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NATURAL MORTALITY
by Dr. Mickey W. Hellickson

High Natural Mortality
Is killing all spikes that bad, even if it represents an average of 40 percent, and as much as 63 percent of the bucks in that age class during any given year? It very well could be because so far we have only been talking about spikes that are killed by hunters. What about yearling bucks that die of natural causes?

During 1992-95, we captured and radio-collared 125 bucks. Of these 125 bucks, 20 were yearlings. We radio-tracked these bucks continuously after their capture to determine their survival rates outside of the hunting season.

Hunters killed none of these 20 yearlings. Two bucks were excluded because one died within a month of being captured and the transmitter on the second buck failed. An average of 39 percent (7 out of 18) of the remaining 18 yearling bucks died of natural causes within one year!
Although it is still not clear what affect hunting has on deer survival rates, we can at least assume that hunting is partially additive. This means that a portion of the spike harvest each year will be added to the 39 percent natural mortality rate. If hunting were totally additive than you may be in danger of losing an average of 80 percent of your yearling bucks each year by intensively culling spikes!

Older Bucks Die Too
Also, so far we still have not taken into account the natural mortality rates of older-aged bucks. Our research indicates that an average of 17 percent of 2.5-year-old bucks die each year of natural causes. Twenty percent of 3.5-year-old bucks die and 5 percent of 4.5-year-old bucks die of natural causes also.

What do all of these different percentages mean? Let's start with a population of 100, 1-year-old bucks and look at their survival based on natural mortality alone. Only 61 of these bucks will survive to 2-years-old. Only 50 will survive to 3-years-old. Only 40 will survive to 4-years-old. And only 38 of the original 100 bucks will survive to 5-years-old without any bucks being removed by hunting.

On average then, 62 percent of all yearling bucks will die of natural causes before they reach maturity at age five! So, without killing even one spike buck, 62 percent of those yearling bucks will still die of natural causes before they reach five years of age. These natural mortality rates need to be considered before implementing an intensive yearling buck program, especially if having a surplus of mature bucks of any antler size is a management goal.


Posted by Dr. Mickey W. Hellickson on 03/21 at 10:54 PM
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