5 8o THE POPULAR SCIENCE MONTHLY. 



The migratory movement of the North American birds is almost 

 wholly limited to the Atlantic coast, a smaller number being perma- 

 nent residents than on the Pacific coast, or in corresponding European 

 localities. In Massachusetts the regular number of summer visitors is 

 106, while there are only 30 species which remain all the year. The 

 number of permanent residents increases as we go southward, but 

 during the breeding-season in any single locality it increases as we go 

 northward until we reach Canada, where more species rear their young 

 than in the Southern States. The extent of the migration of certain 

 birds has greatly altered within a limited period of observation. A 

 Mexican swallow {Hirundo lunifrons) first appeared in Ohio in 1815 ; 

 its yearly range increased, until in 1845 it had reached Maine and 

 Canada, and now its annual migrations extend to Hudson's Bay. The 

 rice-bird, or " bobolink," enters the Southern States in April, passes 

 northward until in June it reaches Canada, and stops in its westerly 

 course at the Saskatchewan River, in 54 north latitude, having 

 widened its range continually as wheat and rice were cultivated over 

 more extensive areas. 



A nocturnal concourse of birds sometimes occurs in the neighbor- 

 hood of large towns near the end of summer, in still, cloudy weather. 

 The notes of well-known birds may be recognized by the skillful or- 

 nithologist, at one time faint in the distance, at another near by, while 

 occasionally the stroke of a wing gives a sense of nearness to these 

 remarkable visitors. It is supposed that these noises proceed from 

 migratory birds which, having lost their way, are attracted by the 

 light from street-lamps. 



It is thus obvious that the migration of birds is no mere arbitrary 

 matter, but is governed by laws susceptible of intelligent interpreta- 

 tion. Want of food is the most evident cause of their journeyings. 

 As it becomes scarce near the end of summer in the extreme northern 

 limits, those individuals which feel the pressure of want seek it else- 

 where, and, in doing so, they press upon the haunts of other birds, 

 until the movement which began in the north has extended to the 

 southern limit. The power of flight in birds makes it possible for 

 them to cross a moderate breadth of sea and unlimited extent of 

 country, and, traveling as they do, mostly at night and high in the 

 air, their movements seem mysterious, simply because they are diffi- 

 cult to observe. But, let us map their comings and goings faithfully 

 as we may, there yet remains the unanswered question, How do these 

 little visitants find their way so unerringly from one place to another, 

 over great distances and apparently unexplored routes ? 



Some of the large'st Mammalia are not stopped by any physical 

 obstacle in their journeys over whole continents. The rhinoceros, the 

 lion, and the tiger, have great powers of dispersal, and their possible 

 range is unlimited wherever there are land and sufficient food. The 

 elephant climbs to mountain-tops, difficult of ascent for man, crosses 



