c 



3 



Mean birthdate of all fawns captured 



Mean birthdate of captured fawns born by 14 June 



% Females 2+ Years and Non-Pregnant 



t t— — r 1 1 1 1 r 



1977 1979 1981 1983 1985 1987 



Year 



Figure 5.1 



Mean birthdate for captured mule deer fawns 

 and % of females 2 years or older that were 

 not pregnant during 1977-1987 in the Missouri 

 River Breaks, Montana. 



Missouri River Breaks during 1958, 1963, 1984, and 1985 

 indicated that 38 (97%) were pregnant. Pregnancy rates were 

 high even though 25 of the 39 females were collected during 

 1984 and 1985 when fawn survival after birth was very poor. 

 The 1 non-pregnant female, a yearling, was collected in spring 

 1985. 



Pregnancy rate as determined by observation of marked 

 females during 1976-1983 was 91% (177 of 194). This method 

 somewhat underestimated pregnancy rates because females 

 abandoning or losing fawns within a few days of birth could 

 have been classified as non-pregnant. Regardless of the 

 source of data, apparently more than 90% of female mule deer 

 in this area conceived successfully. That was higher than the 

 85% pregnancy rate recorded for 129 adult females examined 

 statewide during 1975-1979 ( Pac 1979). 



Ovulation rate for 35 adult females collected during 

 1963, 1984, and 1985 was 1.66 ova per female or 1.71 per 

 pregnant female. Fertilization rate for ova in females 

 collected during spring 1963 was 100% (16 of 16). 

 Fertilization rates for ova during 1984 and 1985 were 82% (22 

 of 27) and 92% (12 of 13), respectively. The 89% 



112 



