196



Egg markings and sunlight.



branch, but the bird Hew off as I approached or I might have in¬

correctly identified it.


The largest and most heavily marked eggs of the common

sparrow were in a very remarkable and quite abnormal open nest

built in the forking branches of a large Hawthorn and vaguely re¬

sembling a duck’s nest: Mr. Frohawk has illustrated two specimens

from this nest in my “ Birds’ Eggs of the British Isles,” pi. IV.,

figs. 142, 143. Examples of the eggs of the tree-sparrow from nests

in shadowed holes in trees proved to be lighter and less heavily

marked than those which I obtained from the stumps of hollow

branches projecting from pollard willows, into which the sun shone

during part of the day, but eggs found in a sand-martin’s nest in

a mole-run extending from the side of a brick-earth cutting varied

a good deal in intensity ; whether the snow-white feathers of the

nest, by reflecting light, have any effect upon tne colouring it would

be difficult to say, the warmth of the nest probably contributed.


The least marked eggs of the linnet were obtained from nests

built near the ground in thick brambles, but startling variation in

the eggs of this species seems to be exceptional. I have only twice

found almost entirely unmarked white eggs of the yellow bunting,

the nests being built in dense short scrub tangled with bramble,

nettles, &c., so that they were completely shaded : one of these

examples is figured by Mr. Frohawk (pi. V., fig. 188) of the above-

mentioned work.


And now I think I have brought forward sufficient evidence

in favour of the view that light and warmth affect the parent bird

during the period of oviposition, producing intenser colouring and

bolder marking in the eggs which she lays ; whereas cold and shade

tend to decrease these characteristics. Of course we require further

evidence touching the correctness of this view, and thus a new field

for experimental study, and I think a fascinating one, is open to the

aviculturist as well as the field-naturalist.


Mr. Beebe has proved that moist heat intensifies the markings

in the plumage of birds, therefore I see no reason why it should not

affect also the colouring of eggs laid by birds subjected to somewhat

similar influences : at any rate it is up to doubters to prove that it

does not.



