National Museum, 9; Philadelphia Academy, 13; Boston Society, 8; Museum,
Cambridge, 15; Cab. G. N. Lawrence, 3; Coll. R. Ridgway, 2. Total, 50.
The true _Buteo borealis_, as restricted, may always be distinguished
from the var. _calurus_, its western representative, by its having the
posterior lower parts (tibiæ and lower tail-coverts) entirely free
from transverse bars, and by lacking indications of transverse bars on
the tail, anterior to the conspicuous subterminal one. It differs from
the var. _costaricensis_, in having the head and neck conspicuously
striped with rufous, and the throat thickly striped with black, almost
obliterating the white; in the conspicuous abdominal belt of large black
spots, and in having the tibiæ lighter ochraceous than the breast;
from the var. _lucasanus_ and var. _krideri_, it is distinguished by
having the black tail-band, more spotted under parts, and in the upper
tail-coverts being white, banded with rufous, instead of plain white, or
deep rufous, uniform with the tail.
A specimen (No. 1,750, Carlisle, Pa.; S. F. Baird) appears at first
sight much like the var. _calurus_, being very dark; the tibiæ, anal
region, and the lower tail-coverts are, however, not barred as in this,
and the tail possesses but the subterminal band.
An immature specimen (No. 21,488; John Krider) from Philadelphia has the
tibiæ quite distinctly barred, but less conspicuously so than in young
of var. _calurus_.
Var. krideri, HOOPES.