40 EXTENT OF MIGRATION 



September 20-30. Herring Gull (May), Yellow-bellied Sapsucker 

 (October 20-30), Junco (May 1-10), White-throated Sparrow (May 1-20). 

 White-crowned Sparrow (October 15-30), Myrtle Warbler (May 5-20), 

 Yellow Palm Warbler (October 15-30), Brown Creeper (April), Golden- 

 crowned Kinglet (April), Ruby-crowned Kinglet (October 20-30), 

 Winter Wren (April), Gray-cheeked Thrush (October 15-25). 



October 1-10. Bronzed Grackle (December), Rusty Blackbird 

 (December), Pipit (October 25-November 5), Hermit Thrush (Novem- 

 ber). 



October 10-31. Horned Lark (April), Pine Finch (April), Snow 

 Bunting (March), Redpoll '(April), Tree Sparrow (April), Fox Sparrow 

 (November 25-December 10), Northern Shrike (April). 



November. Pine Grosbeak, White-winged Crossbill, Red Cross- 

 bill. 



The Extent of Migration. After this glimpse of the swing of the 

 pendulum of migration, from a local point of view, we may extend our 

 inquiry by following the birds to their winter quarters, with the object 

 of learning where they go and the routes they travel. 



Generally speaking, the extent of a bird's migration is related to 

 the character of its food; insect-eating birds journey much farther 

 than seed-eaters, many of which travel but a short distance south 

 of their birthplace. There are, however, some marked exceptions to 

 this statement. The Bobolink, for instance, is in part granivorous, 

 but it winters south of the Amazon, while the Golden-crowned Kinglet 

 is insectivorous and winters as far north as New England. Again, of 

 two insectivorous birds, one, the Short-billed Marsh Wren, does not 

 winter north of the Gulf or South Atlantic States, while the other, the 

 Winter Wren, is found northward to New England in winter. Numer- 

 ous similar instances might be cited, all indicating that some cause 

 other than food has determined the extent of the journeys made by 

 many migratory birds. It will be observed that of the species just 

 mentioned, the Bobolink and Short-billed Marsh Wren are American 

 types of austral origin, while the Golden-crowned Kinglet and Winter 

 Wren are European types and of boreal origin. Further inquiry will 

 show that among land-birds the migrants which go farthest south 

 belong in the first class, while those which winter farthest north belong 

 in the second class. It is not improbable, therefore, that the extent 

 of a bird's migrations may give some indication of its place of origin 

 as a migrant. 



In the western states the migration of birds is not so pronounced 

 as it is east of the Rocky Mountains, and the latitudinal movement 

 is complicated by an altitudinal one. The migrants of this region, 

 which winter south of the United States, pass this season largely in 

 Mexico. Comparatively few land-birds go beyond Guatemala and 

 practically none cross the Isthmus of Panama. 



In eastern North America, not only are migrants proportionally 

 more abundant, but their movements are more clearly defined, and 



