Natural mortality in deer: the inescapable comparison to humans

(An adult female Columbian white-tailed deer marked with an ear tag and a plastic collar for identification in the field.)

For my Ph.D. research I studied a population of white-tailed deer located on a national wildlife refuge in southwestern Washington.  The refuge was situated on the north bank of the mighty Columbia River and this particular subspecies of deer is called Columbian white-tailed deer.  They were placed on the Endangered Species List in the early 1970s, which led to my research project on this rare form of North American deer.  The only other form of white-tailed deer that is considered endangered is the diminutive Key Deer of Florida.

As you all know, most populations of deer in North America are subjected to sport hunting every fall.  Historically, hunts allowed for male-only kills, but this has been greatly liberalized in recent decades to allow hunting of females to reduce the size of this now abundant (= too abundant) species.  One of the demographic observations about deer populations is the sex ratio of adults---it almost always favors females significantly.  Sex ratios among adult deer typically are 3-4 females for every male, and this is generally attributed to the fact that males are hunted and females are not.  That is, more males were removed from the herd every year due to legal hunting than were females, and this resulted in a skewed sex ratio favoring females.  Reproductively speaking, this is not a problem because most species of cervids (which include elk, moose, and caribou) have a promiscuous breeding system, where each male breeds with as many females as possible.  An adult male white-tailed deer can breed with 10 or more females during a single breeding season in the fall, so the skewed sex ratio does not inhibit reproduction at all.  Essentially, all females get pregnant every year regardless of the sex ratio.  Larger, older, and more experienced males probably obtain more copulations than younger, smaller, and less experienced males and, therefore, the larger bucks sire more offspring.

So, I had at my fingertips a non-hunted refuge population of deer to study, and I was free to choose the research questions that were of interest to me.  I decided that this was an opportunity to study natural mortality and demography in this population of about 200 deer found on a somewhat contained (i.e., surrounded by water or habitat not used by whitetails) piece of land of about 2,000 acres.  I lived on the refuge and worked on the population daily for two years.  At the end, an interesting demographic pattern emerged, which informed my view of what makes male mammals tick.

My primary method of studying this phenomenon was to systematically search the refuge with my assistant, Bill Half Moon, for dead deer.  When we found a carcass, I estimated the month in which it had died, its location on the refuge, and I collected the skull for later analysis.  This analysis involved removing a tooth, and staining and sectioning the tooth to reveal cementum annuli that can be counted to determine the age of the animal at time of death.  It is sort of like counting tree rings.  Of course, the sex of the deer was easily determined from the skull as well.  If the carcass was fresh enough, I took it to Oregon State University to be necropsied, and to determine the cause of death.  I also cracked open a femur to examine the bone marrow, which can be scored subjectively for fat content, which is a crude method of evaluating the nutritional health of the deer at time of death.

It turned out that in this population the sex ratio among adults was still 3-4 females for every male.  However, we knew that the sex ratio at birth was nearly 1:1; in fact, there were probably slightly more males born than females, a typical pattern in mammals.  That is, the sex ratio started out about equal, but by the time males and females were two years old or older, there were many more females than males in the population.  We knew that males were not leaving the refuge, or emigrating, so the only other explanation for the skewed sex ratio was mortality.  Between birth and adulthood, males died at a younger age than females.    Males, on average, were living about 3.5 years, while females were living an average of about 6.5 years.  The oldest male skull I recovered was 7.5 years old; the oldest female skull was 13 years old.  In other words, males were cycling through the population at a faster rate than were females.

To put it bluntly, males are just more reckless than females. They get hit my cars, they get caught in barbed wire fences, and they drown in ponds more often than females.  But the most common cause of death in males was their poor physical condition immediately after the rut, or breeding season.  In this population, the rut began in November and lasted about two months.  At the end of the rut, we are in the middle of winter when conditions are not conducive to recovering body condition, and males paid the price.  It is known that adult male deer spend so much time and energy locating and tending females in heat during the rut that they lose significant body weight.  They increase physical activity during this important process and they decrease the time they spend feeding.  The result is that males are worn out and emaciated come January, all because they want to make love to as many females as possible.  In fact, you could say that many males literally mate themselves to death.

The similarities to other mammals including humans is inescapable.  The mortality rate of male humans is higher than females, especially among those just entering age of reproduction.  Males take dangerous chances, largely in an attempt to increase their status in the eyes of females, whether they know it or not.  The winners can win big, with multiple mates during their life and the possibility of siring many offspring.  Of course, modern contraception has changed the outcome of this male behavior somewhat, but our behavioral tendencies produced over the past 4 million years of human evolution continue to play out regardless.

(See full citation and an Abstract of the monograph produced from this research.)

Is your life's path determined at 17?

(The choices that young people need to make are daunting, and possibly made too early.)

