Page:Popular Science Monthly Volume 17.djvu/672

654 more highly developed form of the common vertebrate sensibility. When we reflect upon the purely physical and physiological basis which, as Helmholtz has taught us, underlies the musical intervals and the distinctions of harmony and discord, there is certainly no reason why they should not be perceived by all the higher animals alike, in a greater or less degree.

Considering, therefore, the evident susceptibility of birds to the simpler pleasures of music, and the interest which they show in it even apart from their domestic relations, there is no a priori difficulty in accepting the belief that their powers of song may have been developed by mutual selection, provided no adverse argument can be shown against the probability of such selection ever proving a cause of specific variation. To this last question, the question so ably raised by Mr. Wallace, I shall return on a later page.

Passing on to sight, we have first to observe the effects of mere light or brilliancy upon birds, apart from special effects of color or form. Now, birds certainly share with insects and many other creatures the common fascination for bright lights. "Owls and night-jars have been known to flutter against the window of a lighted room in the small hours." In the tropics, where windows are more constantly left open, birds frequently fly into houses, attracted by a lamp or candle. The reflected light of a mirror is employed to draw down larks. Magpies delight in secreting diamonds, gold, silver, and other shiny objects. The bower-birds use shells, polished pebbles, and like brilliant odds and ends in the construction of their bowers. So, too, metallic iridescence occurs frequently in the feathers of beautiful species, notably in the humming-birds, sun-birds, peacocks, and other flower-feeding or fruit-eating classes. But even the far less brilliant crows, gulls, ducks, and doves show exquisitely burnished gloss or luster on their coats, often specialized upon particular portions of the plumage, and apparently betraying the action of sexual selection.

Of the love for color shown by birds, I have already treated so fully elsewhere, that it will suffice here briefly to recapitulate the main facts. The universality of bright hues in the fruits which depend upon birds for the dispersion of their seeds clearly shows that fruit eating species are attracted by red, blue, purple, and yellow; just as the analogous case of insect-fertilized flowers shows the preference of bees and butterflies for similar tints. Mr. Darwin has collected several instances of interest displayed by birds in colored objects-, and of the attractiveness which color evidently possesses in their eyes. Of these, the most remarkable cases are those of the bower-birds' and the humming-birds' nests. And the constant occurrence of very brilliant hues among flower-feeding species, such as humming-birds, sun-birds, lories, and barbets, or among fruit-eaters, such as toucans, fruit-pigeons,