Glands on a White-tailed Deer Leg
While at work on January 31 this year, I was playing a game of “the hunt” (pretty much “manhunt” but “we hunt everyone!”) I got caught early and decided to follow different animal trails until they led me to where humans might be hiding. I found my co-instructors this way while I was on an Eastern Cottontail (Sylvilagus floridanus) trail and began to think that this was a good technique. The next Cottontail trail led me towards what we call “the back forest” past “the rocky outcropping”. I was looking around back there when I found a Coyote trail. The trail was pretty fresh and I decided I had time to pursue this trail while my co-workers and our students tried to find each other.
I hadn’t been on the Coyote trail long when as I was coming up a small hill I could see ahead of me, at my eyeline, that there was a depression in the snow. I could make out that the Coyote trail led there and that there was a bit of hair of some kind. I walked up and immediately got excited.
Amidst the matted snow there was what looked like a dig, some bone fragments, some loose hair and a White-tailed Deer (Odocoileus virginianus) leg. I ended up calling over the radio and soon enough my co-instructors were there with all of our students. It was a great discovery and an awesome learning opportunity. We had a discussion about Coyote hunting and cacheing behaviours and then followed with a great trailing session on the Coyote trail which led us to another leg, but this time from a domestic Chicken (Gallus gallus domesticus).
I ended up taking the leg. Why? Well, because I thought it would be a good teaching tool for other students and for parents when they came to pick up their kids. It led to a lot of questions like how old was the deer? Which leg was it? Which bones are there? Is this a leg or a foot? The kids, and adults, were very excited to touch the leg, and try and sort these questions out together. After all of the kids were picked up, I brought the leg home to study and learn more about. This post is about my findings, especially in regards to the glands distributed along a deer’s leg.
What is a gland?
A gland, simply put is an organ on the body which produces and secretes a substance, either internally or externally, in the body of an organism. Sudoriferous glands secrete sweat. Nectaries are glands in plants that produce and secrete nectar. As a means to protect the internal body, mucous glands exude slippery slimy liquids which coat internal surfaces of the body which may interact with external particulate. Sebaceous glands make oily substances which can help protect a surface, coat skin or fur, or help to hold chemicals which are used in different forms of non-verbal scent based communications. Of the deers eight glands external glands, I’ll be writing about three sebaceous glands found on the legs of White-tailed Deer.
When it comes to these sebaceous glands, it isn’t really the sebum or waxy fatty substance that is excreted which produces the odour that deer use to communicate. Really what gives the scent is bacteria which grow in these substances. Is the bacteria, which may thrive on deer who have healthier diets, which may signal the health of a deer to other deer?
Interdigital gland with sebaceous goo, also called “sebum”.
Interdigital Gland
A little bit up from between the digits (toes), on each of the deer legs, there is a gland which secretes a fatty substance which is applied to the substrate with each step the deer takes. From what I am learning, this substance appears to be pretty unique in odour to each individual deer. Some humans (Homo sapiens) can perceive this odour, but personally, I cannot. For deer though, this uniqueness is so pronounced that does can find their fawns by following this scent. Bucks, or male deer, can track females during the rut (mating season) following this scent as well. I think it’s kind of funny to think of the scent coming from between their toes being so important during the rut, but, you know, animals be animaling.
In The Deer of North America by Leonard Lee Rue III (The Lyons Press, 1997), the author menti0ns that deer are animals that rely heavily on scent (as can be inferred by their long rostrum) and they tend to track each other using this secretion from their interdigital gland by wandering around smelling the ground where the scent was deposited as the deer walked along. He also mentions that deer predators such as Coyotes (Canis latrans) and other Canid species are air-sniffers who pick up scent in the air as they move along. But I have learned hunters training hunting dogs will train their hounds to sniff out the interdigital gland scent to be able to track deer. This would run counter to Rue’s theory. If I am incorrect, and Leonard Lee Rue III is correct (he’s been watching, photographing, studying, and writing about deer his whole life) than this seems to show that the scent from the interdigital gland doesn’t put the deer in danger of being found by their predators but instead would more-so help the deer by being a big part of their mating and rearing of young. I wonder if it’s a case of both ideas being true?
Another neat thing I have learned about is that hunters will sometimes collect the waxy fatty secretion from the interdigital gland, sebum, and then turn it into a lure to attract other deer in future hunts. It seems like a good idea, leveraging the tools that the deer come with to be able to hunt more deer. Imagine the first person to try this technique, likely thousands of years ago… it would be a groundbreaking innovation for humans trying to feed themselves and their communities. I hope they won a prize.
Tarsal Gland
The tarsal gland sits on the inside of the leg where the tibia articulates with the metatarsal on the deer’s hind leg. If a deer were a horse, we might say they were located on the hocks. For humans, we would call it the ankle. This gland often named as the most important of the leg glands in that the secretions from the glands and the bacteria they accumulate contain chemical notes which may let other deer know, not only who the deer is, but also the relative health of the deer who left the scent. How do they leave the scent? Through a common behaviour known as rub urination.
White-tailed Deer scrape. 2024.11.11
Imagine a mature buck standing in place amidst the rut. He just started scraping at the ground with his front legs. As he is standing there, he puts his hind legs together at the tarsal glands and then urinates on his legs, dripping through the hairs on the tarsal glands. Mature bucks do this behaviour more so than other deer during the rut, and that urine mixing with the oily waxy secretions gets pretty powerful.
The long dark hairs at the tarsal glands catch the oily goo produced by tons of the sebaceous glands beneath the hairs. The fatty goo coats the hair and helps hold some of the urine and then the bacteria get in on it and it creates a powerful rank odour.. As the urine runs down the buck’s leg, he then stamps his into the ground when they create a scrape. The skin underneath these dark tufts of hair also have tiny muscles which can raise the hair on end, giving off a sudden and powerful scent bath.
