About the Herd
The Porcupine Caribou herd is one of the largest migratory barren ground caribou herds in North America. The herd has gone up and down in size over time, but it has always been an important part of the ecology of the Western Arctic. In order to try to understand the herd better, researchers monitor for changes in the herd’s size and composition. They also keep an eye on natural factors that can affect caribou numbers, such as disease.
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.
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.
While it is important to know the overall number of animals in a population, there are other factors that can be monitored that help us understand how the herd is changing. This information helps to support management decisions. The composition or categories of caribou that make up the herd and how these numbers relate to one another is an important part of the puzzle.
Each year, biologists monitor the Porcupine Caribou herd by flying aerial surveys at key times of the year to see what is happening with the following categories of Porcupine Caribou:
The number of adult cows in a population can make the difference between a herd growing or declining. The number of cows is always the basis for comparing the number or the ratio of calves or bulls in a population.
These are caribou less than a year old. It is important to know how many calves are born each spring. On average, biologists see about 80 calves born to every 100 cows. Of those calves, about 85% of them reach one month of age.
Biologists then monitor to see how many live to be about nine months old. If they can reach that age, the chance of them surviving to be a breeding adult is high. Having an idea of the number of caribou that will likely reach adulthood is another way managers can estimate what will happen to a herd over the next few years.
It helps to know the number of bulls in relation to the number of cows in a herd in order to understand if there will be enough bulls to mate with cows each year and to determine the impact of a bull oriented harvest. A healthy population will have at least 35 bulls per 100 cows in a herd. Researchers estimate the Porcupine Caribou herd has around 60 bulls per 100 cows.
It is important to understand and monitor the overall health and survival rate of the herd. The condition of individual animals, any diseases or outbreaks, and predators that kill caribou can all contribute to herd health.
Each year, hunters are asked to take samples from some of the caribou they harvest in the fall and measure the amount of fat on the animals. Observations from hunters and other people on the land are also collected and incorporated into monitoring efforts. This helps to estimate the overall health of animals in the Porcupine Caribou herd.
Diseases and Parasites
Parasites and diseases are a natural part of any wildlife population. However, if there is a change in the frequency of occurrence or if the environment changes, the effects of these parasites and diseases may become more important to the caribou. If you are harvesting caribou and you see anything odd, carefully take a sample (wear gloves if you can) and keep it cool or frozen. Contact your regional biologist or conservation officer and they will help get it tested.
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Caribou can act as hosts to different types of tapeworm larvae. The larvae will grow in cysts in the caribou, but won’t kill them. However, if a wolf or dog eats the cysts, the larvae will grow into tapeworms inside them. The worm’s eggs are then passed through the animal’s feces. If humans come in contact with the eggs, either through handling of feces or drinking contaminated water, the eggs can hatch and a tapeworm will grow inside of them and pose serious health risks.
Here are three common types of tapeworms larvae found in porcupine caribou:
Echinococcus granulosis -
cysts found in the lungs of caribou
Taenia hydatigena –
cysts found in the livers of caribou
Taenia krabbei –
cysts found in the muscles and hearts of caribou
The larvae of these lungworms are passed on through the feces of infected animals and is transferred to others who might be grazing in the same area. If ingested, the larvae migrate to the caribou’s lungs where they grow and eventually lay eggs that pass through the caribou and start the cycle again. Caribou that have lungworms can get pneumonia and can generally be in a weakened state.
This is a parasite that occurs in caribou and reindeer. It can cause a roughening or pitting of bones and tendons in caribou. Caribou with the parasite often have hair loss and areas of thick or crusty skin. Most infected animals do not seem overly affected by the parasite. It does not appear to affect humans.
This is a bacterial disease that is transmissible to humans by caribou. In female caribou, the infection can cause abortion, retained afterbirth (which may cause infection) and giving birth to weak calves with a poor prognosis for survival. Humans can be infected by milk, fetuses or the body organs and marrow from infected caribou. The flu-like symptoms can be severe, and hospitalization might be required.
Adult warble flies lays eggs in hair of caribou. The larvae hatch, penetrate the skin, and travel under the skin to the caribou’s back. The warbles grow there until early summer, when they break through the skin and drop to the ground. The warbles can cause infection and weaken the infected animal.
These are the larvae of bot fly and grow in caribou’s nostrils. They can cause nasal discharge and coughing and may block breathing, but their effect on the overall body condition of the caribou is unclear.
Golden eagles are the most important predator of calves.
Wolverines kill newborn calves, cows giving birth and other weak adults.
Migratory wolf packs kill between 3% and 5% of the herd each year.
These "micro-predators" can take as much as half a cup of blood every day from adult caribou. Mosquitoes can irritate caribou so much that they get distracted from eating. They can prevent cows from nursing their young and can even drive them to the point of injuring themselves as they rush about trying to get away from the annoying bugs.
Grizzlies will eat calves and adult caribou.
Humans kill caribou each year, either intentionally by hunting them or accidentally by stressing them out. Getting chased or disturbed by snowmachines or aircraft can cause a chemical build-up in the caribou’s muscles, which can kill the animal long after the actual event. Panicked caribou can also get injured running or get frostbite in their lungs from panting in extreme cold.
Don't chase the caribou!!!!