ELEVENTH ANNUAL REPORT. GT 
genera of owls. Divided among these are twenty species and 
twenty-two sub-species, or geographical races, making in all forty- 
two different forms. These genera are as follows, with the number 
of forms in parentheses: 
A. SUB-COSMOPOLITAN. 
Strix—Barn Owls (1). Otus—Screech Owls (13). 
Asio—Long- and Short-eared Bubo—Great Horned Owls (6). 
Owls (2). Glaucidium—Pygmy Owls (4). 
Syrnium—Barred Owls (5). 
B. CIRCUMPOLAR. 
Scotiaptex—Great Gray Owls (2). Nyctea—Snowy Owls (1). 
Cryptoglaux—Saw-Whet Owls (3). Surnia—Hawk Owls (2). 
Cy (CONEINEDETLOrRAE NEW WiORED: 
Speotyto—Burrowing Owls (2). Micropallas—Elf Owls (1). 
In tracing the distribution of these dozen groups we find that 
they fall naturally into the three classes A, B, and C. 
Owls have become so well adapted to their peculiar mode of life, 
and are so well protected from strenuous competition with other 
forms, that they have changed but little throughout, perhaps mil- 
lions of years. In the geological periods of the Oligocene and Mio- 
cene, a temperate climate existed as far north as Alaska and Green- 
land, and this, with the land bridge which joined North America 
to Asia, explains the large proportion of cosmopolitan genera of 
owls, Class A. If we may judge by the distribution of insects 
and mammals, the trend of diffusion across this northern con- 
tinental isthmus was chiefly from Asia into North America and 
rarely in the reverse direction. In a strict geographic sense the 
continental mass of North America is still connected with Asia, 
as the continental shelf unites the two, and a rise of the sea 
bottom of only two hundred feet would result in a dry land bridge 
between the Old and the New World. We can but theorize as to 
the early distribution of these owls, it being impossible without 
paleontological evidence, to indicate the center of origin of genera 
which are cosmopolitan. 
The Circumpolar species, Class B, also doubtless inhabited 
North America during these early periods. Later, in the Pleis- 
tocene, all were forced southward by the onward march of the 
