Many people ask the same question in Alaska: "How many moose (caribou, bears, wolves) live in this state?"
No one knows - exactly. But then, no one knows exactly how many people there are here, either. It's usually easier to count humans, because people can talk to each other and ask and answer questions. Animals aren't that cooperative. The numbers of wild animals in the state are estimated using a variety of methods.
Some wildlife populations group together so biologists can determine their numbers using a photo census. Caribou, for example, aggregate in the summer when mosquitoes are thick. When the caribou gather, the groupings are monitored until biologists are convinced that nearly all of the caribou in the herd are included. Assuming the weather cooperates, they fly over the herd in an aircraft fitted with a belly-mounted camera and photograph the entire herd on large-format film. After the film is processed, biologists sit in the office with magnifying glasses and count every caribou on the photos.
Moose don't gather in large groups. Their population estimate surveys are performed in the fall and winter when the right combination of weather, snow depth, and day length allow biologists to fly and see the moose. (Until enough snow covers the ground, a 1000 lb. moose can be invisible from an airplane.)
The area to be censused is broken into smaller sample units based on terrain or habitat types. The sample units are stratified; that is, a team of biologists flies over them and identifies whether moose are present in high, medium, or low densities. Some sample units in each stratum are randomly chosen to be intensively surveyed. The actual densities of moose found within the surveyed units are extrapolated to estimate densities in the other sample units within the same stratum. This information is run through a statistical formula to estimate roughly the total number of moose in the entire large area, even though only 20-30% of it was actually surveyed.
Different methods work for estimating different species.
Biologists begin a bear census by capturing, marking (with radio collars and ear tags), and releasing as many grizzly bears as possible in an area. Then they count as many bears as they can find and note the proportion of marked bears to unmarked bears. Since they know how many bears in the total population are marked, they arrive at an estimate of total numbers of grizzly bears.
Of course, the different methods of counting wildlife are not foolproof. All of them depend on getting humans out to a place where they can see wildlife to count them, often in a plane. Wind, clouds, and snow have prevented many a photocensus and moose census. In some years, snow cover is scant until the days are too short to allow enough flying to get a moose census completed. Too much snow can be a problem, as well. A few years ago, snow was so deep that landmarks couldn't be seen to determine the boundaries of the sample units being surveyed, so the counts were not as precise as desired.
Even when weather cooperates, the estimates of wildlife numbers are only as good as time and money allow. Flying is expensive, and counts take time. It's not feasible to conduct a systematic moose population estimate over the entire state, for example, especially in times of declining revenues. Consequently, in some areas of the state (where systematic surveys have been conducted), moose population estimates are quite accurate, and in others (where they have not), estimates based on fewer data are on the conservative side.
In response to the original question, "How many moose (caribou, bears, wolves, etc.) live in this state?," current estimates are:
- 144,000-160,000 moose
- 576,000 caribou
- 32,000-43,000 brown/grizzly bears
- 4,900-6,200 wolves
...as close as we can tell.
This article was originally published by the Alaska Science Forum on August 10, 1987. The author is a public information officer with the Alaska Department of Fish and Game in Fairbanks.
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