What killed this White-tailed Deer? Part 6: Results and Discussion

I want to start by reviewing the evidence that we observed before I offer some conclusions.

§         We discovered the animal dead within 50 feet of Bissell Rd.

§         There were some external injuries to the hind limbs and although the animal was still warm the crows were already starting to eat portions of the carcass.

§         We determined that the animal was an adult female approximately 6 years of age.

§         The carcass did not exhibit any internal injuries, or at least none were observed. 

§         The kidney fat index and heart fat index were low but small amounts of fat were observed.

§         The bone marrow fat index was marginal. 

I started this examination thinking that there could have been several factors that contributed to the death of this animal.  I hypothesized that it could have been struck by a vehicle, predation, or winter severity.  I feel confident to conclude that it was not struck by a vehicle.  The internal organs were not injured nor were any of the large bones.  This gave you an opportunity to examine relatively healthy white-tailed deer internal organs.  Pretty cool, Huh! 

I was left wondering if this winter was severe enough that the animal depleted its fat reserves and could not procure enough food due to the deep snow.  This doe was an older animal with respect to the rest of Connecticut’s white-tailed deer population.  Old and young animals tend to die during seasons of extreme environmental stress.  All Connecticut residents can attest to severity of this winter.  We had extremely deep snow, cold temperatures, and with relatively no thaw like we usually experience during most winters. 

I also wonder if predators could have wounded the animal enough that the animal died from these injuries.  Coyotes are quite common on the property and are observed eating from deer carcasses.  They quite often employ a strategy of wounding an animal's hind limbs and then letting the animal wander off to die.  This strategy is quite efficient because they do not have to expend more energy to kill a large animal and it reduces their overall risk of being injured by a swift kick from a large animal.  Coyotes are commonly observed scavenging carcasses, which could be an efficient strategy relative to predating their food. 

But why could it not have been a little bit of both factors (winter severity and predation)?  Unfortunately, we can’t say that one factor was the only thing that killed this animal.  So, we have to hedge our bets and say that both factors contributed to this animal’s death.  The animal died at the end of a severe winter and Eastern coyotes are known to predate white-tailed deer when the deer’s movements are limited and they are in a weakened condition. 

We need to be very cautious to not expand this observation to what happens to all white-tailed deer that died this winter.  It only indicates what may have happened throughout the state.  White-tailed deer were observed exhibiting “yarding” behavior throughout the state of CT.  “Yarding” is a seasonal migration pattern usually observed in white-tailed deer populations in Northern New England, Adirondacks of NY, some of the Northern Midwest States and Canada Provinces.  White-tailed deer migrate long distances from their breeding/warm season grounds to a central location that provides several resources that they need to survive.  These locations offer adequate cover, food, water, and space so that they can survive the extreme winter environment; in other words these are their winter “habitats”. 

I hope you enjoyed this series.  It was an unique opportunity to show you not only what a white-tailed deer looks like from the inside and out, but also it gave me an opportunity to demonstrate one activity performed by a Wildlife Biologist.  You have learned what knowledge we have as a discipline by those who created that knowledge before us.  You also have learned how we apply this information to monitor and learn more about the populations we conserve.  I hope to show you more things like this in the future.  So, come back soon and often. 

What killed this White-tailed Deer? Part 5: Bone Marrow Index

WARNING VIEWER DISCRETION IS ADVISED

DUE TO THE GRAPHIC NATURE OF IMAGES PRESENTED 

WITH THE PRIMARY INTENTION OF 

BIOLOGICAL RESEARCH AND ENVIRONMENTAL EDUCATION

We are getting closer to answering our question!  Please remember that occasionally as a biologist, we are also ecological detectives.  Put on your detective hats (Sherlock Holmes style) and let's continue the sleuth.

Lets start with a little review.  So far, we've determined the sex and age of this animal that we are investigating.  We continued by examining the internal anatomy, especially the organs that have fat stored in close proximity.  These organs and the amount of fat around them indicate the overall fat reserves that the animal still has to use as energy when other sources of energy (food) are limited.

