280 DARWINISM chap. 



exposed to the attack of the whole colony ; whereas a hawk or 

 falcon could carry off a sitting-bird or the young at a swoop, 

 and entirely avoid attack. Moreover, each kind of covered 

 nest is doubtless directed against the attacks of the most 

 dangerous enemies of the species, the purse-like nests, often a 

 yard long, suspended from the extremity of thin twigs, being 

 useful against the attacks of snakes, which, if they attempted 

 to enter them, would be easily made to lose their hold and 

 fall to the ground. Such birds as jays, crows, magpies, 

 hawks, and other birds of prey, have also been urged as an 

 exception ; but these are all aggressive birds, able to protect 

 themselves, and thus do not need any special protection for 

 their females during nidification. Some birds which build in 

 covered nests are comparatively dull coloured, like many of 

 the weaver birds, but in others the colours are more showy, 

 and in all the sexes are alike ; so that none of these are in any 

 way opposed to the rule. The golden orioles have, however, 

 been adduced as a decided exception, since the females are 

 showy and build in an open nest. But even here the females 

 are less brilliant than the males, and are sometimes greenish 

 or olivaceous on the upper surface ; while they very carefully 

 conceal their nests among dense foliage, and the male is 

 sufficiently watchful and pugnacious to drive off most in- 

 truders. 



On the other hand, how remarkable it is that the only small 

 and brightly coloured birds of our own country in which the 

 male and female are alike — the tits and starlings — either 

 build in holes or construct covered nests ; while the beautiful 

 hangnests (Icteridse) of South America, which always build 

 covered or purse-shaped nests, are equally showy in both 

 sexes, in striking contrast with the chatterers and tanagers of 

 the same country, whose females are invariably less conspicuous 

 than the males. On a rough estimate, there are about 1200 

 species of birds in the class of showy males and females, with 

 concealed nidification; while there are probably, from an 

 equally rough estimate, about the same number in the con- 

 trasted class of showy males and dull females, with open 

 nests. This will leave the great bulk of known birds in the 

 classes of those which are more or less protectively coloured 

 in both sexes ; or which, from their organisation and habits, do 