When we were kids, I distinctly remember asking my younger brother what he wanted to be when he grew up.  We were sitting on the basement stairs at the time, so he looked around the basement, and answered: "A clothes dryer".  I laughed at him, and attempted to explain that was impossible.  He was a young human being and when he grew up he would just be an older human being, but what would he do for a job as an adult?  I'm sure he didn't understand my logic at the time.  But I have often wondered at the perspective that allowed this young boy to think that he could become a mechanical, inanimate object later in life.

Last night, I had a drink with four of my former undergrad students, all of whom will be graduating in May.  The conversation focused mostly on what they would be doing after graduation.  They are all very bright students and they had been applying to various grad schools around the country.  Should I work on population ecology modeling with Professor X at Penn State or on a topic somewhat less mathematical with Professor Y at University of Georgia?  Should I study fish management at Oregon State or do a study on white-tailed deer at Ohio State?  Should I work on obtaining a M.S. degree now, or go straight for the Ph.D.?  Should I become a clothes dryer or an upright vacuum sweeper?  The conversation with my brother from more than 50 years ago came streaming back into my head.  Was the topic of last night really all that different?

Perhaps the reason I feel somewhat apprehensive about the topic of our beer banter was because I am not at all sure that I would follow the same path again in my professional life, knowing what I know now.  I would likely not go into academia, would not get a Ph.D., and would not have focused so intently on wild animals and ecology as I did.  The details of my thinking will eventually end up in another blog; those details are not germane to my point here.  I have the benefit of hindsight, and these young people do not.  They are pursuing what they THINK will make them happy, but they can not possibly know for sure until after they have spent many more years working on degrees, getting a position, and working at that job for some time.  By then, they will be in their 40s, and it will be tough to turn back.  "You rolls the dice, and you takes your chances", as that old saying goes.

The problem is that these students haven't lived enough yet.  The world has so much to offer, and there are so many interesting challenges and opportunities.  They are bright enough and ambitious enough that they could choose any path they wanted, but they can't possibly know now about more than 1-2% of those potential paths.  They are following the logical direction based on what they chose as an undergraduate major at university.  Think about that.  A 17-year old high school senior picks a major for college based on what they think their interests are at that time, and it generally predicts their life's path for the next 40 years.  Astounding!

I'm even willing to wager my next Social Security check that if these four students did something else in the world for the next two years, that at least two of them would not proceed down the route they are now planning to take.  They might still decide to attend grad school, but the thesis topic they chose, or the major prof they selected, or the degree they pursued would be different than it will now be.  And then, their professional life would become different than it will now become.

Students who read this essay may be disturbed by these ideas, but I think they know there is some wisdom here somewhere.  And by reading this, it will probably only increase some doubts they already have.  I make no apology, because my role in life is largely to make people question.  I guess that is the teenage decision I made all those years ago.  My only advice is to realize that what you currently know or think is only a tiny fraction of all you could know or think, and you don't need to be a prisoner of those limited thoughts.  Perhaps, becoming a ball pene hammer would not be nearly as rewarding as becoming a 5/8 inch socket wrench, but you can't know the answer to that until you have tried them both.  My advice: take the time to explore, investigate, and experiment broadly before you Super Glue your life's map on your chest.

The pooping Labrador retriever

(Zeus and DrTom don't know nothin bout no deer leg.)

I have a dilemma that I would like to share.  Our black Lab Zeus needs to go outside to relieve himself several times a day.  I know, I thought I had purchased the model that didn't need to do that, but I was wrong.  I even thought about not feeding the guy any longer so he wouldn't have to poop or pee, but when I do that he gets all lethargic and isn't any fun. 

But here is the real problem.  I want to just let the dog out when he has to go and let him in when he wants back in.  But Management insists that we walk him on a leash each time (the "we" in that sentence really means "me").  This seems ridiculous, because we live on 12 acres of forested land surrounded by more forested land.  Who wants to walk a dog in their pajamas when there is a foot of snow on the ground and it is 15 degrees, and we are over 100 yards away from the nearest house, and the dog likes to have a little freedom, and I enjoy watching him frolicing around the property, and the traffic on the road is not THAT bad.  But THAT is the problem.  Zeus will go down to the road when he follows the scent of deer that have passed through our woods.  My wife is afraid he will get hit by a car and I understand that.  So Management usually wins this argument, like she wins most of our arguments, and I walk the dog on a leash.

But sometimes, when it is really early in the morning, and my wife is still asleep, and there is almost no traffic, I cheat.  SHE will never know.  So on this frigid Saturday morning, Zeus and I got out of bed, and I let him out the back door.  In a few minutes he returned to the door to be let back in, but he was carrying something in his mouth.  (Dogs only carry things in their mouths.  But if you don't add that phrase, "in his mouth", the reader just might picture the dog carrying an item in some other way, and I don't want that distraction right now.)  When he stepped inside, I immediately recognized the item as a deer leg, a fresh deer leg with hair and skin and sinew and bone marrow dripping out from the femur.  Crap!  You see, there are often dead deer scattered about the landscape, and this Lab can smell one a mile away, and he loves the smell of deer. 

