Pronghorn bucks - Young and big

[Big Fin]

I was aware that pronghorn bucks matured at a young age, but this is even more enlightening. So much for having to find an old buck to make be a big buck.

Might explain why a heavy harvest in some WY units still allows some bucks to reach B&C entry scores.

TROPHY POINTS: Big Game Research Online -- Part 7
Re-posted from www.boone-crockett.org
Monday, January 24, 2011

Pronghorn Evolution and Management

By David Hewitt - Boone and Crockett Club Professional Member

It is an axiom that management for trophy deer, sheep, and goats requires management for older males because antler and horn size increase with age. For example, antlers continue to increase in size each year until white-tailed deer bucks reach at least 5 years of age, bull elk 7 years of age, and bull moose 10 years of age. For this reason, wildlife management programs that seek to produce trophy animals emphasize a low harvest rate of males, or a selective harvest that enables males with the most potential for large horns/antlers to mature.

Pronghorn are an exception to this pattern. In fact, pronghorn are exceptional in many ways. Pronghorn are the only species with a horn (keratinous head ornamentation) that has a prong and is shed annually. Pronghorn are found only in North America, whereas deer, sheep, and goat species are found throughout much of the world. Pronghorn are the only member of their family (Antilocapridae); compared to the 50 species of deer and 35 species of sheep and goats, pronghorn are indeed a North American original.

Another unique aspect of pronghorns compared to other game animals is that their horns reach a maximum size at a relatively early age. Studies of pronghorn from Colorado north to Montana and Alberta consistently show pronghorn achieving a plateau in horn size by 2 – 3 years of age. Pronghorn in New Mexico and Arizona may have peak horn size later, perhaps 4-5 years of age. Furthermore, young bucks (less than four years of age) are often half of the top 10 largest pronghorn harvested in a region. The highest scoring Boone and Crockett pronghorn trophies, in which the animals’ ages are known, are three years old or younger!

Why do pronghorn have this unique pattern in horn growth? One explanation suggests the horn growth pattern is part of a suite of traits that have enabled pronghorn to thrive in variable environments. Southern pronghorn range has periodic drought and northern ranges have periodic blizzards that can, and do, occasionally kill large numbers of animals. Any pronghorn that mature slowly risk not breeding at all before a particularly bad drought or winter killed them. Conversely, pronghorn that matured quickly and bred at an early age had a better opportunity of leaving offspring.

Thus, the pronghorn we see today have been shaped through evolution to mature and breed at an early age. Pronghorn reach adult body size by 1.5 to 2 years of age. Females usually breed as yearlings; males are capable of breeding as yearlings but may not have many opportunities if older, more dominant males are around. And the horns of males reach maximum size at an early age.

Because the horn sheaths are grown anew each year, factors like precipitation and forage quality appear to affect annual sheath growth rates. The roles of maternal condition during gestation, population density, and genetics in modulating horn growth potential need further study.

Management consequences of large horns being possible on young pronghorn:

* An exceedingly low harvest of male pronghorn is not necessary for production of trophy pronghorn.
* Instead, pronghorn managers may allow moderate harvest of bucks, and given good range conditions, reasonably expect most pronghorn to achieve their potential in horn growth.
* More people can be given an opportunity to hunt pronghorn, and possible harvest a trophy, than would be possible if pronghorn horns continued to increase in size until males were much older.


Thanks to Carl Mitchell and David Brown for sharing ideas and literature on pronghorn horn growth.

For more information on pronghorn growth patterns see:

C. D. Mitchell and C. R. Maher. 2001. Are Horn Characteristics Related to Age in Male Pronghorns? Wildlife Society Bulletin 29:908–916.

C. D. Mitchell and C. R. Maher. 2006. Horn Growth in Male Pronghorns (Antilocapra americana): Selection for Precocial Maturation in Stochastic Environments. Acta Theriologica 51:405–409.

