This entry details a portion of my thesis work at the University of Alaska Fairbanks, and is intended to communicate the findings of that work in a four part series. You are reading part four examining the likelihood of competition between wolves and humans. In order to make the article concise, you may review the general background of this work in part one. I have truncated the background and methods of this work and focused on a portion of the results.
In parts two and three of this series I have been examining where humans in the Yukon Flats, Alaska are traveling to harvest moose and where/how wolves are traveling to harvest moose. A key finding of human access was that humans are mostly operating within 1500 meters of navigable water. During our wolf study I found that travel was based around river corridors. Based on this, I will conclude this series of articles by examining the “Beaver Creek” pack which overlapped strongly with navigable water.
I wanted to begin to understand the likelihood of competition around navigable waters for moose between humans and wolves. Remember, moose exist at extremely low densities and humans and wolves depend on them as a food resource. Therefore, I believe understanding competition is particularly important. To understand the likelihood of competition, I applied my model of human access and overlapped it with wolf locations. I found that 75% of wolf use locations fell within the human access model.
My analysis does not contain temporally overlapping data. Wolf habitat selection may differ in September and October when humans are hunting moose. Wolves could also rely on other prey species other than moose during that period. Also, predation in the Yukon Flats extends beyond wolves. Bears take up to 85% of moose calves each spring. As such, my conclusion is just the beginning research for future biologists in the region. A complete analysis would encompass all predation on moose, be spatially and temporally overlapping, and would evaluate how many moose which are predated could be taken by humans. I hope you have enjoyed this four part series! A full copy of the thesis can be obtained by contacting me. Feel free to do so!
This entry details a portion of my thesis work at the University of Alaska Fairbanks, and is intended to communicate the findings of that work in a four-part series. You are reading part three examining wolf movement in the Yukon Flats, Alaska. In order to make the article concise, you may review the general background of this work in part one. I have truncated the background and methods of this work and focused on a portion of the results.
Wolves are highly studied because they are charismatic, exhibit interesting pack behaviors, and are a key predator in the systems where they exist. Their behaviors including movement speed, movement distances, number of prey killed, and travel distances have been well documented in high prey-density systems, but practically no information exists on these behavior in low or very-low density systems. In an attempt to rectify that, a study was initiated in 2008 to understand the kill rate of moose by wolves in the Yukon Flats, Alaska, where moose are held at low densities (<0.20 per square kilometer) by predation. In an interesting twist, that study found wolves are maintaining kill rates (moose per wolf per day) similar to wolves in high prey density systems. Certainly these results counter what I would predict and lead to a natural question – how are wolves accomplishing such high kill rates in low-prey densities? A known mechanism is that wolves in the Yukon Flats keep small pack sizes to cope with low densities of prey; if you have fewer wolves in a pack, more nutrition is available per wolf during each kill. However, if wolves were traveling further or faster in this low prey-density system was unknown. I predicted that wolves in a low prey density system were traveling further, but not faster than wolves in a high prey-density system to maintain these kill rates. I also predicted they were selecting for river corridors when traveling.
To understand wolf movement, I used the same dataset from the 2008 kill rate study. It was composed of Global Positioning System (GPS) collars on six packs. Thanks to diligence in the kill rate study, I knew where kills occurred along each of the paths. For each pack, I characterized if the wolves were traveling, resting, at a kill site, or revisiting a kill site. These behaviors gave me enough information to calculate the rate of speed they were traveling, the distance they were traveling, the number of days traveling to make a kill, and how long they spent at kill sites. I also using a Generalized Linear Mixed Model to understand what landscape features were important for traveling wolves.
I found some interesting results, and put them in context of 16 comparable research papers of movements of wolves in high or medium prey-density systems. I am presenting the most applicable comparisons from the literature review (i.e., systems where moose are prey and studies where GPS collars were used) here. I found search time was slightly longer and search distance was 2.4 times greater in my low prey-density study area. Search time and search length are correlated together given that wolves are (almost) always hunting when moving. Due to that relationship, the search time is expected to go up as search days goes up. I found no evidence that wolves were handling prey longer or traveling faster in the low prey-density system. Those results were not surprising as one researcher found that handling time of moose was not significantly different among packs which varied in size from 2 – 20. Since wolves were not traveling faster in our system, it is probable that regardless of prey density, that on average wolves travel at their maximum comfortable speed that maximizes efficient travel.
I also found that wolves were utilizing river corridors and that they were selecting strongly against brushy habitat. In the Yukon Flats, that means they were selecting against thick stands of alder and willow. This was similar to previous studies where they found that wolves were able to travel 2.8 times faster if they used a river corridor rather than moving through a brushy environment. By using rivers, wolves were traveling faster and are likely taking advantage of increased prey density along river corridors.
