270 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I50 



These hawks frequent low perches in the undergrowth, where they 

 remain concealed and usually slip away unseen at any approach. As 

 stated above, their presence is known mainly through their call, a 

 querulous, single note, sometimes a low keh-h-h and at others a 

 louder keow, repeated at short intervals, most commonly in early 

 morning at sunrise or soon after. I have found it useless to attempt 

 to stalk them as they fly so noiselessly and low that they may not 

 be seen. When I have been calling small birds one of these falcons 

 has come frequently to perch near at hand, though they remain shy 

 and fly into cover at any sudden movement. It appears that they hunt 

 to some extent on the forest floor as occasionally I have seen them 

 fly up from such situations. Immature birds are seen sometimes 

 on open perches where they afford a clear view. In such circum- 

 stances their color and color pattern invariably suggest the much 

 larger collared forest- falcon. 



They appear to feed mainly on small birds and to some degree on 

 lizards. Worth (Auk, 1939, p. 310) saw one take a nestling blue- 

 black grosbeak from the nest. Jewel (Stone, Proc. Acad. Nat. Sci. 

 Philadelphia, 1918, pp. 248-249) found remains of slugs, batrachians, 

 and small lizards in the stomach of one taken near Gatun. 



The variations in this species from the gray-backed populations of 

 the north to the brown birds of the south are highly interesting. With 

 considerable more material than was available to Hellmayr and 

 Conover (Cat. Birds Amer., pt. 1, no. 4, 1949, pp. 249-252) it appears 

 to me to be appropriate to recognize two races in the area from 

 Mexico to northern Colombia. While there is some variation, adult 

 birds from southern Mexico to Nicaragua have the dark barring 

 spaced more widely on the posterior lower surface, so that they appear 

 whiter, and also usually have more or less of a cinnamon wash on 

 the f oreneck and upper breast. These are Micrastur ruficollis guerilla 

 Cassin. Adults from Costa Rica and Panama through western Colom- 

 bia to western Ecuador, the race inter stes, have the black barring un- 

 derneath more evenly spaced throughout, average darker above, and in 

 only an occasional individual is there a cinnamon wash on the fore- 

 neck. 



A few individuals throughout the entire northern area of the 

 range, that includes both these races, display a faint brownish tinge on 

 the head and back, a hint of the fully brown coloration in these areas 

 that prevails through the main part of the South American range. 



