CHARACTER OF THE NEST 
75 
particularly if the temperature is much below the average, is a factor 
here. In some species, notably the Long-billed Marsh Wren, the nest- 
building instinct does not seem to be satisfied by the making of a single 
structure, and the male continues his work after the female is sitting, 
building one or more additional homes in which possibly he may sleep, 
and which are sometimes called ‘cock-nests.' 
Character of the Nest . — From an architectural point of view, nests 
may differ greatly even when the material of which they are composed 
is the same. The tools (bill and feet) with which a bird is provided do 
not often bear any relation to the character of the home their owner 
builds. A Swallow, it is true, could not construct a Woodpecker's 
dwelling; but a momentary comparison of the widely different kinds 
of nests built by various species of Swallows and Swifts (which so far 
as nesting tools are concerned may be classed with Swallows), readily 
shows how little the structure of the bird has to do with nest archi- 
tecture. 
Most of the causes determining the nature of site and material 
are also more or less active in shaping the nest itself, but of them all 
by far the most important is the condition of the young bird at birth. 
Indeed in considering this question we are brought very near to an 
inquiry concerning the origin of birds’ nests. 
As regards their condition when leaving the egg, birds may be 
roughly classified in two groups: First, those which leave the nest shortly 
after hatching; second, those which are reared in the nest. Birds of 
the first class are termed prsecocial; those of the second, altricial. Com- 
pare the newly hatched young of a Grouse and a Robin and we have 
two excellent examples of prsecocialism and altricialism; while a further 
comparison of the Grouse's simple bed of leaves with the Robin’s 
firm, deep cup of mud and grasses equally well illustrates the difference 
in the nests of prsecocial and altricial birds. The former serve only to 
hold the eggs, the latter perform not only this function but must also 
house the young during their period of helplessness. 
The significance of the condition of the young at birth is doubtless 
far-reaching, but unfortunately, it is not as yet understood. It appears 
that most of the older or lower forms of birds — that is, those which 
most closely approach the reptilian types, whence it is believed birds 
have descended — are prsecocial. On the other hand, all the higher 
birds, that is those farthest removed from reptilian ancestors, are 
altricial. For example, among North American birds the Grebes, 
Loons, Gulls, Terns, Ducks, Rail, Coots, Snipe, Plover, Quail, and 
Grouse, are prsecocial, and build, as a rule, nests of the most rudimen- 
tary kind, while the great group of Perching Birds (Passeres), con- 
taining half the known birds, are altricial, and all build more or less 
complex nests. 
It is possible, therefore, that as altricialism has been evolved from 
prsecocialism, so the type of nest has changed, keeping pace with the 
demands which the young birds make upon it. There are, however, 
