May 14, 2008

Horn Growth & Rainfall

Let's take a look at rain and horn growth. A lot of hunter's are excited about the rainfall recently and some even believe that it will impact the horn growth on certain animals. I have no idea how it will affect the deer or elk, but several years ago I researched what differing amounts of rainfall might do to antelope horn growth.

How the research was done:

I am not a researcher or biologist and this is probably a crude attempt at determining any relationship of rainfall and horn growth, but I'll present the findings anyway for your amusement. First, I went through the Arizona Record Book and marked down the number of big bucks. This was several years ago and I honestly can't remember what my cut-off number was for what I was calling a big buck - it could have been 82 or 84 or even 80. I then marked where each buck was taken and what year. Next I looked up records on the rainfall in those areas in those years. I then compiled this little graph. More or less. The accuracy of these results are up in the air, but it's interesting nonetheless.

How to read the graph:

Obviously the number of big bucks taken is on the left side. The bottom indicates during what period I grouped together for the relationship of horn growth to rainfall. For instance - the first three bars represent the number of record book bucks taken the year after "poor rainfall", "average rainfall", and "good rainfall". This does not take into account the year that the bucks were actually taken. From the graph you can see that if the rainfall was poor the year before the buck was taken then there were only 5 big bucks taken. If the rainfall was average the year before the buck was taken then there were about 7 or 8 big bucks taken. If the rainfall the year before was good then there were about 17 big bucks taken.

The P/Y stands for the rainfall the Prior Year and Year of being taken. So, 1/0 means that just the prior year was taken into account. And 1/1 means that the prior year was taken into account and the year that the buck was taken.

I know this all seems complicated (even to me now), but when I actually did all this many years ago it made sense at the time. If I haven't explained it good enough just post your questions in the comments below.


John said...

I think this is some good info, I would like to know if this info has passed the "EYE" test. A picture of said antelope in a poor year, then the next year was a good year and the same said antelope was bigger or smaller or same. From the info you have presented next years tag will be the golden one!!!

Eli Grimmett said...

One problem with the eye test is that I believe a lot of the bucks are experiencing the spurt in horn growth from their second year to their third year. What this would mean, if it was the case, is that it would be extremely hard to keep track of a buck from one year to the next. Most two year olds aren't very big and they can jump 10 or more points in one year.

Another problem with the EYE test is that antelope have such a short period of time when they can be big - between the years of 3, 4, 5, and 6 is pretty much it. Just a natural progression should have a buck getting larger in at least one or two of those years, so it might be tough to distinguish the exact cause - whether it be rainfall or simple maturation and genetics.

If any of you haven't checked out AAF's website, you should do so and read through some of the research studies they have posted there. Some of them talk about rainfall and horn growth. Pretty neat stuff.

John, we do have a ton of pictures of bucks from one year to the next. Maybe I'll look back and see what the rainfall looked like in those years. :)

Eli Grimmett said...

Also, and this is kind of a tricky way to look at things, check out how high the 3+1 bar is! This could indicate the buck was probably born 4 years ago and is a 4 year old buck which would support some of the other studies that have said a buck is biggest in it's 3rd and 4th years.

John said...

you bring up some really good points.

Thanks as always