224 
SEXUAL SELECTION: BIRDS. 
Part 1 
nearly tlie same dangers. It is therefore probab^ 
that strongly-pronounced colours have been acquit 
by tree-haunting birds through sexual selection, b° 
that green tints have had an advantage throws , 
natural selection over other colours for the sake 0 
protection. 
In regard to birds which live on the ground, ev' eT -' 
one admits that they are coloured so as to imitate t' 1 *' 
surrounding surface. How difficult it is to see a P 8 j 
tridge, snipe, woodcock, certain plovers, larks, 
night-jars when crouched on the ground. Animals J”' 
habiting deserts offer the most striking instances, for ^ 
bare surface affords no concealment, and all the 
quadrupeds, reptiles, and birds depend for safety ^ 
their colours. As Mr. Tristram has remarked, 6 ' 
regard to the inhabitants of the Sahara, all are Py| 
tected by their “ isabelline or sand-colour.” Calli°p 
my recollection the desert-birds which I had seen 1 
South America, as well as most of the ground-b )r ^ 
in Great Britain, it appeared to me that both s e * 
in such cases are generally coloured nearly alike. •“ 
cor lingly I applied to Mr. Tristram, with respect to 1 
birds ot the Sahara, and he has kindly given m e . ^ 
following information. There arc twenty-six sp et !' j 
belonging to fifteen genera, which manifestly have 1 
their plumage coloured in a protective manner ; ‘‘ l ^ 
this colouring is all the more striking, as with ^ 
ot these birds it is different from that of their 
geners. Both sexes of thirteen out of the tweidf^ 
species are coloured in the same manner ; but t 1 
belong to genera in which this rule commonly P 
vails, so that they tell us nothing about the protc c ^ 
colours being the same in both sexes of desert- bird 15 ' 
‘ Ibis, 1859, vol. i. p, 429, et seq . 
J 
