[35] 



are included within the hmits of three of these faunse, the Ca- 

 nadian, Alleghanian and Carohnian and a small part appears to 

 be comprised within the Louisianian. 



" In attempting to determine the number and limits of the or- 

 nithological faunEB of a large area" writes Prof. Allen " it is ev- 

 ident that the distribution of the birds in the breeding season 

 siiould be taken as tlie basis for the investigation rather than their 

 entire range, since during no other portion of the year can the 

 migratory species be regarded as being at their true homes." 

 The climate of a region is the most important factor in influ- 

 encing this distribution, but the faunal boundaries are not so often 

 the yearly isotherms as the isotheral* lines since the mean tem- 

 .perature of the breeding season must necessarily more affect birds 

 especially the migratory species than that of any other part of 

 the year. Applying these principles the Louisianian or Austro- 

 riparian fauna was provisionally considered by Prof. Allen as 

 limitetl to the northward by the isotheral line of 77 F. A con- 

 siderable district in the south-eastern portion of Virginia, princi- 

 pally comprised in the Southside Peninsula, lying between the 

 James and Nansemond Rivers and the North Carolina line, has 

 a mean summer temperature above this, but witii regard to the 

 avifauna, we must class with it also the Norfolk Peninsula and a 

 part of the Eastern Shore, or in general the country south of the 

 yearly isothermal of 60° which runs in a south-westerly direction, 

 through Eastville, Northampton County, and Hicksford, Greens- 

 ville County. 



This region of the State however cannot be regarded as quite 

 typically Louisianian in its fauna, but rather Carolinian with 

 a very decided infusion of Louisianian species, such as ^uiscalus 

 niajor^ Dendroica dominica^ Sitta pusilla^ Antrostomus caro- 

 linensis and probably several others. 



The Carolinian fauna extends from the limits of the Louisian- 

 ian to about the isotheral line of 71 which, near the latitude of 

 the North Carolina line, passes through Virginia at the approxi- 



fauna of Prof. Allen are included in an area called by Prof. Cope, the Austro- 

 riparian, while the true Floridian fauna is an ofiFshoot along the coast from the 

 tropical fauna of the West Indies. For information in regard to this subject, 

 I am indebted to Dr. C. H. Merriam. 

 *L,ines which connect places of equal mean summer temperature. 



