I look forward to the holiday season with excitement, anticipation, and dread. Thanksgiving is preceded by bear season followed by 3 weeks of deer aging. With my expanded work schedule, there is little time for that extra holiday cheer. Not to mention the current unpleasantness that has overshadowed the entire year.
Me neither. I don’t think 2020 delivered what anybody wanted for Christmas or anything else. I mean it snowed in May. MAY!
It wasn’t a total wash. The Deer Forest Blog did get a new website. That was pretty awesome even if Duane and I sprouted a few more gray hairs in the process. And we followed what might be the best summer project ever with Duane’s rat eviction campaign. You have no idea what joy I felt getting the daily text updates. Yes, I’m serious. And while we are not rodent biologists, the principles discussed and the responses recorded are directly related to deer and deer management.
What will 2021 bring? Who knows. One thing is certain – the future is ahead of us! Surely we will face the world…wiser. Our plan, of course, is to bring you more posts about project results, current deer research, and fun field stories. But we’ll see. Duane still has rats in his barn.
–Jeannine Fleegle Wildlife Biologist PGC Deer and Elk Section
Drooling for Evidence
Picture this: a death is reported to authorities, but they find only 1 bone, can’t interview anyone about what happened, and have no fancy diagnostic tools to evaluate DNA left at the scene.
That’s what fawn survival researchers are usually up against.
At a fawn mortality site, there is often not enough evidence to uncover what contributed to the fawn’s death. Predators may gobble up any evidence of disease or malnutrition before investigators can even get there. And I can assure you, those predators aren’t talking to us to confess their involvement in the crime or whether they were just an innocent passerby.
When there is just a carcass, the evidence that is available can cover up what really happened. Bite marks are easier to see than parasites. Bear poop with fawn hair in it doesn’t tell you that his meal was skin and bones to begin with. Moreover, disease samples are rarely evaluated because they are expensive. And DNA isn’t a slam dunk in identifying the killer.
If you’ve ever seen a murder mystery, you know that there are often red herrings at the beginning leading investigators and viewers to think they know who’s guilty. But, alas! At the last minute a scrap of evidence points to the REAL killer.
Right now, predators are often the red herring. Study after study has found predators to be main source of fawn mortality. But almost no studies look at fawn survival outside of predation. What if we are missing something? Researchers need evidence to determine what made a fawn susceptible to mortality in the first place.
So, that’s what we did. We looked at fawn susceptibility to mortality before a fawn died. No mortality site mysteries and no evidence covered up by bite marks and poop.
How did we do this? Hormones.
Cortisol is a hormone released by mammals (yes, humans have it too!) when they are stressed. Hence the term “stress hormone.” Researchers often measure cortisol concentrations in wild species to understand what things in the environment stress them out.
In adult deer and elk, salivary cortisol has been used to understand how populations and individuals respond to hunting pressure, habitat variation, and environmental conditions like weather. We know that high levels of the stress hormone may be harmful to an individual’s health, but no study of wild ungulates has ever linked it to survival.
Cortisol can be good or bad. Helping to make stored energy quickly available, cortisol can help fawns respond quickly to stressors. Running from a predator, for example, is stressful and requires a quick burst of energy and cortisol helps make that happen.
When cortisol is released into the body for a long time, however, it can have negative effects. Being prepared and ready all the time means energy is being diverted to behaviors that keep fawns on high alert instead of using it for normal body functions. Studies of many mammal species show that food digestion, immune system support, and general growth of the body and brain are all negatively influenced by long-term cortisol release.
To look at fawn cortisol levels and link them to survival, we sopped up fawn spit during the capture event and then scurried back to our lab. The amount of cortisol in the saliva told us how much of this stress hormone each fawn’s body was exposed to each day.
Since there is a lot of evidence that suggests cortisol can be bad for an individual’s survival, body condition, brain development, and immune system, we hypothesized that high cortisol concentrations would be bad for fawn survival too.
And guess what! Fawns who had higher cortisol concentrations in their saliva had lower survival.
An important distinction is that we don’t know if the high cortisol concentrations CAUSED higher mortality or not. It could be that fawns with higher cortisol levels experienced stressful conditions that caused mortality. For example, a fawn may be starving, which can elevate stress hormone levels, and the lack of food kills the fawn rather than the elevated stress hormone levels.
