BREWERS BLACKBIRD 329 



but when the hawk resamed the general direction of its flight, the 

 blackbirds again took up the chase until they were out of sight. 



When a subject for mobbing, as a gray squirrel, for instance, appears 

 in a tree near a nest at the colony the effect on a large part of the 

 colony is almost instantaneous; there is a sudden outburst of rapidly 

 repeated tschup notes and many birds gather nearby. Some of them 

 swoop at the animal and even strike it. Even though the attack is 

 strenuous and prolonged it is not certain that it has any effect in 

 routing the squirrel. I have no proof that the squirrel preys upon 

 the eggs or nestlings, but since the nests are often built resting on one 

 or more cones, the nests could, of course, be destroyed by the squirrel 

 in taking cones. 



On two occasions, at the river-mouth colony the birds were seen 

 harassing weasels. One of these was on May 13, 1947, when 35 

 redwing and Brewer's blackbirds were seen hovering about 5 or 6 

 feet above the weasel and following it as it ran over the marsh in 

 which the redwing colony was situated, adjacent to the Brewer's 

 colony. The Brewer's uttered loud, excited tschup notes, sometimes 

 lighting on the tule stems or the grass as close as 5 feet behind the 

 mammal. The cloud of noisy birds thus followed the weasel for about 

 150 feet, until it disappeared. 



Death along highways has been considered by several writers. 

 Robertson (1930) covered the same 30.3-mile route over paved and 

 unpaved roads 287 times during one year. He found 136 dead birds 

 of at least 27 species, 9 of which were Brewer's blackbirds. R. M. 

 Bond (MS.) remarks that he has been impressed by the fact that, in 

 his experience, Brewer's blackbirds almost invariably fly clear of ap- 

 proaching cars on the highways, in contrast to the frequency with 

 which redwings and tricolored redwings are struck. He counted 156 

 traffic casualties for the three species on roadsides in Oregon, Cali- 

 fornia, and Nevada during his travels in those States in the years 

 1935 to 1937. Only four of these casualties were Brewer's blackbirds. 

 The proportion of Agelaius would have been even higher if counts had 

 been made where redwings and tricolored redwings were crossing a 

 highway from nesting colony to feeding grounds." 



Baumgartner (1934) records only one Brewer's blackbird among 

 the 353 specimens of 42 species of birds recorded as automobile 

 casualties during two trips by car to the Western States, totaling 

 16,700 miles, in the summers of 1927 and 1929. 



Other accidental causes of death are recorded by Linsdale (1931, 

 1932), who found this bird to be an indirect victim of "pest control" 

 programs in California, where it eats poisoned grain put out for ground 

 squirrels; and by Lincoln (1931), who mentions two banding returns 

 of Brewer's that were killed by flying into structures. 