Zeus was so proud of this prize, but you see my dilemma.  If Management discovers the leg, she will know I let the dog out without a leash, and I will receive a tremendously forceful tongue lashing that I would really prefer to avoid.  If I just throw the leg in the woods near the house, the dog will simply bring it back again the next time I cheat.  Remember:  I didn't buy a poodle that never has to relieve themselves.  I bought a pooping retriever.  This leg will be like a piece of scotch tape that you can't get off your fingers.  Throw away, and retrieve, throw away, and retrieve.

So I put the leg in our kitchen wastebasket under the sink.  And as soon as the bag is a little more full, I will tie it up and take it to the can in the garage.  Zeus knows the leg is in there and I know the leg is in there, but Management is clueless.  Thank goodness she does not have a Lab's nose.  I know that Management thought it weird of me to be anticipating when she wanted to throw some trash in that wastebasket.  I immediately jumped to her side as she wiped her mouth with a napkin and said, "Here, let me throw that away for you."  And that is the way I played it, although I replaced her napkin six times for one bowl of soup.  I know she thought that napkin:soup ratio was a little over the top, but it worked.  I kept her away from the leg-filled wastebasket, and the secret was safe with Zeus and me forever.  Until Zeus returns for another helping of that carcass that is out there, somewhere.

Car Rider: the deer who liked to ride in cars

(Would you share a ride with this deer in your Volvo?)

We have had many different kinds of pets over the years. I use the term “pet” very loosely, because many of these critters remained with us for a very short time, and they were not pets in the normal sense of that word. I will write about some of them in the future, if all of you behave yourselves.  During the past 40 years, we have had hawks, owls, foxes, rabbits, kangaroo rats, deer mice, gray squirrels, various salamanders and snakes, a red-eyed vireo, a black bear cub, and a black-tailed deer. And it is the latter animal that is the subject of this brief anecdote.

When I was studying Columbian white-tailed deer in southwestern Washington during grad school, Fred Lindzey, a fellow grad student, called me up and asked me to come over to his study area on the Washington coast. Fred was studying black bears on an island just off the coast adjacent to Willipa National Wildlife Refuge. Apparently, someone had raised a black-tailed deer fawn to yearling age, and it had become too much for them. The deer was hanging around refuge headquarters, so the personnel there thought it would be a good idea to get rid of the animal somehow. Fred immediately thought of me. I was only an hour away, I was studying a closely related species of deer on a deer refuge, we lived on the refuge, and there was plenty of space to turn the deer loose. Plus, he thought I might learn something by watching a black-tailed deer amidst a population of white-tailed deer. Sounded reasonable.

So I drove over to Willipa to pick up this deer in my Dodge truck. Now, this deer thought it was a dog or something, because it tried repeatedly to get through the front door of any house and, most curious of all, it would jump into the front seat of a car or truck if the door was left open. It actually liked to ride in moving vehicles. Thus, it was given the name “Car Rider”. In this instance, we encouraged the deer to jump into the back of the pickup truck and I drove it back to my study area on the deer refuge.

When I arrived back at the refuge, I promptly put a neck collar on the young male, similar to the one I used on my study animals. After a few hours of entertaining ourselves with this weird deer, I decided it was time to introduce Car Rider to his new home. I put him in the back of the truck and drove down the gravel road to the center of the 2,000 acre deer refuge, and released him. I began driving back to my house and after about 100 yards, I looked in the rear view mirror only to see that Car Rider was chasing after the truck and was only a few yards behind me. I couldn’t drive fast enough on this rough road to distance myself from him, so I ended up back at the house with a winded deer. Introduction of black-tailed deer to white-tailed deer population = failure!

The next morning I received a call from the refuge manager who wanted to meet with me in his office, which was about 3 miles on the other side of the refuge. I got in the truck, and drove about 45 miles per hour to his office. The road made a bend about half way there where I needed to bear right to get to his office; another small road took off to the left at the bend, and this was the only other road that intersected the route I took. About 20 minutes into our meeting, we got a phone call from Hobie's grocery store in Skamokawa, the tiny town nearby, that they had a very hot and tired deer standing in their store with a white collar around its neck. Damn! Car Rider had apparently tried to follow my truck, unbeknown to me, but I had been able to drive fast enough to put enough distance between us so that when he got to the bend in the road, he went left instead of right and ended up at the store.

Needless to say, my cohabitation with this deer had already become an untenable situation. At this point I was cursing Fred Lindzey, because I had little time for all this. In the end, I found that research biologists with the Washington Department of Game needed a trainable deer for a food habits study, and that is where Car Rider was sent. What a dear.