What’s important is that hormones may be a way to evaluate things in the environment that affect fawns but are difficult to evaluate when just looking at a carcass. Because predators are the most detected mortality source in North America, it is often hypothesized that fawn stress would be greatest in areas where predators are abundant. But that isn’t what we observed. When we looked at two study areas, fawns from a study area with fewer predators and lower predation rates had the higher stress levels.
What could be stressing fawns out if not predators? Momzillas. The study area where fawns were more stressed had more young mothers in the population. Young mothers can be less successful at rearing fawns. Maternal condition also influences offspring condition, potentially leaving fawns stressed and malnourished. As a result, it’s possible that these factors elevated fawn stress more than predators. This is all speculative, however, because very little is known about how maternal condition influences fawn stress or survival.
With this being the first study of its kind, more research is needed to evaluate links between cortisol and survival in other populations. Spit may be the evidence that helps better understand what influences fawn mortality! The plot thickens as it does in every murder mystery.
One thing is very clear- fawn researchers need more evidence.
Recently, a study from Delaware showed that only 54% of fawns survived even when there were no predators around. The culprit? Disease. Often overlooked and difficult to quantify, disease may contribute to fawn mortality by directly killing fawns or making them more susceptible to other mortality sources. It was likely easier for the Delaware study to detect disease because predators weren’t there to cover up any evidence.
Pairing our results with the Delaware study, it’s clear that mortality events don’t give us the whole picture on fawn survival.
Disease and hormones are only two of the many poorly understood factors that can affect fawn mortality. It’s high time we stop blaming those passersby predators for every death in the woods.
-Tess Gingery Research Associate The Deer-Forest Study
It Bears Repeating
We have written blog posts about how the most important component of a deer population is adult females. Their survival primarily determines whether a deer population increases or decreases. But as usual, they get snubbed. When it comes to survival or mortality, fawns still get all the attention – I guess because they mostly die from 4-legged predators instead of 2-legged predators.
Also, we have written how fawn survival in Pennsylvania is not a concern because
any changes in fawn survival can be countered with changes in antlerless harvest.
In an analysis of fawn survival studies across North America, survival increases as amount of agricultural land on the landscape increases. However, Pennsylvania’s survival rates are above-average (above the regression line) given the amount of agriculture present.
Interestingly, a recent study came to the same conclusion in Louisiana. Researchers monitored fawn survival and adult female survival to investigate population growth and harvest potential.
The predator suite on the 120-mi2 study area included bobcats, coyotes, and a restored population of Louisiana black bear (Ursus americanus luteolus, a subspecies of the American black bear).
Fawn survival rates on their study were only 27% – which is about half of what they are in Pennsylvania (~60%).
Survival rates for yearling females was 85.7% and for adult females 81.5% – similar to Pennsylvania.
Are these fawn survival rates worrisome for our southern counterparts? Nope. Basically, it’s what we’ve been saying all along – with fawn survival as low as 25% and adult female survival about 80% or greater, a deer population will be stable or increasing.
In fact, in this Louisiana study, researchers estimated that with the current survival and harvest rates the population was increasing at a rate of 6% per year! To stabilize it, they estimated yearling and adult female harvest rates would have to increase to be just under 20%.
If the antlerless harvest were completely eliminated, the population would grow by 15% per year. Under that scenario, the population would double in 5 years.
More evidence showing that throughout most of the range of the white-tailed deer, populations can be managed by adjusting the antlerless harvest – regardless of fawn survival rates.
-Duane Diefenbach
Pulling the Trigger
My dad would always say “The work begins once you pull the trigger.” I’m sure this quote did not originate with my dad. Here in America it is assumed that your harvest – be it deer, turkey, grouse, or woodcock – is yours to prepare and enjoy. Wild game has been served many a time at my table to family and friends.
But what if your deer wasn’t your deer? In many countries outside North America, just because you kill it doesn’t mean it’s yours to keep. In Europe, wild game is the property of the landowner and although you may have been given or even paid for the right to hunt, you may not be able to keep the meat.
That’s because in Europe wild game is something that can be bought and sold and served in restaurants. And wild game can be an important source of revenue for landowners of large estates. (We can debate the merits of this type of management system at a later date.)
In the U.S., meat processing is regulated by the USDA. All animals are inspected before slaughter and all carcasses are inspected after slaughter. Consequently, animals cannot be slaughtered, and meat cannot be processed if an inspector is not present. Any meat that was slaughtered or processed without inspection is considered adulterated and cannot be sold.
