Fig. 10.—Field sparrow. Length, about 5½ inches.
The snowbird[28] and tree sparrow[29] are perhaps the most numerous of all the sparrows. Examination of many stomachs shows that in winter the tree sparrow feeds entirely upon seeds of weeds. Probably each bird consumes about one-fourth of an ounce a day. In an article contributed in 1881 to the New York Tribune the writer estimated the amount of weed seed annually destroyed by these birds in Iowa. On the basis of one-fourth of an ounce of seed eaten daily by each bird, and an average of 10 birds to each square mile, remaining in their winter range 200 days, there would be a total of 1,750,000 pounds, or 875 tons of weed seed consumed in a single season by this one species. Large as are these figures, they unquestionably fall far short of the reality. The estimate of 10 birds to a square mile is very conservative, for in Massachusetts, where the food supply is less than in the Western States, the tree sparrow is even more abundant than this in winter. The writer has known places in Iowa where several thousand tree sparrows could be seen within the space of a few acres. This estimate, moreover, is for a single species, while, as a matter of fact, there are at least half a dozen birds (not all sparrows) that habitually feed during winter on these seeds. Farther south the tree sparrow is replaced in winter by the white-throated sparrow,[30] the white-crowned sparrow,[31] the fox sparrow,[32] the song sparrow, the field sparrow, and several others; so that all over the land a vast number of these seed eaters are at work during the colder months reducing next year’s crop of worse than useless plants.
[28] Junco hyemalis.
[29] Spizella monticola.
[30] Zonotrichia albicollis.
[31] Zonotrichia leucophrys.
[32] Passerella iliaca.