Vol. II, Pt. I] GIFFORD— BIRDS OF THE GALAPAGOS ISLANDS 



73 



MEASUREMENTS OF IMMATURE BIRDS (in millimeters) 



Birds showing the fourth plumage, usually mixed with 

 either the third or the fifth, are common in the Academy's 

 series, and have been included in the measurements of adults, 

 for to all outward appearances they are adult. Occasional 

 specimens in this plumage have dark edges to the rectrices, 

 but this was also noted in one full adult. I am not prepared 

 to say positively whether the primaries of this fourth plumage 

 are those of the third, but apparently they are, as are also the 

 axillaries. Just how long a time elapses between the hatching 

 of the chick and the assumption of the adult plumage is hard 

 to say, as the birds evidently breed at different times of the 

 year on different islands, making it exceedingly difficult to 

 judge from a series of skins alone. However, I believe that 

 the full adult plumage is assumed at the first postnuptial moult. 



Nineteen specimens in the Academy's collection show the 

 fourth plumage in some stage. One October specimen from 

 Charles Island retains' tertials of the third plumage, and has 

 worn feathers of that plumage hidden beneath the feathers of 

 the neck. Otherwise it is in worn fourth plumage, with new 

 feathers of the fifth plumage putting in an appearance in the 



^No. 2206 has not lost the down from the tips of the feathers of the breast, yet 

 it is a larger bird than No. 2201. which has lost it. 



