526 ANIMAL LIFE IN THE YOSEMITE 



replacement of the body feathering, which takes place in August and 

 results in the 'first winter' plumage, the males and females present differ- 

 ences. The males gain considerable clear yellow on the chin, while in the 

 females the chin is only indistinctly yellow. Both males and females then 

 acquire the yellow rump. Thus the young birds, within about three months, 

 have three distinct plumages. The last of these is retained until the follow- 

 ing spring (April) and then another molt of the body feathers brings the 

 bluish gray back and bright yellow patches on sides and crown, of the 

 'first nuptial' plumage. Not until August or September, however, when 

 the birds are about fifteen months old, is there renewal of the flight feathers 

 of the wing and tail, which were acquired with the juvenal plumage. Such 

 long service usually results in these feathers becoming badly worn, and 

 bleached to a pale brown. 



In this same molt, the second or adult fall molt, both sexes show more 

 or brighter yellow on the chin, crown, and sides, and in the males the breast 

 and sides are rather heavily mottled with black. These features make 

 possible the distinguishment of birds fifteen months or more old from those 

 only three months of age. It is thus possible to recognize eight different 

 feather assemblages or 'plumages' in this warbler. 



The above brief outline of the molt program of the Audubon Warbler 

 will serve to explain why so much variation is apparent among individuals 

 seen in the field at different seasons and even at the same time. 



The Audubon Warbler is considerably larger than any of the other 

 common warblers of the Yosemite region. One species, the Alaska Myrtle 

 Warbler, a sparse winter visitant here, is similar in size and general 

 appearance to the Audubon. (See pi. 9e.) It has a yellow rump and 

 white-spotted tail, but its chin is always clear white. In the Audubon 

 Warbler ten of the twelve tail feathers (all but the innermost two) are 

 marked with large white patches near the ends, whereas in the Myrtle 

 Warbler only the three outer feathers on each side are so marked and the 

 spots are smaller. (See fig. 57.) The mass effect of the white on the 

 spread tails in the two species is thus quite different. The Audubon and 

 Myrtle warblers are the only warblers with white-spotted tails, yellow 

 rumps, and dark backs to be found in the region. 



A feature common to both of these warblers in comparison with the 

 other warblers of the region, is the relatively great length and breadth of 

 the tail feathers. This may be a special adaptation for the twofold purpose 

 of aiding in the short circuitous flights and in the displaying more con- 

 spicuously of the white markings, possibly directive in their function. 



Through most of the year the only note heard from the Audubon 

 Warbler is a sharp tsdp or chit, but this is given frequently both when the 

 birds are engaged in foraging and when they are in flight. This note is 



