BLACK-BILLED CUCKOO 77 



the nest. Professor Herrick (1935) says: "Thus at one stroke one 

 or more of the juvenal contour feathers are exposed and quickly fluff 

 out in all their shapely proportions. * * * The change actually 

 occupies about twelve hours, and it is really not complete, since the 

 sheaths of the wing- and tail-quills flake off gradually, as in other 

 birds, and those feathers of head and neck out of reach of the 'comb' 

 remain sheathed for a considerable time longer." 



By the time that the young bird leaves the nest, at the age of 8 

 or 9 days, it is in nearly full juvenal plumage; the wings are fairly 

 well grown, but the tail is still very short. In this plumage the soft 

 plumage above is "buffy brown," each feather tipped with white; 

 the under parts are silvery white, tinged with pale gray on the belly 

 and with pale buff on the breast and throat. During late sum- 

 mer and early fall, most, if not all, of this juvenal contour plumage 

 is molted and replaced by the first winter plumage, but the flight 

 featliers of the wings and tail are retained until spring. This first 

 winter plumage is much like that of the adult, but it is more brown- 

 ish on the head and back and more greenish olive on the scapulars 

 than in adults; the throat is more buffy and the upper breast more 

 grayish buff than in the adult; the young bird's tail is quite different, 

 the grayish white tips are smaller and are not bordered inwardly 

 with the dusky space, which is clearly visible in the adult tail. The 

 molts are apparently the same as in the yellow-billed cuckoo; the 

 adult plumage seems to be acquired before the young birds return 

 from their first winter in the south, but we have no specimens show- 

 ing a spring molt. 



Food. — The black-billed cuckoo is just as good a caterpillar de- 

 stroyer as the yellow-billed; in fact the food habits of the two 

 species are almost identical in all respects. An abundance of cater- 

 pillars in a locality is very likely to bring with it an invasion of 

 cuckoos. Frank L. Farley writes to me: "As far as I am aware, 

 the blaclc-billed cuckoo was unknown in central Alberta until the 

 summer of 1923. That year the central portion of the Province 

 was infested with tent caterpillars, which, in 1924-25, assumed plague 

 proportions. Entire bluffs of poplar trees, several acres in extent, 

 were entirely denuded of their leaves, while houses and other build- 

 ings were overrun with the pests." In June 1924 the cuckoos began 

 to appear for the first time, birds entirely unknown to the residents. 

 "Although caterpillars gradually disappeared after 1925, cuckoos 

 were reported from widely separated parts of central Alberta, the 

 most northerly one being about 150 miles north of Camrose, which is 

 in latitude 53° N. The presence of cuckoos and caterpillars in the 

 same territory during these years would tend to bear out the claims 

 of other observers, that the insects are particularly relished by these 



