Vol. XXIII I 

 1906 J 



Jenkins, Variation in the Hairy Woodpecker. 



171 



greatly doubt if aridity and humidity has anything to do with the 

 wing spotting. We might say that the more highly developed 

 form has had more enemies and more competition, but such a 

 statement needs yet to be proven. 



As for the darkening of some colors of birds, it has been said 

 that it is an advantage in any humid region where there is a great 

 deal of shade. So we find the range of the darkest woodpecker 

 (J), v. Jiarrisi) exactly coinciding with that region of North Amer- 

 ica which has the greatest total shade, namely the Pacific Humid 

 Coast Belt. D. v. jardini is said to inhabit an extremely humid 

 region in southern Mexico, but scarcity of data from that region 

 prevents forming definite conclusions in regard to it. 



If we draw geographical lines separating forms of equal size, 

 these lines will nearly coincide with parallels of latitude. Very 

 likely either the more rigorous climate of the north has eliminated 

 all birds except the larger and hardier, or else there is a direct 

 physical effect on the individual causing it to grow larger. 



It is a strange fact that the Downy Woodpeckers vary exactly 

 as the Hairy in size, wing spotting and coloration, and for every 

 continental form of the Hairy Woodpecker north of Mexico there 

 is a corresponding form of the Downy. In Mexico the latter is 

 not found. 



Averages of Measurements (in Millimeters) of the Forms of Dryobates 



VUlOSUS, TAKEN ONLY FROM SPECIMENS EXAMINED BY THE AUTHOR. 



1 California north of 35° N. Lat. 



2 Except California north of 35° N. 



Lat. 



