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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!
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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.