The amount of moisture an area receives from year to year is a critical factor in regulating the size of antelope horns. For example, a study in Montana's Fort Belknap Indian Reservation found that the area typically supported bucks with larger horns, on average, than those in other test areas. However, in drought years bucks on the reservation grew shorter horns. The study also concluded that pronghorns attained adult horn size at 2 to 3 years of age and bucks' horn size failed to increase much in following years. So chances are good of seeing a big buck, even in an area with lots of hunters, and especially following a year or two of good rains.