Annual report . a-tures above 43°F. (6° C.) as determining the northern limits of the respec-tive zones, the plants and animals of the Lower Austral require an annualtotal of at least 18000° F. (10000° C), those of the Upper Austral 11500° F.(6400° C), and those of the Transition 10000° F. (5500° C). The south-ward distribution is governed by the mean temperature of a brief periodduring the hottest part of the year, the normal mean temperature ofthe six hottest consecutive weeks furnishing a satisfactory basis of deter-mination. Thus the southern limit of the Hudsonian is estimated to bethe is
Annual report . a-tures above 43°F. (6° C.) as determining the northern limits of the respec-tive zones, the plants and animals of the Lower Austral require an annualtotal of at least 18000° F. (10000° C), those of the Upper Austral 11500° F.(6400° C), and those of the Transition 10000° F. (5500° C). The south-ward distribution is governed by the mean temperature of a brief periodduring the hottest part of the year, the normal mean temperature ofthe six hottest consecutive weeks furnishing a satisfactory basis of deter-mination. Thus the southern limit of the Hudsonian is estimated to bethe isotherm for the six hottest weeks of ° F. (14° C), while the southernlimit of the Canadian is found to be 64°.4 F. (18° C), of the Transition71°.6 F. (22° C), of the Upper Austral 78°.8 F. (26° C). The actual dis- TheGeographic Distribution of Life in North America. Smithsonian Inst. Rept, 1891, p. 365-413.^XJ. S. Dept Agric, Biol. Bur., Bui. 10, 1S98, p. 18-31. 19 20 NEW YORK STATE MUSEUM ///. Bartramian sandpiperKnown breeding range in New York, 1906
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