Wildlife Necropsy, CSI Biologist Style

Much like an autopsy for humans, a necropsy is a scientific examination to determine cause of death in wildlife. Unlike medical examiners, biologists usually are required to conduct necropsies in the field without the luxuries and equipment of a lab.

Even though biologists aren't able to witness an animal dying, by collecting and analyzing all of the available information around a death, a reliable cause can be determined. Necropsies can take from 1-2 hours in easily identifiable cases (e.g. gun shot) to over several days where cause of death isn't obvious (e.g. disease).

There are 3 primary steps when conducting a necropsy:

Step 1) Biologists conduct a site inspection looking for blood, tracks, scat, hair, bedsites, cache (pile of dirt or sticks covering a carcass), soil and vegetation disturbance, and drag trails. Photographs are taken, measurements are made, and samples are collected for submission to diagnostic labs.

Step 2) After a site inspection has been completed, biologists begin a physical examination of the carcass. First, the entire body is evaluated for obvious puncture wounds, broken bones, scratches, blood, and abnormalities. Next, the biologist begins to carefully skin the entire animal. Once the skin is removed, the body cavity and throat are opened up to look for abnormalities in the internal organs. Samples of suspicious looking irregularities are collected and sealed in individual containers. Samples of brain tissue, heart, lung, liver, stomach contents, feces, and blood may also be collected.

Step 3) After the site and carcass inspections have been completed, biologists will assure their notes are complete and submit samples to a diagnostic lab for testing if a cause of death isn't apparent. Results from lab testing are analyzed along with the physical evidence from the site and a cause of death is assigned. A biologist will typically consult with other biologists to assure cause of death is supported by the evidence.

Cause of death is generally classified as predation, malnutrition, disease, harvest, other, and unknown. A tell tale sign for animals dying from predation is hemorrhaging (bleeding) around wounds caused by claws or teeth. Animals fed on by predators, but not killed, will not display hemorrhaging. Evidence from the death site including tracks, scat, tooth puncture measurements, location of wounds, and hair are used to determine what type of predator was involved. Each predator has a distinct style of attacking and consuming prey. Malnutrition is assigned to those cases where other causes can be ruled out and the animal is in very poor body condition, including having little to no fat in bone marrow. Animals typically use body fat during winter and fat in bone marrow is the last available stored energy for animals. Disease is assigned as the cause of death when lab results confirm a fatal disease was present. Animals dying from gunshot wounds are classified as harvest related. "Other" causes of death include those where the cause of death is known, but not assigned to predation, malnutrition, disease, or harvest and includes such causes as falls, vehicular collisions, and complications with birth. When not enough evidence remains to clearly determine a cause of death, biologists assign it as unknown.

The next time you come across a dead animal, don't jump to conclusions about how it died. Rather, poke around and look for clues. Sometimes cause of death is quite surprising. Besides, playing CSI biologist style can be enlightening.