Local in Ann Arbor

“I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer.” – Aldo Leopold, A Sand County Almanac.

As we said at the very beginning, much of the controversy surrounding the solution to Ann Arbor’s deer problem is based on values.  One set of values that is crucial to this question is how one views the importance of the natural world, and how one judges its components.  There are some major philosophical and functional questions here, and often they are not examined so much as taken for granted.

Does “nature” have an inherent value, or is it only valuable in economic terms and its usefulness to humans?

Is there a moral basis for preserving wilderness, or is it to be judged solely on recreational use and conservation of certain resources (lumber) for future exploitation?

Are some species more worthy than others?  Or is every species deserving of protection?

These questions first emerged in America toward the end of the 19th century, as the expansion of civilization across the continent was drawing to its finish. President Grant signed some of the first legislation establishing Yellowstone National Park.  (The second national park was Mackinac National Park in Michigan.) John Muir, who died in 1914, was a major leader in the preservation of wilderness and conservation of wild species and the founder of the Sierra Club.  He was influential in Theodore Roosevelt’s moves to strengthen and expand National Parks.  He saw natural areas as having a transcendent value, a source of spiritual inspiration, rather than as treasures to be exploited. The questions are still relevant today, as every fight between mining operations, lumber interests, developers or ranchers and conservationists demonstrates.  (Note the recent battle over the fate of wolves in Michigan.) Aldo Leopold, who was most active during the first half of the 20th Century, furthered the discussion with his early work on ecology.  We quoted his careful work on “deer irruptions” previously.  Leopold brought some rigor and analysis to the understanding of how wild systems work, but he also enunciated a philosophical position which he called the “land ethic”.  He had a strong empathy for all parts of the natural system, beginning with the soil and incorporating the plants and the animals.  In the foreword to his landmark book, A Sand County Almanac, (1949) he says,

“That land is a community is the basic concept of ecology, but that land is to be loved and respected is an extension of ethics.”

Unfortunately (from my perspective), that is an ethic that is not universally shared.  Even many supporters of maintaining biological diversity often justify it on an utilitarian basis, e.g. “there might be a new antibiotic or a cure for cancer there”.  For Leopold, and for me, every part of the natural community (what he calls the “land”) is of value in itself. There is an aesthetic but also a reverence for all these members of the natural community and the beautiful fabric that they weave.

Favored Species

But of course any of us do discriminate among species.  When I was a child, I couldn’t figure out why God created the mosquito or the rattlesnake.  Now I ruthlessly weed out “invasive” plants (usually plants that are not native to our area and are weedy in behavior, crowding out other plants).  I certainly favor songbirds over starlings (another invasive).  But if we care about the natural world, we recognize that most species, especially those native to the community, have a place in the “web of life”, where there are many dependencies.  Even the less glamorous deserve some measure of respect. What has been distressing in the current discussion about deer is that some people evidently do place the welfare of individual deer above that of all the rest of the natural world.  In the A2 Open City Hall survey (we summarized it here) the question was asked,

In general, do you believe deer are a more valued species than other urban mammals (coyote, rabbit, squirrel, skunk, woodchuck, etc.)

to which 26% of respondents answered “Yes”.  The question does not ask about birds, plants, reptiles or amphibians, much less invertebrates like insects.

A Question of Balance

A simplified food web illustration. Arrows point to the one who eats.

The notion of the “balance of nature”, in which the various members of a native community interact with each other to form a more or less stable condition, is based on the concept of the food web.  Plants form the basis of several food chains (combined in the web) in which energy is captured by photosynthesis and passed along from animal to animal, where prey animals are ultimately consumed by predators.  (Prey animals may be herbivores, omnivores or carnivores.)  Predator-prey relationships exist at each step (see our explanation), including between herbivores and plants.  This means that an excess of any predator can depress the ability of critical parts of the food web to supply the needs of the rest of the web. As we noted previously, without a predator (and you’ll notice the wildcat is missing in this web), deer will employ their tremendous reproductive capability to exceed the ability of the plants in their community to support them.  But the rest of the food web suffers, too.  This has been especially evident in the forests of North America.  A post originating from the august Nature Conservancy states,

In our opinion, no other threat to forested habitats (than the white-tailed deer) is greater at this point in time — not lack of fire, not habitat conversion, not climate change.

