species such as the great black back. Like most gulls black backs are omnivorous, highly opportunistic feeders taking eggs, young birds as well as marine invertebrates and fish.
While it is not too difficult to decide whether an adult black backed gull is a great or a lesser, distinguishing between their chicks is much more difficult. It takes four years for great black backs to reach adult breeding plumage and during their juvenile lives they vary between various and confusing blackish-brown mottled plumages. You need to be a real expert to be confident on identification of the age of these juvenile gulls and certainty depends on spotting small changes in their chequered plumage patterns. 
Hamish’s photograph here shows a chick whose species is best identified by its attendant adult.

Robin Hull


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