This is not the case in Europe. The human consumption aspect of harvested wild game necessitates a unique chain of custody. The system that exists in Scotland can trace wild red deer meat back to the hunter that pulled the trigger. That means care must be taken in how the animal is killed, field dressed, transported, and processed.
Take a look at the video below on how a wild stag is field dressed. My daughter and I watched it several times. There are a number of techniques that were unfamiliar to us. Not to mention some terms!
For example, “gralloch” is Scottish Gaelic for the entrails of an animal. And “pluck” refers to the lungs, heart, and liver – key ingredients for authentic Scottish haggis.
What I found fascinating was how the chest cavity is drained of blood with the animal facing downhill followed by the esophagus being tied off so that the stomach and entrails can be removed without cutting the diaphragm. This essentially eliminates blood in the body cavity and the digestive tract can be visually inspected for any abnormalities. Finally, the large intestine is stripped of feces, cut, and tied off.
Done correctly, the pluck stays with the carcass and the body cavity is rinsed only to remove blood with no contamination from the contents of the stomach or intestines. The hide protects most of the meat from contamination while removing the carcass from the field.
This approach to field dressing a deer has given me something to think about and try the next time I pull the trigger. I may be changing how I do things!
-Duane Diefenbach
P.S. Not that I plan to use the pluck anytime soon to make haggis but we do save the heart. Here’s a recipe that we have adapted.
Moosylvania
Pennsylvania is home to two cervids – elk and white-tailed deer (of course). But on rare occasions, a third makes an appearance.
I am not referring to Alces alces, the largest and heaviest member of the deer family whose species range falls well short of Pennsylvania. But instead to Odocoileus virginianus bullwinklus.
Ok, there isn’t a new species of deer in Pennsylvania or anywhere else. But when your nose swells to the size of a moose, it seems appropriate. Whispers about Bullwinkle syndrome began at the turn of the last century. Since then, there have been 27 reported cases in 14 states including Pennsylvania.
Photo Credit: Anthony Davis, USFWS
There is nothing that gets wildlife veterinarians and some biologists (like me!) more excited than critters with new or uncommon potential disease syndromes. Recently, a group of these cool and smart people published the case series on this aptly named phenomenon.
When you find something weird or unusual, the first thing you should do is take a few pictures and describe what you see. This is a good life rule. Bullwinkle syndrome is characterized by swelling at the end of the muzzle and upper lip. The lower lip does not appear to be affected in most cases.
Once the outside is properly documented, it’s time to CUT IT OPEN! That is the most fun and best part of the whole process. And this, of course, is exactly what the smart people did. Inside, “the swelling was isolated to the subcutis, underlying muscles and other soft tissues. There was typically no significant thickening of the epidermis, and alopecia was not evident or was minimal.” Translation, swelling was only in the soft tissues under the skin; the skin was not affected; and there was no hair loss on the nose.
After gross examination, which is needed to rule out any sort of physical cause, like trauma, they broke out the microscopes. What they found were granulomas associated with multifocal inflammatory infiltrates, fibrous connective tissue, macrophages, neutrophils, and Splendore-Hoeppli material. Granulomas are small areas of chronic inflammation and were found through the affected tissue. Beyond that don’t ask me to explain. I told you these were smart people.
Photo Credit: Dr. Nicole Nemeth, SCWDS
Within the Spledore-Hoeppli material, they did find colonies of small rod-shaped bacteria. They were seen in all 27 cases and were consistently gram-negative. Petri parties were setup to try to culture this bacterium. But they didn’t find just one species. Lots of fun cellular critters grew like Trueperella pyogenes and Pseudomonas aeruginosa. Nineteen different species in all. This is normal because chronic inflammation usually gets all sorts of secondary bacteria associated with it. But those bugs didn’t throw the party. They just showed up to it. Of the 19 party goers, none had the characteristics of the gram-negative bacteria seen in the granulomas. So who was this mystery microbe?!
Time to break out the BIG, or I should say the little, guns – laser-capture microdissection and DNA amplification. Oh yeah! With this technique, researchers can specifically remove the part of the granuloma with the mystery microbe and then sequence its genes without being distracted by the other party goers.
Photo Credit: Dr. Nicole Nemeth, SCWDS
Mannheimia granulomatis was found in 7 of 8 deer for which samples were available. Score! There have been no previous reports of granulomatous (inflammation) disease in deer caused by this bacterium. Although it has been documented to cause disease in cows in South America called lechiguana.
