I 



we attempt to explain abundance and distribution of 

 pheasants by weather factors. We know too little about 

 these factors and their effects. As McCabe ct al. (1956: 

 324) pointed out, "What to the pheasants are ideal 

 climatic conditions are not necessarily those measured 



by weather stations " Undoubtedly, weather e.xerts 



a considerable influence on established phea.sant popula- 

 tions, particularly with respect to annual fluctuations. 

 On areas occupied by only a few pheasants, unfavorable 

 weather may limit the dispersion and abundance of the 

 population by annually depressing production or by in- 

 creasing the mortality rates, or both. In unoccupied 

 range, the cumulative effect of these factors might be so 

 great as to preclude the establishment of self-maintaining 

 populations. 



A\'e hypothesize that, in areas where factors other 

 than weather are favorable to the bird, pheasant popu- 

 lations may be limited not by adverse weather conditions 

 in any one year but rather by the frequency, severity, and 

 duration of adverse conditions over a period of years. 

 We may therefore speculate that adverse weather, as 

 well as other adverse environmental factors, occurs less 

 frequently, with less severity, and for shorter periods in 

 the range occupied by pheasants than in the range un- 

 occupied by pheasants. The validity of this hypothesis 

 will be determined only after completion of long-term 

 ecological studies of pheasants in areas characterized by 

 different levels of pheasant abundance. 



Summary 



In Illinois and other midwestern states, populations 

 of pheasants are characterized by discontinuous distribu- 

 tion and by variable abundance. This paper reviews pub- 

 lished findings and presents new data on three factors, 

 land use, calcium, and weather, all commonly considered 

 as important influences on the distribution and abun- 

 dance of pheasants in Illinois. 



The intensively cultivated cash-grain area of east- 

 central Illinois has consistently supported the best popu- 

 lations of pheasants in the state since the late 1930"s. 

 The following land-use practices were found to be char- 

 acteristic of many of the counties in Illinois whera 

 [pheasants were most abundant: (i) a high proportion 

 of the land in cultivated crops and a low proportion in 

 woodland, (ii) a high proportion of the farms classified 

 as cash-grain faiTns and a lower proportion as dairy farmsi 

 and livestock farms, and (iii) about 50 per cent of thu 

 cropland in corn and soybeans, about 5 per cent in hay, 

 and about 15 per cent in pasture. A multiple regression 

 analysis indicated that a combination of three land-use 



factors, (i) the proportion of land in culti\ated crops. 

 (ii) the proportion of farms classified as cash-grain farms, 

 and (iii) the proportion of cropland in hay, when tested 

 against all other land-use factors, exerted the greatest in- 

 fluence on the distribution and abundance of pheasants 

 in Illinois. 



In Illinois and other North Central States, the distri- 

 bution of pheasants coincides closely with that area 

 blanketed by the Wi.sconsinan glacier, the last of the 

 major ice sheets. Pheasants ha\-e seldom established 

 themselves on Illinoian glacial drift, which in Illinois 

 underlies and extends south and west of the Wisconsinan 

 drift. The Illinoian glacier was the immediate predeces- 

 sor of the Wisconsinan glacier. A supposed deficiency 

 of calcium in the soils and grit on areas of exposed 

 Illinoian drift has long been regarded as a factor limiting 

 the southward spread of the pheasant in the North 

 Central .States. In Illinois, the amounts of calcium in 

 the soils and grit in an area of Illinoian drift, where 

 phea.sants have not established self-maintaining popula- 

 tions, were equal to or greater than the amounts from 

 similar items in an area of Wisconsinan drift, where 

 pheasants are abundant. The amounts of calcium in the 

 grit from gizzards of hen pheasants and young pheasants 

 on Illinoian drift were very similar to those amounts 

 found in the grit from gizzards of hens and young on 

 Wisconsinan drift; also, the subsequent utilization of in- 

 gested calcium by hen pheasants on the Illinoian drift 

 appeared to be equal to that by hens from a thriving 

 population on the Wisconsinan drift. It is unlikely that, 

 in Illinois, the establishment of self-maintaining pheas- 

 ant populations on areas of Illinoian drift is prevented 

 by a deficiency of calcium. 



Unfavorable weather is partially responsible for year- 

 to-year fluctuations in numbers of pheasants within their 

 established range. On areas occupied by only a few 

 pheasants, unfavorable weather may limit the dispersion 

 and abundance of the population by annually depressing 

 production and by increasing mortality rates. In unoc- 

 cupied range, the cumulative effect of these factors might 

 be so great that the establishment of pheasants would be 

 prevented. In areas where factors other than weather 

 are favorable to the bird, pheasants may be limited not 

 by unfavorable weather in any one year but rather by 

 the frequency, severity, and duration of adverse weather 

 over a period of years. Adverse weather, as well as other 

 adverse environmental factors, probably occurs less fre- 

 quently, with less severity, and for shorter periods in the 

 range occupied by pheasants than in the range not oc- 

 cupied by pheasants. 



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