540 LAND ANIMALS 



great number of individuals in environments of this uniform type, as 

 so often occurs elsewhere under partially adverse conditions. 



The environmental formations produced under the influence of 

 civilization are more or less analogous to primitive natural habitats, 

 and exhibit relations with the latter in their faunae. Cultivated land 

 may be compared to the steppe; it is, in fact, an artificial steppe and 

 comprises the greater part of the area dominated by man. The set- 

 tlements of the stone age in central Europe occupied only a few areas 

 of grassland. At that time the greater part of the area now under cul- 

 tivation was forested. Still earlier, this region was a natural savanna, 

 and typical steppe animals which had persisted here and there as 

 relicts spread over the new artificial steppe and found favorable con- 

 ditions for life. Grass-feeding animals are an important element in 

 the communities of the natural steppe. Under agricultural conditions 

 these attack the grains (cereals) and thus become serious pests for 

 agriculture. Of insects, the cutworms, Agrotis and Hadena, which live 

 in grain fields in all parts of the world, may be named. The North 

 American aphid, Taxoptera gramineum, has increased from time to 

 time (1890, 1901, and 1907) to such a degree as to become a serious 

 pest for growing grains. The chinch bug {Blissus) has already been 

 mentioned. The Hessian fly which attacks wheat in the United States 

 and the migratory grasshoppers which devastate grain and pasture 

 fields in semi-arid steppes in all parts of the world are especially nota- 

 ble. 2 



A large number of birds have become naturalized in cultivated 

 land. 3 Many species are directly dependent on field grains; others find 

 shelter and nesting places in the thick stands of grain fields and hay 

 meadows, but feed on insects or small seeds. Sparrows, especially 

 Passer domesticus and P. montanus, are attracted by grain farming, 

 and are to be found everywhere in the cities, where they formerly fed 

 mainly on the grain to be found in horse dung. They follow the settle- 

 ments sooner or later, according to distances and degree of isolation by 

 forests and mountains. Neither of these sparrows was in Siberia previ- 

 ous to the penetration of that country by the Russians. 4 In Java, where 

 English sparrows were introduced, they are to be found only near the 

 dwellings of Europeans, 5 and the rapid spread of the English sparrow in 

 North America and New Zealand after its introduction was also strictly 

 conditioned by the presence of man. Other sparrows are less dependent 

 on grain farming, and are to be found in permanent meadows, but are 

 certainly benefited by grain culture. The vesper sparrow frequents 

 roadsides; the indigo bunting requires trees and shrubbery. 



The early presence of skylarks (Alauda arvensis) in Germany has 



