An Ode to Voles

It's time to plant my peas, but I've been watching a series of holes appear around the foot of my garden's raised beds that suddenly began to appear in Februrary.  It looked like the lawn was undergoing a slow-motion boil, but in each spot where a bubble popped, a vole burst forth leaving a new burrow system behind it.  They've got their own plans for my vegetables, I'm afraid, because at least one new tunnel opened right into the bed itself among some overwintering beets.

Time to set some snap traps in the garden beds, and I've already sheathed our young orchard's tender trunks in hardware cloth.  Even as I take defensive action, though, I have to admit I admire these animals greatly.  An ounce or three of fur and digestive system, taken in the whole, has a tremendous impact on the ecosystem.

Gray-tailed vole, Microtus canicaudus. Photo by Jerry Wolff

Voles have fascinated ecologists for over a century with their high-latitude cycles of boom and bust; it's been a hundred years and literally thousands of scientific papers and we still don't really understand what drives those catastropic plunges in density that inspired the legend of mass suicide by drowning.  We are, however, making progress.  Regardless of what happens to the majority of them, a few voles survive the cataclysm, and the start of another wave builds from those survivors.

It turns out that the wave analogy is actually a very good one.  A number of organisms, from larch bud moths and pine beetles to voles and lynx, seem to display population dynamics that can be modeled as waves moving across the landscape.  There are a number of recent papers in the scientific literature by Jonathan Sherratt and others that apply the mathematics of periodic travelling waves to the population dynamics of animals.  Leaving the mathematics behind for now, imagine a wave of animals rising up on the landscape, their impact rising with their numbers, then abruptly dropping down as the peak of the wave moves on.  You can actually view a simulation of these waves on Dr. Sherratt's website.

When voles explode, they provide a ready protein source that is exploited by every carnivorous or omnivorous animal able to swallow them.  Some animals, such as the snowy owl and the least weasel, seem to be quite tied to the cycles of their prey; others are blatant opportunists.  I studied burrowing owls for many years.  The year the California vole populations were so dense I could sit on the cab of my truck and actually hear them grazing, the burrowing owls raised up to 11 young per pair.  The result: a wave of young predators spreads from the wave of available food, spreading concentric rings colliding and melding across the landscape.

Burrowing owl young. Photo: D. K. Rosenberg

Voles are small, but their numbers during a peak year can be impressive: estimates of voles' maxium densities run from 3,000 to 25,000 per hectare.  That works out to roughly three-quarters of a ton of small herbivore per acre.  Henry Howe and his colleagues put out exclosures in a prairie system and demonstrated that vole herbivory greatly affects the plant community.  What that study didn't consider is the dynamic nature of that herbivory as the populations crest and trough in any particular place.  So, imagine that wave sweeping over the landscape again, perhaps leaving behind distinct age classes in the vegetation.  I'm not sure anyone's looked for that yet.

Voles don't just eat and get eaten; they also dig and poop and pee.  Anyone who has ever looked after 750 pounds of herbivore living in a barn knows how much manure can be produced out the back end by non-ruminants especially, where so much of the bulk is passed undigested.  Voles dig, depending on the species; I've counted ten burrow entrances per square yard after a good outbreak year in western Oregon.  They create a vasculature of sorts, a series of pores and veins into the living soil which they then fertilize for good measure.  We've demonstrated that voles affect nitrogen in the soil profile.  We know the hollows in the soil allow both air and water to penetrate.  In western Oregon, the burrows may last longer than the voles that created them, in some cases up to a year or more before the burrows collapse again.  Even after the burrows have collapsed, the soil profile remains altered with pockets of less-dense soil.

Cross section of vole tunnel in soil sample.  Photo by J. A. Gervais

Imagine that wave again, flowing across a landscape, changing communities of plants and animals, changing the very properties of the soil, the foundation of the terrestrial ecosystem, and then abruptly receding.  Voles' impacts travel in both space and time, and after a century, we have only the most basic grasp of those dynamics and their consequences.

