Biologists usage a variety of techniques to estimate populations. Counting animals like this camouflaged snowshoe hare deserve to be difficult. Kari Rasmussen photo.

One the the good perks of living in is sharing our space with a range of wildlife. Whether we space curious about our next hunting opportunities, or eager to clock wildlife, we frequently wonder around the animals living in our very own backyards. Have you ever considered how plenty of bears are hibernating near you ~ above cold winter evenings? as soon as you view a moose external your window do girlfriend imagine there might be much more you execute not see? Wildlife managers and also researchers work-related diligently to uncover out how plenty of individuals the a particular varieties live in a details area. Their tasks are crucial to for sure the conservation of wildlife, particularly for pets that room hunted.

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Tim Peltier, a biologist for the room of Fish and also Game (ADF&G) in Palmer, explains one of the factors why biologists have actually such critical job.

“We counting moose, caribou, sheep, and also to a lesser degree bears and wolves,” that said. “The board (of Game) has identified the population and harvest target in every area and we room tasked with determining exactly how close we are to those objectives. We need to have an idea of the populace size.”

How execute biologists identify the number of animals living in an area? A range of approaches are used to recognize populations. A biologist must think about the ecosystem, terrain, the species being counted; and also must additionally factor in weather, costs, and also time.

It would certainly be appropriate to see and also count each individual pet in a population. This is referred to as a census. Unfortunately, there is no simple means to carry out this. Animals move from location to place, lock hide, they hibernate, and they are often camouflaged and complicated to watch in your environment. The closest point to conducting a census in is count caribou such as the west Arctic Herd on the north Slope. Throughout the summer, caribou huddle increase on snow areas for relief indigenous mosquitoes and also other insect pests. Viewed from above, the brown caribou ~ above the white, snowy lift are relatively easy come see. Biologist fly end these teams of caribou, systematically taking photos as castle go. Ago in the office, every photo is analyzed and biologists zoom in and also count every caribou individually. It is an essential and time consuming task – hundreds of thousands that caribou have the right to be counting in much more than 1,000 pictures.


Another efficient method researchers have occurred to estimate populations is called “capture-mark-recapture.” rather of trying to counting every animal, biologists randomly capture a sample group of the population, mark it, release it, and then perform a series of recaptures that will enable them to calculation the entire population in a certain study area. One easy means to recognize this method is to see exactly how teachers are discovering to usage ADF&G’s curriculum Wildlife because that the Future in their classroom lessons.

Last fall in Nome, 16 teachers were each provided a container filled through beans. Their an initial task was to create down the variety of beans they believed were in your container. The teachers provided a variety of methods to come up v their intuitive estimates. Many took random guesses without much forethought, part relied specifically on their sight by count as countless beans as were visible to them, and others counted the rows and also columns that the beans and multiplied to determine their estimate.


teachers Josie Bourdon and Justin Heinrich in Nome, use ADF&G’s Wildlife because that the Future lessons come learn around the population estimate method: capture-mark-recapture.

Then they used the “mark-recapture” technique. Each teacher reached into the bowl of bean to “capture” a grasp of “animals.” castle counted the caught beans and also recorded this number ~ above a data sheet. Before putting the beans earlier in the bowl, they “marked” the recorded beans by replacing them v the same variety of beans of a different shade – these then became the “marked animals.” After extensively mixing the bean they go a series of “recaptures” by again grabbing a grasp of beans, counting the total variety of “animals” captured, recording that number, and also then record the number of significant “animals” in each recapture. They go this 10 times. As soon as all 10 recaptures were finished castle calculated the average variety of beans for the recaptures and also then the average variety of “marked,” or various colored beans, in the recaptures. They placed these two averages along with the number in the an initial sample count in to a mathematical formula and also calculated the clinical estimate the the population of bean in the container. Finally, lock dumped the bean out and also counted each individual p for an exact count, or census, of the bean “population.” virtually every teacher came up v a less than 5 percent error rate between their clinical estimate and the yes, really count, a much narrower margin of error than their very own visual estimate.


State wildlife biologist Stephen Bethune, based in Sitka, explains how this works in real life. Top top Baranof Island mountain goats are captured and also fitted with bright red or orange collars and also ear tags.

“We know we never ever see all the goats in a offered area, yet having significant goats top top the landscape allows us to identify the sightability of goats throughout that survey,” the said. “For example, if there are 10 marked goats in an area and we watch seven, us would use a 70% sightability correction factor to a survey. For this reason if us counted 50 goats, using the correction element we can estimate there to be 71 goats in the area.”

Biologists then usage the collars to command what are referred to as aerial surveys, whereby they screen survival and kid production to aid build population models. “The more sightability surveys we conduct, the much more refined our sightability factors can it is in calculated,” Bethune said. “We room able to monitor the basic health of the populace to help set appropriate harvest share in hunt zones.”

Other animals, such as brown bears on Kodiak Island, space surveyed from above. Biologist Nathan Svoboda uses extensive aerial surveys (ISA) come derive estimates for brown bear on Kodiak Island. His goal is to control for a sustainable harvest and populace and, “to certain a healthy, robust, viable brown bear population exists in perpetuity, together brown bears space the cornerstone of ecological integrity ~ above the archipelago,” that said.


These ISA’s need to be done after bears departure winter dens in the spring, but prior to vegetation green-up so surveyors have the right to identify both individual bears and family groups without vegetation obstructing your view. Time is that the essence. In recent years, earlier green-up 보다 normal has actually presented some difficulties for biologists. They should start surveying previously in the year when making sure they acquire accurate estimates of all bears, as some bears may not have exited dens yet, particularly females v young. Despite challenges, Svoboda continues managing because that a sustainable harvest and also sustainable populace and is investigating options to build a robust population estimate because that the Kodiak Island brown bears.

Obtaining a population estimate is a large job for management and also research biologists. Even if it is conducting a census, an aerial survey, a capture-mark-recapture survey or one of the many other techniques used come obtain an accurate estimate, every one provides necessary information to better understanding wildlife. So, next time you see a moose exterior your door and you wonder if more are out there, rest assured that’s wildlife biologists room curious around that too. And, castle will proceed to job-related to aid keep’s wildlife populaces healthy and sustainable, now, and also for future generations the wildlife enthusiasts.

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