g NORTH AMERICAN BIRDS. 



maritime portions of the United States, the European representatives of both 

 species being generally distributed throughout that continent. On the other 

 hand, the northwest-coast race of our Scops asio {S. hennicotti) seems to be 

 nearly identical with the Japanese aS'. semitorques (Schlegel), which is un- 

 doubtedly referrible to the same species. 



As regards their plumage, the Owls differ most remarkably from the 

 Hawks in the fact that the sexes are invariably colored alike, while from 

 the nest to perfect maturity there are no well-marked progressive stages 

 distinguishing the different ages of a species. The nestling, or downy, 

 plumage, however, of many species, has the intricate pencilling of the adult 

 dress replaced by a simple transverse barring upon the imperfect downy 

 covering. The downy young of Nyctea scandiaca is plain sooty-brown, and 

 that oi Strix Jiammea immaculate wliite. 



In many species the adult dress is characterized by a mottling of various 

 shades of grayish mixed with ochraceous or fulvous, this ornamented by a 

 variable, often very intricate, pencilling of dusky, and more or less mixed 

 with white. As a consequence of the mixed or mottled character of the 

 markings, the plumage of the Owls is, as a rule, difficult to describe. 



In the variations of plumage, size, etc., with differences of liabitat, 

 there is a wide range, the usually recognized laws ^ applying to most of 

 those species which are generally distributed and resident where breeding. 

 Of the eight species common to the Palsearctic and Nearctic Eealnis, all but 

 one {Otus hrachyotus) are modified so as to form representative geographical 

 races on the two continents. In each of these cases the American bird is 

 much darker than the European, the brown areas and markings being not only 

 more extended, but deeper in tint. The difference in this respect is so tan- 

 gible that an experienced ornithologist can instantly decide to which con- 

 tinent any specimen belongs. Of the two cosmopolitan species one, Otus 

 hrachyotus, is identical throughout ; the other is modified into geographical 

 races in nearly every well-marked province of its habitat. Thus in the 

 Palsearctic Realm it is typical Strix Jiainmea ; in the Nearctic Realm it is var. 

 pratincola ; while Tropical America has at least three well-marked geo- 

 graphical races, the species being represented in Middle America by the var. 



entirely restricted to the western portion, or else are much more abundant there than in the 

 east. Tlie European genera Cinclus, Coccothraustes, Nucifraga, and Columba have representa- 

 tives only in the western portion of North America. 



Instances of a similar relation between the plants of the Western Province of North America 

 and those of Eurojie, and more striking likeness between the flora of the Eastern Region and 

 that of Ea.stern Asia, are beautifully explained in Professor Gray's interesting and instructive 

 paper entitled "Sequoia, and its History," an address delivered at the meeting of the American 

 Association for the Advancement of Science, at Dubuque, Iowa, August, 1872. The poverty in the 

 species of tortoises, and richness in lizards, and the peculiarities of the ichthyological fauna, as well 

 as absence of forms of Western North America and Europe, compared with Eastern North America 

 and Eastern Asia, aff'ord other examples of parallelism in other classes of the Animal Kingdom. 



1 See Baird, Am. Journ. Arts and Sciences, Vol. XLl, .Ian. and March, 1866 ; Allen, Bull. 

 Mus. Comp. Zobl. Cambridge, Vol. II, No. 3 ; and Ridgway, Am. Journ. Arts and Sciences. 

 Vols, IV and V, Dec, 1872, and Jan., 1873. 



