38 NORTH AMERICAN FAUNA. 



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



Measuremenis of Jiuteo horeaVia fumosua and Buteo b. socorroensis. 



Falco peregrinus anatum (Bon.ip. ). Duck Hawk. 



Falco pereyrinus var. iiigriceps liraysou, Proc. B().ston Soc. Nat. Hist.. XIV, ji. L'()8, 

 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 ilid 

 not see this species during our visit to the islands. 



Falco 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 Daudin. White-tbroated Falcon. 



Eypotriorchia rvUgularis Grayson, Proc. Boston Soc. Nat. Hist., XIV, ]>. 269. 1871 ; 

 Lawr., Mem. Boston Soc. N.at. 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 cheriwray pallidus Nelson. Tres Marias Caracara. 



Vohjhorus audiibonii Grayson, Proc. Boston Soc. Nat. Hist.. XIV, ]>. 268, 1871, 



'(part). 

 Poliiborua tharus var. auduhoni Lawr., Mem. Boston Soc. Nat. Hist., II, p. 303, 



1874, (part). 

 I'dlijboriia clierin-aii pnllidio. 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 Mailre were 

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

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