Not being a moose, this type of nose job looks awful on and for the deer. However, no mortality has been attributed to this condition. In fact, one deer had been seen for 3 years before it was collected. But mortality isn’t the only concern surrounding wildlife disease – why are we seeing this now? Why is the nose only affected? How are animals infected? What makes an animal susceptible?
These are not new questions and hover around all novel wildlife disease outbreaks. Understanding them can give us insights into changing environments, emerging threats to both wildlife and people, and advance techniques for studying disease.
If you see a deer sporting a Bullwinkles schnoz (or other out of the ordinary appendage) on your trail camera or in the woods, drop your wildlife agency a line. Because we aren’t in Moosylvania.
–Jeannine Fleegle Wildlife Biologist PGC Deer and Elk Section
Duane and I talk a lot. Topics are vast and far reaching – his rats, my mice, dogs, hunting, deer, current events, publications, research, woodworking, sewing, roadkill oryx, and, of course, this blog.
The blog is a beast that is never full. Content isn’t always easy to create, and we sometimes struggle. So why do we write The Deer-Forest Blog anyway? It’s not like either of us is needing more work.
The answer is marvelously simple: JOY!
For me, it is my one joy at work. A creative outlet, freedom, a way to reach outside the sometimes dull and tedious wildlife management box. For Duane, it is the same. A metric by which a research career cannot be measured.
Our most recent conversation about the “Why?” of the blog was sparked by a reader comment on Smoke and Mirrors. Specifically, Gregg T.’s compliment wishing that “the NYSDEC or ESF had a crew as dedicated as those who post this blog working for them to make sure that the public is educated” (Thanks Gregg!).
Duane and I have selfish reasons for writing this blog but the byproduct obscures that. The byproduct being the sharing of results from the Deer-Forest project and other research conducted in the deer world.
Almost 90% of hunters agreed that controlling deer populations and keeping deer populations in balance with natural food supplies was necessary. We are all on the same page here.
But there was a real disconnect among some hunters about the relationship between deer and habitat. 20% of hunters disagreed that deer have the ability to affect plant and animal communities and 44% disagreed deer caused serious conflicts with other land uses, such as forestry and farming. Research has shown this not to be untrue.
And while nearly 6 in 10 hunters disagreed with the statement “We don’t have enough deer unless some are starving to death each year,” 20% of hunters were unsure and 24% agreed with the statement! Deer are tough, adaptable creatures. If they are starving, something is very, very wrong.
Historically, deer numbers have been the focus of deer management. The focus of deer and forest research has traditionally been on the effects of lots of deer (outside fences) versus no deer (inside fences).
Managing based on a single number or research with all or nothing parameters are relatively straightforward. Not easy, mind you, but straightforward.
But the real world is not about an absolute number of deer or deer versus no deer in a block of woods. We need functioning ecosystems. Only then will we be allowed to keep both deer and trees.
I’ve been accused of many things over my 20-year career in deer management. I’m sure you can guess most of them. One stands out – that I (or deer managers in general) hate deer, favor trees, and want to eliminate deer from the landscape.
This is the biggest insult anyone could sling. We have spent decades trying to understand deer and their place in ecosystem; how our actions alter and affect them; and how their actions alter and affect their environment.
I see deer every day. And it never gets old! Because we advocate for healthy habitat that may support fewer deer, it is not a betrayal of our beloved cervid.
If we can show how soil chemistry, plant diversity, and deer are interconnected; how the health of the whole influences the parts; then the Deer-Forest project will be a success.
If we can share how soil chemistry, plant diversity, and deer are interconnected; how the health of the whole influences the parts; then the Deer-Forest blog will be a wildly successful endeavor.
Thanks for sharing in our JOY!
–Jeannine Fleegle and Duane Diefenbach
Magic!
Deer management, in the condensed version, has 3 steps:
Identify goals and objectives
Collect data to assess deer population and habitat with respect to Step 1
Make a management recommendation to decision makers.
Repeat Steps 2 and 3 annually.
Simple, right? There is one small problem: Step 2. In particular, the word “assess.”
And while these 3 steps have remained consistent over the last 5 decades, how we “assess” deer populations using those collected data has changed.
The first peer-reviewed deer population model was published in 1976 by Game Commission Biologist Lincoln Lang (Lang and Wood 1976). William Shope, also a Game Commission biologist, developed a more sophisticated model in 1978 (Shope 1978). It worked well until antler point restrictions were implemented. So Coop Unit graduate student, Andrew Norton, developed the current model used by the agency today (Norton et al. 2011).
