Monday, May 24, 2010
The Pronghorn (Antilocapra americana) is the sole surviving member of a family that, during the Pleistocene, consisted of twelve species. They are the fastest land mammal in North America and are built for the open plains of the west.
Although speedy, they are poor jumpers and would rather find a way under a fence than try to jump over it. However, they can move surprisingly fast underneath barb wire fences and even faster if the bottom wire is raised even a couple inches above what is traditionally used when constructing fences. Woven wire fences (see the photo above), used to confine sheep, are effective barriers to pronghorn movement.
Roads and traffic are also deadly for antelope during their migrations or when the roads bisect their wintering areas.
The area just north of the Milk River in Eastern Montana is a primary wintering area for a number of pronghorn. We have known that many of these animals spend their summer in Canada from past studies of collared animals, but little was known of the routes and obstacles these animals faced or how they used habitat configuration at landscape levels.
About 40 doe antelope have been captured and outfitted with GPS collars each of the last two winters to get a more detailed view of their habitat use and movements in relation to the larger landscape of the Northern Great Plains. Andrew Jakes, a PhD candidate at the University of Calgary, is conducting the work which is funded by a number of governmental and non-governmental entities.
The pronghorn are captured on their wintering areas near Malta and Glasgow, MT by Quicksilver Air, a crew that specializes in capturing animals using net guns fired from helicopters.
These guys are really good at this and it was a blast watching them work the animals. They were very good at minimizing the time spent with each herd and would capture an individual quickly and have it up and running again soon after the initial capture. In the photo above you can see the orange net covering a doe antelope and below is that antelope being released a few minutes later.
Below is a map of the capture locations in Valley County from February 2010. The pronghorn capture photos above are of number 166 (the furthest south capture, just northwest of Glasgow).
Below is the location of the animals at the end of April. Notice that 166 was about 200 miles north of her capture location (Glasgow and Malta are located along the bottom edge of the map and the dark line through the map is the US/Canada border).
The collars have a VHS transmitter and a GPS receiver. The VHS transmitter enables us to occasionally check the location and status of the animals (as above) and the GPS collars store the location of the animal every 2 hours or so. Then in February the following year, the collar is programed to blow off the animal and the VHS enables us to locate the collar and get the stored location information.
The map below depicts the cumulative locations of thirty nine animals from Feb 2009 to Feb 2010.
It is amazing the amount of land these animals cover annually. I imagine that if we had this level of information for all the animals that spend their winter along the Milk River, this map would be even more impressive, but even as it is we will be learning a lot about how these animals react to changes and challenges in their world.
Andrew has agreed to provide me with information on 166 as he gets her location throughout the year and next year when we recover her collar we will be able to see her how she moved between those spots. Stay tuned.
Posted by John Carlson at 8:00 PM