YELLOW HOUSE-SPARROW 65 



a great advantage over the dominant species in 

 placing its nest out of the reach of the parasitical 

 MolothrtiSf the destroyer of about fifty per cent* of 

 the Chingolo's eggs, I can only attribute the great 

 disparity in the numbers of the two species to the 

 fact that the Yellow House-Sparrow will breed only 

 (out of towns) in nests not easily taken, and to the 

 stubborn pertinacity which leads it to waste the 

 season in these vain efforts, while the other species 

 is rearing its brood. This is a blunder of instinct 

 comparable to that of the Minera (Geositta cuni- 

 cularia), mentioned by Darwin in the Voyage of a 

 Naturalist, where the bird made its hole in a mud 

 wall a few inches wide, and on coming out on the 

 other side simply went back and made another hole, 

 and then another, unable to understand that the 

 wall had not the requisite thickness* 



In such a case as the Yellow House-Sparrow pre- 

 sents, in which the colour of the sexes differs, the 

 female being without any of the brighter hues found 

 in the male, and which makes an elaborate nest and 

 lays deeply-coloured eggs, it is impossible not to 

 believe that the bird originally built in exposed 

 situations, and subsequently perhaps in very recent 

 times acquired the habit of breeding in dark holes. 

 The frequent destruction of the exposed nest, and 

 an abundance of vacant domed nests, into which 

 some individuals occasionally penetrated to breed, 

 would lead to the acquisition of such a nesting- 

 habit ; for the birds inheriting it would have an 

 advantage and be preserved, while those persisting 



