SEASONAL CHANGES OF PLUMAGE IN BIRDS. 225 
On June 8th found a nest containing two half-grown young. 
Their breasts were a spotless cream-colour, their backs mottled 
not unlike an unfledged Lesser Black-backed Gull. We reared 
these two young ones; by the beginning of July they had moulted 
their nest plumage ; the breasts and under parts still remained a 
spotless cream-colour, the upper parts coming mottled brown, but 
divided by broad pale yellow stripes running longitudinally down 
the back. The tails were already a fine russet colour, barred 
with brown. We kept these two birds till the autumn of the year 
after they were hatched, and at this time they still maintained the 
plumage of the first moult unchanged. Their irides, however, 
which had been a pale transparent blue, were now gradually 
turning yellow. This change in the colour of the irides seems to 
be, in some cases, contemporaneous with the change of colour in 
the plumage of the bird’s head, and is especially conspicuous in 
the case of the Marsh Harrier (Circus @ruginosus) and Red Kite 
(Milvus ictinus). 1n both of the latter the irides change with the 
colour of the head, being nearly black when the head is very dark- 
coloured (as in the young Marsh Harrier), hazel when the head 
is brown, and pale yellow, approaching to white, when the head 
becomes white, as in the old birds. 
With regard to the plumage of the parent birds of the two 
young ones which we reared, nothing could exceed the beauty of 
the male. With the exception of a fawn-coloured bar across the 
breast, the dark primaries and secondaries, a few bold blotches of 
brown on the back, and a golden-coloured tail barred with brown, 
his whole plumage was nearly pure white. The female had a 
cream-coloured breast and under parts, a handsome brown and 
white checkered back, the head brown, and the tail as in the male. 
Though I have seen a good many nests of both the Rough- 
legged and Common Buzzard, I never saw the former nesting in a 
tree, or the latter otherwise than in a tree, usually rather high up. 
All the nests of the rough-legged species which I have seen have 
been on fell-crags, nor does the plumage of this species seem to 
exhibit nearly so great a variation as in Buteo vulgaris. 
The irides in B. lagopus darken in colour with the age of the 
bird, the adults having a hazel iris, those of the immature birds 
being yellow. This is certainly a striking anomaly, and shows 
how difficult it is to establish, even from observation, any reliable 
code for Nature’s rules. 