As global climate changes, so apparently are the cycles of the voles, and we have no idea what will happen to the ecosystems they inhabit when the voles no longer exert this incredible, dynamic force on the landscape.  The cycles may be disappearing in Scandanavia.  In other areas, the spikes in numbers may become greater or more frequent, heralding a different sort of change.  I don't know exactly what is driving the numbers of voles in my back yard, but I don't mind if they graze a few beets as long as they leave my peas alone, and they can help themselves to all the grass they can eat.  I'll be watching for young bobcats and barn owls later in the spring as the vole biomass (powered in part by my vegetable garden) works its way through the food web.

Trillium

Trillium chloropetalum, the sessile trillium or wake-robin, flowers in mid-March in the woods of western Oregon.  It blooms just before the start of the spring chorus of birdsong.  This plant's mottled leaves are  almost as showy as its greenish-white flowers, which don't open into broad showy blooms like the western trillium. Both species of trillium produce a seed with an eliasome, a fleshy body particularly attractive to ants who disperse the majority of the seeds.  Yellow jackets also disperse trillium seeds.  These plants are pollinated by beetles, bumble bees, moths, and the non-native honeybees.

I didn't find any published research on the sessile trillium, but the western trillium can live to be over seventy years old based on counts of the annual restrictions on its rhizome. It does not even begin to flower until its fifteenth year. Trilliums don't survive disturbances such as logging, and the increased numbers of mice associated with clearcut and edge habitat take a toll on their seeds.  Long-lived, slow-growing plants affected by human disturbance face an uncertain future.

Even so, the sessile trillium persists in some unlikely places.  Along the overlooked urban banks of a local river, a thin strip of trees between the pedestrian path and the water's edge ducks under a series of overpasses.  Scotch broom, English ivy, and Himalaya blackberry tangle old plastic bags, broken bottles, and other refuse in the understory.  Nobody looks to these places for conservation.  But sessile trilliums bloom here every spring, refusing to relinquish this patch of forsaken ground.

Trillium chloropetalum. Photo by Linda Hardie-Scott

They remind me of the hand-held candles used in protests and memorial services, the flame borne above a flimsy shield.  These past few weeks have been marked in the human world by much upheaval and anguish in many countries torn by civil war, government violence against the unarmed, and the disasters in Japan.  The Japanese ceremony of floating candle lanterns, Toro Nagashi, honors the dead.  The trilliums blooming in the local woods have their own purpose, but they are still bright spots of both hope and memory in these dark times.

Liars, Cheats, and Moral Standing on Campus

Years ago I took an environmental ethics class in college.  One of the essays we read made the argument that cats cannot have moral standing because cats do not lie.  According to this line of thinking, moral standing belongs only to beings that can recognize the difference between what is real and what is not real.  A lie is a deliberate trip into an alternate reality, requiring advanced cognitive ability.  Moral standing therefore rests on advanced capabilities that belong to humans, not to animals such as sea cucumbers or wombats.  Cats give no indication that they engage in deliberate deception, therefore they have no moral standing.  Bad behavior such as pilfering food doesn't count. 

In my years of scientific training, I was indoctrinated against the sin of ever, ever projecting human thoughts, ideas, or emotions onto other animals, domestic or otherwise.  I still accept that the principle is basically sound.  It helps remind us that the perceptions of our fellow organisms are likely very different from our own.  Taken too literally, however, the doctrine denies us insight into our shared biology particularly with other social species.  In other words, cats might lie, but proving it is more than a little tricky in practice.  So much for determining the moral standing of cats, or any other organism besides ourselves.

I am delighted to report that eastern gray squirrels and scrub jays do in fact engage in deceptive behavior. Squirrels appeared to deliberately pretend to bury nuts in empty holes when other squirrels were around.  The researchers who study these sorts of things assume that this kind of behavior pays off as long as everyone steals and everyone cheats- which in the world of squirrels, appears to be the case.  Western gray squirrels haven't been examined for their honesty, but they probably do the same thing.

