458 THE POPULAR SCIENCE MONTHLY. 



plains and begin to straggle eastward after the cattle were intro- 

 duced ? An allied form in the West, the yellow-headed black- 

 bird, has similar habits, trooping among the cattle and horses on 

 the plains, though it is a good householder, unlike the loose, vaga- 

 bond cowbird. 



The bobolink may have been a denizen of the river marshes 

 of the East long before the discoverer first set foot upon these 

 shores, though from its wide range toward the West, breeding on 

 the plains of the Saskatchewan, we might infer that it had come 

 eastward with the opening of the country. Similar conclusions 

 might be adduced concerning the red-winged blackbird from its 

 life and distribution, but it is a bird more of marshy land than 

 of upland fields. Certain shore birds seem also to have taken 

 advantage of the- clearing of the country, as the killdeer and the 

 grass plover, both being frequenters of plowed and fallow land. 



Several characteristic prairie birds have at times by some ac- 

 cident found their way East, notably in the case of the lark finch, 

 a beautiful Western form, and the yellow-headed blackbird above 

 mentioned, both of which have wandered east as far as Massa- 

 chusetts and Pennsylvania. This fact at least shows the capa- 

 bility of a bird to wander far from its original home, the regular 

 phenomena of migration being still another proof. 



Birds, owing to their superior organization and power of 

 flight, have, more than any other forms of life, a constant tend- 

 ency to widen their ranges and to occupy adjacent territory when- 

 ever the proper physical conditions are presented. This has been 

 very clearly shown in the case of certain species along the Mexi- 

 can border occupying the lands on which chaparral has lately 

 grown up as a result of the invasion by cattle.* We can picture 

 to ourselves a few prairie stragglers finding their way into the 

 newly cleared lands of the settlers and gradually establishing 

 themselves in the Eastern fields. By what route they came is a 

 matter of conjecture — probably from the southwest in the north- 

 ward-setting tide of the spring migration, or possibly by way of 

 the Great Lakes and St. Lawrence Valley. 



Thus has man in his history of progress and discovery uncon- 

 sciously affected the distribution of other living beings. It is a 

 very small fragment in the history of a country, but one of espe- 

 cial interest as showing how remotely and by what strange means 

 causes and effects operate. Man appears in a new land, clears its 

 face of timber, and erects his home. By and by the swift for- 

 sakes the hollow tree to build in the settler's chimney, and the 

 swallow leaves the overhanging tree trunk or rocky ledge for the 



* See a paper by S. N. Rhoads on The Birds of Southeastern Texas and Southern Ari- 

 zona, etc. Proceedings of the Philadelphia Academy, January 26, 1892. 