K. Morton, P. F. Jones, and M. Grue. 2008. Comparison between Pronghorn Age and Horn Size in Southern Alberta. Proceedings Pronghorn Workshop 23:104–114.

D. E. Brown, W. C. Keebler, C. D. Mitchell. 2010. Hunting and trophy horn size in male pronghorn. Proceedings Pronghorn Workshop 24:In press.


Trophy Points: Big Game Research On Line is complied and edited by David G. Hewitt, a Professional Member of the Boone and Crockett Club and the Stuart W. Stedman Chair for White-tailed Deer Research at the Caesar Kleberg Wildlife Research Institute.

 

[drthornton]

That is very interesting. Like most I assumed the age structure was by far the most important ingredient but it looks like genetics and habitat are higher on the management bucket.

 

[JCS]

Learn something new every day. This was very informative.

 

[Oak]

Yep, that's why I laugh when someone says a pronghorn buck needs another year. It very likely is as big as it's going to get.

Here's an interesting study that was done in NM. There is some bias, since they were targeting trophy pronghorn, but they do mention it.

http://www.azantelope.org/Facts___Research/Horn_Growth_Study/horn_growth_study.html

The funny thing is, although they may be big, a 2 year old buck is probably not going to be dominant. Have Buzz tell about the buck he shot with me in WY about 4 years ago. Classic example. I was also thinking about that when Big Fin had an average buck run the booner he was after clean out of the country a couple of years ago (as seen in Seasaon 2). Probably a young buck with big horns that was not dominant yet.

 

[EliAGrimmett]

Here's a link to a study by David E. Brown on horn growth. He's been studying this stuff for a long time. We've sent him probably over 100 antelope teeth over the years to include in his studies.

http://www.azantelope.org/Facts___Research/Horn_Growth_Study/horn_growth_study.html

This next link contains several links at the bottom of the page that will show a lot of the actual bucks and their ages.

http://www.azantelope.org/Facts___Research/Pronghorn_Aging_Study/pronghorn_aging_study.html

EDIT: Oak - looks like I was typing my post when you posted the same link.

 

[EliAGrimmett]

One thing of note - I know this tooth aging stuff is supposed to be pretty accurate and all, but they have made incorrect aging estimates on several bucks we've sent them before.

One of them was "DW". His teeth were aged at 2 years old. We had video of him for two years and both years he was probably a World Record and according to D. Brown there's no way he could have been a World Record as a 1 year old, so clearly the tooth aging was wrong. They did try to convince me that we could have been wrong and that it could have been two different bucks...you tell me how often two nearly identical 95-inchers are found in back to back years in the exact same location while the one from the year before magically vanishes...

The first year we found him:


The second year:

 

[BuzzH]

That buck Oak is talking about was interesting...and both of us noticed, mainly because we watched that buck for a couple days.

He was a nice buck, around 15.5 inches, good prong, good mass. He was being pushed around by another buck that had much smaller horns. Oak and I both thought it was odd and we both also had a hunch he wasnt very old. I ended up shooting him and he was only 2.5 years old and scored in the upper 70's...

I learned something that day.

 

[Bwana]

Now that is very interesting.

 

[xrayts]

Amazing to think a B&C buck might only be 2 or 3 years old. That should be encouraging to any hunter!

 

[hardscrabble]

I found this out as well after the 2009 season. In 09' the state of ND was asking for the lower jaw bone from the antelope. The numbers were down that year and good goats were few and far between. I was finally able to take a nice buck that scored 74" and some change. I was shocked when the report from the G&F came back with an age of 2 1/2 years. I would have guessed this goat to be 4 1/2 given the genetic pool that is in the area.

Deffinetly and eye opener.

 

[----]

Really interesting.
We killed two bucks out of an area last year, and the better scoring buck was definitely smaller bodied and younger.

 

[BuzzH]

On the same subject, I've looked at a lot of dead buck antelope and its pretty easy to age them based on the adult teeth or lack there-of.

Its interesting how may bucks I've seen taken that are 4+ years old that are VERY average antelope (12-13 inchers).