This entry will explore one more body region that we can use to indicate the nutritional status of this animal and it is not the stomach!  This is the bone marrow.

Figure 1:  White-tailed deer femur bone marrow color indicates
the nutritional status of the animal  in the winter at the time of its death.
Photo By James Fischer 

Biologists have selected the femur bone to examine bone marrow fat levels for two reasons.  It is a large bone  and it provides a large amount of bone marrow to inspect (Figure 1).  The femur bone is about an inch or more in diameter.  Imagine a bone that is about the same size of two adult fingers held together, specifically the largest fingers, the fore and middle fingers held next to each other.  This is about the same size as some of the bones found in an adult human's skeleton.

I exposed the femur by cutting the muscle tissue away from the right hind leg.  I struck the bone with several sharp strikes with the back of my knife to break the bone and to expose the marrow in it.  We examine the marrow color, white marrow indicates that there is more fat in the marrow, while redder colors indicates less fat.  The bone marrow of this animal indicates that it had a little fat in the marrow because it is pink in color but probably less than it did in the autumn after it had fed on acorns and other nuts.  Now you can compare the bone marrow (Figure 1) with the kidney fat in our previous blog entry for yourself.  Pretty Cool!

The femur marrow indices corresponds closely with kidney fat indices.  Kidney fat indices are closely associated with the nutritional status of white-tailed deer.  It is important to realize that we don't always have an intact carcass to work with in the field because scavengers quickly clean carcasses.  So, when we approach a heavily scavenged carcass then we are limited by what we can observe.  The femur may be one of the only bones remaining.

Fortunately, we follow explorers who discovered this pattern and so we can use it.  Fat is energy, when food is limited or the landscape is difficult to navigate because the snow is as deep as a deer's legs are long or more.  Storing fat on their bodies is a natural process that every animal performs every year and it is a very good strategy for surviving winters that are variable.

If you are interested in reading more about this topic, then I suggest reading Susan C. Morse's latest contribution to Northern Woodlands Magazine (Spring 2011, Marrow Core Analysis p. 18 - 19).  It gets to the heart of the issue. :)

What is all of this evidence telling you?  Think about it and next time I will reveal the answer to our mystery!

Previous Blog Posts:

What killed this White-tailed Deer?

What killed this White-tailed Deer? Part 2: Sex Determination and Tooth Wear Pattern

What killed this White-tailed Deer? Part 3: Age Determination by Tooth Wear Pattern

What killed this White-tailed Deer? Part 4: Examination of Internal Organs

Advisory:  Please do not touch, feed, or disturb wild animals of unknown origin.  If you see an animal in distress please contact a licensed animal control officer, licensed wildlife rehabilitator, or other trained and certified wildlife professional.  You may expose yourself or the animal to unnecessary injury, distress, or disease.  This procedure was performed by a professional wildlife biologist who took proper precautions to avoid exposure to pathogens and other potential human-wildlife diseases.

What killed this White-tailed Deer? Part 4: Examination of Internal Organs

WARNING VIEWER DISCRETION IS ADVISED

DUE TO THE GRAPHIC NATURE OF IMAGES PRESENTED 

WITH THE PRIMARY INTENTION OF 

BIOLOGICAL RESEARCH AND ENVIRONMENTAL EDUCATION

The next stage of this field necropsy was to examine the internal organs.  If a vehicle collision caused its death then there could be internal bleeding, damaged organs, and broken bones.  This winter has been an extremely cold and snowy winter for Connecticut, at least the historical records suggest it.  This environment may have put more stress onto the animal and it had to use more stored energy (fat) than other typical winter environments to maintain certain bodily functions.  This animal died at the end of the winter season so the lack of fat would indicate its nutritional status.  If the animal was lacking fat deposits around certain vital organs then this would suggest that the animal was utilizing its fat resources this winter and maybe depleted them detrimentally.   

