100 U. S. NATIONAL MUSEUM BULLETIN 211 



may be found wherever there are lakes bordered with suitable aquatic 

 vegetation, or marshes or sloughs with permanent water of sufficient 

 depth. Damp marshes are not suitable for them, neither are the 

 shallow-water sloughs; they prefer to nest over water that is from 

 two to four feet deep, or even much deeper. 



Deep water serves to protect the nests and young from prowling 

 predators, and a thick growth of tall vegetation, tules, reeds (Scirpus 

 or Phragmites), or cattails (Typhus), serves to shield them from birds 

 of prey. 



In the Rocky Mountain region, the breeding range extends to 

 somewhat higher levels. Fred M. Packard (1946) says that, in 

 Colorado, these birds "nest commonly from the plains to about 5,500 

 feet in the foothills, rarely as high as 6,000 feet." There is some evi- 

 dence that the bird is extending its range somewhat farther east than 

 formerly. And Gordon W. Gullion writes to me (in 1948) that this 

 blackbird is becoming widely distributed as a breeding bird in the 

 Willamette Valley, in western Oregon. 



Spring. — The yellow-headed blackbird winters as far north as 

 some of the Southwestern States, not far north of the southern limits 

 of its breeding range. The northward movement starts about the 

 middle of March, continues through April and reaches the breeding 

 grounds before the middle of May. Thomas S. Roberts (1932) writes: 



In the northward spring movement the vanguard of the Yellowheads that are 

 to breed in Minnesota arrives during the first half of April, the males preceding 

 the females by a few days. Stragglers may enter the southern part of the state 

 during the very first days of that month, but it is not until toward the last of 

 April or early in May that they become numerous. While the females are busy 

 building their nests in the sloughs, the males assemble in little parties and feed 

 on the adjoining uplands. Should they select a grassy plot where dandelions 

 are in full bloom, the bright yellow of the blossoms and the heads of the birds 

 match so well that they are almost indistinguishable. 



Arthur C. Twomey (1942) noticed the first migrants in Utah on 

 May 2, when "from forty to two hundred males could be seen flying 

 in compact flocks, but no females were in evidence. It was not 

 until May 15 that females were noticed, and they likewise were in 

 segregated flocks. * * * By May 20 there were females among the 

 flocks of males, and soon after this the nesting season commenced." 



At a colony studied by George A. Ammann, in northwestern Iowa, 

 the adult males were first seen on April 8 and were numerous on April 

 23; the adult females came on May 2, but were not common until 

 May 12; the first-year males arrived on May 11, and were numerous 

 on May 22, the young females coming about the same time. These 

 dates are taken from a manuscript copy of his thesis (submitted to 

 the University of Michigan), which he has very kindly loaned me. I 



