XV1 INTRODUCTION. 
young in comparative safety. Soin like manner the sombre Sand-Martin, 
for a similar reason, seeks the sand-banks. Sparrows (Passer domesticus) do 
not nest in holes because the plumage of the female demands concealment 
during the nesting-season, but from other motives, perhaps the result of a 
deeply rooted habit acquired during different conditions of life or inherited 
from a common ancestor of far more brilliant tints requiring concealment 
during the nesting-season. Again, we have the case of the Wren (Tro- 
glodytes parvulus), which builds a domed nest, and is yet one of the most 
soberly arrayed of our native birds. But this is undoubtedly from other 
motives of safety than concealment ; for from the peculiar structure of 
her nest few enemies indeed are able to storm her little citadel. Weak 
and defenceless as this little creature is, she attains by subtlety what she 
would fail to procure by prowess. The Dipper (Cinclus aquaticus) builds a 
domed nest, possibly for the purpose of shielding her eggs and young 
from the spray which so often surrounds them in her rock-bound watery 
haunts, as is also the case with a little dull-coloured Australian bird 
(Origma rubricata) which also frequents rocky streams and gullies. The 
Willow-Warblers (Phylloscopus) build domed or partially domed nests, 
perhaps because a remote ancestor built a domed nest, but more probably 
to shield their tender offspring from the moisture which surrounds their 
usual nesting-places amongst herbage or tall vegetation. The Willow- 
Warblers are an Arctic group of birds breeding in a climate subject 
to sudden changes of temperature; and this, I think, may explain their 
domed nests. As another instance we have the Owls (Strigidz), which, 
as a rule, rear their young in holes in buildings, rocks, or trees, from 
no motive of safety, but simply because they dislike the light of day, 
and naturally breed in situations which are their daily haunts. Our next 
group consists of 
Birds in which the female is duller in colour than the male, and 
which nidificate in covered nests.—This group is one of the most in- 
teresting, and furnishes convincing proofs of the truth of the theory of 
sexual selection. We will take as our first example the gay little Redstart 
(Ruticilla phenicurus). The female of this bird is dull indeed in com- 
parison with the male, yet the young are reared in all cases in a concealed 
nest in a wall, tree, or the crevice of a rock; but I can assert from 
personal observation that the bright-plumaged male assists im no small 
degree in the duties of incubation. The Pied Flycatcher (Muscicapa atri- 
capilla) is a similar instance. Others may be found in the Rock-Thrushes 
(Monticola), the Chats (Saxicola), and the Robin Chats (Thamnobia), in 
most of the species of which genera the female is far less brilliant than 
the male; nevertheless she sits in a covered nest, although we cannot. see 
any valid reason why she should require concealment during the period 
of incubation; in all cases her colours are dull and well adapted for 
