Knowing the overall number of caribou, or the population, and how that number changes over time is important for managing the herd, particularly when it comes to harvest. To monitor population, researchers try to conduct a census of the Porcupine Caribou herd every two years. Since the first census was conducted in the early 1970s, the herd has shifted between 100,000 and 200,000 animals.

No one is sure what causes the herd to get smaller or larger, but ongoing monitoring programs indicate that changes in adult survival might be one of the things that affects the population the most.

Why do we collar caribou?
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How do we conduct a census?


In the summer when the bugs come out, the caribou will gather in large groups to try to avoid getting bites.


Biologists fly over the herd’s range looking for these groups with the help of radio collars.


Once the groups have been located, a special airplane with a camera attached to its belly will fly over the groups and take pictures.


These photos are then put together like a puzzle and over several months biologists examine them and count all the caribou they can see.


The number of caribou counted in the photos is then adjusted by an estimate of the number of caribou found by the search planes but not photographed or not found but known to be alive to get a population estimate.