BREWER'S BLACKBIRD 311 



La Rivers (1944) found that on a 15-acre tract 14 miles northwest 

 of Reno, Nev., during the period May 17 to June 16, 1934, there were 

 107 nests of this species, a density of "slightly more than 7 nests per 

 acre." This indicated, he adds, a "heavy infestation for the region." 



In the area within about a 12-mile diameter around the river-mouth 

 colony I found nine other colonies and no pairs nesting singly, al- 

 though it is possible that a single pair might have been overlooked. 

 Some nests on the peripheries of the colonies were considerably more 

 isolated than the majority of nests toward the centers. The river- 

 mouth colony was a quarter mile west of the nearest other colony, 

 the second nearest being a mile to the north. 



Monterey pines were used for nesting, at some of the nearby 

 colonies, and also live oaks, Monterey cypress, and Baccharis. One 

 colony was at a golf course, another at a dairy farm, and another in 

 trees in the business district of Carmel. All these colonies were 

 adjacent to favored foraging areas. 



In no year did the river-mouth colony exceed an area covering 9 

 acres. Every year the greatest density of nests was confined to the 

 center area of 1 acre. Considering only the first nesting for the 

 season of each female in the years 1944-46, the density for the whole 

 colony varied from 4.1 nests per acre in 1944 to 6.7 in 1946, whereas 

 in the center acre alone the density varied from 14 in 1944 to 23 in 

 1945. Three or four pines in the center acre were particularly attrac- 

 tive to the birds. One pair of these trees, with trunks 4 feet apart 

 and branches intermingling, but separated from the other trees, had 

 a height of 45 feet and a combined spread of about 48 feet. This 

 pair of trees contained 7 nests in simultaneous use in 1945. The 

 nests varied from 21 to 42 feet above the ground; no two nests were 

 closer together than about 9 feet nor farther apart than about 37. 

 This represents the maximum crowding in the colony. Possibly such 

 crowding was partly due to the fact that the trees were not evenly 

 distributed over the 9 acres. 



The arrangement of nests of polygynous males does not suggest 

 a territory embracing them all, as is the case in some polygynous 

 species, such as the yellow-headed blackbird (Xanthocephalus xaniho- 

 cephalus). Although the nests of a polygynous male may be in the 

 same tree, one of the nests may be as near or even nearer to the 

 nest of another male than to its own second nest. But frequently the 

 nests of a polygynous male were in different trees, often considerably 

 farther separated than the nests of different males, with one or more 

 other nests in between. The distance between two nests of one male 

 has been as much as 282 feet. 



The height of nests above the ground at the river-mouth colony 

 varied from 7% to 42^ feet. Thirty-five nests in 1945 averaged 27.2 



380928—57 21 



