408 Vniversity of California Publications in Zoology [Vol. 21 



These modifications in the flight equipment of the nuthatches of 

 the San Pedro Martir plateau, it may be suggested, have been devel- 

 oped as a result of long existence in the very open type of forest there 

 prevalent; the individual trees are far apart as compared with the 

 forest stands in which White-breasted Nuthatches live in Upper Cali- 

 fornia. This necessitates more extensive flights from tree to tree in 

 the usual course of foraging; and numerous studies have shown that 

 "sharpness" as well as length of wing and length of tail vary in 

 direct correlation with extent of flight, whether in migration or in 

 day-by-day foraging. 



The only other race of Sitta carolinensis known to exist in Lower 

 California is S. c. lagunae Brewster (1891, p. 149), restricted to the 

 Sierra de la Laguna, which are included within the Sierra de la 

 Victoria in the Cape district of the Peninsula. Some six hundred 

 miles of forbidding country intervene between the ranges of alex- 

 andrae and lagunae; and both races, so far as known, are of fixed 

 residence throughout the year — absolutely non-migratory. These cir- 

 cumstances are significant in view of the sharp distinctions which 

 obtain between these two forms, greater in aggregate amount, indeed, 

 than between alexandrae and aculeata. Lagunae differs from alex- 

 andrae in much smaller size, relatively thicker as well as shorter bill, 

 darker toned, more leaden-hued sides and flanks, lesser white-tipping 

 on inner primaries, less extensive subterminal white patches on outer 

 rectrices, and much narrower black tips to outer rectrices. This latter 

 feature alone, judging from the material I have examined, by itself 

 is perfectly diagnostic of lagunae among all the eight races of Sitta 

 carolinensis now recognized. In certain respects (shape of bill, color 

 of sides and flanks) lagunae resembles nelsoni and mexicana, of the 

 Rocky Mountain region of the United States and Mexico, rather than 

 alexandrae and aculeata of the Pacific Coast region to the northwest. 



Referring to aculeata again, the nearest point, from which I have 

 seen examples, to the Sierra San Pedro Martir, is the Cuyamaca 

 Range, in San Diego County, California. Several specimens from 

 that locality (including males nos. 3958, 3961, Mus. Vert. Zool.) do 

 not depart appreciably from aculeata toward alexandrae, as might 

 be expected. In all the critical characters they are essentially 

 aculeata, and do not in themselves constitute "intergrades" between 

 that race and alexandrae. In other words, there is likely a consider- 

 able hiatus between the southernmost point in the geographical range 

 of aculeata and the northernmost point in that of alexandrae. To 



