38 NORTH AMERICAN FAUNA. 



Below are averages showing the relative size of the two island forms: 



Measurements of Buteo borealls fumosus and Buteo b. socorroensis. 



Falco peregrinus anatum (Bonap. ). Duck Hawk. 



Falco peregrinus var. nigriceps Grayson, Proc. Boston Soc. Nat. Hist., XIV, p. L>68, 



1871. 



A single duck hawk was taken by Colonel Grayson, who mentions 

 that it was shot while in close pursuit of a sparrow hawk. We did 

 not see this species during our visit to the islands. 

 Palco sparverius Linn. Sparrow Hawk. 



The sparrow hawk was recorded from the islands by Colonel Gray- 

 son, but we did not see a single individual, and it probably occurs 

 merely as a straggler. 

 Falco columbarius Linn. Pigeon Hawk. 



Colonel Grayson records this species as very common upon the 

 islands. Not a single individual was seen by us, and it probably 

 occurs only as a winter visitant or stray migrant. 

 Falco albigularis Daudm. White-throated Falcon. 



Hypotriorchis rufigularis Grayson, Proc. Boston Soc. Nat. Hist., XIV, p. 269, 1871; 

 Lawr., Mem. Boston Soc. Nat. Hist., II, p. 301, 1874. 



Colonel Grayson took a specimen of this fine little falcon on the 

 islands. None were seen by us, and it must, no doubt, be classed as 

 one of the numerous accidental visitants from the mainland. 



Polyborus cheriway pallidus Nelson. Tres Marias Caracara. 



Polyborus audubonii Grayson, Proc. Boston Soc. Nat. Hist.. XIV, p. 268, 1871, 



"(part). 

 Polyborus tharus var. auduboni Lawr., Mem. Boston Soc. Nat. Hist., II, p. 303, 



1874, (part). 

 Polyboriis cheriway pallidus Nelson, Proc. Biol. Soc. Washington, XII, p. 8, 1898. 



Very abundant about the settlement on Maria Madre and rather 

 commonly distributed elsewhere over the island. They were also 

 rather common on the other islands, including San Juanito. The old 

 log roads and dry bottoms of the canyons on Maria Madre were 

 favorite resorts. The birds were met in many unexpected places, and 

 were frequently seen perched in tree tops in the midst of the unbroken 



