YELLOW HOUSE-SPARROW 65 
a great advantage over the dominant species in 
placing its nest out of the reach of the parasitical 
Molothrus, 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 
E I 
