Calving Grounds - A Scientist's Activities


May to Mid-June

Calving is a busy time for caribou scientists. Since the early 1970s, scientists have been traveling to the calving grounds of the Porcupine Herd to observe exactly where and when the calves are born each year, and to find out how well the calves survive. There are no roads in the calving grounds, and the caribou are spread out over vast distances of 100 miles or more. Therefore, scientists must use airplanes to find and follow the caribou. To get a general idea of where the caribou are having their calves, scientists usually fly in a fast airplane like a 4-seater Cessna-185. The scientists use special radio receivers and antennas to track down radio-collared caribou. Usually they fly high, often one or two miles above the ground so that they have the best chance of receiving the signals, but they can still see caribou tracks and trails and even some caribou on the ground. Sometimes the scientists descend lower to get a better look. A fast airplane is especially useful along migration trails and toward the edges of the calving area, where caribou are very widely scattered.

For a closer look at caribou in the main calving area, scientists use a slow flying, highly maneuverable airplane like a 2-seater Piper Super Cub. In these planes, the scientists can slow down to about 40 mph and fly very close to the caribou. The scientists look for newborn calves, but they can also tell just by looking carefully at cows which ones have been pregnant. Both sexes of caribou grow antlers, but bulls and nonpregnant cows shed their antlers during winter or early spring. Some of those caribou may be growing new fuzzy or "velvet" antlers, but the only caribou that still have hard bony antlers at calving time are the pregnant females.

A few pregnant cows drop their antlers before calving, and some cows never grow antlers, so fortunately there is another way to tell whether a cow is pregnant or has already had a calf. Pregnant females develop a large udder full of milk, which the scientists can also see if they fly very close. The udder usually becomes obvious at least several days before a calf is born and will remain visible for some time even after a calf dies.

Scientists track all the radio-collared cows for a week or so in early June. They initially determine which cows are pregnant by looking for udders or hard antlers and then keep relocating the cows until they see a calf. Sometimes they watch a pregnant cow the whole time and never see a calf, but they then know the calf must have been born and died. Many calves die shortly after birth from birth defects, predation, and other causes. Therefore, scientists also go back to check on the calves they have seen, so they can determine which of those have survived through the early calving period.

Whenever the scientists spot a radio-collared cow, they record her exact position using a GPS (Global Positioning System). Later, back in the office, they can map where calving occurred, how caribou moved during the calving period, and what habitats they used. The scientists can also determine how calf survival was, related to all these variables.

Return to A Caribou Year.