Would you be surprised to learn not every doe raises a fawn each year? Zero is an option, even when fawn predators are not a factor. For some does to skip years, though, there must be other does in the population that go beyond the call of duty. Super Does, if you will. New evidence is unmasking these heroes, and their existence has some important implications for your deer population management efforts.
The new evidence is from a 12-year study of the deer population at Auburn University’s 431-acre enclosed deer research facility in Alabama. In his master’s research, Tristan Swartout found Super Does that represented less than half of the doe population and yet produced three quarters of the fawns recruited during the study.
Tristan focused on 86 whitetail does that recruited 260 fawns later connected to them through DNA. Before we begin their story, remember “recruitment” is not the number of fawns born but the number that reach 6 months of age and join the fall population. This will be an important distinction.
Super Does Were Repeat Recruiters
To me, the most remarkable finding of Tristan’s study involved what he called “consecutive recruiters.” By his definition, these are does that recruit fawns in back-to-back years at least once in their lifetime. Of the 86 does he studied, 40 of them, just under half, achieved this distinction. Though this group represented 47% of the does, they recruited 75% of all the fawns in the study!
Consider a few Super Does that were elite even among the best fawn recruiters:
- Three of the consecutive recruiters contributed at least one fawn for five straight years.
- One doe, beginning at age 2½, recruited at least one fawn for seven straight years.
- One doe recruited triplets at age 6½ followed immediately by twins.
- One doe recruited a total of nine fawns in nine seasons, from age 2½ to 10½.
Consider these additional facts about all consecutive recruiters:
- Of 36 does known to have twin or triplet litters, 28 (78%) were consecutive recruiters.
- Consecutive recruiters had longer lifespans, living 5.2 years longer on average than does that never consecutively recruited a fawn.
- They recruited their first fawn one year earlier in their lifetime on average.
- They recruited their last fawn 4.3 years later in life than does that never saw back-to-back recruitment success.
Interestingly, Tristan found no significant difference in body size between consecutive recruiters and other does. We’ll come back to body size in a moment.
With some animals, there’s evidence that females might experience “gap years” where they recover from the physical and nutritional stress of bearing and raising young by skipping years before getting pregnant again. Obviously, Auburn did not see this with its whitetails. Whatever created them, Super Does were resistant to fatigue and were able to keep recruiting fawns even back to back to back. To back.
The Mere Mortals
For Super Does to produce the majority of the fawns while being the minority of potential mothers, there had to be a few does with low success at giving birth to or raising fawns to the recruitment goal line of 6 months old. One obvious explanation would be the doe dying young. However, a small number of does in Tristan’s study lived long lives and rarely recruited fawns.
One was born in 2007 and was still alive at the end of the study period in 2019, when she was 12½ years old. According to Tristan, she only recruited three fawns in that time: twins at 5½ years of age and one fawn at 9½years of age.
A doe born in 2008 that was still alive through 2019 recruited only two fawns – a single fawn at age 1½, followed by a four-year gap, and then a second fawnat 6½. This was followed by four more years without a recruited fawn before the study ended.
Another doe also born in 2008 recruited one fawn at 2½ and again at 3½, and that was her last fawn recruited through the end of the study, when she was 10½. This is the doe shown in the photo above with Tristan when she was recaptured at age 14½.
Finally, a doe born in 2007 that died in early 2018 at almost 11 years old only recruited two fawns, the first at age 8½and a second at age 10½. She holds the record for oldest doe to recruit her first fawn –8½ years!
What About Supervillains?
I know what you are probably thinking. Isn’t there a supervillain in this story? Didn’t predators get the fawns of those not-so-super does? There are no predators known to have infiltrated Auburn’s 430-acre research facility. While the odd coyote might have wormed its way in over the years, Tristan said no one has ever documented a fawn predation event in the facility.
Those under-achieving does can’t blame predators, but Auburn cannot tell us why those does were less successful. Did they never enter estrus? Did pregnancy fail in gestation? Was the fawn stillborn, abandoned, or killed by weather exposure?
“Further research is warranted to examine all the stages of reproduction, including fertility and fawn production through weaning,” said Tristan. “We only have recruitment data that indicates different qualities of mothers. It is tough to say why exactly some does are having low recruitment success.Just another reason science is important, and why it is a never-ending process.”
