122 The history of birds' nests.


Was the tucking in of loose ends the first step towards this

accomplishment ?


The building up of the sides of a cup-shaped nest was probably

the first step towards the construction of over-arched nests, in which

only a comparatively small opening is left in front, this over-arching

being due to an effort to protect the parents, eggs and young against

inclement weather, the fall of undesirable matter into the nest and

attacks from above ; the addition of a tube leading into the opening

was almost certainly a later development, since it is frequently

wanting in nests built by captive birds.


In the case of some birds which nest in holes where the

opening is so wide as to be a source of danger to the occupants, as,

for instance, in that of the Nuthatches, the entrance is filled up with

clay, leaving only a small aperture for the entrance of the parents.

The Hornbills go even farther, for the hen is imprisoned by a resinous

secretion commingled with woody particles (before the period of

incubation and for two or three w 7 eeks after the hatching of the

young), a slit only being left in front through which the male bird

feeds her. The origination of this kind of defence does not require

any great intellectual development, since we note analogous means

adopted for protection by the larvae of some insects, as, for instance,

those of the Psychid moths* and Caddis-flies ( Phrygctneidce ).


When caves became insufficiently numerous to house our savage

ancestors, or when they migrated from the vicinity of such shelters,

it became necessary for them either to burrow in the sides of hills

or construct huts of clay: with birds in all probability a similar

course was adopted. This would account for the solid nests built

by the Oven-birds of the New World and the Pied Grallina of

Australia, as well as by the numerous birds which inhabit burrows.

In the Swallows we find both types, those species which construct

the outer walls of their nests of mud or clay being, I should judge,

more advanced intellectually than the burrowing species, since

Trap-door Spiders, with their marvellous silk-lined burrows closed

at the entrance by a hinged and bevel-edged lid, show far more

intelligence.


* I think the popular name for these in English is Gipsy, but in America they are


called Bag-worms.



