As is to be expected, these posts generally revolve around birds.
However, it would be foolish to leave mammals out of the picture, as they are an integral part of the lives of birds and our own lives. Here on the tundra there are five species of mammals that we regularly see (not including humans): caribou, Arctic Fox, Arctic Ground-Squirrel, Greenland Collared Lemming, and Brown Lemming. Occasionally we encounter a Gray Wolf or a Brown (Grizzly) Bear. Our team has dreams of encountering a Wolverine someday, which has become a common discussion at our campsite. If we hike the three miles to the edge of the Arctic Ocean, there are usually at least a few Ringed Seals around, and perhaps a Beluga Whale or a Narwhal if you spend enough time watching.
Caribou, the mammal we see most frequently each year, seem to live highly unenjoyable lives. In their annual migrations they spend the winter in the Arctic, migrate thousands of miles while being hunted by bears, wolves, and sometimes people, and then spend the summer trying to escape death by insects.
Mosquito levels affect the arrival dates and total number of caribou that come through the Canning River area. Since the insects come out when the temperatures rise, in a warm year the caribou come back earlier (about 20-25 June), and in a cooler year they come back later (about 25 June-5 July). The caribou numbers increase on the coast in warmer weather since coastal regions are generally cooler and windier and offer caribou a break from the winged insect hordes that haunt them as they trudge across the tundra.
These insects, especially mosquitoes, have such an effect on the caribou that the drop in blood pressure from blood loss to insects can potentially result in death – a process known as exsanguination. We usually encounter groups from the Central Arctic caribou herd, in numbers that vary annually between about 5,000 (this year), to 30,000+ (2013). When caribou numbers are high they can have a massive effect on shorebirds as they can trample nests by random chance when they move through the study area. We lost at least 6-8 nests this year due to caribou trampling.
When the caribou arrive, so do the large predators. This year we have seen two Brown Bears in the study area, but we haven’t seen any wolves yet. The number of predators we see is also variable and is tied to how many caribou we see. It is not a surprise that we have not encountered any wolves, since we have only seen a few thousand caribou. Last year we did not see any wolves, but we found wolf tracks 200 meters from our sleep tents, indicating that one that silently trotted by in the middle of the “night”, unfortunately unseen. In 2012 some members of this camp watched a small group of wolves take down a caribou a couple of miles away from camp, followed by a Brown Bear that chased the wolves off of the carcass to take a turn.
Arctic Foxes are the primary predator here on everything but the caribou, and we see them almost every day.
Slightly larger than a house cat, these small canines spend their days bounding around the tundra in search of lemmings and shorebird nests. We researchers share the foxes’ goal of locating shorebird nests, but unfortunately once the shorebird nest is located our goals diverge. We want to monitor the birds and the foxes want to eat them. As a result, we don’t always enjoy the presence of the foxes as much as we should, especially in years like 2012, when over 80% of the nests fell victim to predation, almost entirely due to an active fox population.
No matter how unfortunate it might seem to us, the foxes are an integral part of the arctic ecosystem, and not having them would paint an entirely inaccurate picture of the breeding success of the shorebirds that we study. Some years there are active fox dens, which ramps up the food needs of the adult foxes to provide for their large litters of fox kits. This year we have a den right near camp that had at least eight kits at one point. We have watched the adults make food runs back and forth with mouthfuls of lemmings and occasional shorebird chicks, attempting to sate the voracious appetite of a young fox.
Arctic Ground-Squirrels live in all the higher bluffs and small ridges that stand about 30 feet above the surrounding tundra. Since we live on one of these bluffs, we have 3-4 resident ground-squirrels that reside near our tents. One of them is exceedingly bold and will often venture right into camp, poking around in our bucket of dirty dishes in an attempt to find a tasty morsel. Luckily, we keep our camp clean. In fact, while I was typing this post in the main cook tent, our bold squirrel friend came right into the tent, less than a foot away. When they’re not nosing around, the ground-squirrels usually stand at attention by their tunnels (think prairie dogs), giving alarm calls whenever a fox or jaeger gets too close for comfort.
The last of our regularly encountered mammals, our two species of lemmings, are also the smallest. Lemming numbers follow an annual cycle, where they will increase in abundance until reaching a peak year, upon which the population crashes to a small size before beginning the cycle all over again. This year was a good year for lemming sightings (the reason for the abundance of avian predators was talked about in a prior blog post), and both the Brown Lemming and Greenland Collared Lemming have been seen most days during the field season. Lemmings live all winter long under the snow pack up here, eking out an existence in little spherical nests they make out of grass and stock with food in the fall.
The number of lemmings in any given year has a strong effect on shorebird success in that year and the couple of years following because of their role in the diets of the Arctic Foxes. In years when lemmings are abundant, the foxes will focus more on hunting for lemmings. This spares more shorebird nests and results in higher shorebird breeding productivity.
If there are enough lemmings, like this year, the foxes will breed. This means that no matter how many lemmings are around in the next couple of years, the injection of more foxes into the local ecosystem will have a negative impact on shorebird nest success for at least the next year or two.
The most amazing thing about all of the species up here is how they are so intertwined in this ecosystem. The number of mosquitoes affects the presence of caribou and the amount of food available for shorebird chicks. Whether there are lemmings around in high numbers determines how many avian predators there are, whether foxes eat more shorebird nests, and if foxes will be more numerous in future years. In the three summers that I have been fortunate enough to spend at the Canning, I have been struck by how no two years are the same. You can miss much of the larger picture by simply spending one field season in a location, thinking you understand the deeper processes of the area when you are really only scratching the surface of the mysteries of the tundra.