Saturday, December 11, 2010
Rugged up until Spring: A Mammalian Digression
By the calendar it isn’t winter yet, but winter weather closed down the last lingering greenery in the Home Bug Garden in November. Temperatures plunged to -29 C (-20 F) and the North Saskatchewan River froze over 3-4 weeks ahead of schedule. Other than the occasional fungus gnat in the bathroom or spider in the basement, that is it for this year’s bugs: same for the Moose Pasture. Last weekend the snow at the MP wasn’t quite deep enough for snowshoes, but the thermometer had registered -32 and even birds were few and far between. The only sign of insects were the honeybee hibernation hotels. So, my choice this Saturday morning is either shovel the snow off the driveway or invent a post on the HBG. If only all of life’s choices were so easy!
One thing still in evidence at the Moose Pasture last weekend were its mammals. And since there were mammals, of course, there were arthropods, because mammals are a year-round tropical beach for their arthropod ectoparasites. Well, at least for those that take up residence, as opposed to just stopping by for a meal (fair weather fiends). Ditto for the Home Bug Garden’s mammals or at least those that live outside. We HBGardeners like to think of ourselves as bug-free zones and, except perhaps for the transient mosquito and resident follicle mites (and let’s just not think about them) we are and so are our house-bound cats. But that isn’t true of the ‘native’ mammals: each is the potential home to several species of lice, fleas, mites and ticks.
So, let’s take Middle Earth Garden’s question one step further and see how similar the HBG is to the MP in terms of mammal habitat for bugs. Now, we don’t actually do much mammal collecting, so our estimate will be mostly theoretical, but it seems a reasonable comparison (and much better than shoveling the driveway).
If you were to look out at the front of the HBG this morning, you’d see a garden covered in snow and crisscrossed with tracks. Among these are a few cat paws, bird claws, and squirrel scratches, but the vast majority are contributed by one animal: the White-tailed Jackrabbit (Lepus townsendii).
Jackrabbits are born ready to run and adults don't make burrows, but get by with resting in a slight depression in the soil or snow, so their contribution to the arthropod fauna would be limited to their ectoparasites (mammals that den or burrow are much more arthropod friendly). These are big hares – to 5.4 kg (12 lbs) and over 2 feet in length – and they pay no attention to cats and little attention to people. Dogs do give chase, but with top speeds of over 70 kph (Wood et al. 2006), one tends to feel sorry for the dogs (unless they are trampling the garden). If a dog, or more likely a coyote, does get close, jackrabbits are capable of sudden near 90 degree turns – and their black tipped ears go one way while their bodies go the other, with the coyote left snapping at a vanished ear and the jackrabbit vanishing in the other direction.
While limited to open areas and rare outside the City (<1 per 4 km2), White-tailed Jackrabbits thrive in residential areas of Edmonton with densities averaging about 4 per km2 in the winter (Woods et al. 2006) or about 1300 shrub snipping hares. I regularly see a half dozen or more of these nocturnal munchers during my pre-dawn walk to work. Anything in the Rosaceae except spiny roses seem to be a preferred winter browse, so every autumn I have to spend a day putting wire cages around the saskatoons, cherries, crabapples, and chokeberries or they will be eaten down to the snowline by spring. In comparison, the Moose Pasture has no jackrabbits at all, but does host a few Snowshoe Hares (Lepus americanus). These also are nocturnal, but somewhat smaller and prefer forested cover. I sometimes see one in the River Valley and we often see their tracks at the Moose Pasture, but they do not make it into the HBG.
Coyotes (Canis latrans), however, do occur both here and at the MP, although only as transients in the HBG. Some estimate that 600 reside in the City. I see one every now and then on the way to work or coming home late at night and always make a point of giving it a chase (well, I try to look threatening anyway). Attacks on people, usually children, joggers, or someone walking a meal (aka small dog) are rare but increasing in frequency as coyotes learn to associate people with food rather than fear (Timms et al. 2004). Coyotes may eat more house mice than house cats, but the telephone poles littered with posters of missing cats bear mute testimony to another aspect of their diet. At the MP coyotes are very common - it sounds like 4 packs (probably male-female pairs with young) are within howling distance - and their tracks, turds, and the occasional bloody remains of dinner are everywhere. Since coyotes also dig dens, as well as produce feces and bits of carrion, they contribute significantly to the arthropod fauna of the Moose Pasture. We watch them watch us, but in the country they know that people are dangerous, so we camp amongst them with little concern.
