TEE BROWN-HEADED, OR MASKED GULL. 
337 
to that of L. ridibundus. Through a telescope, I have frequently 
remarked some of these birds when feeding, at distances between 60 and 
100 yards, to have the black disposed as in L. capistratus ; i. e., the bird 
when looking towards me, displayed a black head ; but when walking 
from me, its head appeared pure white. This was particularly noted on 
the 17th of April, the 3rd, 18th, 27th, and 28th of May, 1832. In favour 
of the view that the black taking a masked form is occasional or accidental, 
rather than transitional, is the fact, that I have seen immature birds when 
first assuming the black head, displaying black feathers, as low down on 
the back of the head,* as L. ridibundus ever has them at any age.f 
Fourthly. — My specimens of L. ridibundus and L. capistratus do 
not present any marked difference in the shade of colour of the under 
surface of the wings. — See Temminck, part ii. p. 786. 
Fifthly. — This author (p. 787) states that the eggs given to him 
as those of L. capistratus , are rather smaller than the eggs of L. ridi- 
bundus . Smaller individuals may be expected to lay smaller eggs, and, 
as mentioned of those at Ram’s Island, no two eggs in the same nest 
were exactly of the same size or form. If the species be different, we 
may certainly expect to find a difference in the eggs, but it is essential 
that a number or series of these be seen before their differential cha- 
racters can be properly known. 
I have many more notes in addition to those already given, which show 
that the size of bill and feet, and length of tarsus, three of the chief cha- 
racters by which L. capistratus is distinguished from L. ridibundus , are 
liable to much variation. I shall only add a comparison of an adult with 
a young bird of the preceding year, which were killed from a large flock 
at the same shot near Belfast, on the 15th of February, 1838. 
ADULT. YOUNG, 
in. fin. in. lin. 
Length (total) 159 143 
„ of bill above, in a straight line . 1 2|- 12 
* I once remarked a young bird of the year, in the month of August, with brown 
feathers on the head forming the regular hood ; the lower part of the back of the 
head, as well as the upper, being of this colour. 
f This bird is believed by Temminck to attain full plumage within a year ; but I 
have often had proof of individuals, at least, not doing so until the second summer 
after birth. 
November 1850. — An adult L. ridibundus (as I consider) of the ordinary size 
added by Dr. J. D. Marshall to his collection of living birds in October 1849, and 
still in his possession, exhibited a mask like that of L. capistratus , as figured by Yar- 
rell, during the whole of last summer. It was of a pale broccoli-brown colour. 
YOL. III. Z 
