180 U. S. NATIONAL MUSEUM BULLETIN 211 



the San Joaquin and Sacramento Valleys there are many small 

 irrigation reservoirs fringed with a dense growth of tules. From 

 these in spring and early summer issues a medley of droning and 

 braying sounds, and lines of blackbirds fly out in all directions to the 

 neighboring fields or fly back with food for the young." 



Courtship. — Lack and Emlen (1939) made extensive studies of the 

 breeding behaviour of tricolored redwings: "Intensive watching in 

 an uncrowded portion of the Willow Slough colony showed that each 

 male held a territory some six feet square, to which it usually confined 

 its movements when in the colony, in which it sang and courted, and 

 from which other males were driven out. An immature male was once 

 tolerated in an adult's territory for two minutes, but it was promptly 

 driven out when a female arrived. Fighting never seemed serious and 

 boundary demonstrations, so common in typical territorial birds, 

 were not seen." 



They were unable to distinguish separate territories in the central 

 part of the colony, where the population was denser. 



Both male and female often showed similar raising and lowering of expanded 

 wings and tail as a preliminary to copulation. When inviting the male, the female 

 usually arched the body and pointed the beak vertically upward, sometimes 

 quivering the wings or raising and lowering the beak. * * * Once, from a tree 

 in the colony, a male flew down in song and with expanded wings to copulate with 

 a female below; this is the only case we observed of an aerial song-flight. * * * 



As in phoeniceus, polygamy seems the rule. Of three males in contiguous 

 territories with known boundaries, two had three and the other had two building 

 females; laying occurred in seven of the eight nests. Occasionally a male dis- 

 played to two females in quick succession. All the females laid at about the 

 same time. The females usually ignored each other, but occasionally chased each 

 other short distances. 



At times, two males were seen displaying to the same female, but usually one, 

 the trespasser, was chased away. As already noted, in an owner's absence, his 

 neighbor trespassed and courted one of his females. One female, which was 

 individually distinguishable, returned with building material when her own male 

 was absent; the next-door male postured sexually, whereupon she flew over to his 

 territory and both displayed. Her own male then reappeared, and she returned 

 and displayed with him. In neither case did copulation follow. These incidents 

 suggest that promiscuity may occur at times, but polygamy, not promiscuity, 

 would seem the rule where we watched; we do not know that this is true for the 

 denser parts of the colony. 



Nesting. — The tricolored redwing is one of our most highly gregari- 

 ous species. It nests in enormous, most densely populated colonies, 

 the nests being placed more closely together than in any other colonies 

 of marsh-nesting blackbirds. Estimates of population density have 

 been made by many observers; these estimates are subject to wide 

 variation and some of them are evidently inaccurate or were carelessly 

 made. Johnson A. Neff (1937) devoted six seasons to a careful and 

 thorough study of the nesting colonies of this species over most of its 



