EASTERN FIELD SPARROW 1231 



Young birds in summer are finely streaked below like yoimg Chippies, 

 but lack the well-marked head-stiipings." 



Enemies. — Field sparrows are subject to predation by the usual 

 animals capable of catching small birds. Cats, dogs, foxes, raccoons, 

 skunks, and weasels must all take the contents of ground nests 

 occasionally. Evidence points to cats killing a number of females 

 on theh' nests at night in my study area. Dogs destroyed at least 

 one nest, and probably more. Once a weasel working through the 

 neighborhood of several nests came to my squealdng. Smaller 

 mammals such as spermophiles, chipmunks, and field mice were 

 also present, and I was sure some of them took eggs or young at 

 times, usually when the nest contents disappeared one at a time. 



Among bird predators, Cooper's and sharp-shinned hawks were 

 present during most of the nesting season, and whenever they ap- 

 peared the field sparrows took to cover. They also showed alarm 

 when blue jays came near. Jays foraged commonly in family groups 

 over the sparrow territories from mid-summer on, and definitely 

 destroyed at least one nest. Crows also appeared now and then, 

 but seldom fed in the sparrow nesting area. M. P. Crooks (MS.) 

 watched a house wren destroy a set of field sparrow eggs in Iowa. 

 E. A. Mason (1938a) reports a loggerhead shrike capturing a field 

 sparrow he had just banded and released in Summerville, S.C. 



Snakes also take a considerable toll of birds nesting on or near the 

 ground. I (1943) reported incidents of nests of the chipping sparrow, 

 prothonotary warbler, and goldfinch despoiled, respectively, by a 

 garter snake, a pilot snake, and a blue racer in Michigan. On July 11, 

 1943, I found a milk snake swallowing the eggs from a field sparrow 

 nest in my study area; I killed the snake, extricated the eggs, and 

 put them back in the nest. E. D. Nauman (1929) reports a rattle- 

 snake eating an adult and a nestful of nearly grown young field 

 sparrows in Iowa. 



Unquestionably the chief enemy of the field sparrow in northern 

 United States is the brown-headed cowbird. Cowbirds are almost 

 always present in or near the fields where the sparrows, whose nests 

 are not too hard to find, are among the commonest breeding small 

 birds. Though I have seen them outAvit the cowbirds many times, 

 nevertheless 182, or 27.4 percent of 664 nests in my study area were 

 parasitized. G. O. Hendrickson (1953) reports 80 percent of 16 

 nests parasitized at Ames, Iowa, and R. T. Norris (1947) only 15.8 

 percent of 57 nests at Butler, Pa. In my 182 nests the cowbirds 

 laid 234 eggs — 135 had one, 42 had two, and 5 had three eggs. The 

 field sparrows immediately deserted 100 of the 182 nests (with 134 

 cowbird eggs) and from the 234 eggs fledged only 27 cowbirds, a nest- 

 ing success of 11.6 percent. While the average production of only 



