546 LAND ANIMALS 



the city, while 7 are recorded from the buildings within the area. 

 In city parks the white-footed mouse of the country is largely replaced 

 by the house mouse. Both shrews {Blarina and Sorex) are still present. 

 The 13-lined spermophile is very common, and a few chipmunks are 

 to be found. The mole is a pest. Gray and fox squirrels are increasing 

 under protection. The flying squirrel appears to be rare. Stragglers 

 from the country, such as the opossum and muskrat, also occur within 

 the city limits. While wild mammals are by no means lacking, the com- 

 pletely man-dominated communities within Chicago differ from the 

 neighboring grassland or woodland by a general reduction in the num- 

 ber of species and of individuals. 14 



In irrigated regions the character of the vegetation and of associated 

 bird and animal life usually resembles that of the parks, gardens, and 

 orchards rather than of the cultivated fields of mid-United States. The 

 San Joaquin valley since 1900 has been changed from an arid plains 

 region with xeric grasses and herbs and scattered tracts of lupine or 

 atriplex bushes to a region of orchards, alfalfa fields, green pastures, 

 and artificial streams of running water lined with willows. 15 



In 1900 the winter birds observed included a few horned larks, 

 fewer meadow larks, and occasional burrowing owls with more fre- 

 quent savanna sparrows and, in damp places, pipits. Grinnell now esti- 

 mates the bird population at that time to have been one per acre or 

 less. In 1923 in the same region one finds more species and vastly 

 more individual birds. The horned larks and burrowing owls are 

 gone, but the meadow larks have increased in numbers and in addi- 

 tion there are great numbers of Brewer blackbirds, of mocking birds, 

 goldfinches, swallows, phoebes and kildeers. 15 The present population 

 is estimated at ten birds per acre, an increase of more than tenfold 

 as the result of the activity of man. The increase in the Imperial 

 Valley has been still greater, and in California as a whole Grinnell 

 thinks that while a few birds, such as the trumpeter swan and the 

 whooping crane, have become nearly or quite extinct, the introduction 

 of the English sparrow and of the ring-necked pheasant and others has 

 left the bird fauna of California at as high a number of species and 

 subspecies as it had in 1848 before the gold rush. Similar relations 

 hold in Illinois. 16 



Buildings. — Houses and other structures afford for many animals, 

 primarily for birds, a substitute for their native rocky cliffs and may 

 be regarded as artificial cliffs. The barn swallows (Hirundo rustica 

 and H. erythrogaster) are now dependent on man for nesting sites. 

 They accompany stock-raising, with its attendant insect life, and the 

 former nests on the block houses of the Ostiaks, the yurtas of the 



