THE CONDOR 
Von XII 
68 
described as A. ft hoc nice us neutralis , and shows black innermost coverts with some 
slight tipping and spotting on the others. Now what are we going to call the 
middle bird from Stanislaus County ? The Marin County bird has a slightly smaller 
bill than the other two in this photograph, but many specimens overlap in measure- 
ments, which intergrade just as much as the coverts in the males and the streakings 
in the females. (See Fig. 23.) 
In these tables the principal measurements are the wing and bill measure- 
ments. While the former is not to be altogether depended upon I have used it to 
some extent, discarding those cases where the primaries seemed to be so badly worn 
as to be valueless for comparison. I have included the tail, but this was no criterion 
of any great value, and in the breeding season is generally very badly shortened by 
wear. The birds from Stanislaus County show a peculiar thickness of the upper 
Fig. 23. THREE mates OF AGELAIUS IETUSTRATING THE VARIATION IN THE MARKINGS 
OF THE TESSER WING COVERTS 
mandible in most cases, and I have endeavored to show this in the form of a meas- 
urement by taking the width of the bill at the center of the culmen. In order to do 
this a little instrument was rigged up, with a horizontal ring which could be raised 
or lowered above a plane surface, to which it was parallel, by means of a screw, the 
ring being adjusted at half of the culmen as each individual was measured, the bill 
inserted perpendicularly therein and the width taken by means of a parallel ruler, 
so arranged that the sharp edges faced each other, laid flat on top of the ring with 
the bill between the thin edges. As the bills of this species vary so greatly this 
measurement does not exactly express the differences in heaviness it was intended 
to show, but it helps to give the idea. 
The depth or width of a bill from base is a difficult matter to obtain correctly 
in bills that are of such conical shape as in Agelaius, and probably no two persons 
would get exactly the same figures, but with care they would come very near doing 
