124 FALCONID^. 



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. Duges 29 and Sumichrast *8 state that T. 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 northern 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 ^^ ; 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 ^^ ^^. 



Subfam. POLYBORIN^. 



This is another purely American subfamily of Falconidae, with some affinity to the 

 Falconinee, 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 Falconidae,' defined four genera of 

 Polyborinse, dividing Phalcolmnus 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. 31 ; 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 Ibycter) by certain 

 well-ascertained characters. The proportions of the tarsus and the middle toe and 