But let’s go back to the 1970s. Bill Shope recently shared with me a history of data processing at the Game Commission when he started (1970) until his retirement (1999). In the beginning, the tools available to him for analyzing all the data collected on deer were, in his words, “…12 legal tablets, a box of pencils, a Monroe adding machine, and an old manual typewriter. My only computer was a slide-rule that I used at PSU.”
Bill further explains, “The primary data processing [device] for the Commission was IBM Tabulation equipment from the mid 1940’s. From the pictures I was able to find online, I believe it was an IBM 602A from 1946. This equipment used electronic boards with wire jumpers to do tabulations. Hank McCauley was the programmer and he prepared the electrical circuits for each job. The equipment was primarily used to do accounting work for payrolls and summary reports required by the Commission for all its operations. It was also used to tabulate deer report cards and to summarize data from harvested deer examination forms.
“Early on it became apparent that this equipment would be of limited use for statistical work. For example, I wanted to do standard errors for game-take survey estimates. I approached Hank about the programming that would be involved. I found out that he had no idea how to calculate the square root of a number. So after I explained how to calculate a square root, he spent about a week programming the old tab equipment to do square root calculations. The first run to calculate a single square root took 2.5 hours. I concluded from this experience that it would not be very practical to use this equipment for statistical work. Consequently, I did not do much with statistics in my early years with the Commission because I lacked a practical way to do the calculations that were involved.”
Sir Arthur C. Clarke once said “any sufficiently advanced technology is equivalent to magic.” Magic was about to happen to deer management.
In 1983, the Game Commission purchased its first desktop computer: an HP 86B and an HP drum plotter for $30,000. The HP 86B was a 64K machine that could be expanded with 128K memory cards that could be added to three card slots in the back of the machine. The operating system was MS-DOS. The software available for this computer consisted of mapping software, a VisiCalc spreadsheet, a word processor called Word Star, and a programming language called HP Basic. For comparison, the laptop on which I am typing this is a 32 Gigabyte (32,000K) machine with 100s of programs that can be run simultaneously (within reason) and costs under $1,000.
HP 86B desktop computer.
Bill notes, “It took me about two weeks to learn HP Basic. After that I began writing a variety of programs for different jobs including a program to calculate deer populations. By early 1984, I had completed and tested the first computerized version of the deer population management program in HP basic.”
A single run of the deer program on the HP 86B took 26.5 hours. Because this was the only computer in the Game Commission, scheduling was a real issue. So in 1987 the Bureau of Wildlife Management purchased an IBM desktop. Bill converted the deer program to TurboBasic and processing time was reduced to less than half an hour. The magic of technology knows no bounds!
Bill wrote, “The deer program I wrote in 1984 was used until 2002 to estimate deer populations and determine antlerless allocations. When the Commission instituted antler restrictions, this created a bias in the age structure of the antlered harvests that violated a key condition [of the model]. As a consequence, the program I wrote is no longer being used to estimate deer populations in Pennsylvania.”
Today, the Game Commission’s deer program relies heavily on computer technology. About 200,000 harvest reports are submitted via the internet, phone, or mail-in report cards. All that information is tallied in a computer system.
Agency staff check over 20,000 harvested deer each year to age and sex the harvest and estimate reporting rates (percentage of harvests reported to the agency). All those data are recorded on handheld computers.
Although the basic approach to deer management hasn’t changed, the technology is far beyond that first HP 86B purchased by the PGC. As Bill said, “Sometimes we need to look behind us to see where we have been to appreciate how far we have come.”
-Duane Diefenbach
I would like to thank Bill Shope for sharing his knowledge about the history of deer population modeling since the 1970s.
Photo credit (inline image): HP 86B, CC BY-SA 3.0, (no modification to image).
Smoke and Mirrors
It is no secret that not everyone likes antler point restrictions (APRs). However, they are supported by about 60% of Pennsylvania hunters both before and after they were implemented in Pennsylvania. That is fact. And Pennsylvania is the only state that has ever truly evaluated the biological and social outcomes of this management action.
Besides just letting more male deer live to an older age, there are two schools of thought about why APRs should be implemented.
The first we debunked in the previous post – that APRs change breeding behavior. Before APRs were implemented in Pennsylvania, we did not know if they would or not. It was a plausible hypothesis. At that time, the conventional wisdom was that older, mature bucks did most of the breeding. This was based on observational research conducted in the 1970s and 1980s.