Figure 1:  White-tailed deer gastrointestinal cavity with internal organs labeled,
the presence of feces in this cavity was caused by damage to the large intestine by observer.
Photo By James Fischer 

I began by rolling the animal onto it's back and then creating an incision into the lower gastrointestinal cavity (Figure 1) .  I did not notice any damage to these organs, except for a small incision that I made into the large intestine.  When hunters remove the internal organs from the animals they harvest, they try not to cut the intestinal organs because these organs contain pathogens that could make you sick if you consume them.  Fortunately, I don't make a living as a butcher.  Notice the different diameters of the large intestine and cecum (ceacum) versus the small intestine.  Most of the stomach can not be observed in Figure 1, but it is quite large because it has multiple chambers to digest the vegetation it consumes.  The diaphragm is the muscle that separates the lower body cavity from the upper body cavity and it is the muscle that is used to expand and constrict the lungs.  You can observe the liver in this body cavity and it was not injured (Figure 2).  Some of you may be wondering what an internal injury would look like.  There would a great deal of blood in the body cavity and the organs would be difficult to distinguish because they would be covered in blood.  The organs of this animal are relatively unblemished.   

Figure 2:  White-tailed deer chest cavity with organs labeled.
Photo By James Fischer

I then opened the chest cavity to examine these organs.  The rib cage was not damaged and neither was the lung on both sides of the body (Figure 2).  

Figure 3:  An adult white-tailed deer heart is a little larger
 than the size of an adult human's fist.
Photo By:  James Fischer

The two vital organs that we use to index the nutritional status of a white-tailed deer are the heart and kidney, specifically the amount of fat layered around these two organs.  I exposed the heart, which is a little larger than  the size of adult human's fist, to find that there was some fat deposited around it (Figure 3).  The fat around the heart is really important for any individual's survival, it provides padding and insulation for a vital organ.  Without this fat, an animal would probably die.  So, it was a good thing to find some fat, but not as much as it probably had in the autumn after eating loads of acorns.  

Figure 4:  An adult white-tailed deer kidney is similar in size to a tennis ball...
Photo By James Fischer

I had to turn the animal onto it's side so that I could gain access to the kidneys, which are located along the back near the spine but in the gastrointestinal cavity.  The kidney is similar in size to a tennis ball and is kidney shaped (Figures 4 & 5).  

Figure 5: ...and is kidney shaped.
Photo By James Fischer

I observed a little bit of fat around the kidneys (Figure 4 & 5), but like the heart, there was probably more in the autumn after a diet rich in nuts and fruits.    

Next time, I'll show you another organ in a white-tailed deer's body that we can observe to indicate it's nutritional status and it is not it's stomach!

Next Blog Post:

What killed this White-tailed Deer? Part 5: Bone Marrow Index

Previous Blog Posts:

What killed this White-tailed Deer?

What killed this White-tailed Deer? Part 2: Sex Determination and Tooth Wear Pattern

What killed this White-tailed Deer? Part 3: Age Determination by Tooth Wear Pattern

Advisory:  Please do not touch, feed, or disturb wild animals of unknown origin.  If you see an animal in distress please contact a licensed animal control officer, licensed wildlife rehabilitator, or other trained and certified wildlife professional.  You may expose yourself or the animal to unnecessary injury, distress, or disease.  This procedure was performed by a professional wildlife biologist who took proper precautions to avoid exposure to pathogens and other potential human-wildlife diseases.

What killed this White-tailed Deer? Part 3: Age Determination by Tooth Wear Pattern

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DUE TO THE GRAPHIC NATURE OF IMAGES PRESENTED 

WITH THE PRIMARY INTENTION OF 

BIOLOGICAL RESEARCH AND ENVIRONMENTAL EDUCATION

So without further ado, what is the age of this animal?  I judged it to be almost 6 years old!  You might be saying one of two things "How?" and "Wow, thats slick!"  How did I judge this to be a 6 years old animal or a better stated question would be, what characters were use to distinguish the age?  I describe this further below.  For those of you exclaiming "Wow, thats slick!", I can't agree with you more.  It is cool that we can use tooth wear patterns to determine the age of an animal with such accuracy.  It shows that we are indeed standing on the shoulders of those who worked before us.  I would like to thank Erin Victory, Michigan DNRE Wildlife Biologist, for her corroboration.  Compared to the small number of animals that I have aged during my career, Erin has accurately assessed many more white-tailed deer jaws (in the thousands), so Thank You, Erin.  

