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. 4. Biologists count wildlife in Wisconsin by...

a. conducting surveys and estimating with a mathematical equation.

[Frog Graphic] And you thought they counted each animal on their fingers and toes? Animals are very secretive and Wisconsin is far too large to cover every square inch of ground looking for animals to count. It would also be difficult to keep from counting the same animal twice! Biologists have designed several types of surveys to estimate the number of animals in a population.

Deer Surveys

Deer are one of the most watchable wildlife species in Wisconsin. Why is that? Probably because they are the most visible to us as they move between woodlands and the edge of fields. Deer are also a popular animal for photography, hunting, and as a source of food for people. Biologists must estimate the deer herd in Wisconsin in order to determine the number of deer people may take during the hunting season.

Biologists use a method known as "Sex-Age-Kill." To begin the estimation process, biologists must first collect lots of information. They begin in the fall when deer hunters bring their harvested deer to be registered at a check-in station. At the registration station, the registrar checks to be sure the hunter has a valid hunting license; they check the hunting permit to be sure the hunter has harvested a male or female deer according to the rules, and they check to be sure the deer has the proper tag on it. From the registration information, biologists can find out how many deer were harvested in specific areas in the state and whether they were males or females. They also collect age samples from many deer by examining the teeth of the lower jaw of the deer. All of this data allows the biologists to calculate the number of males and females, how many fawns are born each year, and how many deer die in specific areas called "deer management units." From all of this, they can estimate the number of deer living in Wisconsin that winter.

In the summer, wildlife biologists and volunteers also keep track of deer that they observe between July and September. Deer are observed during the daylight hours only, from dawn to dusk. Many of the deer will be seen during the early and late hours of the day when the sun is low in the sky. Surveyors record the number of deer, if they are male or female, and if there are fawns with them. This information helps estimate the number of deer that can be harvested each deer hunting season. The winter population of Wisconsin's deer herd is now about 1 million deer. Wow, that's a lot of deer.

Here's what some of the mathematical equations look like...




Sex-Age-Kill Formula:
Fall Buck Population = Registered Buck Kill -------------------- Buck Harvest Rate Fall Doe Population = Fall Buck Population x Doe:Buck Ratio Fall Fawn Population = Fall Doe Population x Fawn:Doe Ratio Total Fall Population = Buck Population + Doe Population + Fawn Population Overwinter Population = (Total Fall Population) - (Fall Harvest and Harvest-related Mortality) where Doe:Buck Ratio = number of adult does per adult buck in the fall population and Fawn:Doe Ratio = number fawns per adult doe from Summer Observation

Whew, that's a lot of math and there's more to be done! When all of this calculating is finished, groups of people interested in deer gather together to decide how many deer can be harvested by hunters. This way, everyone has a voice to express their feelings about the deer population. Many people enjoy deer whether they hunt, photograph them for fun, or just like to watch them out in their back yard. Without a hunting season, the deer population would increase, causing more car-deer accidents, an overbrowsing of trees, crops, parklands, and your gardens, not to mention deer suffering from starvation in the winter time. Also, the license fees and taxes hunters pay on their equipment goes directly to help maintain habitat for all wildlife, not just deer.


Frog Surveys
Wisconsin is home to 12 native species of frogs and toads. Recently, many people have been concerned with how the population of some types of frogs has decreased. Biologists are also concerned about the habitat that frogs live in. Frogs and toads like many other aquatic (water-loving) organisms are sensitive to changes in water quality and how land is used around their habitat. Biologists know that the number of frogs can help tell us how healthy the environment is.

Because of this, biologists designed a frog and toad survey to help them learn more about the number of frogs and toads and where they can be found. Volunteers who know several frog calls by heart, go out into a wetland and listen for frogs in the same places every year. Each volunteer has 10 different wetland sites to visit 3 times each year. They go out in the early spring, late spring, and summer.

At each site the volunteer finds a quiet spot and listens closely for about 10 minutes for frog and toad calls or "songs." Then the volunteer identifies each type, or species that is present. They make a simple estimate of the number of frogs and toads there are by listening for specific individuals and the types of sounds each one makes, the number of calls they hear at once or whether the calls are overlapping and continuous and cannot be told apart (called a "full chorus"). Some calls are drowned out by others, especially by a full chorus of spring peepers or chorus frogs. When this happens, the volunteers try to silence the chorus by making a loud noise with their voice or by clapping. Then they listen for individual calls as the frogs and toads resume their "singing."

Volunteers record on paper the county they are in, the exact location of the wetland, the date, observers names, weather conditions, time of the survey, additional comments on noise levels (if they tried to silence loud choruses), and the water temperature. They also record changes in habitat since the last visit, like nearby construction or extensive flooding. This information is gathered together and evaluated by the biologists. From this data, they can find trends and changes from year to year in the numbers of the different types of frogs and toads.

With some practice, you can try this the next time you are near a pond or a wetland. Find a quiet spot and listen for a while. Then clap your hands to silence the frogs and toads and listen again more closely. How many types of frogs can you identify? What time of the year do you hear them most? What time of the day do you hear them calling? These surveys are important and help provide scientists with a valuable amount of information on the numbers of frogs and toads there are all over Wisconsin. They can also help biologists know how healthy the environment is.


These are just two examples of surveys conducted by Wisconsin's biologists with the help of volunteers. There are many other surveys that take place every year. All of them give us a better idea of how many animals there are in our state. Biologists must keep a close eye on wildlife populations to prevent extinction as well as overpopulation.

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