studied game birds is that this source of calcium is cal- 

 careous grit. 



For a number of years, investigators disagreed on the 

 function of grit in the diet of gallinaceous birds— whether 

 grit was reciuired by the birds for its mineral content or 

 as a grinding agent in the mastication of food. Nestler 

 (1946: 141) reported that grit as a grinding agent in the 

 gizzard was not essential for the growth, welfare, or re- 

 production of pen-raised bobwhites {Colinus virginianus) . 

 McCann (1939:33-36) concluded that the consumption 

 of grit by pheasants appeared to be conditioned pri- 

 marily by a need for calcium. 



The belief that glacial grit is required as a source 

 of calcium for pheasants re]Dresents an elaboration of the 

 glacial hypothesis set forth by Leopold (1931:12,5-126). 

 Leopold's hypothesis is strengthened by the fact that 

 many years after the initial establishment of the pheasant 

 in the North Central States its distribution still nearly 

 coincides with the area of most recent glacial acti\ity. 



In Illinois, the relationship between pheasant dis- 

 tribution and the area of most recent glacial activity is 

 evident. Four independent stages of glaciation have been 

 recognized in Illinois; these are, from oldest to most 

 recent, the Nebraskan, Kansan, lUinoian, and Wiscon- 

 sinan (Horberg 1950:17). The major patterns of dis- 

 tribution of pheasants in Illinois approximately coincide 

 with the moraines deposited by the substages of the Wis- 

 consinan ice sheet. The center of greatest pheasant abun- 

 dance, located in Livingston and Ford counties of cast- 

 central Illinois, is closely associated with the Chatsworth 

 and Cropsey moraines of the Wisconsinan ice sheet. The 

 southwestern boundary of the contiguous range occupied 

 by pheasants teiniinates ap]5roximately at the southwest- 

 ern boundary of the Shclby\ille moraine, terminal mor- 

 aine of the Wisconsinan glacier (Fig. 4). Some self- 

 maintaining pheasant populations of relati\ely low 

 numbers are found in areas in which the Illinoian was 

 the most recent glacier and even on the unglaciated 

 areas in the northwestern corner of Illinois, but areas 

 supporting the greatest numbers of pheasants are foimd 

 within the area of Wisconsinan drift (Fig. 4). 



The logic behind Leopold's glacial hypothesis on the 

 positive relationship between pheasant distribution and 

 recently glaciated areas and the subsequent hypothesis 

 that grit from recent glacial drift is needed to proxide a 

 source of calcium for pheasants becomes apparent when 

 we recognize that the drift from recent glacial activity 

 has undergone less weathering and, consequently, less 

 leaching than have the older drifts. The a\ailabilitv to 

 l^heasanls of grit from the less weathered and less leached 

 glacial drift must then be considered. \Vith the cxce])- 

 tion of areas of some alluvial deposits, lake sediments, 

 and sand dunes, the state of Illinois is covered by wind- 

 blown deposits of loess originating from the Wisconsinan 

 age. These loess deposits can be eliminated from con- 

 sideration as a source of calcium over much of the 

 pheasant range in Illinois. In a large portion of Illinois, 

 including most of the northeastern thiid of ilie state 

 where pheasants are most abundant, deposits of loess 



are shallow— 4 feet or less in depth— and noncalcareous 

 (Leighton & Willman 1950:604. 607). The speculation 

 may be made that pheasants are more abundant in some 

 areas of shallow loess than in areas of deep loess because 

 erosion, plowins;, or some other acti\ity has exposed the 

 t;lacial drift, thus making calcium-bearine; grit that may 

 be in this drift available to the pheasants. If this specu- 

 lation is valid, the drift on which pheasants are most 

 abundant (Wisconsinan) should contain more calcium 

 available to the birds than the drift on which pheasants 

 are not established f Illinoian). 



In 1956, 1.726 pheasants originating from stock ob- 

 tained from California were released by the Illinob Nat- 

 ural History Survey and the Illinois Department of 

 Conservation on an area of Illinoian drift in Cumber- 

 land Coimty. The release was made as part of a program 



Illinoian , 



Fig. 4.— Distribution .iiid abundance of phca.s.iiits in Illi- 

 nois in relation to the most recent gl.ioi.ition, the Wisconsin.in. 

 The hc;uy lino dosi^iLTtes the terminal Imundarv- of the ^Vis- 

 consinan ice sheet (after Kkhlaw & Lamar 1964:4). The 

 liajure for each county within the pheasant range represents 

 ])h('asant abuiulaiue. as deti-nnined by the moan number of 

 ]ib('asaiits loportod by niral mail carriers per 100 miles of 

 driving during six censuses in 1957 and 1958 (Table 1). 



10 