It wasn’t until the early 2000s that genetic research demonstrated that dominance by older bucks was not occurring. Sure, they did slightly more breeding than younger bucks, but yearling bucks still did a lot of breeding – practically in proportion to their abundance in the population!
The research Jeannine wrote about in our previous post suggests that in states where harvest rates on antlered deer are very high (like PA used to be), APRs are unlikely to have much effect on breeding behavior. Examples of such states would be Pennsylvania, Wisconsin, and Michigan.
The second reason for implementing APRs is based on the hope that hunters will shift their focus to harvesting antlerless deer. In places where more antlerless harvest is needed, instituting APRs might support this action. But decades of human dimensions research suggests that this should not be an expected outcome. Hunters have many different motivations for hunting and obtaining meat is an important one, but it is not the sole motivation.
New York studied whether instituting APRs might cause hunters to harvest more antlerless deer. They found that it did not.
I find this argument that APRs will encourage hunters to harvest more antlerless deer particularly dangerous. Some have claimed that instituting APRs in areas with chronic wasting disease would reduce deer populations. There is no evidence for this at all. History has shown that reducing deer populations depends on issuing more antlerless harvest permits, and that hunters are willing to use those permits.
These 2 schools of thought can be a distraction and provide hunters with much to debate. The truth regarding APRs is that they can increase the number of older, antlered deer in a white-tailed deer population. But there is one very important caveat – APRs will only do this if you already have a high harvest rate on antlered deer. Where APRs have failed, or at least had minimal effect, is on populations where there is already an older age structure and a relatively low reproductive rate (so that both antlered and antlerless harvest is limited). Examples of failures tend to be with species like mule deer and elk.
Pennsylvania is one of the few states where APRs were recommended by the agency to sportsmen and sportswomen. That is why Dr. Gary Alt traveled around the state talking to >100,000 people about the potential benefits of APRs. The PGC distributed 35,000 videos about the rationale for APRs. It is estimated that these efforts directly reached approximately 318,000 hunters.
Given the more than 100-year history of buck harvest in the state, APRs were quite the departure from the norm. And while they didn’t change breeding behavior or increase antlerless harvest, they are still supported by hunters almost 20 years later. Letting bucks live an extra year or two doesn’t hurt or help deer behavior or deer management, but it does make most deer hunters happy!
-Duane Diefenbach
Who Run the World
Moon, rain, wind, temperature – we’ve looked at them all when it comes to how they might affect the rut.
Conclusion: They don’t.
The timing of the rut is based on when does come into estrous and that is based on day length. Hunters continually focus on bucks when it comes to the rut. As a biologist (and a woman), it’s kind of annoying.
However, it does take two to tango. So what if we implemented something that manipulated the buck population on a large scale? Could that change the rut?
In 2002, Pennsylvania made substantial changes to deer management regulations for the first time in decades. The most notable was an increase in antler point restriction from 3 inches on one side to 3 points on one side (or 4 depending on the Wildlife Management Unit).
For 80 years, Pennsylvania hunters harvested about 80% of all antlered deer annually. Each year those antlerless button bucks would sprout antlers, dominate breeding, and be harvested during the gun season. There were 3.7 yearlings for every 2.5-year-old or older buck. One thing 8 decades of this should teach us – yearling bucks can get the breeding done.
There were questions surrounding this breeding system, however. With the female-biased sex ratios, was breeding delayed because there were just too many females in estrous at the same time and not enough bucks (yearling or otherwise) to fill the demand? This could affect breeding synchrony and maybe flatten that peak.
With the new antler point restriction, the number and age of antlered deer would increase. Would more and more experienced bucks get the job done more efficiently? Would the peak be higher and tighter?
So have antler point restrictions (and the addition of older bucks) made the rut more intense over a shorter period of time?
No changes in timing or synchrony of breeding were detected!
These boxplots show the median date of conception, and the variation about the median date, of fawn embryos in fawn, yearling, and adult female road-killed deer in Pennsylvania, 1999-2006.
We all know who controls the timing of the rut. It’s high time everybody acknowledges the supreme status of the doe.
Timing of breeding is predicated on optimal birth date for fawns. Not too early (too cold for babies) and not too late (need to fatten up before winter) to maximize survival. Female investment in reproduction is high with a 200-day gestation period and 8 weeks of lactation. She is the linchpin to rut timing.
Old bucks, young bucks – makes no difference. The timing of breeding will remain the same. All old bucks do is make hunters happy. Which is fine, but we know who run the world.