It’s not only the mature bucks though… old and young, male and female, will all demonstrate this rub urination behaviour. It seems from the literature I am reading that perhaps folks once only saw this behaviour in males, but now, especially with a ton of trail camera footage, it seems researchers are noting that females have been doing this behaviour as well.
In another species of deer on Turtle Island/North America, the Black-tailed Deer (Odocoileus hemionus), the hairs at the tarsal gland have comb-like structures to help hold the sebum and urine a bit better. These structures are called osmetrichia, from the Greek osme meaning “odour” and thrix meaning hair. White-tailed Deer not have these structures, but the hair at the tarsal gland still gets the job done.
And boy does it get the job done. They urinate on their hind legs so much that the hair becomes that dark brown colour you see in the photos above. I wonder if this colour change is also of benefit to the deer? Author Rue mentioned above also wrote that in a similar way that domestic Dogs (Canis lupus familiaris) may sniff each others butts to get to know each other, deer will sometimes approach each other and sniff, and lick, each others tarsal regions. I wonder if the colour change brings a little more attention to the spot similar to how flowers draw in pollinators using colours and patterns to seduce pollinators? Much research is probably necessary here.
Metatarsal Gland
The metatarsal gland is a small gland which sits on the outside of the hind leg, circled in white hair. This circle of hair is about 25 mm (1 in) long for White-tailed Deer. For Mule Deer (Odocoileus hemionus), the gland is between 75-150 mm (3-6 in) long, and for hybrids between the two, it’s going to be some intermediate length. In the middle of the circle of white hair there is a black hard material which appears a little bit bumpy and rigid, reminiscent in texture, at least to me, of a dried out citrus peel.
If I am correct in my research, the black textured area isn’t really a gland after all as it does not exude any material, but the area around this black spot does. The area around the spot exudes both sebaceous (waxy oily goo) and sudoriferous (sweaty) material on to the base of the hair, which, again, when come into contact with bacteria can help produce scent to communicate between deer.
Metatarsal gland close up.
You know what the metatarsal gland is specifically for? No? Well, I don’t either. Neither do the researchers. Sure, there are hypotheses, but no one is certain and I think that’s kind of cool. I like to think of the deer having their secrets which we cannot yet decipher. A little magic and mystery doesn’t hurt. In fact I think it draws us in a bit deeper.
Some believe the metatarsal gland may help with thermoregulation to some extent. I have also read that some believe that when the deer lay in their beds, they tend to press the gland into the bed sites perhaps marking them with individual scent? The gland itself is also in good position to brush up against vegetation as the deer walk by, leaving scent on the plants as they go. But again, these are hypotheses. No one is sure.
The few things folks seem to be sure about is that there is no observable difference between the glands of bucks and does, and that White-tailed Deer further North have larger glands than those further South. In fact White-tails in South America do not have a metatarsal gland at all, though they still have a patch of hair in a slightly different location.
Outer toe is longer… usually.
So, can we tell which leg it is?
A couple of years ago in collaboration with my friend Alastair, I wrote up a post on what we can learn from looking at the toes of White-tailed Deer. One of the questions I hoped to get answered was can you tell left or right foot from the length of the toes, or as Alastair more clearly phrased it, which part of the hoof is the longest, the inside or outside? According to Alastair’s measurements, the longer toes tend to be the outside toes, but this isn’t always the case. Of 12 legs he examined, 9 of the legs demonstrated that the outside toe was longer, while the inside toe was longer for two legs, and on one left foot, the toe lengths were even. To corroborate this, in Mammal Tracks and Sign (2nd ed) Elbroch and McFarland note that “toe 3 is often slightly smaller than toe 4, but not always” for both the fronts and hinds.
In light of this question, I looked at the toes of the deer leg I had found and it showed that one of the toes was longer. But was there an additional way to determine whether this was the inner toe or outer toe? Turns out there was, based on all the information we have reviewed above.
1) Tarsal gland :
As stated above, “the tarsal gland sits on the inside of the leg where the tibia articulates with the metatarsal on the deer’s hind leg.” The tarsal gland is located on the inside of the back leg. Looking at the photo above this would indicate that this is a right hind.
2) Metatarsal gland :
The metatarsal gland sits on the outside of the hind leg. This indicates, from comparing with the images above, that this must be a right hind.
3) Toes : According to the study which Alastair and I did, and to Elbroch and McFarland, the outer toe is longer. This implies that this is a right foot.
If we put it all together, we have to determine that the leg is a right hind. I get stoked knowing I can figure this out now.
It all seems pretty weird to communicate via scent and strange chemicals, but we humans do it too. We may not pee all over ourselves to try and show how healthy we are, and we might not try to rub our toe jam into the carpet to let everyone know we’re home, but we do it in other ways, through pheromones and body odours. A nasty fart might let someone know something is funky in their diet, or sweet odorous breath can tell a doctor that someone might have diabetes. These may seem crude and weird, but we do learn a lot from the body odours and ecto-hormonal chemicals emanating from all over our bodies. It also reminds me that I, you, we, are animals and share so much weird and wonderful ways with the wilder world. I am grateful for that.
To learn more :
The Deer of North America by Leonard Lee Rue III. The Lyons Press, 1997.
Deer (The Wildlife Series, Book 3) edited by Duane Gerlach, Sally Atwater & Judith Schnell. Stackpole Books, 1995.
Deer of the Southwest by James R. Heffelfinger. Texas A&M University Press, 2006.
Biology and Management of White-tailed Deer Edited by David G. Hewitt. CRC Press, 2011.
What The Toes Show - A question of deer hooves - another blog post
Mammal Tracks and Sign by Mark Elbroch and Casey McFarland. Stackpole Books, 2019.