As professional white-tailed deer biologists, we are constantly prodded by friends and family for some type of insider information that could help improve their odds of encountering mature deer. It is always a tough question to answer, and it wasn’t until we began a collaborative research project between the University of Delaware and the Delaware Division of Fish and Wildlife in 2014 that we started to glean something that could be considered unique insight for a curious deer hunter: information that changed the way we hunted.
We spent four years capturing adult bucks and does of all ages in southern Delaware, placing GPS collars on them, and following their every move throughout the hunting season. While the main objectives of the research were big-picture population management questions, we were also able to look at their day-to-day movements through the eyes of a deer hunter. Although we would obviously never use this information to pursue our own study subjects, poring through the data for each animal and pinpointing the best place to theoretically encounter them from a treestand became somewhat of an obsession. Even before we started analyzing the data and crunching the numbers, we noticed two things.
First, the good news for hunters: No deer was unkillable. Every individual, mature or not, at least occasionally used an area during daylight hours that was both accessible and open to hunting.
Second, the bad news: That window of opportunity was often shockingly narrow, particularly for some of the more mature bucks.
Buck #668 stood out above the rest. In 2015, buck #668 was a 5½-year old whose relatively small antlers seemed out of place on his massive body. We were shocked to receive a phone call one afternoon to find a happy hunter on the other end. He had just killed #668 and was following the instructions on the ear tag to report his successful hunt. When we asked where he managed to get the drop on the buck, he was understandably vague… a pretty common response to that line of questioning among most hunters.
“Did it happen right at first light, 20 yards off the southeast corner of the middle CRP field on the edge of the swamp?” we prodded.
The phone went silent for a second, but you could almost hear his jaw hit the floor.
“Yes, in fact that’s exactly where and when it happened… how in the world did you know that?” he responded.
Simple! For the previous three months that’s the only way anybody would have been able to kill him!
Buck #668 seemed to do just about everything right when it came to avoiding hunters. He clearly knew how to go unnoticed, yet he ended up on a skinning pole anyway. It was a pattern that seemed to play out more often than not. Deer that used the landscape in seemingly reckless ways slipped through the season unharmed while the ones who acted like ghosts often didn’t. As both avid deer hunters and as scientists, we were determined to find some answers. We began to crunch the numbers with three questions in mind. How much variation was there between individual deer in the way they used the landscape? How much did their age class and sex influence that variation? Finally, how did their use of the landscape affect their chances of surviving the hunting season?
A Lesson in Habitat Selection
Before getting into the results of the study, we need to provide a quick explanation on how wildlife biologists attach numbers to the way animals select or avoid certain characteristics of the landscape, and what those numbers mean. Because we have GPS collars on the deer and know what type of vegetation is in their home range, we know how much of any given cover type is theoretically available to them (whether they use it or not). We can then plug that availability data, along with the locations they actually did use, into a computer model. The model generates a number that indicates the strength of their selection or avoidance of different cover types. What it boils down to is if the deer frequently use a cover type that isn’t very common in their home ranges, the number will be high and will indicate strong selection.
A buck shifting the way he uses the landscape as he grows older is almost certainly the result of one too many close calls or bad experiences.
Think of your bedroom. It makes up a relatively small area of your home, but you spend a disproportionately large amount of time there in every 24-hour period. That’s selection. On the opposite end of the spectrum, if there is a cover type that is very common in a deer’s home range, but barely ever used, the number will be low and we can assume that type is avoided. Those numbers indicating the strength of selection or avoidance can then be used to study how their habitat use may influence their probability of survival.
Differences Between Individuals
The first observation that stood out was just how much difference there was between each individual, no matter if it was a buck, doe, mature or immature deer. Hunters spend countless hours watching videos, listening to podcasts, and reading magazine articles like this one to better puzzle out why deer do the things they do. While an understanding of general patterns can certainly give you a valuable advantage in the deer woods, it’s important to remember the deer don’t decide how to behave by watching a video, listening to a podcast, or reading a magazine. For instance, while the deer in our study generally avoided roads, many individuals actually selected for areas closer to roads, including a few of our mature bucks. They were not supposed to do that according to what we know about deer behavior, but they did it anyway. Maybe they were using more urban areas as a strategy to escape hunting pressure, or maybe they just didn’t know any better. Whatever the reason, we saw the same variability in selection between individual deer for all cover types we measured, and in all different age and sex classes.
Differences Between Bucks and Does
Not surprisingly, there were many differences between the way bucks and does used habitat. Does were not overly picky, only showing a slight selection for corn and soybean fields. Interestingly, does showed no selection or avoidance of roads, wetlands, upland forests, or habitat edge. Bucks, on the other hand, were generally much more selective, preferring agricultural fields and uplands forests while avoiding roads. Bucks in general showed no selection or avoidance for wetland areas, which was admittedly unexpected. Given that bucks are harvested at a much higher rate than does in our study area, we thought the fellas would hide out in the swamps pretty frequently during the hunting season while the does could afford to be a little more reckless. It wasn’t until we looked a bit closer that the lightbulb really went off.