–Jeannine Fleegle Wildlife Biologist PGC Deer and Elk Section
Graphics by Tess Gingery
Old Spice
While approaching traps, I could sometimes tell we had been successful before the trap even came into view. It wasn’t some crazy deer-telepathy, or a special Spidey Sense, but a whiff of that distinctive scent on the breeze. For particularly smelly deer, the scent emanating from the trap almost always indicated a buck. So, what is the origin of this smell? And what social implications does this “cologne” have for bucks?
First, some background information. Deer have many glands. Arguably the most important ones for a hunter to study and understand are the tarsal glands. Much of the odor that we associate with deer is produced by the tarsal glands, located behind a dark patch of fur on the inside of the deer’s hind legs. A behavior that contributes to the strong deer aroma is rub-urination.
Photo Credit: J Dingel PA Game Commission
Rub-urination is exactly what it sounds like. A deer will urinate over its tarsal glands while rubbing them together. The dark coloration of the fur on top of the glands is an effect of the frequent urination. The tarsal glands produce a fatty substance that attaches to the hair. Fat-soluble compounds from the urine remain on the hair. The smell produced from rub-urination comes from a combination of bacteria attracted to the moist warm environment, the fatty glandular secretions, and possible hormones in the urine. All deer rub-urinate, but the purpose and frequency differ based on the sex and age of the deer and the time of year. Adult bucks tend to rub-urinate more frequently than does and fawns, especially during the rutting season.
Photo Credit: J Dingel PA Game Commission
For males, scent is extremely important during the rut. It has been suggested by researchers that bucks rub-urinate to attract does and to show dominance. The odor produced by rub-urination contains a lot of pieces of information. Scientists have conjectured that the scents contain individual identification, reproductive status, and social standing information.
For all deer, the scent produced at the tarsal glands can serve as a basic identifier between individuals. Each deer scent is unique and deer have amazing olfactory abilities allowing them to detect it. While roaming around the woods, deer can keep track of the movements of other deer by picking up their scent on the breeze, on vegetation along the deer’s path, or in scrapes. It has even been suggested that deer may lick the tarsal area after rub-urinating and then lick trees in order to transfer the scent to their surroundings.
Photo Credit: J Dingel PA Game Commission
Researchers from the University of Georgia compared the bacteria of the tarsal region to bacteria found in areas with no glands and no urine contamination. Many more species of bacteria exist at the tarsal areas with many of these bacteria only found at the tarsal areas. The bacteria found was of the odor-producing variety, and males had higher concentrations than females. They also found a species of bacteria known to convert steroids to odorous substances. Their conclusion was that the tarsal glands are indeed hotspots for odor production. The presence of the steroid converting bacteria suggests that steroids may be present in deer urine contributing to the overall scent of the deer and may contain reproductive and social information.
At a molecular level, scientists have also studied the chemical composition of urine in dominant and subordinate white-tailed bucks. Differences in the composition included higher or lower concentrations of certain components based on the social status. There were also some components that existed exclusively in one group or the other. Concentration and presence of certain components is also specific to the season (breeding vs. nonbreeding). These differences in urine composition may contribute to differences in the odor produced by rub-urination. Thereby communicating reproductive and social status through scent.
A lot of research has been conducted on deer-scent and communication, but there are still many questions pertaining to such behavior. This leaves the door open to many anecdotes and wive’s tales. For instance, it is said that an older, more dominant buck may have darker tarsal fur due to a higher frequency of rub-urination. It has also been suggested that less dominant bucks may even lick their tarsal glands to reduce scent to avoid a confrontation with a more dominant buck.
One thing is for certain, cologne is a must-have for bucks regardless of brand.
-Carolyn Degurski Field Crew Leader PGC Deer and Elk Section
Field Notes
Deer Crew Diaries may go on hiatus in the summer and fall but that doesn’t mean the field techs do. There is still work to be done but deer aren’t always involved. Below is an update from Kate on how she spent a recent week in the field.
After a mid-day break and nap, Levi Peterson and I went out to assist with woodcock captures. Levi has been out on previous nights, but this was my first time helping and it was pretty neat! Of course, the deer team had to show up and make things interesting. Levi saw a small road-killed deer on his way over and had to pick it up for CWD sampling. So our workspace had an extra critter at it.
