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 How to Study Birds 93

after birth, while all the great group of perching birds (Passeres) are altricial, that is, their young are reared in the nest.

It is possible, therefore, that the condition of the bird at birth may be connected with its evolutionary development; and, if this be true, birds' nests have been evolved with the birds themselves. as, in passing from przecocialism to altricialism, a nest has become a necessity,

It happens, however, that some birds admittedly low in the evolu- tionary scale are altricial and build a well-formed, substantial nest. The young of the Steganopodes, for example, are born naked; and the Water Turkey (Anbinga), Brown Pelican and often the Cormorants build large, strong nests. rhe Noddy, as Dr. Thompson shows in this number of BIRD—LURE, builds a nest which its single young may occupy for two months. The Herring Gull also builds a tree nest in some localities, which its young occupies for some period. In the latter case the Gull is said to have taken to the trees for protection from nest robbers. But it is difficult to believe that the Noddy, tame. unsophisticated breeder on keys far from the haunt of man and uninhabited by predaceous mammals, can have become a nest-builder from a similiar cause: though possibly crabs may have forced it to adopt the nestsbuilding habit. Herons and Ibises are also considered old types of birds. but they also build nests, even if rude ones, and in or on them their young exist for a time in a helpless condition.

Evidently, then. a nest may be built, whether the builder be high or low in the scale of life, when the condition of its young at birth demands a cradle in which they may live. In a number of cases, however, shelter is provided for the young without actually building a nest, but by using a natural cavity in a tree or cliff, by making a burrow in a bank, as do Kingﬁshers, or a hole in a tree, as do Woodpeckers. in each case without adding a lining or actual nest material,

We are still, it is true. far from learning the origin of the nest»building habit, nor can we do more than speculate upon it until we know whether primitive birds were przcocial or altricial. What were the young of the Archaeopteryx like? Were they active, or were they born in a helpless condition? Archaeopteryx itself was assuredly arboreal. and hence its young must sooner or later have been ﬁtted for a life in the branches. Possibly they may have clambered about shortly after birth, as do the young of the Hoatzin of South America; when the nest may have been simply a rude platform, as is the nest of the Hoatzin. It seems natural, also, to believe that many early birds deposited their eggs in holes or hollows of various kinds. It is worthy of note that, with the exception of the Hoatzin, most, if not all, truly praecocial birds nest on the ground. The Ducks that build in trees, and the Gull and Noddy before mentioned, are exceptions which in no way affect the general rule.