Think about it.  Most deer, even those in our luxury setting, are hungry all the time.  They need a high-quality diet.  Estimates of how much vary, but about seven pounds a day seems fairly conservative.  And they want it to be high in protein and low in toxic compounds.  They are not grazers of grass, but nibblers of buds and tender young foliage.  In fact, much of what they eat is what we would seek out if we had to live in the wild and had no animals to eat.  Buds, fruit, tender growth, nuts, acorns, even mushrooms.  They have also been observed to eat baby birds.  (Protein is hard to come by.)  They go through a habitat relentlessly, scooping up everything edible – by their standards. There are numerous studies of how deer have affected the Northern forests.  I like this one from Wisconsin.  It is based on rigorous studies using exclosures and plant assessment techniques. From the article:

Deer account for at least 40 percent of the change seen in the forests over the past half-century or so. “The study links microcosm to macrocosm. We have exclosures in the same region where we have documented long-term changes in the plant community over the past 50 years. These are giving us the same message.”

Some previously common plant species (trees and shrubs) have become so rare that they are no longer included in the assessment studies.

A Formidable Influence

Aldo Leopold killed a wolf early in his career and then regretted it.  In the fires of the eyes of the dying wolf, he saw a truth.  He realized that without the wolf, the mountain where it lived would suffer.

“I have watched the face of many a newly wolfless mountain…have seen every edible bush and seedling browsed…every edible tree defoliated to the height of a saddlehorn.  Such a mountain looks as if someone had given God a new set of pruning shears and forbidden Him all other exercise…I now suspect that just as a deer herd lives in fear of its wolves, so does a mountain live in mortal fear of its deer.”

Deer are extremely adaptive, have a high reproductive capability and an unending appetite.  They are a very old species on this continent.  In her recent book The Sixth Extinction, Elizabeth Kolbert relates how the introduction of humans to the North American continent finished off many large mammals (megafauna), including mammoths.   But “white-tailed deer have a relatively high reproductive rate and probably remained plentiful even as the number of mammoths dropped.”  This is referring to the likelihood that deer were able to supply meat to the new predator on the continent and yet survive and prosper.  Unfortunately, we are no longer filling our role as the top predator in the food web.  The balance of nature is off kilter.  I don’t think that we want to bring back the wolves in sufficient numbers to keep them in check. For the sake of the deer as well as all the other species dependent on the wilderness,  we need to fill our place in the natural order.

UPDATE:  An important study of the effects of deer in an Ann Arbor natural area has now been released.   The study, White-tailed deer (Odocoileus virginianus) browse damage in Ann Arbor, Michigan Bird Hills Nature Area, Winter 2015,  is by ecologist (and specialist in deer/vegetation interactions) Jacqueline Courteau and her independent study student at the University of Michigan, Moriah Young; it is based on data collected in February through April 2015.  (The authors have released the study for use and quotation, but it is not yet published in a journal.)

The study finds significant damage in tree saplings and shrubs.

This survey of 142 tree saplings (less than 2 meters tall) and shrubs in Bird Hills Nature Area shows that 80% have been browsed by deer, and 51% have half or more branches browsed. This level of browsing could interfere with forest regeneration and diminish the flowers and fruit available for birds, butterflies, and bees.

The study uses direct, painstaking counts of deer browse on specific woody species.

The discussion also makes an important point about deer population counts.  As it notes,

A small population of deer that browse repeatedly in a small area due to barriers (roads, fences, etc.) or because of the lack of predators may damage vegetation as much as a larger population that ranges more widely.

 There are numerous figures and tables with specifics about the sampling areas.

The City of Ann Arbor conducted a visual deer count by helicopter fly-over on February 10, 2015.  There are a couple of methods for assessing deer populations.  According to one recent study, use of a helicopter for visual counts while there is snow on the ground is as accurate as infrared, another frequently used, but more expensive, method. The City chose a day with good light and a good snow cover.  As reported by the Ann Arbor News, all areas of the city other than downtown and “near hospitals” were surveyed. According to the News, a second fly-over was conducted in early March.

Aerial survey of deer in a Washtenaw County natural area, 2014. Photo by Shawn Severance, WC Parks.

The point of the survey, of course, is to determine the number and also geographical distribution of deer in the city.  This will be part of the report to Council as now promised for late March. (No results have been reported as of this writing.)  One of the problems with this technique is that deer tend to clump or “yard” under trees and shrubs in cold weather.  However, an independent observer using a drone noted that many deer trails were readily visible.  (One image is posted in the comment section of the News article.)

Once we have some numerical information (ideally, this would pinpoint herd numbers in different areas of Ann Arbor), we’ll need to identify the method to reduce – or, euphemistically, “manage” the population.  Ann Arbor is coming late to this discussion.  Wildlife biologists and managers all over the U.S. have been studying this issue for at least 25 years.  A great deal has been learned from careful observation of deer population dynamics and behavior.  We reviewed a critical part of this question in our previous post about deer population growth.  Deer have tremendous reproductive and regenerative capability.  So a program intended to reduce their numbers and their impact on our local environment must take that into account.