Figure 1:  White-tailed deer mouth with additional labels numbering
 the premolars and molars, as well as some of the characters
 used for aging animal by tooth wear patterns.
Photo By: James Fischer

The characters that we use to age an animal by tooth wear are subtle and can be complicated to learn by the novice.  Therefore, I don't plan to explain every detail.  The first that caught my attention was that second and third premolars were permanent and they were quite "flat" (Figure 1).  Flat is a relative term so compare the second and third molars to the premolars, the molars are more jagged and this is similar to what "newer" teeth look like.  Now we shift our attention to the molars, particularly the first and second molars.  The letter "A" in Figure 1 points to the lingual crest of the first molar, while "B" directs your attention to lingual crest of the second molar.  Observe how this ridge is quite taller on the second molar and the ridge is shorter on the first molar.  Also notice the overall height of the first molar that is exposed above the gum line is relatively short.  I apologize that my photo does not allow you to compare this feature to the other molars, but they are relatively taller than the first molar.  Another feature to examine is the amount of brown dentine (dentyne) that is exposed on all of the molars relative to the amount of white enamel that can be observed.  You see a greater amount of  dentine than  enamel on these worn teeth, while "newer" teeth you would observe a greater amount of enamel than dentine.  There are several other characters to observe, however they are challenging to learn without a accompanying image.  So, there you have it, a challenge to learn but very useful to know and fun to practice.  

My next blog post will describe the condition of the internal organs with loads of figures!

Next Post:

What killed this White-tailed Deer? Part 4: Examination of Internal Organs

Previous Posts:

What killed this White-tailed Deer?

What killed this White-tailed Deer? Part 2: Sex Determination and Tooth Wear Pattern

Advisory:  Please do not touch, feed, or disturb wild animals of unknown origin.  If you see an animal in distress please contact a licensed animal control officer, licensed wildlife rehabilitator, or other trained and certified wildlife professional.  You may expose yourself or the animal to unnecessary injury, distress, or disease.  This procedure was performed by a professional wildlife biologist who took proper precautions to avoid exposure to pathogens and other potential human-wildlife diseases.

What killed this White-tailed Deer? Part 2: Sex Determination and Tooth Wear Pattern

WARNING VIEWER DISCRETION IS ADVISED

DUE TO THE GRAPHIC NATURE OF IMAGES PRESENTED 

WITH THE PRIMARY INTENTION OF 

BIOLOGICAL RESEARCH AND ENVIRONMENTAL EDUCATION

I wanted to determine the sex and age of the animal, first.  It was a female because I observe nipples that lacked hair where she nursed her young previously this year.  I also did not observe pedicels, which is where antlers would be attached to the frontal bone on the skull of males.  The best way to age white-tailed deer is to examine the teeth's wear pattern.  I needed to cut the cheek of the animal so that I could expose the teeth better (Figure 1).

Figure 1:  White-tailed deer cheek cut to expose teeth
for better inspection of tooth wear, notice eye was removed by scavenger.
Photo By James Fischer

Examining the tooth wear patterns looks complicated at first but it gets easier with practice.  We are examining the patterns of tooth loss and eruption/replacement for the first 2 years of their life.  Animals older than 2 years old have permanent teeth which wear down as the animal chews the vegetation it eats everyday.

