ECONOMIC BIOLOGY 369 



potatoes and other crops. At the height of the plague, it was estimated that 

 there were from 8,000 to 12,000 mice per acre, while the total loss to the 

 valley was estimated at $300,000. The abundance of mice in the Humboldt 

 valley attracted hawks in large numbers. But failing to recognize in the 

 hawks their best ally in their war against the mice, the ignorant residents 

 seized their guns and proceeded to slay their best friends. 



So too thought the legislature of Pennsylvania when they passed the no- 

 torious "scalp act," providing for a bounty of fifty cents for every hawk and 

 owl killed within the state, as a result of which half-baked legislation more 

 than 100,000 valuable birds were killed, at an expense of nearly $100,000 to 

 the state for bounties and notary fees, and an estimated loss of more than 

 $4,000,000 from the increase of harmful rodents resulting from the destruc- 

 tion of their enemies, the hawks and owls. And yet all this in the short space 

 of a year and a half. 



Hawks and owls have the habit of throwing up the undigested portions 

 of their food in the form of pellets containing the hair, bones, feathers, etc., 

 of their prey. For many years a pair of barn owls were wont to nest in the 

 tower of the Smithsonian Institute in Washington. An examination of two 

 hundred pellets found beneath their nesting site revealed 454 skulls, of which 

 412 were those of mice, 20 of rats, 20 of shrews, one of a mole, while only 

 one was that of a bird (sparrow). 



An examination of 562 stomachs of the red-tailed hawk showed remains 

 of poultry or game birds in 54, other birds in 51, mice in 278, other mammals 

 in 131, insects in 47, miscellany in 59, and nothing in 89. 



The habitue of field and forest, who seeks his favorite haunts after the 

 first snow fall of the winter, is likely to encounter companies of little birds, 

 who, in spite of winter and its snow, are busily engaged in reaping a bounti- 

 ful harvest of the weeds. Flitting from stem to stem, they pick out the seeds 

 from their shells, while others follow in their wake to pick up the gleanings 

 from the snow. The late Dr. Judd of the Biological Survey, in his studies 

 of the food habits of sparrows, examined a piece of ground eighteen inches 

 square in a patch of smartweeds where several species of sparrows had been 

 feeding. On this patch he counted 1,130 half seeds and only 2 whole seeds. 

 During the ensuing season no smartweed grew where the sparrows had 

 caused this extensive destruction. It has been estimated that in Iowa alone a 

 single species, the tree sparrow, destroys in one year 875 tons of weed seed, 

 and that in the United States as a whole the different species of native spar- 

 rows, numbering more than one hundred, save $35,000,000 for the farmers 

 every year. 



Many a wild creature is the farmers' inveterate enemy and does untold 

 damage to his cattle or his crops. As an indication of the losses due to preda- 

 tory animals it may be stated that the chairman of the State Live Stock Board 

 of Utah estimates an annual loss in that region amounting to 500,000 sheep 

 and 4,000,000 pounds of wool. The president of the New Mexico College 