After that experience that Oak and I had some years back I've also paid more attention to the way bucks are interacting during the rut. I think age makes a big difference in dominance in antelope...

 

[tarheel]

Yep, that's why I laugh when someone says a pronghorn buck needs another year. It very likely is as big as it's going to get.

Here's an interesting study that was done in NM. There is some bias, since they were targeting trophy pronghorn, but they do mention it.

http://www.azantelope.org/Facts___Research/Horn_Growth_Study/horn_growth_study.html

The funny thing is, although they may be big, a 2 year old buck is probably not going to be dominant. Have Buzz tell about the buck he shot with me in WY about 4 years ago. Classic example. I was also thinking about that when Big Fin had an average buck run the booner he was after clean out of the country a couple of years ago (as seen in Seasaon 2). Probably a young buck with big horns that was not dominant yet.

Saw a similar event in WY this past season. I was waiting for what appeared to be a 15'er to stop long enough for a long poke when the herd buck (about 13") spotted him and chased his butt out of the county.

 

[1_pointer]

Wonder if many of the older bucks get older because of the smaller horn size? Could we be inadvertantly selecting for smaller bucks? Just a thunk...

 

[BuzzH]

pointer,

I've the same questions myself...and definately worth a thunk.

I think theres a lot of variables to consider though.

 

[Big Fin]

Wonder if many of the older bucks get older because of the smaller horn size? Could we be inadvertantly selecting for smaller bucks? Just a thunk...

Interesting thought.

Unrelated, but another strange observation is this. The guy who spent his entire career studying mule deer in the Bridger Mountains of Montana has some theories as it relates to mule deer.

Back when budgets allowed him to collar a lot of deer and fly often, he would go during the rut and track where the bucks were. The biggest bucks he saw, usually opted out of the heavy rutting activity and were away from the doe groups, all by themselves.

His theory is that opting out made them more likely to survive the harsh winters, grow to older ages, and when winter ended, they would have more fat reserves allowing them to start growing antler quicker than the bucks who were beat down from heavy rutting.

Not sure if this is true, or just his observations, but it seemed that if the biggest of these bucks were opting out of the rut, they were not necessarily passing on their genetics.

I know that is not the topic of this antelope discussion, but it is another strange variation of what I had always assumed was the norm for male dominance and rutting behavior of big game animals.

 

[Oak]

I think it would be possible to select for smaller bucks, but right now I don't think there are enough selective hunters out there to have an effect. The vast majority of tags are filled in the first 2-3 days of the season, on average 12-14" bucks. Dominant bucks are probably the ones getting picked off...the ones that are highly visible, running all over hell, getting themselves in trouble. Subordinate bucks are likely by themselves and less visible.

Then again, really big bucks are few and far between (thinking WY...not NM or AZ). Maybe it wouldn't take many selective hunters to have an effect.....

 

[xrayts]

His theory is that opting out made them more likely to survive the harsh winters, grow to older ages, and when winter ended, they would have more fat reserves allowing them to start growing antler quicker than the bucks who were beat down from heavy rutting.

Another theory is that the bucks grow to older ages by being less visible to hunters. By having little or no participation in rutting activity, they don't put themselves in the view of hunters as often.

 

[Terry aka Coydog]

Very interesting.I had always heard that weather and food affected horn growth but never knew or expected that a young buck could be of B&C quality. Thanks for the thread on this

 

[shoots-straight]

I think it would be possible to select for smaller bucks, but right now I don't think there are enough selective hunters out there to have an effect. The vast majority of tags are filled in the first 2-3 days of the season, on average 12-14" bucks. Dominant bucks are probably the ones getting picked off...the ones that are highly visible, running all over hell, getting themselves in trouble. Subordinate bucks are likely by themselves and less visible.

Then again, really big bucks are few and far between (thinking WY...not NM or AZ). Maybe it wouldn't take many selective hunters to have an effect.....

Oak, I select smaller bucks. Just doing my part for wildlife.