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Merriam, Preliminary Report on Bird Migration. 



Bird Migration at the Straits of Mackinac. By C. 

 Hart Merriam. M. D. 



Data resulting- from a sino-le season's observations seem to in- 

 dicate that the Straits of Mackinac lie in the line of a somewhat 

 remarkable avenue of migration. It is probable that the great 

 bulk of those birds which, on their way to the upper peninsula 

 and Canada, pass between the west end of Lake Erie and the 

 southernmost point of Lake Michigan, cross the Straits of Mack- 

 inac. The southern peninsula of Michigan, with a narrow strip 

 from the northern borders of Ohio and Indiana, may be regarded 

 as a great wedge with a base two hundred miles in length. Birds 

 entering this wedge are apt to follow it northward, hemmed in 

 on the east by Lake Huron, and on the west by Lake Michigan, 

 till they arrive at its apex, at Mackinac. Hence it appears, in the 

 spring migration, that the Canada-bound birds which, between 

 the south end of Lake Michigan and the west end of Lake Erie 

 are spread over a tract two hundred miles broad, are gradually 

 condensed, so to speak, dimng their northward passage, till, in 

 crossing the Straits of Mackinac, they occupv a belt but a few 

 miles in width. 



It must not be understood that all the birds which cross the base 

 line between lakes Michigan and Erie, and enter the Michigan 

 wedge, pass out at the Straits. From this total must be subtract- 

 ed all those that breed in the southern peninsula — over an area of 

 forty-one thousand, six hundred square miles — and those (a far 

 smaller number) that migrate by other channels. The remainder, 

 constituting the great bulk of the northern peninsula and Canada- 

 bound individuals, cross at or near Mackinac. It is evident, 

 therefore, that stations located in this vicinity possess unusual 

 facilities for the study of successive bird-waves ; and that the 

 keepers of lights in these waters can, with little trouble, furnish 

 the Committee with information of the utmost value. 



Spectacle Reef, in Lake Huron, lies just east of the entrance 

 of the Straits, and about midway between shores. The light- 

 house rises directly from the water and is surrounded by a wood- 

 en pier ninety-five feet square. The light is of the second order 

 and shows alternately a red and white flash every 30 seconds. 

 It is eighty-six feet above sea-level and is visible, in clear weather, 



