of incubation or early in ilu- lnoociint; ])oiiod, she adds 

 few, if any, young to the ])opulation. If she dies alter 

 llic chicks are able to sur\i\e on their own, but prior 

 to fail, her death has little or no effect on the annual 

 |)roduction of young; however, the absence of this and 

 similar hens from the fall population results in higher 

 young-to-adult age ratios than are justified by the hatch. 



Adverse weather that diuing the reproductive season 

 places unusual stress on adult hens may reduce the 

 I)roduction and survival of chicks by causing the hens 

 to give less than the normal attention to eggs or young. 

 Laboratory experiments by MacMuUan & Eberhardt 

 ( 1953 : 330) suggested that inattenti\'e incubation by nest- 

 ing hens, ])articularly during late incubation in cold and 

 wet spring weather, might cause lethal exposure of eggs. 

 These workers reported that young chicks were less 

 tolerant of cold, especially when accompanied by pre- 

 cipitation, than were eggs. If production of young is 

 depressed and death of adult hens accelerated by adverse 

 weather during the reproductive season, age ratios the 

 following autiunn might indicate erroneously that an 

 average hatch of young pheasants had occinred. 



When Graham & Hesterberg (1948: 10-13) compared 

 rainfall-temperature climographs for four areas in Ore- 

 gon, Minnesota, North Dakota, and Michigan where 

 pheasants had established self-maintaining pojjulations, 

 they found the greatest similarities in the climographs 

 of these four areas during April and May. Climographs 

 for areas in Missouri, Ohio, and Tennessee where pheas- 

 ants had not established themselves showed little or no 

 similarity during April and May to the climographs for 

 the four areas occupied by pheasants. Graham & Hester- 

 berg (1948:10) concluded that "if the distribution of 

 pheasants is limited in any way by temperature or pre- 

 cipitation the effects must be during the spring season." 



Thus far, in this paper, little attention has been 

 given to measuring directly the influence of summer rain- 

 fall on the hatch of pheasant chicks. In the established 

 ]oheasant range in Illinois, Jime is the month during 

 which about 50 per cent of the annual crop of chicks 

 is hatched. Heavy rainfall during June might exert two 

 opposing influences on the hatch of pheasant chicks in 

 this area. First, heavy rainfall so timed as to occur 

 during a period when a sizable ])ortion of the annual 

 hatch was very young might result in the mortality of 

 many young chicks, particularly if the rains were ac- 

 companied by cold (MacMullan & Eberhardt 1953:330). 

 Second, excessive rainfall during early June would tend 

 to delay mowing of tame hay, thereby allowing many 

 nests to hatch that would normally be destroyed by 

 mowing. 



To determine what efl'ect, if any, the amount of rain- 

 fall in Jime, 1957 and 1958, had upon tlu' hatch o( 

 chicks within the established range of pheasants in Illi- 

 nois, we plotted rainfall for this month against the 

 number of chicks obser\i'd per 101) miles of driving by 

 rural mail carriers during August of the same years in 

 each of the 25 counties in which ])hcasants were most 

 abundant (Fig. 7). Thr iDiig-lcrin average rainfall dur- 



ing June for the.se 25 counties (Page 1949:201-294) 

 was 3.9 inches. In 1957 and 1958, rainfall in June 

 averaged 5.1 and 7.0 inches, respectively, for the 25 

 counties; thus, in June of both years, rainfall was above 

 the long-term average. The average amount of rainfall 

 recorded in June. 1958, was significantly greater than 

 that recorded in June, 1957 (/ = 3.73: P < 0.01). The 

 nicnn number nl chirks per I DO miles ol dri\ in>j; in the 



I 23456789 10 

 INCHES OF RAINFALL IN JUNE 



Fig. 7.— Abundance of pheasant chicks reported by rural 

 mail carriers per 100 miles of driving during AuE;iist in rela- 

 tion to rainfall during (he preceding June for each of the 25 

 Illinois counties in which pheasants were most abundant 

 (Table 1), 1957 and 1958. The rainfall data are from the 

 United States Weather Rureau (1957, 1958). 



25 counties during August was 6.8 in 1957 and 6.0 in 

 1958. The difference in the abimdance of chicks between 

 August of 1957 and August of 1958 was not significant 

 (/^0.48; P> 0.50), but fewer chicks were observed 

 in 1958, which was characterized iiy more rain during 

 June than was 1957. 



Statistical tests by linear regression indicated that 

 there was no significant correlation (0.05 level) between 

 the amount of June rainfall and the abundance of chicks 

 in the 25 top-ranked ])heasant counties of Illinois in 

 August of 1957 or 1958 (Fig. 7; 1957: fo = 0.216, F = 

 0.10, Reference f = 4.28 at 1 and 23 H.f.; 1958: fe = 

 0.,589, F^ 1.25, Reference F = 4.28 at 1 and 23 rf./.). 



The aijundance of chicks in .August appeared to be 

 li'ss in counties where lainfall measured between 5 and 

 6 inches during June than in (ounlies with amounts of 



15 



