200 SCIENCE-GOSSTP. 
ON COLOURING 
By J. A. 
Pe interesting theory on the colouring of birds’ 
eggs advanced by Mr. R. J. Hughes in your 
November issue (a7z¢e, p. 172), will be read with plea- 
sure by ornithologists. Years ago, before the fas- 
cinations of botany had monopolised all my limited 
leisure hours, I devoted a good deal of thought to this 
interesting problem, although, I regret to have to 
confess, with no practical result. If anything, my 
studies of the subject left me with some leaning 
towards the theory of protectivé colouration. 
In condemning this latter hypothesis, I think Mr. 
Hughes is rather unfortunate*in the instances he 
adduces of the hedge-sparrow and the thrush. Pre- 
suming that the enemy they have to guard against 
would most likely be a feathered one, who would 
look down upon the nest through a leafy screen ; it is 
not difficult to imagine that eggs of a blue or greenish 
tint would most easily escape detection. The point 
raised with regard to the hen bird, and not the eggs, 
requiring protection in colouration, also seems to me 
unconvincing. As birds do not sit closely until the 
full complement of eggs is laid, it is as necessary for 
the eggs to be protectively coloured as for the mother 
bird. 
Whilst I admire the ingenuity of Mr. Hughes’ main 
postulate, I fear the proofs advanced do not warrant 
its fullacceptation. I fully grant one of the author’s 
contentions, that the plumage of a bird may be 
influenced to a small extent by the nature of its food. 
Such is matter of common observation in cayenne- 
pepper fed canaries, hempseed-fed bullfinches, and 
fowls fed on highly-spiced food, the basis of which 
is often carbonate of iron and cayenne pepper. 
Similar variations of tint have been noticed in 
the insect world by breeders of lepidoptera. Yet, in 
all these instances, no fresh colouration is introduced, 
the result being only to deepen and intensify colours 
already existing. It would be difficult to prove that 
the acquirement of dark colours by birds of nocturnal 
or crepuscular habits tended to diminish the supply 
of pigment to the eggs. In the swallow tribe, the 
nightjar, with much less white about it than the 
swallows and martins, lays the most deeply-pigmented 
egg of any of our British species. 
Can birds be divided into the five classes proposed 
by Mr. Hughes? I fear not, without a most embar- 
rassing number of exceptions. In endeavouring to 
so divide them, I should be inclined to include the 
hedge-spairow in the first class. Why should the eggs 
of this bird and the robin differ so widely in colour, 
when their food is apparently similar? Is there not 
a wide difference between the cold neutral tints of 
those of the wagtail, the rich warm tones exhibited 
by the tree pipit and grasshopper warbler, and the 
pure white egg of the black redstart? Presumably 
the swallows, as insectivorous birds, are included in 
OF BIRDS’ EGGS. 
WHELDON. 
this section. Amongst these the food is probably 
less heterogeneous than in any of ‘the species men- 
tioned by Mr. Hughes, yet we have represented, eggs 
of three distinct types—plain white, red spotted, and 
grey marbled. 
In class 2, I suppose, would be included, with the 
domestic fowl, the pheasant and its allies. How does 
Mr. Hughes account for a pen of poultry or pheasants, 
all fed alike, producing, the former both white and 
dark brown eggs, and the latter both pale greenish- 
stone-coloured and rich brown-stone-coloured eggs ? 
The colour here is evidently not due to the nature of 
the food. Parrots fed entirely on seed lay white 
eggs, as do doves and pigeons, and the canary of 
confinement, which rarely or never gets insect food, 
has eggs very closely resembling some of those in 
class 1, whilst the linnet and greenfinch frequently 
lay eggs that have feeble evidences of blue or green 
in their ground colour. 
The author very frankly admits his difficulty in 
bringing into agreement the diverse features presented 
by the eggs he places under class 3. Here again it 
appears to be an impossible feat to ‘‘ put all the eggs 
in one basket.” The gannets are a conspicuous 
exception to the other fish-eating species of section (a), 
for they contrive to lay an almost colourless, un- 
blotched egg, without apparently requiring much 
dark pigment to adorn their plumage. Probably all 
guillemots feed alike, yet, on looking over my 
specimens, I find their eggs varying in ground colour 
from white to the deepest green, and the markings 
from none at all to the most intense brown blotching. 
Under classes 4 and 5 I think it is impossible, on 
a dietary basis, to separate the owls from some of the 
hawks. Perhaps the barn owl and the kestrel will 
serve for the purpose of contrast. I think it can be 
assumed that their menu is practically the same. 
Yet the owl lays a white egg, and the kestrel’s is 
heavily blotched, perhaps one of the most richly 
marked of its tribe. The owl cannot be said to 
absorb the egg pigment to dye its somewhat light 
coloured raiment, for the kestrel, with its deeper 
tinted egg, wears a much more intensely coloured 
dress. 
I hope Mr. Hughes will accept these criticisms in 
the friendly spirit with which I write them; I am 
actuated by a desire for further information on a 
subject which has long interested me, and I shall be 
very glad if he can throw more light on the points 
I have endeavoured to raise. I agree with him that 
the subject affords an excellent field for future work, 
and as he has had the courage to embark on a novel 
course of investigation, I trust his efforts will be 
eventually rewarded by the discovery of some clue to 
what I consider one of Nature’s inexplicable secrets. 
—H. M. Prison, Liverpool. 
