169 
species of the Genus Lams , or Gull Tribe. 
the histories of birds in the works of systematic Writers, are 
drawn from the communications of different individuals, who 
perhaps have not possessed the command of that combination 
of circumstances necessary to accurate narrative ; and thus au- 
thority itself unconsciously imposes on the judgment, and con- 
tributes to the propagation of error. 
It is not my intention, neither would it suit the limits of* a 
paper of this kind, to enter into a detailed account ab ovo of 
each individual species of the gull tribe ; but I shall endeavour, 
in successive communications, to point out some essential diffe- 
rences among them, which have been overlooked by ornitholo- 
gists, and to state some of those peculiarities in their instinct 
and habits of life, which the Care and frequency of observing 
them have enabled me to acquire. 
1. Larus parasiticus , (Lin. Syst.) Arctic gull, Scouti Allen , 
Spool, (Zet.). Ornithologists mention only one species of this 
gull. Pennant and others describe the male as having “ the 
crown of the head black, the back wings dusky, and the whole 
under side of the body white.” The female is said to be en- 
tirely brown, but of a much paler colour below than above 
I had, by numerous dissections, discovered males corresponding 
in their external appearance with the individuals described by 
Pennant as females, and females exhibiting ail the external 
marks which he had ascribed to males. This contradiction led 
me, some years ago, to investigate the subject with a good deal 
of attention, and the following is the result of my observations. 
The Arctic gulls are migratory. They come to Zetland in 
April and May, and leave it in September and October, and 
breed in different places in the country. The Island of Has- 
cassey is between two and three miles long. The south end of 
it is occupied by dark coloured Arctic gulls of both sexes, resem- 
bling exactly the female described by Pennant, and the north 
part of it by these gulls of both sexes, resembling the male de- 
scribed by the same author. Each kind occupies separate parts 
also of a hill on the Island of Unst, and they fight obstinately 
when either kind approaches too near to the ground possessed 
by the other. 
* British Zoology, vol. ii, p. 534. 
