202 
Mr. H. Durnford on the Birds of 
another have always been composed of birds of its own kind. 
Adults, after once attaining their pearl-grey hood, never lose 
it, though in winter it becomes rather lighter, and those 
with white heads are immature birds, which do not attain 
their full plumage till after their second moult. I have seen 
many birds throughout May and June of the present year 
with well-defined dark grey hoods. Some specimens, when 
first killed, have a delicate faint pink tinge on their under¬ 
parts, also observed in L. maculipennis , which, however, 
quickly fades after death. The colour of the iris varies a good 
deal in different examples, being pale grey, grey with a tinge 
of yellow, and grey with a tinge of light wood-brown. This 
is probably attributable to age. The narrow rim of naked 
skin round the eye is dark coral-red ; legs and feet the same, 
but of a duller shade; beak rather darker than the legs. 
140. Larus maculipennis, Licht.; Scl. et Salv. Nomencl. 
p. 148. 
Common in the neighbourhood, except in the spring. After 
their second moult they attain adult plumage; previously to 
that they very much resemble the young Larus ridibundus. 
Their times for moulting and changes of plumage are very 
curious. I have observed and shot adult birds in April, May, 
and June in what is usually considered winter plumage, viz. 
with a white head and black spot behind the eye, and from 
June to October with perfect black hoods. It is impossible 
to establish any thing like a hard and fast line on this subject; 
for I have seen adult birds in the same flock, some with white 
and others with smoke-brown heads. Their moults probably 
take place in January and February and June and July; but 
this doubtless depends a good deal on the age of the bird. 
This Gull was common about Baradero in April; and one 
fine warm evening, whilst steaming down the “riacho,” I 
saw a curious sight: a considerable flock of Black-headed 
Gulls were hawking over some low marshy ground with 
Swallow-like flight, apparently in pursuit of some sort of 
moth; for they kept about a foot above the ground, never 
wandering far from each other. 
