rainfall less than 5 inches or greater than 6 inches (Fig. 

 7 ) . However, when tested for curvilinearity of regression 

 (Snedecor 1956:452-457), these data yielded no statis- 

 tical significance (0.05 level) for either August, 1957, or 

 August, 1958 (1957: estimated 7 = 220.0 - 1.189Z + 

 0.l:H3A'^ F = 0.15, Reference F = 3.42 at 2 and 22 

 d.[.: 1958: estimated 7 = 22.94 - 6.490^ + 0.551 SAT^ 

 f = 0.67, Reference F= 3.42 at 2 and 22 d.f.). 



Another weather factor, that of evapotranspiration 

 (evaporation from the soil surface and transpiration from 

 plants) has been suggested by McCabe, MacMuUan, & 

 Dustman (1956:322-325) as a possible influence on the 

 distribution of pheasants in the Lake States. These 

 workers reported "an almost perfect correlation" be- 

 tween the distribution of pheasants in the Lake States 

 and the mesothermal B\ region as classified by the 

 climatologist Thornthwaite (1948:81, 87, and pi. IC). 

 This region has a potential evapotranspiration of 22.44 

 inches along its northein boundary (north of the central 

 portions of Wisconsin and Michigan) and 28.05 inches 

 along its southern boundary (near the central portions 

 of Indiana and Illinois) . An exception to this "correla- 

 tion" is found in Illinois, where a portion of the best 

 pheasant range in the east-central sector of the state falls 

 south of the mesothermal B'j region. The cause-and- 

 effect mechanisms of the apparent relationship between 

 evapotranspiration and pheasant distribution are not 

 known. 



Bennitt & Terrill (1940:428) established a working 

 hypothesis that the barrier limiting the southward ex- 

 tension of the range of the pheasant might be "high egg 

 temperature and the resulting mortality of embryos," or, 

 in other words, embryonic mortality resulting from the 

 exposure of clutches to high air temperatures in spring 

 or summer. Graham & Hesterberg (1948:12, 14) postu- 

 lated that the southern limit of pheasant distribution 

 might be determined by the extent of embryonic mor- 

 tality caused by direct exposure of clutches of eggs to 

 the sun's rays during the preincubation period. 



Yeatter (1950:529-530) was the first worker to con- 

 duct exjx-riments to determine the influence of air tem- 

 peratures in defining the southern limits of the range 

 of the pheasant. He observed a sharp decline in suc- 

 cessful hatches and in the number of chicks produced 

 per clutch along the southern fringe of the pheasant 

 range in cast-central Illinois after the first week of July: 

 nest studies suggested that this decline in production re- 

 sulted from a decline in hatchability of eggs, a decline re- 

 sulting from embryonic mortality and not from decreased 

 lertility. To test the [Mistulate that the mortality of em- 

 bryos might be attributed to exposure of the clutch to high 

 temperatures during the preincubation period, a time at 

 which the hen does not control the temperature of the 

 clutch, Yeatter obtained jjlieasant and bobwhite eggs from 

 Illinois game farm slock and expost'd llicni to dilTerent 

 air temperatures between 62 degrees F (control) and 88 

 degrees F during 9-hom- periods (8:00 a.m. to 5:00 

 p.m.) for 7 conseculi\e days prior to incubation. The 

 pheasant eggs exposed undrr these conditions showed a 



progressive decline in hatchability from a high of 75.0 

 per cent at 62 degrees F, the control temperature, to a 

 low of 42.1 per cent at 88 degrees F, while hatchability 

 of the quail eggs, similarly exposed, declined from a high 

 of 76.2 per cent at 62 degrees F to 68.4 per cent at 88 

 degrees F. These data suggested that high air tempera- 

 tures during the laying period had an important influence 

 in limiting the southward spread of the pheasant in Illi- 

 nois and other states. 



To further test this postulate, Yeatter obtained eggs 

 from two strains of pheasants, one strain from California 

 and the other from Wisconsin. When the eggs from 

 these two strains were subjected to similar preincuba- 

 tifin temperatures of 62 degrees F (control) to 88 degrees 

 F, the eggs from the California stock showed greater 

 hatchability than did the eggs from the Wisconsin stock 

 (Ralph E. Yeatter, Illinois Natural History Survey, Ur- 

 bana, 1962, personal communication). These experi- 

 ments, when considered alone, suggested that the ability 

 of pheasant embryos to survi\e under conditions of high 

 air temperatures may have been the operati\e force 

 in the natural selection of a strain of pheasants able 

 to withstand the climate of California, and that the 

 pheasant now resident in the Midwest has failed to be- 

 come established when it has been released south of its 

 present contiguous range because of its lack of genetic 

 adaptation to high air temperatures. Howe\er, it seems 

 illogical to assinne that natural selection of individuals 

 with the genetic a]3titude necessary to withstand higher 

 air temperatures would not occur along the southern 

 margin of the range currently occupied by the pheasant 

 in the Midwest, thus allowing the bird to gradually ex- 

 tend its range southward into previously unoccupied 

 range. Perhaps not enough time has elapsed to create a 

 gene jjool of traits that would allow a measurable and 

 permanent spread of the jihcasant into areas of higher 

 tem]3cratures. 



That high air temperatures alone probably do not 

 limit the southward extension of pheasants is indicated 

 by the observations of Ellis & Anderson (1963:225). 

 Pheasants originating from California stock failed to 

 establish .self-maintaining populations after being released 

 on two areas south of the contiguous pheasant range in 

 Illinois (Ellis & Anderson 1963:225). Among the Cali- 

 fornia jjheasants and their progeny, Ellis & Anderson 

 (1963:234) reported, "There were no differences in the 

 average mmiber of chicks in broods hatched from nests 

 exposed to temperatures that exceeded 79 F on 7 or more 

 days during the preincubation period when compared to 

 the average number of chicks in broods from nests not 

 ex])osed to such tem])eratures." These workers (Ellis & 

 Anderson 1963:236; Anderson 1964:263) concluded that 

 the faiUne of liberated pheasants and their progeny to 

 (■stal)lish themselves south of the contiguous range occu- 

 pieii i)y pheasants in Illinois was due more to inadequate 

 sursival, particularly diuing fall and winter, than to in- 

 adetjuate rejiroduction. 



This discussion of ])heasants and climate has shown 

 the deuiee of comph-xitv with which we are faced when 



16 



