152 ON THE GEOLOGY AND NATURAL HISTORY 
Fatco ANATUM, Bonaparte. 
Duck Hawk. Baird, General Report on Birds, p. 7. 
This very rare bird in the West was killed on the Vermilion river in the autumn of 
1856. No other specimen was obtained by our Expedition, and the above locality is the 
most western range yet known of this bird. 
HYpoTrRIORCHIS COLUMBARIUS, Gr. 
Pieron Hawk. Baird, General Report on Birds, p. 9. 
One of the most common and abundant birds in the Northwest. It is usually found 
along the woody bottoms of streams, where it may be seen in large numbers perched upon 
the dry limbs of trees apparently watching for its prey. 
FALCO POLYAGRUS, Cassin. 
Prarie Fatcon. Baird, General Report on Birds, p. 12. 
Is found at various localities along the Missouri, though not abundant. It also occurs 
on the Platte. 
‘TINNUNCULUS SPARVERIUS, Vieill. 
Sparrow Hawk. Baird, General Report on Birds, p. 18. 
One of the most abundant birds on the Upper Missouri. It is very common along the 
woody bottoms of the Missouri and Yellowstone, where it may be seen at all hours of the 
day darting from tree to tree or sitting upon some dry limbs almost motionless watching 
for its prey. Its an exceedingly noisy and saucy bird, often provoking a shot from the 
hunter when silence would have enabled it to have escaped unnoticed. 
AcciPiteR Mexicanos, Swains. 
BLUE-BACKED Hawk. Baird, General Report on Birds, p. 17. 
Not abundant on the Missouri generally, though found quite numerous on the Yellow- 
stone river. It seems to be confined to Western North America, Three specimens were 
obtained by our party. 
Butro Swatnsont, Bonap. 
Swatnson’s Hawk. Baird, General Report on Birds, p. 19. 
We were enabled to secure four specimens of this rare and interesting hawk. It seems 
to be confined to the sources of the Missouri and Yellowstone. 
Burro Barrpu, Hoy. 
Bartrv’s Hawk. Baird, General Report on Birds, p. 21. 
This, also, like the last, is quite rare and interesting to ornithologists, of which three 
specimens are included in our collection. Its range is Northern and Western North 
America. 
