BIOLOGY. 265 



Birds' nests may be divided into two classes : the first, com- 

 prising those in which the nest is either full}' exposed or imper- 

 fectly concealed : the second, in which the nest is either roofed in 

 or placed in a dark hole, so that the eggs and young, as well as 

 the sitting bird, are effectually hidden. The thrushes, warblers, 

 finches, pigeons, and birds of prey of temperate regions, and the 

 tanagers and chatterers of the tropics, furnish examples of the 

 first kind of nest ; while the kingfishers (which build under 

 ground), the parrots and woodpeckers (which build in holes in 

 trees), the Icteridce (with hanging .nests), and the common wren 

 (with a domed nest), afford instances of the second class. 



From the point of view of color and markings, birds may also 

 be divided into two classes, according to the difference or identity of 

 color in the two sexes. In some groups, as in the toucans, the va- 

 ried and brilliant colors are found in both sexes ; but in the majority 

 of birds the female is far less brilliant than the male. With very 

 few exceptions, Mr. Wallace finds that whenever both sexes are 

 of bright or conspicuous colors, the nest is of the second class, or 

 such as to conceal the sitting bird ; while, whenever there is a 

 striking contrast of colors between the sexes, the female being 

 dull and obscure, the nest i> open and the bird exposed to view. 

 The bright-colored kingfishers, motmots, barbets, toucans, plan- 

 tain-eaters, hoopoes, todies, trogons, woodpeckers, parrots, me- 

 tallic starlings of the East, ground-cuckoos, nuthatches, American 

 hangnests, some titmice, etc., in which the females are almost, if 

 not quite, as brilliant as the males, build their nests either in the 

 ground or in holes of trees, or make them in a roofed form, or 

 carefully concealed in dense foliage, or by various external de- 

 vices. On the other hand, the birds of showy plumage, which 

 build open nests, almost all have the females of a dull color, as in 

 the brilliant chatterers, tanagers, manakins, tropical fly-catchers, 

 shrikes, thrushes, and warblers. The females in these are deficient 

 in the bright patches of color on the head and tipper parts, which 

 would render them visible when sitting on their open nests, and, 

 moreover, have the earthy brown or oli^e green tints best adapted 

 for concealment. 



These facts, taken in connection with innumerable others in the 

 insect world, show the remarkable provisions in nature for the 

 protection of the female from carnivorous enemies while rearing 

 the young. The absence of color, when the structure and situa- 

 tion of the nest are insufficient, protects the female bird during 

 the important process of incubation. This view is confirmed by 

 certain anomalous facts in the natural history of birds. There are 

 some instances in which the males perform a part or even the 

 whole of the duties of incubation. In these cases, when the bird 

 is so defenceless as toneed protection, the usual colors of the sexes 

 are reversed, the female becoming the larger and brighter bird, 

 as in the sooty phalarope, the dotterel plover, and the small In- 

 dian quails of the genus turnix. He thinks that this curious and 

 unexpected connection between the manner of a bird's nesting 

 and the color of 'the female plumage, is best explained by the 

 action of the laws of variation and hereditary transmission, and 



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