BREWSTER: BIRDS OF THE CAPE REGION, LOWER CALIFORNIA. 85 
they furnish a nicely graduated series connecting those most heavily barred 
with the nearly plain-tailed type of /ucasanus. As the Arizona specimens of 
calurus show quite as wide a range of variation with respect to the tail mark- 
ings as do Mr. Frazar’s birds, and as none of the other characters originally 
ascribed to Jucasanus prove more satisfactory or constant, it is evident that 
the type of this supposed subspecies represents a mere accidental or extreme 
variation of a form which, as already stated, does not normally differ in eitner 
color or markings from Buteo borealis calurus of the western United States. In 
other words, all the Red-tailed Hawks thus far found in the St. Lucas Region 
are one and the same thing, and if they are to be separated from calwrus — in 
which case they must bear the name lucasanus—it must be by size alone. 
The difference in this respect is so trifling that I cannot think it worth special 
recognition. 
None of the Lower California or Arizona specimens resemble at all closely 
B. b. socorroensis, but I have two adult birds (No. 26,206, Jan. 8, 1887 and No. 
26,207 Feb. 16, 1888) taken at Nicasio, California, by Mr. C. A. Allen, which 
differ from this form, as represented by the three U. S. Nat. Museum examples 
before me, only in having somewhat more black on the jugulum and throat 
and in being slightly larger. Another specimen (No. 24,780) in my collec- 
tion from Alamos, western Mexico, is generally similar, but has more black 
spotting on the abdomen, and the breast and thighs are deeper colored. I see 
no alternative but to refer both this and the two Nicasio specimens to socor- 
roensis. Such reference need not be prejudicial to the subspecific standing of 
the latter, for there is no reason why this bird, even if confined to Socorro 
Island during the breeding season, should not wander, at other times of the 
year, as far as Alamos, or even Nicasio. i 
B. costaricensis differs so very widely in coloring from any of the phases of 
calurus as not to require comparison in this connection. 
In the following tables of measurements no birds not fully adult (7. e. red- 
tailed) are included: — 
Buteo borealis socorroensis Ripew. 
| | ao 
2 ° co) 9 ~ 
go ashes | Ge | 
Bey ee 3 5 3 BE cs 
3 2 = == SG fo § #6 29 
a ed E 2 aise Saotg S32 28 espe 
a n = A = = = Be Of Of OF AB 
117,4991 @ Socorro Isl.,Mex. Mar. 8,’89 15.70 8.63 3.50 1.65 1.56 1.33 .85 .78 
50,7611 ff aS cs oe — — — 14.94 847 3.54 1.67 142 1.32 .85 .77 
26,2072. g Nicasio, Cal. Feb. 16,88 16.72 9.20 3.73 1.70 1.56 1.34 91 .72 
24,7802 g Alamos, Mex. Mar. 8,’88 16.31 9.06 3.67 1.67 1.55 1.26 .90 .80 
26,2062 g Nicasio, Cal. Jan. 8°87 16.02 8.90 3.54 1.70 1.70 1.38 .92 .77 
Average, 15.94— 8.85+ 3.59+ 1.68— 1.56— 1.33— .89— .77 
8 
117,500! @ Socorro Isl., Mex. Mar. 8,’89 16.76 9.53 3.80 1.95 1.73 1.43 1.03 
1 Collection U. S. Nat. Museum. Type, 50,761. 
2 Collection William Brewster. 
