426 



SCIENCE. 



[N. S. Vol. V. No. 115. 



they are unquestionably due, is well known. 

 Nearly all the cases cited by authors relate 

 to colors as seen by daylight. I wish to 

 call attention to the importance of studying 

 the forms and colors of animals with refer- 

 ence to their appearance and protective 

 value as seen by moonlight, staiiight and 

 in the dusk of early morning or the twi- 

 light of evening, when vast numbers of in- 

 sects, birds, small mammals, etc., are most 

 in need of protection against their preda- 

 cious enemies, which generally hunt their 

 prey at such times. The danger to most 

 birds and to diurnal insects is dne to their 

 sleeping more or less exposed to view, but 

 the danger to most, of the smaller mam- 

 mals and nocturnal insects, fishes, etc., is 

 due to the fact that they are most active 

 at night or in the twilight, and therefore 

 more easily observed by their enemies. 

 Moreover, the predacious species need 

 protective or imitative colors at night, 

 in order to approach their prey unob- 

 served. 



Moonlight and skylight give very black 

 shadows in which dark brown, dark gray 

 and black animals are nearly or quite in- 

 visible. Black shadows of foliage are apt to 

 be broken up by patches of white moonlight. 

 Therefore patches of white or light yellow 

 on dark or black animals are imitative of 

 such moonlight effects, and as they serve to 

 break up the dark outlines of beast or 

 bird, they are very effective as a protection 

 at night. 



Thus we find among nocturnal carnivores 

 many instances of black colors, as the mink, 

 fisher, bear, etc., and of black and white 

 ones, as the skunk, badger, etc. So among 

 the small species preyed upon, there are 

 numerous birds that are black, black and 

 white, black and yellow, etc. All such 

 strongly contrasted colors are more likely to 

 be of value for protection at night than in the 

 daytime. This also applies to the butter- 

 flies and other bright colored diurnal insects 



whose colors often have no obvious rtlation 

 to their diurnal surroundings, but blend 

 with the colors of the flowers or foliage on 

 which they roost at night. Many of our 

 large red and bi'own butterflies of the 

 genus Argynnis, etc., have bright silvery 

 spots on the under side of the wings, so 

 that they are conspicuous objects in the 

 daytime. But I have observed them at 

 roost on the golden-rods and other favorite 

 flowers by moonlight, when the colors of 

 their folded wings blend well with those 

 of the flowers, and their silvery spots glisten 

 like the dewdrops around them. Thus their 

 conspicuous markings become protective at 

 night. 



A great number of field mice, shrews, 

 moles, etc., have dark gray or grayish brown 

 colors, more or less like the common rat and 

 mouse. Such animals are nocturnal in 

 their habits, usually hiding in holes by day. 

 Their colors are not protective in the daylight 

 amongst green herbage, but at night they 

 are eminently so, for they are almost in- 

 visible in green grass, if quiet, as I have 

 often observed, even in good moonlight. 

 Animals that live among the stalks of reeds 

 or shrubs may gain protection by having 

 conspicuous dark stripes. No doubt the 

 tiger is better concealed by his stripes, while 

 in his native haunts, in the night than in 

 the daytime. The same is true of the 

 leopard and jaguar, and perhaps of the zebra. 

 Many fishes that rest at night among eel 

 grass and sea weeds have conspicuous ti-ans- 

 verse or longitudinal black stripes, which 

 are highly protective in a dim light, for they 

 look like the dai'k stems and shadows of 

 the weeds, and serve to break up or conceal 

 the outline of the fish. Black tails and 

 fins serve the same purpose. Such mark- 

 ings of fishes are often more conspicuous 

 at night than in the daytime. All the 

 cases referred to above seem to be the di- 

 rect results of long-continued natural selec- 

 tion. 



