PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 153 



mens from the Pampas, and which is the only color present in the 

 specimens identified by Dr. M. Instead, it is marked all over its surface 

 with handsome spots and blotches of a deep reddish-buff, almost 

 cinnamon in shade, completely obscuring the ground. Excepting in 

 size, it most resembles an egg of Hierofalco islandicus. — T. M. B. 



138. Falco columbarius, Linn. 



Not uncommon during winter. — (Dresser, Ibis, 1865,323. — Sennett, 

 B. Rio Grande, 42.) 



139. Falco sparverius, Linn. 



Abundant from about the middle of September until the early part of 

 April. All the specimens obtained were var. sparyeriMS, — (Sennett, B. 

 Rio Grande, 42. — Tinnunculus s., Dresser, Ibis, 1865, 323.) 



140. *Polyborus cheri-way, (Jacq.) 



A common resident, but more abundant in winter than in summer. 

 This seems to be due to a partial migration, from the north, of birds in 

 immature plumage, for the number of mature individuals does not seem 

 to vary. I do not think that the perfect plumage is acquired for at least 

 two years. I have but little to add to the many accounts already given 

 of this bird, except to say that, at times at least, it is more active than 

 some of the descriptions would lead one to infer. I have seen a Caracara 

 chase a jackass-rabbit for some distance through open mesquite chapar- 

 ral, and while they were in sight the bird kept within a few feet of the 

 animal and constantly gained on it, in spite of its sharp turns and 

 bounds. If one bird has caught a snake or field-mouse, its companions 

 that may happen to see it at once pursue, and a chase follows very dif- 

 ferent from what is seen among true Vultures. The nests are bulky 

 platforms of small branches, with a slight dei)ression lined with fine 

 twigs, roots, and grasses, or sometimes altogether without lining : they 

 are placed in trees or on the tops of bushes, at no great height from the 

 ground. Both sexes incubate. I have not found more than two eggs in 

 one nest, and these are laid at an interval of three or four days. Eleven 

 eggs average 2.28 by 1.84. The ground-color is a deep chocolate or red- 

 dish-brown, more or less thickly covered with several darker shades of 

 the same. — (P. tharus, Dresser, Ibis, 1865, 329. — P. tharus auduboni, 

 Sennett, B. Rio Grande, 42.) 



141. Elanoides forficatus, (Linn.) 



This beautiful bird I have observed on but few occasions, and do not 

 think that it breeds in this immediate vicinity. Nothing can be more 

 graceful than its mov^ements when pursuing insects, and for such a large 

 bird it is very active.— (Sennett, B. Rio Grande, 42. — Nauclerus fur- 

 catus, Dresser, Ibis, 1865, 325.) 



142. Elanus leucurus, (Vieill.) 



Seen on a few occasions, but is rare. 



