510 
LARIDiE. 
eggs. They are the merciless persecutors of the other 
species of sea-birds in their neighbourhood, sucking their 
eggs whenever they are left uncovered by their owners, 
and with unavoidable speed of wing pursuing them over 
the surrounding sea, in order to compel them to disgorge 
those fish which tiiey have just captured for themselves 
and their young ones. They are the hawks amongst the 
feathered inhabitants of the ocean, fearlessly attacking 
even the greater black-backed gull, and evincing in their 
amazingly rapid evolutions of flight, when in pursuit of 
each other, a rapidity of wing which J have never seen 
surpassed. Upon some of the larger islands, where we 
observed two or more pairs, they were quite distinct, 
occupying each its own particular spot. 
There is something unaccountable in the variation of 
plumage of the L. Richardsonii, no other species with 
which we are acquainted assuming, as it does, in different 
individuals at the same time, and in both sexes, and when 
breeding, and consequently in a state of maturity, two 
distinct variations of plumage—some being of the deep 
uniform brown, as in the figure of the “ Fauna Boreali- 
Americana,” others with all the under parts white, or 
nearly so. Those of the lighter variety are, I should 
suppose, the more adult birds; they are larger, as no¬ 
ticed by Dr. Edmonston ; this may, however, be account¬ 
ed for by their being much more frequently females than 
males, the many specimens which Mr. J. Hancock dis¬ 
sected whilst in Norway being of that sex. I doubt 
not, however, that the male is subject, though very rarely, 
to the same change of plumage, not having more than 
twice met with the light-coloured birds in pairs, although 
I have in hundreds of instances seen a dark and lioht 
© 
one together, as well as two dark ones. It is a curious 
fact, that whilst on the Shetland Islands the light variety 