Photo: Dr. Lloyd Glenn Ingles. Copyright: California Academy of Sciences

Western scrub jays also deceive.  The jays buried food in trays of soft soil rather than pebbles if they thought another scrub jay was listening, but didn't make that distinction otherwise.  A jay that is hiding food and is caught in the act will move the food- if the jay has stolen other jays' caches.  Naive birds who have never had the opportunity to steal don't move their caches if observed by other jays.  Apparently, only sneaky jays worry about other sneaks. 

Photo: Dr. Lloyd Glenn Ingles. Copyright: California Academy of Sciences.

Which leaves us with some interesting questions: does moral standing therefore require possession of a brain designed to deal with complex social interactions?  And why should we think engaging in behavior most human value systems would consider unethical is necessary for moral standing? 

I always have enjoyed watching squirrels and jays, because they are so able to adapt to human disturbance and engage in their own business right under our noses.  College campuses and parks provide convenient settings for scientific observations on a daily basis.  In any case, the drama of social interactions with all their complexity, nuances, and even deception are played out not just among the humans around campus.  It seems that drawing the line between anthropomorphizing and conducting legitimate research may be much more difficult than we once thought.

How do we identify members of our own group?  Who or what is "like us", worthy of our consideration and some level of sacrifice?  What influences those choices?  These questions came to my mind again during a talk by Kelly Benoit-Bird of Oregon State University at the recent Song for the Blue Ocean conference, hosted by the Spring Creek Project.  Benoit-Bird gave a summary of some of her work with the hunting strategies of spinner dolphins, and how they find food in the vast ocean.  Turns out the dolphins prey mainly on fish and other animals that spend their days in deep water, at the deep scattering layer, but rise to the surface during the hours of darkness.

Myctophids or lanternfish at the deep scattering layer. Photo by OAR/National Undersea Research Program

Benoit-Bird's work has pioneered the use of acoustic tools to track the dolphins as they hunt.  She presented a video of some of her data on a group of dolphins moving along in a line, looking for food.  Their air bladders were clearly visible.  The animals then encounter a school of fish that have come up to the surface. The dolphins begin to swim in a circle around the school, but incredibly they did so in pairs.  Each pair circled the school at a constant depth, and pairs took turns moving into the school to feed, then returning to the perimeter.  As each pair of dolphins retreated, the pair on the other side of the circle moved in.

Hawaiian spinner dolphin, Stenella longirostris longirostris, photo by Andy Collins

Did we doubt that dolphins are smart?

It was an amazing demonstration of behavior that is impossible to see without technological tools that give us a glimpse of the private lives of other animals.  I wasn't the only one in the audience that was impressed.  The swelling of respect and affection for the dolphins from the audience was palpable.  Of course, dolphins are pretty likeable anyway.  Ever the science nerd, I asked if anything was known regarding the social structure of these feeding groups, which number roughly 20 individuals.  Not yet.

But the really interesting question is why there wasn't a person in that room who would argue that dolphins are not worthy of conservation- especially after the presentation.  The connection was already there, and it had been strengthened.

How do we choose?  Are marine mammals with complex social structure and communication more worthy than some other animal with neither?  We would probably disagree if we thought about it.  But it is the emotional connection that counts, the visceral identification with some other living being that brings us to consider another's needs even at the potential expense of our own.

As the world's resources are under ever greater pressure from human populations, we're going to have to make choices about what we will try to save.  This is already true, although we rarely acknowledge it.  Identifying some other living being as "other" allows us to fight wars, perpetuate injustice, and ignore the consequences of our choices.  Understanding how we draw the lines among those who are "like us" and those who are not is going to determine who is going to be allowed entry into the metaphorical ark as the extinction crisis and climate change bear down upon us.  If we can act with our heads as well as our hearts, we'll be more likely to save the crucial system parts required to sustain us.