23 July 2012

Chasing bison in PANP: The Count

This is part of a series by Jerod, about his bison research.  All photos are by Jerod, unless noted otherwise.

The grass in Prince Albert National Park can be quite tall, often obscuring the animals in the meadows. Wolves can rarely see their surroundings when plowing through tall grass. Although bison are the largest North American mammal, when they are in meadows sometimes you can only see the tops of their backs and in some cases you cannot see them at all. In these cases, calves and young animals just disappear. 

While the park has a variety of meadow types, bison tend to spend most of their time in wetter meadows - this is where their favorite food grows. Carex atherodes, or slough sedge, is a large sedge that loves to grow in wet areas. It can grow over 3 feet tall, particularly when it needs to grow through some water to reach sunlight. Basically, the plant is one of the most nutritious for its size. Almost everything that bison do on a daily basis is directly related to where this plant grows. Bison can take large bites, filling their rumen faster while still gaining lots of energy. Other large grasses and sedges just cannot provide the high quality forage that slough sedge can. 

For someone who is trying to count bison, like me, getting a good count in tall grass can be quite a challenge. This is especially true when bison are eating and resting in a patch of slough sedge, where only the backs of the largest animals are visible over the top of the grass. Most of the time, the best way to get a good count in this situation is to be patient and wait. Sooner or later, each and every animal will stand up and stretch (or defecate), or the entire group will line up and walk right in front of you. In these cases, I can get a good count of the group, and identify which individuals are calves, juveniles, and adults. 

Today, my first total count of the group is 51, but I am only seeing 3 calves, and I know there are more. I count 5 males, which is a typical count for early summer (most males are solitary this time of year). Males are easier to identify because they are almost twice the size of females, and they stand out quite well. My counts of juveniles and calves are going to have to wait, as much of the group is laying down, and it is difficult to see their body size and horn shape in the tall grass. 

There are many ways to tell the age of bison in the field, and calves are the easiest. When they are born in May, they have a reddish coat, which lasts until sometime in the fall. After that, one of the best methods is based on the horns. During their second summer of life, we refer to bison as yearlings. Then, usually we classify the 2 and 3 year olds as juveniles. Finally, animals over 3 years old are classified in most cases as adults. 

As the minutes pass, I check the group, looking for individuals who are facing me. If I catch one scanning its surroundings, I’ll snap a photo, record the age, sex, and whether or not it has other distinguishing marks (e.g., some bison are missing some of their tail). I also am counting and recounting the group, making sure I have the best count and composition possible. 

After about 1.5 hours go by, the entire group is up, beginning to forage on the slough sedge patch right next to where they were bedded down. They forage for about 15 minutes, and then I notice one of the bison is heading towards the forest. It is an adult female, and she likely is the leader of the group. I can hear her grunting - I assume she is trying to get the others to follow. She succeeds, and within 10 minutes the entire group is walking out of the meadow. At this time, I am able to finalize my group count and composition, as all the animals are up and moving. Wow, what a day! 62 bison in total (35 females, 12 calves, 9 juveniles, and 6 males). Yes I know that is another male, but he was bedded down in a particularly tall section of grass earlier, and I did not see him until he stood up. 

I finish up the last few lines on my data form, noting my location and time the group went out of sight. I look up to see the sun glaring down onto the meadow. Like the bison, I think it is time for me to get back into the shade, and out of the heat of the day. I head back into the forest, the same way I came. I hop on my bike and carry on to the next meadow of the day.


Georges said...

De bons souvenirs :) C'est très agréable à lire. Jerod Merkle don't you think that the juvenile is a male while the adult is a female? Did you really take that wolf picture? This is really impressive... Where was it?

Jerod said...

Georges: you are right about the male and female. They were just good pictures, so I used them. Yes, I took the wolf photo in Tap creek. I think the wolf was hunting for duck and crane eggs. It was a cool experience. The tall grass obscured me, as it moved towards me in the meadow. That is how I got so close.

Gene said...

Great report, thanks!

Bethann said...

Thank you!  I agree - it's really fun to hear what this research project is actually like, isn't it?  So often, we hear from the field only the "mud, mosquitos, etc." or just the highlights (like sighting a bear).  I really enjoy hearing how an actual day of data collection goes, and what it is like to make decisions, change your plan, etc. in the middle of a day - all while keeping the big picture of the project in mind.  :)

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