490 J - A - ALLEN ON BIRDS 



some time since separated, in a general way. into the Canadian, Alleghanian, and Louisianian, 

 fauna? and florae, which divisions later special investigations of the subject tend to support 

 whether with regard to the distribution of plants, mammals, birds, reptiles, or insects. 1 The 

 several avi-faunse already definitely recognized seem to be characterized in part by the abun- 

 dant occurrence, in the breeding season, of the following species : Commencing with Florida, 

 the southern portion of it is clearly West Indian in its affinities, through the presence espe- 

 cially of Quiscalus agelceus, Tyrannus dominiceiisis, Coccygus minor, Crotophaga nigirostris, Zenceda 

 amaUUs, Asturina nilida, Polyborus tharus, Phenicopterus ruber, etc. The Louisianian by Peuccea 

 cestivalis, Cyanospiza ciris, Pyranga cestiva, Antrostomus carolinensis, Quiscalus major, Collyrio ludo- 

 vicianus, Chamcepelia passerina, Elanus leucurus, Ictirm mtsmrippiensis, etc. The Alleghanian has 

 but few if any species that do not occur either in the Louisianian or Canadian, though 

 differing widely from either in the association of the species. Many that breed abundantly 

 here, but do not in the Louisianian, breed also in the Canadian, while many others that 

 breed here breed also in the Louisianian, but not in the Canadian. Of the first class we 

 may mention Tardus migratorius, Turdus fuscescens, MniotiUa varia, Hirundo ( Tachycincta ) bicolor, 

 Hirundo ( Petrochelidon) lunifrons, Qidscalus versicolor, Tringoides macularius, Pipilo erythrophihalr 

 mus, Chordeiles popetue, etc. ; of the second : Icterus spurius, Icteria virens, Dendrosca discolor (?), 

 Colurnicidus passcrinus, Euspiza amcricana, Ortyx virginiana, etc. Of the Canadian, Turdus Pal- 

 lasi, T. Swainsoni, a large proportion of the Dendrcecce, Spizella monticola, Junco hyemalis, Passe- 

 rella iliaca, Zonotrichia leucophrys, Z. albicollis, Scolecopliagus ferrugineus, Parus hudsonicus, Picoides 

 arcticus, Astur atricapillus, Tetrao (Canace) canadensis, and a considerable list of others. Of 

 the Hudsonian or Sub-arctic, Lagopus albus, Archibuteo lagopus, Colymbus scptcnlrionalis, Sum- 

 materia mollissinia, S. spectabilis, Histrionicus torquatus, Graculus dilophus, and several others, mostly 

 aquatic and marine. A few others, chiefly circumpolar marine birds, will characterize a still 

 more northern or the Arctic fauna. From the above it will be seen that the Alleghanian 

 fauna differs from the others in having few if any species peculiarly its own, forming, as it 

 were, transitional ground between the two adjoining it. It is here, too, — but perhaps only 

 because the region is better known, — that as we advance from the south northward, species 

 are seen so conspicuously to fade out one after another at frequent intervals throughout 

 the whole area, though in greater numbers relatively near its boundaries. 



From the facts at .command, the division between the West Indian fauna in Florida and 

 the Louisianian seems to coincide nearly with the line of mean temperature of 79° F. for the 

 months of May, June, and July ; 2 between the Louisianian and Alleghanian, nearly with that 

 of 72° for the same time ; between the Alleghanian and Canadian, nearly with that of 65°; 

 between the Canadian and Hudsonian or Sub-Arctic, nearly with that of 56°. The line of 

 72° for the northern limit of the Louisianian fauna embraces the low lands of the coast as 

 far as Cape May, and perhaps farther north, but, running a few miles only into the interior, 



l Comrneneinn' our investigations without reference to what 2 We prefer to take the months of May, June, and July 



had been done previously, and with the question, " Do physical rather than April, May, and June, since but few species, com- 



causes really influence the distribution of animals and plants?" paratively, breed so early as April, especially north of the 



our study thus far but corroborates the general views on this Louisianian fauna, while the breeding season with many spe- 



subject already advanced by others (see especially Prof. Verrill, cies, and especially at the northward, continues through July, 



on the causes that influence the distribution of birds in latitude, and in some species still later. 

 1. a). The results of a detailed study of the available data on 

 the distribution of American birds we hope to be able to pre- 

 sent at no distant day. 