Hunting these wetlands is very difficult, so they function as sanctuaries, and bucks used them as such. You may not have “wetlands” where you hunt, but you have areas where hunting pressure is relatively low for whatever reason.
Differences Between Age Classes
We separated both bucks and does into two age classes: deer age 4½ or younger (in this article, we’ll refer to this group as “immature”) and those 5½ or older (mature). After breaking apart the age classes, it became clear why we didn’t see bucks taking advantage of wetlands to avoid hunting pressure: Immature bucks were avoiding getting their feet wet at all costs, while mature bucks barely ever left the swamps until the cover of darkness. In our analysis of all bucks, the behaviors of the two age groupings were canceling each other out and showing no preference! The same pattern held true for nearly every cover type. Mature bucks also selected for edge habitat and avoided both upland forest and agricultural fields, while their younger counterparts did the exact opposite. The only behavior bucks of all ages agreed on was a similarly strong avoidance of roads.
Because we now know how each individual deer chose to use the landscape, and we also know if and for how long each deer survived the hunting season, we can start to look for similar trends in selection for both individuals that survived as well as those that didn’t make it past opening weekend.
We’ll start with the one that stood out clear as day: Bucks that used wetlands and swamps survived, and those that didn’t died. It really was as simple as that. Not using wetland areas increased a buck’s risk of mortality by a factor of 2.7, meaning he was nearly three times more likely to be killed compared to a buck who regularly hid out in swamps and forested wetlands.
“Wetlands” in our study ranged from open forested wetlands to what is called ghost timber – brackish marsh with thick, invasive Phragmites reed and multiflora rose among mostly dead or dying trees. Hunting these wetlands is very difficult, so they function as sanctuaries, and bucks definitely used them as such. You may not have “wetlands” where you hunt, but you have areas where hunting pressure is relatively low for whatever reason. Think of these low-pressure areas as “wetlands” for purposes of this discussion.
Interestingly, use of wetland areas had no influence on survival probability for does. In fact, there wasn’t much that influenced survival for adult females at all. Using larger, more contiguous upland forest areas seemed to give does a slight edge, but the relationship was not strong.
What was even maybe more surprising was that selection or avoidance of roads had no impact on survival for either bucks or does. Deer that spent a lot of time near roads were just as likely to survive as those that avoided them like the plague. Although we don’t have any data to back it up, our best guess is that roads are probably more dangerous to deer that don’t have much experience crossing them, meaning deer living closer to roads don’t necessarily have a greater risk of being hit by a car.
One buck in particular didn’t have a reckless bone in his body. No other deer in the study avoided roads more than him. So strong was his aversion that he didn’t attempt to cross a paved road once in the three months we tracked him, until one night in late November something made him decide the grass was greener on the other side. You probably already guessed how this story ends. His first encounter with a road would end up being his last.
Learning the Hard Way?
So, we now have proof that not only do older bucks use wetland areas – again, think “low-pressure areas” – more often than young bucks, but that behavior actually does pay off. It would seem logical that bucks learn this behavior as they age, but it’s hard to know for sure. Maybe old bucks use wetlands more frequently simply because all the young bucks that didn’t use those areas never became old bucks! If they are truly learning though, which seems likely, those lessons must be occurring the hard way. Bucks are much more solitary than does during the fall, and there is no dominant, wise mentor to show a young buck the ropes like the matriarchs in the doe groups. A buck shifting the way he uses the landscape as he grows older is almost certainly the result of one too many close calls or bad experiences.
It should come as no surprise to most deer hunters that bucks get a little more savvy and harder to kill as they get a little gray around the muzzle. There are two important pieces of information that hunters can pull from this research, however.
First, bucks need to learn from experience before they begin to use sanctuary areas, and once they do, they become harder to kill. It is in your best interest to not be their teacher! Limiting hunting pressure should help keep them on dry land a little more often, which makes life easier and walks to the stand a little more enjoyable.
Second, once the lesson has been learned, it’s time to invest in a good pair of rubber boots and get in after them because, while you probably always knew it in the back of your mind, the research now proves it… old bucks just don’t use the landscape recklessly in areas where they don’t feel comfortable.
About the Authors: Dr. Jacob Haus is an assistant professor in the wildlife biology program at Bemidji State University in Minnesota. Joe Rogerson is the Program Manager for Species Conservation and Research with the Delaware Division of Fish & Wildlife. Dr. Jacob Bowman is a professor and department chair for the entomology and wildlife ecology program at the University of Delaware. This research was supported by a grant from the U.S. Fish & Wildlife Service’s Wildlife Restoration Program.