250 BULLETIN 2 03, UNITED STATES NATIONAL MUSEUM 



much duller and browner, the yellow being less conspicuous and the 

 black cheeks lacking. Young birds and fall adults are much like the 

 female, but the yellow rump, showing plainly as the bird flies away 

 from the observer, will distinguish the species at any season or age. 



Enemies. — So much of the breeding range of the myrtle warbler is 

 beyond the normal breeding range of the cowbirds that, until recently, 

 it was supposed to be largely free from the imposition of this para- 

 site. When Dr. Friedmann (1929) published his book on the cow- 

 birds he had only three records of such molestation, but more have 

 turned up since, particularly in the Middle West where the ranges of 

 the two species overlap considerably. Dr. Paul Harrington writes to 

 me from Toronto : "Sixty-five percent of the nests examined contained 

 eggs or young of the cowbird ; it would not be exaggerating to say 

 that two-thirds of the initial nests are parasitized. The egg or eggs 

 of the cowbird are often deposited before the nest is completed, lead- 

 ing to many a deserted nest. Twice I have found a cowbird's egg 

 imbedded, as so often happens in the yellow warbler's nest, but in both 

 cases yet another was in the nest with the owner's. Twelve percent 

 of the nests with eggs of the cowbird were deserted, but none in which 

 the owner's eggs were also present. Generally but one of the parasite's 

 eggs was found, occasionally two and rarely three." 



Dr. F. A. E. Starr says in his notes from Ontario : "Occasionally, 

 when a cowbird usurps a nest, the birds continue building till the 

 cowbird's G^gg is imbedded. This is all in vain, however, as out of 

 30 nests, I have yet to find one which did not contain from one to three 

 eggs of the cowbird." And A. D. Henderson mentions in his notes 

 from Belvedere, Alberta, a nest that held five eggs of the myrtle 

 warbler and one egg of the Nevada cowbird, and another nestf ul con- 

 sisting of four eggs of the warbler and two of the cowbird. Probably 

 very few young of the warbler are likely to survive in nests with young 

 cowbirds, which means that this parasite must seriously interfere with 

 the normal increase in the warbler population. 



Harold S. Peters (1936) lists two lice, two flies, and two mites as 

 external parasites on the myrtle warbler. 



Fall. — The myrtle warbler is one of the latest of its family to move 

 southward and is also one of the most leisurely in migration; the 

 migration covers practically the whole of September and October and 

 much of November, the earliest arrivals sometimes reaching the Gulf 

 States before the last ones have left Canada. Abundant in the spring, 

 it is much more so in the fall, when it can often be seen in enormous 

 numbers. As the birds drift along southward, many stop along the 

 way where food is abundant and some spend the winter at no great 

 distance from the southern limits of the breeding range. In Massa- 

 chusetts, we usually look for them during the latter half of September 