You may also be wondering whether inadequate nutrition could explain does going years between recruiting fawns. Auburn’s 430-acre enclosed facility contains forests, fields, food plots and streams. The habitat is managed with prescribed fire to encourage natural forage, and deer have unrestricted access to high-protein feed all year long. Nutrition was not likely a factor explaining low fawn recruitment among some does.
What other explanations are there? It’s possible low-recruiting does did produce fawns that slipped through the annual capture efforts and the conservative confidence levels for DNA parentage (the bar was 95% confidence in the DNA analysis, and a few fawns that didn’t meet this level were excluded). Tristan told me he feels they documented and identified the “large majority” of fawns, however. And, if any were missed, it’s just as likely they were the product of a Super Doe as an under-achiever.
Bottom line, Auburn’s study provides strong evidence that some does are just better-than-average fawn recruiters.
Fawn Recruitment and Doe Age
“Fawn recruitment success increased up to 6½ years of age, where it peaked before declining in older age classes,” said Tristan.
This confirms previous science suggesting prime-aged does are more reproductive than the youngest and oldest does. However, that’s a general summary, as you can see from the scatter chart above (which shows the total number of fawns recruited, not the total number of mothers).
There were 14 cases of a doe fawn successfully recruiting fawns, so while age is important, it doesn’t mean younger does aren’t successful. Same for older does. There were 24 cases of a doe age 8½ or older recruiting fawns. The oldest mother in this group was 12½ when she recruited a single fawn!
What about body size? Across the entire group, larger body size did not mean more fawns recruited. Instead, there was an interesting relationship between age and body size. Younger does with larger bodies for their age had higher recruitment rates, but smaller-bodied does caught up and recruited more fawns at older ages. It was as if bigger-bodied does were able to get started earlier but used up their fertility a little sooner, while smaller does had the same fertility potential but achieved it later once they caught up in size.
How This All Affects Doe Harvest
What could all this mean for your herd management strategy? Primarily, it provides you with some additional leverage to increase or decrease your pressure on deer reproduction, as needed. You have more options than just shoot or don’t shoot does.
Doe harvest is not a one-size-fits-all prescription, and it’s not even fixed across time for the same deer population or area. “Balance” between deer numbers and available nutrition is temporary and fragile, so you can easily swing from a situation where you need to harvest a lot of does to one where you should take only a few or even none. You can quickly swing back the other direction, too.
Knowing that some does may be super recruiters is knowledge you can use for adjustments. If you’re in a high-density situation and need a heavier reduction of herd size, a Super Doe is exactly the deer you want to take home. But if you’re in a more balanced situation, and you still would like to take a doe for the freezer, taking a less productive doe will have little or no impact on population growth.
I realize that’s easier said than done. If you are hunting and see an adult doe that appears to have two or maybe even three grown fawns-of-the-year with it, odds are fair this doe is a good recruiter. She may not be a Super Doe that consecutively recruits, but she was skilled enough to bear and raise fawns successfully and get them out of their spots and into the fall months when they can survive without her. Whether or not she gets a green light for harvest is up to you depending on your harvest goals.
Meanwhile, if you are hunting and see a lone adult doe with no fawns in the fall, odds are you’re looking at a less successful recruiter and one that offers venison with a lighter reduction of population growth if that’s what you need.
Trouble is, you may see all of the above, together, and with friends along. You may encounter half a dozen or more antlerless deer in a single close group, including adult does and that year’s fawns. There’s no reliable way to know which does raised which fawns. In such a case, sort them younger to older using body characteristics (watch our video below for guidance on sorting does). For greater impact on future reproduction, take a mature doe. For lighter impact, take home a younger one.
In the end, don’t worry too much about getting this exactly right. There’s no “wrong” doe to take. Do your best to take the right number of deer, and if you miss the mark a little low or high, it’s okay. Deer populations are resilient and bounce back quickly, especially if you are improving habitat quality, forage abundance and cover.
Tristan’s study of fawn recruitment is the companion to a larger study that looked at buck and doe breeding success relative to age and body size. You can read more about the Auburn facility and study setup in our report on those results.
