40



A. G. Butler—Colour in Feathers



I think, is a regular winter visitor on suitable ground. The Long-eared

Owl is rare ; the Little Owl has invaded the county during the last

two years, and is spreading. None of these three are numerous enough

to discuss. The Brown Owl is very common, and the Barn Owl fairly

so. The former has two calls, the most startling being something like

“ Tch-vac ! Tch-vac ! ” pronounced with great sharpness.


This, however, is nothing to the call of the Barn Owl, or as many

country people call it, the Screech Owl, and those who have heard it

suddenly give vent to its cry in the darkness might well imagine that

it would send every Rat or Mouse within hearing to its hole for the rest

of the night. The cry of the Eagle Owl is said to be very much worse,

and yet it must serve some purpose in the economy of the bird. It is

well known that most animals in all classes escape their enemies by

“ freezing ”—i.e. becoming absolutely rigid until the danger has passed.

Assume an Owl conscious of the presence of prey by (possibly) scent or

sight, and the animal lost to sight by the rigid attitude it has assumed.

If an Owl after flying around and failing to discover the position of

the animal suddenly lets fly its startling cry, it might well cause that

animal, especially if young, to start, and that movement would disclose

its position and mean capture, if so, these cries, which to us appear

to give alarm to the hunted, would really be of great assistance to

Owls.


This, of course, is only a theory, and should be supported by facts

before it can be accepted as an explanation of such weird and apparently

harmful cries.


Do those who keep Owls notice that they take their prey mostly

after uttering their cries ?



COLOUR IN FEATHERS


By A. G. Buti.er, Ph.D.


It is difficult to understand how the elimination of yellow from green

could so modify the structure of feathers as to leave them blue and the

elimination of blue leave them yellow. If the absence of yellow

pigment left the structural blue effect, how could the latter be got



