prolonged than previously documented, 

 completed by early June (Table 7) . 



Most calving (76%) was 



Rutberg (19S4) sugaests that birthing synchrony in bison 

 is an adaption to minir.ize stress related to winter severity 

 The two winters preceding the reduction (1986-87, 1987-88) in 

 YNP were less severe than normal (Merrill et al. 1988), which 

 could partially explain the prolonged calving season indicated 

 by our data. 



Effects of brucellosis on calving success of YNP bison is 

 unknown and may also influence the length of the calving 

 season. 



Table 7. Determination of conception and potential calving 

 periods for 50 bison fetuses collected during the 

 1988-89 removal. 



ADULT PHYSICAL MEASUREMENTS 



Physical measurements were obtained from 158 bison in the 

 field. Appendix J shows measurements by age class and sex. 



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