Figure 2:  White-tailed deer mouth showing
the animal's upper and lower right mandible's cheek teeth,
as well as the tongue and the lining inside the cheek .
Photo By James Fischer

We examine the pattern of enamel and dentine (dentyne) wear patterns to accurately age white-tailed deer (Figure 2).  Deer teeth have exposed dentine which is softer than enamel but denser than skeletal bone.  Human teeth are composed of dentine but it is surrounded by hard enamel.  The layering of dentine and enamel create a surface with different friction gradients which is very effective for masticating (chewing) vegetation and exposing the vegetative cells to flora that is found in their gut, which occurs when the animal regurgitates and chews it cud.   Although this is an effective strategy for chewing vegetation, it also allows the teeth to wear down.  The habitat that the animal lives in can change the wear pattern slightly.  For example, animals that live in an area with sandy soils will have teeth with a slightly different wear pattern than animals that inhabit a area of loam soils.  The sand will occasionally be chewed because it is on the plants that the animal eats.  Although there are overall patterns that remain consistent across all white-tailed deer populations, some interpretation is needed when judging the age by tooth wear.  It takes lots of practice, but it can be fun.  The best way to learn this pattern is by practicing with jaws of differently aged animals (new born fawns to 10+ yrs old).  

Tune in tomorrow to learn the age of this animal and what characters I used to distinguish it's age!  

Next Blog Post:

What killed this White-tailed Deer? Part 3: Age Determination by Tooth Wear Pattern

Previous Blog Posts:

What killed this White-tailed Deer?

Advisory:  Please do not touch, feed, or disturb wild animals of unknown origin.  If you see an animal in distress please contact a licensed animal control officer, licensed wildlife rehabilitator, or other trained and certified wildlife professional.  You may expose yourself or the animal to unnecessary injury, distress, or disease.  This procedure was performed by a professional wildlife biologist who took proper precautions to avoid exposure to pathogens and other potential human-wildlife diseases.

What killed this White-tailed Deer?

WARNING VIEWER DISCRETION IS ADVISED

DUE TO THE GRAPHIC NATURE OF IMAGES PRESENTED 

WITH THE PRIMARY INTENTION OF 

BIOLOGICAL RESEARCH AND ENVIRONMENTAL EDUCATION

We received a report from several people about a fresh white-tailed deer carcass in Pine Island on Wednesday March 2, 2011.  The body was slightly warm and the limbs were starting to get stiff with rigor-mortis.  There were a couple differences about this animal that made me wonder how the animal had died.  The first thing that intrigued me was that it was located about 50 feet north of Bissell Rd., so I wondered if this animal was struck by a car and walked a short distance into the woods and died.  The other odd thing is that the animal died right in the center of the Mattatuck Trail with no obvious signs of struggle.  Deer and other wildlife frequently use the human trails to travel when the snow is deep because the snow is compacted on the trail and it is easier to walk on.  However, I did not observe any tracks or sign in close proximity of the carcass that indicated a predator could have killed the animal.  The animal's hind quarters were injured, which may suggest a coyote had attacked it before and it died some time after.  But these injuries could have been caused by scavengers because there was not a large amount of blood lost on the snow near the injury.  American crows were observed scavenging the animal on other body parts.  There were no other external injuries that suggested it was hurt by a vehicle.  So, why and how did animal die? Was it hit on the road by a vehicle? Did a predator injure it, which lead to its death?  Did this animal die because it was an extreme winter and it died from exposure?  The scavengers were already working on the carcass and I had to make a fast decision.  I decided to do a quick necropsy to see what clues I could find.  Check back for future blog entries this week to learn what I discovered.

White-tailed deer carcass after I performed a quick necropsy
to examine what may have caused it death.
Photo By James Fischer

Next Blog Entry:

What killed this White-tailed Deer? Part 2: Sex Determination and Tooth Wear Pattern

Advisory:  Please do not touch, feed, or disturb wild animals of unknown origin.  If you see an animal in distress please contact a licensed animal control officer, licensed wildlife rehabilitator, or other trained and certified wildlife professional.  You may expose yourself or the animal to unnecessary injury, distress, or disease.  This procedure was performed by a professional wildlife biologist who took proper precautions to avoid exposure to pathogens and other potential human-wildlife diseases.