168 Dr Edmonston on the Natural History of some 
Art. XXVI .—Observations on the Natural History of some 
species of the Genus Larus , or Gull Tribe . By A. Edmon- 
ston, M. D., Fellow of the Royal College of Surgeons of 
Edinburgh, &c. 
Part I. 
jAllthough there are no birds more universally met with on 
the British coast than the different species of gulls, there are 
none respecting whose natural history more doubt and con- 
tradiction prevail. The colour of the bill, of the foot, and the iri- 
des, are the external parts in the structure of birds which are 
supposed to undergo the least change during the different 
periods of their age, and hence these points have been assumed 
by many ornithologists as invariable tests of positive distinc- 
tion among them. A little observation might have shewn, that 
even these parts are greatly changed in size and colour at diffe- 
rent ages among individuals even of the same genus, and where 
the plumage differs also from what we expect it to be, it is im- 
possible to ascertain, by an adherence to these fallacious texts, 
the particular species of birds under examination. External 
characters, as far at least as the form and shape of the bill, and 
the structure of the feet, are concerned, are eminently useful in 
establishing generic differences between different orders of birds ; 
but those characters which relate merely to the size and colour 
of parts, are extremely vague and uncertain, when applied 
singly to fix discriminating marks between similar species of 
the same genus ; and a misplaced confidence in these has not 
unfrequently been held as sufficient reason for the addition of a 
new species, wdien a variety only existed. The form and posi- 
tion of the nest, the colour of the young at different ages, the 
differences observeable in the general economy and habits of 
birds, and their anatomical structure, are the points on which 
accurate comparisons alone can be founded. But as it requires 
considerable time to trace them, so it but seldom occurs that the 
opportunity of observing these progressive changes, is present- 
ed throughout in detail to the same person, and hence many of 
