NOTES ON HOATZINS 181 



distinctly chestnut, while the secondaries and tail feathers 

 showed the huffy-white markings. The remainder of the 

 down was a dark brownish black, paler on the chin and 

 throat. 



There were three thumb feathers in the alula, extend- 

 ing almost to the tip of the claw, but these interfered not at 

 all with its use, as it worked forward and inward, reaching 

 out at right angles to the claw of the first finger. The tail 

 feathers were the longest and strongest of all of the sprout- 

 ing plumage, this precociousness unquestionably having to 

 do with their rudder function. 



The upper mandible was brownish black, the lower 

 greenish horn: the iris, olive-brown; the legs and feet black. 

 These were very large in proportion to the size of the bird. 



Thrashing about with their flight feathers through the 

 thorny branches, the plumage of these birds suffers unusual 

 wear and tear, and it is seldom that an individual can be 

 found with perfect wing and tail. The six months' old 

 hoatzins were, however, in full molt. The molt of the five 

 pairs of tail feathers is peculiar, beginning almost simul- 

 taneously with the outer and inner pairs and progressing 

 evenlj^ toward the third pair. One bird showing this par- 

 ticularly well had the following retrice formula, the right 

 and left sides corresponding: 



1st tail-feather (inner) three-quarters grown 



2nd pair blood sheath 



3rd pair old, unshed 



4th pair one-quarter grown 



5th pair (outer) new, nearly full-grown 



This same individual showed the primaries about half 

 through their molt, which was progressing outward: 



1st primary (inner), and 2nd new, full grown 



3rd nearly grown 



4th blood sheath 



