Case in point for Roosevelt elk. I spent 10 hours on the coast on 4/9 and of the 15-20 bulls I saw that day (mostly *censored*s) most had both antlers. A couple had one antler, and there was an older herd of about 6 bulls that were already crowing out with brow tines and heavy main beam buds. I found one antler that day and it was a 4pt (bloody). In that same area in years past, they've all been dropped by 4/1. It does fluctuate depending on the photo period, nutrition, and other factors. You can figure that by the end of April all elk will have dumped their headgear. I found four elk spikes on opening day of turkey hunting one year. They usually are last to drop so that is another data point to consider.