Driving about 2 miles an hour in a UTV on mowed paths and using a spotlight, we searched. When we spotted a woodcock, we would spotlight the bird while one person would sneak up with the net and catch it. Once captured, we brought the woodcock back to the trucks where it was measured, weighed, aged, sexed, and finally banded. If the bird was big enough, it also received a little backpack transmitter. Then it was free to go. It was a very cool experience, and I’m glad I got to be a part of it!
We also went to Sproul State Forest to help track some collared black bears that had ventured off the study area. Once we located the bear, we took a walk to see why the bear might have left to set up camp somewhere else. For the most part, the bears found nice pockets of black gum trees. Bears really like black gum. If you find one of these black gum groves, look up. You can see all of their branches pulled down toward the trunks. A bear will sit in the tree, reach out, pull all the branches in, then eat all the berries it can. Other bears found their way to cornfields. Corn is an easy source of food. When a bear finds a cornfield, it will take up residence to pack on the pounds for the winter.
We also checked up on a couple mortalities and found one had died in a little crevasse that went back into a cave. It was probably the coolest mortality location yet! Both mortalities were a few months old and the remains were just some hide and bones. So we don’t know what exactly happened to those bears, but it was a cool investigation anyway.
From the field, Kate Derstine
Synchronous Serendipity
While we have put the topic of fawn predation to bed on this blog, it’s still shows up. A recent publication in Functional Ecology took a look at reproductive synchronization in white-tailed deer as it relates to predator defense strategies.
Reproductive synchrony is just a fancy way of describing how spread out or clumped births are.
Before we get into how this might affect predation, let’s talk about the weather or more specifically seasonality. It’s widely acknowledged that climate factors (think food and temperature) are the muscle behind whether how much births are synchronized. Indeed, deer exhibit a wider birthing season in the mild and relatively seasonless south than in the north where there are distinct windows of plant growth.
But can predators reinforce or increase birth synchrony too?
There are two strategies used by prey species that may have arisen as defense strategies against predation. Predator swamping and predator avoidance hypotheses.
Predator swamping hypothesis predicts a high synchronization of births. Strength in numbers or, in this case, it’s a they-can’t-get-all-of-us mentality. If all young are born at the same time (birth pulse), it’s like an all you can eat buffet. Predator bellies are too full. They can’t eat all of them so overall young have a better chance of survival.
If predators really influence birth synchronization, then you might expect fawns born on either side of the birth pulse to be at greater risk of predation and experience lower survival.
Predator avoidance hypothesis predicts asynchronous births. If you are a hider like the white-tailed deer fawn, then fewer of you playing hide and seek will make it more difficult for a coyote or a bear to find you than if everyone is playing at the same time.
These seem like plausible theories.
But to which strategy does the white-tailed deer subscribe? And are there data to support it?
This research looked at birth timing and survival data for fawns from 9 study areas including Pennsylvania. If the predator avoidance hypothesis was at play, population level survival probability would increase with asynchrony (more spread out births) and individual fawn survival would not be affected by its birth date relative to peak fawning.
I’ll cut to the chase: Patterns of fawn survival better support the predator swamping hypothesis, not predator avoidance; and predators may present a selective force great enough to shift reproductive synchrony.
That means that along with temperature and food availability, predation may also influence when does give birth.
I’m a fan of the predator swamping hypothesis because it makes complete intuitive sense. I like things that make sense!
However, one of the findings didn’t quite jive. Remember our pyramid of births showing predator swamping hypothesis? When looking across data from 9 different areas, fawns born AFTER, but not before, peak parturition were at increased risk of predation.
If predators really had an influence on synchrony then fawns born on either side of the peak should be at greater risk, not just those on the tail end.
Why did only fawns born AFTER see higher mortality?
The upside of this paper is the large scale and giant sample size. The fates of over 860 fawns were analyzed. This allows us to see patterns that are invisible with smaller studies or on individual study areas.
The downside of this paper is that it ignores other aspects of deer biology. Fawns born on the back side of the peak already have a strike against them and it’s not just their birth date. Their fate may already be sealed, and it has nothing to do with coyotes, bears, or bobcats lobbying for synchronicity. Proximate vs ultimate mortality – an underweight fawn born at a subpar birth site to a yearling doe is eaten by a bear. The bear is blamed but really that fawn was going to die no matter what.
I love the predator swamping concept. But it’s just a happy byproduct of climate seasonality. Serendipity as they say. Like when I realized I could use Nature’s Miracle to clean up cat pee AND get the stink out of my running clothes!
