THE PRACTICAL VALUE OF BIRDS. 9 



Introduced into Australia for purposes of sport, in the absence of predatory 

 animals, spread over the whole country like a scourge, and immense sums 

 have been expended in the effort to check their depredations. In New Zea- 

 land, ferrets, stoats and weasels were imported to destroy the rabbits, and 

 as a result some of the native birds are threatened with extermination (10). 

 The introduction of the English Sparrow into the United States, the con- 

 sequent decrease in the number of insectivorous birds and the increase of 

 such pests as the hairy caterpillars, is too well known to need discussion (11). 



RESCUE OF CROPS, FOLIAGE AND FORESTS BY BIRDS 



Birds which ordinarily take small numbers of insects, take them in 

 much larger quantities when they are abundant. This fact and the ease 

 with which birds pass from one locality to another in search of food, have 

 often saved crops from destruction. A few instances chosen at random from 

 many will illustrate this. 



When the myriads of crickets threatened the crops of early settlers at Salt 

 Lake, Utah, California gulls arrived "by hundreds and thousands," and 

 saved the crops (12). California orchard crops have several times been 

 saved from outbreaks of the canker worm by Brewer's blackbirds, which 

 flocked to the rescue, and, working from tree to tree, completely cleaned 

 them out (13), and the same well-known bird of the West saved the foliage 

 in northern California from a plague of caterpillars (14). A canker worm 

 outbreak in a Massachusetts orchard was checked by a large flock of cedar 

 waxwings, which also cleaned the elm trees of their greatest foe, the elm-leaf 

 beetle (15). 



The destruction of hawks and owls, which prey extensively upon field 

 mice, has been followed by plagues of these destructive rodents, and unusual 

 abundance of the mice in various parts of the world has frequently at- 

 tracted large numbers of predatory birds to feed upon them, including 

 hawks, owls, gulls, storks, spoonbills, cranes, herons, crows, ravens, magpies, 

 jays, etc. (16). 



Forbes collected a large number of robins, catbirds, dickcissels and indigo 

 buntings in a canker-infested orchard, and other specimens of the same 

 species elsewhere, and compared the contents of their stomachs. He found 

 in every instance that the caterpillar element of food of those collected in 



(10) Palmer, op. cit., pp. 87-100. 



(11) Palmer, op. cit. Barrows, Walter B., et al., The English Sparrow (Passer 

 domesticus) in North America, Especially in its Relation to Agriculture, U. S. Dept. 

 Agric., Div. Econ. Orn. & Mam., Bull. No. 1, 1889. See especially pp. 107 and 122. 



(12) McAtee, W. L., and Beal, F. E. L.. Some Common Game, Aquatic and 

 Rapacious Birds in Relation to Man, L'. S. Dept. Agric., Farmers' Bull. No. 497, pp. 

 21-22, 1912. 



(13) Beal, F. E. L., The Relations Between Birds and Insects, U. S. Dept. Agric., 

 Yearbook for 1908, p. 345, 1909 ; U. S. Biol. Surv., Bull. No. 34, p. 60. 



(14) Bryant, Harold C., The Relation of Birds to an Insect Outbreak in Northern 

 California During the Spring and Summer of 1911, The Condor, Vol. XIII, pp. 195-208, 

 1911. 



(15) Forbush, E. H.. Fourth Ann. Rept. Mass. State Ornithologist, pp. 19-21, 1912. 

 (16) Beal, F. E. L., How Birds Affect the Orchard, U. S. Dept. Agric., Yearbook 

 for 1900, p. 300, 1901. Fisher, A. K., Hawks and Owls from the Standpoint of the 

 Farmer, Yearbook for 1894, pp. 219, 224-225, 1894, (revised and published as U. S. 

 Biol. Surv. Circ. No. 61. 1907). Lantz. David E., An Economic Study of Field Mice, 

 U. S. Biol. Surv., Bull. No. 31, pp. 47-48, 52-53. Piper, Stanley E., Mouse Plagues, 

 Their Control and Prevention, Yearbook for 1908, pp. 303-309, 1909. 



