124 FALCONIDE. 
Mr. Witmer Stone met with specimens up to an elevation of 10,000 feet. Grayson 
records the species from the Tres Marias Islands, but Mr. Nelson did not observe 
it there. Dugés29 and Sumichrast 4® state that 7. sparverius is generally distributed 
in Mexico between October and April. 
In habits the American Kestrel resembles its European congener, and frequently 
hovers in the air when in search of prey. Its food consists principally of insects, 
especially grasshoppers, also small rodents, lizards, &c.; but during the stress of the 
breeding-season, and in severe winters in more nortbern localities, when insect-food 
fails, it occasionally kills birds. 
In the absence of trees, the clefts and ledges of rocks are inhabited for breeding- 
purposes, but, where trees exist, the hollows formerly frequented by Woodpeckers 
are often used; occasionally, however, fresh nests composed of twigs and leaves are 
built 14; it is but seldom that those deserted by other birds are utilized, as is the case 
with its European ally. 
The eggs are usually four or five in number, though seven have been found; they 
vary from cream-colour to bright cinnamon, and also in the intensity and distribution 
of the brown or rufous markings 4°. 
Subfam. POLYBORINA. 
This is another purely American subfamily of Falconide, with some affinity to the 
Falconine, but also with wide differences of structure and habits. Most of the genera 
belong to South America, some of them spreading as far north as Guatemala, Polyborus 
itself ranging into the Southern States of the Northern Continent. 
Mr. Ridgway, in his ‘ Systematic Analysis of the Falconide,’ defined four genera of 
Polyborin, dividing Phalcobenus and Ibycter each into two subgenera. From his 
differential characters we select the following :—“ Posterior toe abbreviated, very much 
shorter than the lateral pair; tarsi and toes covered with small hexagonal scales, larger 
in front. Nostril small, round or oblique, with a bony-rimmed margin and central 
tubercle. Tomia with or without a small tooth or notch. Superciliary process of the 
lachrymal abbreviated, reaching only halfway across the orbit. Posterior margin of the 
sternum with a pair of deep indentations. Three or more outer primaries sinuated 
near the middle portion.” 
POLYBORUS. 
Polyborus, Vieillot, Anal. p. 22 (1816) ; Sharpe, Cat. Birds Brit. Mus. i. p. 81; Ridgw. Bull. 
U. S. Geol. & Geogr. Surv. i. pp. 451-460 (1876). 
Following Mr. Ridgway’s classification, we find that Polyborus can be separated from 
the other Central-American genera of Caracaras (viz. Milvago and Jbycter) by certain 
well-ascertained characters. The proportions of the tarsus and the middle toe, and 
