PREEAGE 
OrnitHoLoGy is the science of birds (Gr., opwdos, ornithos, of a bird; Adyos, logos, 
a discourse), and to become an expert ornithologist requires years of hard work, com- 
bined with a love for the study itself; but there are many students of nature who 
would like to know the birds about them, but do not have the time nor desire to go 
deeply into the subject. To meet such a want, the present ‘* keys” have been pre- 
pared, in which the species are grouped according to size, and it is believed they will 
enable the novice to accurately identify any of our birds. 
‘areful comparison of large series of birds has shown that while adult birds of 
the same species differ considerably in length, the wing measure is very constant, the 
variation in a large number of specimens being so small that, allowing for possible 
extremes, we may safely arrange our birds in groups according to length of wing. 
A Song Sparrow may vary slightly in size, but the largest Song Sparrow is never as 
large as the smallest adult Robin, and vice versa. By grouping the various birds from 
the Humming Bird to the Eagle and Albatross, according to the length of wing (allow- 
ing, of course, for unusual extremes), the identification of any species then becomes a 
comparatively simple matter, as usually the birds contained in each group are so few 
in number that characteristic differences in each species are easily indicated. 
Let us, for example, assume we have a bird before us which we wish to identify ; 
we first should find out to which family it belongs. Turning to the Key to Families, 
page 10, we find this an easy matter (as the families are few and the illustrated differ- 
ences in the bills and feet very characteristic), we discover our bird to be a duck. 
Having ascertained the family to which our bird belongs, we turn to the Key to 
Species. We have, of course, measured the wing and found it to be 5.90 inches long, 
measured from the carpus (bend of wing) to tip. (See illustration, ‘* How to Measure 
a Bird,” on page 8.) 
We now turn to the Ducks, and discover they are divided into subfamilies, the 
say and Sea Ducks having a flap or lobe on the hind toe, and the fresh-water ducks, 
or River and Pond Ducks, have no large flap on the hind toe. Our bird has a flap on 
its hind toe, and is evidently a salt-water duck, belonging to the subfamily Fuliguline. 
This subfamily, we find, contains two sections. Section 1 having the tail feathers 
(Vv) 
