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 praecocial; those of the second, altricial. Com- 

 pare the newly hatched young of a Grouse and a Robin and we have 

 two excellent examples of praecocialism 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-reachifig, 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 praecocial. 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, 



