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 

 praecocialism 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 {Anhinga) , Brown Pelican and often the Cormorants build large, 

 strong nests. The Noddy, as Dr. Thompson shows in this number of 

 Bird-Lore, 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 nest -building 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 prascocial 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 prscocial birds nest on the ground. 

 The Ducks that build in trees, and the Gull and Noddy before mentioned, 

 are exceptions which in no way afifect the general rule. 