Deer as Gas Molecules

As we acknowledged in our first post in this series, the suggestion that we might employ lethal methods (i.e., killing or “culling”) to reduce the local deer population is truly horrific to some members of our community.  The lead speaker for this viewpoint is Tanya Hilgendorf, the President and CEO of the Humane Society of Huron Valley.  She and others have included as part of the argument against a cull the notion that it is pointless and ineffectual because killing deer in one location will create what is often called a “vacuum effect” by which more deer will inevitably be pulled into the void created by killing the deer in one region.  The basic argument from those opposed to culling by lethal means is this:

Killing the deer will only result in bringing more deer into the city from adjoining areas.  Because it will be ineffectual, it is therefore pointless and needless cruelty.

If gas molecules are suddenly given access to a vacuum (by lifting the barrier), they will rush in and fill the space so that density evens out.

The “vacuum effect” is based on an assumption that deer behave as gas molecules do.  Supposedly, if a vacancy is created in one area, deer will somehow sense that and there will be a massive flow of deer into the opened-up area.  Soon we’ll be back to the same numbers as before.

Many studies have shown that deer don’t behave this way.  Instead, deer favor a home range.  They mostly migrate into new areas only because they have exhausted the food in their home range.  In other words, if they have exceeded the carrying capacity of their current range, they may migrate.  But this is not caused by a vacuum created by the removal of other deer.

Home Ranges

The key to understanding deer behavior is the concept of the home range.  There are tens or perhaps hundreds of studies examining how deer modify the size of the home range under certain circumstances, and what factors cause them to leave the home range.  A landmark paper from 1992,  The Rose Petal Theory: Implications for Localized
Deer Management introduced the key model for home ranges of does. This was one of a long series of papers by  William F. Porter (now at MSU) and his students in which meticulous research (using radio collars and other increasing refined and sophisticated tracking mechanisms) has followed individual deer to map their behavior under different conditions.

The rose petal model, after Mathews and Porter, 1992. Circles are home ranges of individual does, about 1/4 mile in diameter.

The rose petal model proposed by Mathews and Porter states that deer are matrilineal in social organization; does stay close to their mothers.  The first circle is the home range of a doe (these home ranges are quite small, only about a quarter of a mile in diameter).  Her daughter establishes a home range that slightly overlaps hers. Subsequent generations continue to overlap the original doe’s home range in a pattern resembling rose petals.  This type of close association within a family structure is termed philopatry.

The significance of this behavior to management is that if the deer in a particular very localized area can be eliminated (or significantly reduced), that area will likely stay empty of deer for quite a while.  Over time, adjacent family groupings will begin to encroach on the area, but that will not be immediate.

Bucks have larger home ranges. And yes, does will move farther under certain circumstances, usually when the food available no longer supports the herd, in other words when they exceed the carrying capacity of the immediate area.  (We discussed this concept in the previous post about Deer and the Numbers Explosion.)  This movement to a new feeding ground is called dispersal.

Much of the literature on deer migration and deer management acknowledges the importance of home ranges and their use.  Wildlife biologists have used increasingly sophisticated measurement methods to determine how specific population management approaches (i.e., culling) affect home ranges and migration.  This 2001 study by Kilpatrick et al. is just one example.  They found that reducing deer densities actually reduced the size of home ranges, as deer did not forage as far (because vegetation became more available with lower deer densities).  Here is their conclusion:

Population reduction programs at our study area did not cause the resident deer population to expand home range size or shift into adjacent habitat. We believe that localized deer reduction programs can be effective tools to manage problem deer herds. Deer removal efforts initiated to reduce deer damage to vegetation, particularly in urban areas, may have an added effect of reducing foraging range of the remaining resident deer.

Presumably, a program of deer management for Ann Arbor can use similar pinpoint deer population reduction.  This will benefit our wild and cultivated areas, and even the health of the surviving deer themselves.  Even in our lush urban environment, some deer are beginning to show signs of food deprivation.

Deer browsing in a vegetable garden in Ann Arbor. Note the visible rib structure.

Note: An ongoing list of posts on this subject, together with some other resources, is on our page, What Do We Do About the Deer?

UPDATE: The City of Ann Arbor has now posted maps of its two fly-over deer counts.   Here is the February 10 and here is March 6.

The Ann Arbor City flyover deer count from March 6, 2015

Many of us believe that this represents an undercount. Observations by residents reporting to the Washtenaw Citizens for Ecological Balance have indicated much more penetration by deer into the central section of Ward 5, for example. Here is that map. It is being updated through March 2015.  (Reports may be made via deerannarbor@gmail.com.)