That attitude would be inappropriate for the two largest carnivores in the region. Both cougars and black bears wander through the Edmonton River Valley on occasion, but were generally considered extirpated south of the River. That is no longer true and our MP neighbours, especially the beekeepers, were treated to a bit of ursine drama two summers ago. Fortunately, no one was hurt and losses were limited to bees (wiped out) and damage to homes (and to bears) and to Disneyesque views of Nature. The new hives are now protected by scarebears (apparently somewhat effective), electric fence (ineffective), and relocation to the middle of cleared agricultural areas (very effective if you have such land).
The cougars have yet to cause a problem (but see David Barron’s excellent book) and probably subsist primarily on the large population of White-tailed Deer (Odocoileus virginianus). Mule Deer should also be in the vicinity, but we have yet to see any. Larger, but not as numerous, is the largest member of the deer family: the Moose (Alces alces). We have at least 5 moose that wander the MP, but fortunately for our shrubs, none in the HBG and only rarely have we seen deer nearby. In the spring after the snowpack melts, the ground at the MP is covered with piles of decomposing moose and deer pellets that support a diversity of beetles and flies (and fungi).
Although moose are potentially dangerous, they are more likely to hurt us if we crash our car into them, then if we upset them some other way. In Alberta, you are far more likely to be killed or maimed by a car, then by all of the wildlife put together (including West Nile Virus vectoring mosquitoes). However, the Moose Pasture does have one significant wildlife danger to those camping there – being crushed by a beaver-felled tree.
Of all of the mammals in Alberta other than people, beavers clearly have the greatest impact on the environment. They also probably contribute more to arthropod diversity than any other mammal. They build and inhabit large, permanent lodges along with their fleas, parasitic beetles, and a host of detritivores. The meadows they flood eliminate some insects, but the new marshes support hosts of dragonflies, damselflies, water bugs, beetles, and more.
The trees beaver fell are a bonanza for beetles, flies, parasitic wasps, and anything that likes to nest or hide in decomposing wood. Beaver love aspen and will clear it as far from water as they feel safe. This opens up browse for moose and deer, but also spots for herbaceous perennials to bloom and feed more bees, wasps, beetles, butterflies, and moths. The cleared, sun-warm ground is a boon for ants and ground nesting bees and wasps. If you like arthropods, then you should love beavers – just don’t set your tent up anywhere near an aspen or poplar.
Muskrat benefit from the marshes beavers create and smaller rodents benefit from the open areas covered in herbs and grasses. Deer Mice build burrows and our bumblebees like the abandoned burrows for nesting sites. Voles with their mites and fleas graze on the grasses and herbs that sprout amongst the stumps and most everything is both changed and generally more diverse when beaver are present.
This beneficial effect is especially true during one of the frequent droughts in the Parkland when lush, verdant areas are restricted to around beaver ponds. Porcupines may benefit indirectly, since they like birch and beaver don’t, so the prevalence of birch may increase with beaver present (and with that all the birch-loving insects).
Beaver are a bit ornery and noisy (it takes a lot of gnawing to bring down a tree – which can make for a restless night), and if you like trees and meadows they are harder to appreciate, but as far as mammals go, they seem a boon for arthropod biodiversity.
Well, I suppose that is enough effusion about beavers for the moment. The Home Bug Garden has no Castor canadensis and few of the other mammals that inhabit the Moose Pasture. Alberta has about 90 species of 'native' mammals and almost half of them (>40) show up at Elk Island National Park, so several more of these will show up at the Moose Pasture if we get serious about finding them.
Not all of these would be welcome in the Home Bug Garden, and I would put deer and Deer Mice at the head of that list.
Even without these peculiarities of taste, mammal-driven biodiversity gets short shrift in the Home Bug Garden. Except, of course, for the only mammal more potentially arthropod biodiversity friendly than the beaver: the naked ape! In my own small way (and usually well clothed) I have made this small lot more diverse and bug-friendly and I guess that will just have to do for the mammal contribution for the moment. Good fences make for good neighbours, and the fewer mammals in the HBG, probably the better for all.
Baron D. 2005. The Beast in the Garden: The True Story of a Predator's Deadly Return to Suburban America. W. W. Norton & Company.
Timm RM, Baker RO, Bennett JR & Coolahan CC. 2004. Coyote Attacks: An Increasing Suburban Problem. pp. 47-57, in: Proc. 21st Vertebr. Pest Conf. (R. M. Timm and W. P. Gorenzel, Eds.) Published at Univ. of Calif., Davis.
Wood JR, Krenz J & Boyd-Zhang T. 2006. Urban White-tailed Jackrabbits of the Edmonton Region (1992-2002). pp. 119-133, in: RW Wein (Ed). Coyotes Still Sing in My Valley. Spotted Cow Press.