I OA Allen, Origin and Distribution of N. A. Birds. X April 



return of birds to the same locality — even to the same nesting 

 site — for many successive years. There is so much indubitable 

 proof of this, that it is commonly assumed as the rule in most 

 species. It is certainly beyond question that birds do not select 

 their breeding stations in any hap-hazard way, journeying north 

 along a vague course and stopping to nest wherever the proper 

 conditions of season and other surroundings happen to prove 

 favorable. Hence the impulse that governs their spring move- 

 ments has been loosely termed the 'home instinct.' 



If we consider that migration consists really of two move- 

 ments — that is from the breeding station to the winter quarters 

 and then back again — and that the one movement is the necessary 

 complement of the other, it is hardly necessary to seek for a 

 separate cause for the two movements ; the two together consti- 

 tute migration in a complete sense, which, as already explained, 

 is an inherited habit, — an inherent, irresistible impulse, closely 

 blended with the function of reproduction. The promptings 

 which lead to the migratory movement, respectively in fall and 

 spring, have unquestionably a different origin ; the autumnal 

 movement being doubtless prompted by a reduction of tempera- 

 ture and a failing food supply, while the spring movement is 

 incited by the periodic activity of the reproductive organs, result- 

 ing in the necessity for the return of the species to the peculiar 

 conditions and surroundings to which for long ages it has been 

 undergoing special adaptation — in other words, to its home. 



In the present paper, North America is considered in its faunal 

 rather than its geographical sense, and in the synopsis here 

 following the area covered by the A. O. U. Check-List and its 

 Supplements is the region mainly considered, namely, North 

 America north of Mexico, but including the peninsula of Lower 

 California. The number of species now recognized in the A. O. 

 U. Check-List as occurring within this area is about 795' with 

 nearly 270 additional subspecies, making a total of about 1065 

 species and subspecies. These are arranged under 303 genera, 

 with about 65 additional subgenera. Of these, however, 75 

 species and 25 genera occur merely as accidental stragglers from 

 the Old World, the West Indies and Mexico. Deducting these 

 as not valid components of the North American fauna, leaves 

 about 720 species and 278 genera as legitimately North American, 

 under the present restriction of the term. In the following 



