 The gestation period ranges from 41 to 47 days . More litters are born in warm climates : the number of litters born each year ranges from two per year in Idaho to seven in Arizona . Litter sizes are largest in the northern portions of black @-@ tailed jackrabbit 's range and decrease toward the south . Average litter size has been reported at 4 @.@ 9 in Idaho , 3 @.@ 8 in Utah , and 2 @.@ 2 in Arizona . 
