Wildlife managers estimate the population size of a wildlife species using many different field methods. Some of these methods include camera trap surveys, hair snares, scat and track counts, mark-recapture surveys, harvest data, GPS collars, and radio telemetry.
While these approaches are very good at obtaining the data that professionals use for management decisions, they can’t be perfect. It is hard to properly account for EVERY SINGLE one individual animal of every species of wildlife in the world.
So, managers create scientific population estimates based on the data that they know to be true and always leave a margin of error when making management decisions.
For example, harvest quotas for hunting season are set based on these population estimates – so it is extremely important to be as accurate as possible so as to not overpopulate an area or completely decimate a population. Black bear (Ursus Americanus) populations can be estimated by placing GPS or radio collars on select individuals to track movement and reproduction.
Many times, the female bears (sows) will be fitted with these collars and tracked while raising their cubs. This can tell us how many new bears are being introduced into the population each year. But, aside from tracking their movements, denning sites, and population numbers, managers also collect biological data from these individuals whenever they can.
Things like hair and blood samples can tell us a lot about how certain populations of bears are doing, what their diet is, and much more. Below is a walk-through of some of these important biological indicators and what they tell wildlife professionals.
Hair Samples
Hair samples can tell us not only about the genetics of certain bears, but also about their diet. Collecting genetic information from multiple bears in an area can give scientists a better idea of the gene pool and how many bears are related within a population. While hair samples can tell us a lot about the DNA of an individual bear, the integrity of a sample matters greatly in the analysis of such information.
For example, a hair sample must contain the root when collected – as the root is where all the DNA is stored. Hair can also be chemically analyzed and reveal what a bear has been eating. The presence of mercury or other heavy metals would suggest a diet of salmon. Hair can also be tested for carbon and nitrogen to determine other protein sources.
Blood Samples
Similar to hair samples, a blood sample can help assess the nutrition and physiological condition of an individual bear. Blood samples also can tell us a great deal about how bears alter their bodies in order to overwinter. While oftentimes referred to as hibernators, bears are in fact not true hibernators.
Instead of practicing something called torpor, bears can actually awaken from their winter sleep much easier than an animal who would be practicing true hibernation (like a ground squirrel) could. Similar to hibernators, animals that experience torpor have decreased body temperatures, heart rates, breathing rates, and run on little to no food or water.
However, bears do not HAVE to den up in the winter, but rather involuntarily fall into this state of torpor as their environmental conditions dictate. As long as there is enough food, there will be active bears!
Tooth Samples
Tooth samples are sometimes also taken from a bear when conducting a biological workup. The standard tooth that is removed is a very small pre-molar, located behind the large canines. This tooth removal is very minor and not pertinent for browsing or hunting success in the wild. Once removed, a tooth can tell us how old a bear is by counting the rings of cementum. Much like counting the rings of a tree!
If female, a bear’s tooth can also tell us what years she was raising cubs and what years she was not. The years that a mother is raising cubs shows narrower cementum lines in the tooth sample. This is because, during a breeding year, females invest more of their nutritional intake in raising and feeding cubs.
Body Measurements & Weight
Just as in humans, body weight and body measurements can also give scientists a better idea of a wild bear’s body condition and overall health. In the field, weighing a bear is a group effort. Laid onto a tarp and sedated, the bear will then be lifted from all sides of the tarp and clipped onto a hanging digital weight.
Measurements collected at the time of a workup include total body length, ear length, head width, head circumference, paw pad length and width, height, tail length, and others.
Body Fat Percentages
Body compositions of captured bears are also sometimes measured during a workup. This is done using small, harmless bioelectrical circuits that measure body fat on an animal. These measurements can tell us a lot about how the environment is influencing an individual’s body condition and preparedness for winter denning – when they may not eat for up to six months at a time!
Identification Markers
EAR TAGS
- There are multiple different types of ear tags – but all are usually marked with a unique number and the wildlife agency or department’s name. These are a good identifying marker from a distance and help to engage local citizens in reporting an individual’s whereabouts when spotted.
COLLARS
- GPS and VHF collars are the most viable options to track specific wildlife movement over long periods of time. GPS collars can be tracked from an office setting on a computer and will load locations at differing time stamps. VHF collars allow biologists to find bears in the field using telemetry equipment.
LIP TATTOOS
- In some cases, bears are also “tattooed” on their upper lip as a form of identification that will not easily fall off or get lost/worn over time.
PIT TAGS
- Passive Integrated Transponders are a lot like the microchips we use in our pets. These rice-sized radio devices sit right under the skin and can be detected by a special scanner when the tag is in range.
Depending on the reason for trapping and working up a bear, the above identification markers are sometimes used individually, specifically selected, or all used together. These bear workups not only allow managers to estimate more accurate numbers for the population, but also aid in important research findings.
Things such as nuisance bear relocation and coexistence efforts as well as finding surrogate mothers for orphaned cubs all come about because of such work and biological sampling.
As with all wildlife work, the wildlife’s well-being is our first and greatest concern and all are treated with the utmost respect and thoughtfulness when being worked on in the field.