The results of this work have some useful applications in helping us broadly understand wolf behavior. First, wolf territories are very large within low prey-density wolf systems. The mechanism that creates these large territories was unknown, but long-distance movements by wolves would create large territories by default. Next, back in the mid 1980s a researcher suggested that 0.20 moose per kilometer squared was the lowest density that wolves could persist at. Within the Yukon Flats, they are already persisting at lower densities than that, and since they are able to extend their travel distances to maintain kill rates it seems a minimum prey-density threshold could be much lower. A final implication of this work is that managers should expect wolf territories to increase in size if prey density decreases. In other systems (for instance deer in the mid-west), wolf territories should inflate in size as they move further in search of prey.
I look forward to presenting part four to you soon, which ties together moose hunting by wolves and humans by starting to understand the likelihood of competition.
I was excited to head far into the Alaskan bush by river to help a friend open his cabin for the season. Almost a week of packing led up to the Wednesday we were supposed to leave. However, when the middle day of the week arrived, high water reports from Fort Yukon and the Upper Porcupine River were ominous. Record snowfall in Old Crow, Yukon Territory, had swollen the giant river systems. They were far above travel-able levels, and over-flooded banks were pulling dangerous amounts of debris, ‘drift’, into the river. Our final destination was 220 river miles through the high water and drift of the Yukon and Porcupine Rivers, and the experienced judgement of Joe dictated that we would wait a few days before heading up to his cabin. Four days later the river had dropped to acceptable levels. It was go-time : the river was saying so!
Before I get into some of the stories of the trip. Come along on the trip with me by watching this video:
The notion of taking a boat far into the Alaskan bush is exciting! A long-time resident of the bush, Joe was anxious to open his cabin, and assess his estate because bears, humans, or weather can all impact an unoccupied cabin. The boat-trip up river started in Circle, Alaska on a cloudy day. As we headed downstream in the Yukon River, we quickly entered the Yukon Flats National Wildlife Refuge. This expansive refuge is critical, critical habitat for breeding waterfowl and birds. In fact, the refuge hosts 150 species of breeding birds from 11 countries, 8 Canadian provinces and 43 of the 50 states. That’s remarkable diversity!
The Yukon Flats is aptly named. As we cruised along in the boat, the shores were a steady patchwork of riparian habitat consisting of willows, birch, and spruces. There was no perceptable climb in elevation. The fast, high water of the river kept progress slow, and Captain Joe was constantly vigilant for pieces of drift. Three foot-long sticks and entire trees were coming down the river at the rate of several or more pieces per minute. Hitting a small branch may result in a dented prop, but a large stump could have ended the trip. By the time we reached Curtis Slough to stop for the night, the intense driving had drained Joe (and rightfully so!). Overall we made it about 135 river miles from Circle.
We pulled into a small log cabin along the banks Curtis Slough, hoping to spend the night. The traditional landing was underwater, but I jumped ashore with the bow rope and headed to tie off to a nearby tree. I glanced at the cabin, and immediately saw that the plywood door had been torn in half; peeled back like the lid of a sardine can. “Hey Joe”, I stated, “A bear broke into the cabin, by tearing the door off”. “Ok, does it look fresh?”, he questioned. I assessed the raw wood in the torn door from 25 feet away and responded, “yup, sure does!”. By that time Joe had climbed up with Delta, our dog companion. Delta moved towards the cabin and sniffed the door; her demeanor immediately told us that it was a very fresh break in, and then I heard a can rattle from inside. The bear was still in the cabin! In two flicks of a lamb’s tail we were in the boat and headed across river to camp on a more desirable (bear free) gravel bar. Joe, knowing the owner of the cabin, made a satellite phone call to inform them of the situation. Remarkably, this bear encounter was the only one of the whole trip!
The next morning we continued up the Porcupine River, and moved out of the Yukon Flats and into the Arctic National Wildlife Refuge. The Arctic NWR is the largest piece of land in the refuge system, and home of the Porcupine Caribou Herd. No longer in the flats, we saw a mountain on the horizon! More significantly, that mountain was the beginning of the rocky ramparts which would line the river for the rest of our trip. The tall and colorful ramparts and bluffs of the Porcupine Rive were a welcome contrast to the Yukon Flats! As we moved through the landscape, the smile of enjoyment could not have been erased from my face by the spray of a skunk. The area was absolutely stunning; on a small scale, I was reminded of the Grand Canyon. Red, orange, and black rock walls rose high above the water. The bluffs held countless caves and spires shaped by wind, ice, and snow. The refuge of the high cliffs provided important nesting habitat. As we passed we noticed nests of golden eagles, ravens, and a peregrine falcon protected on all sides by the vertical rock faces.
Two hundred and twenty-two miles upriver we passed the final bluff across from Joe’s cabin. The boat swung around towards the opposite bank and soon I tied it off onshore. Already I felt connected to this beautiful region, and was excited to spend the next five days exploring it. The next chapter of cabin life to come soon!
Oh, and as one last, unrelated note the blog turned two on May 28th. Thank-you ALL for your continuing support. Your feedback, comments, and enjoyment of the material here is much appreciated!