What Damage Might Deer Do?

A Drama of Many Mouths, and Some Data

There are things we think we know about rare ecosystems but cannot prove. Indeed, we don’t want to inflict the necessary damage. (Does this sound unscientific?) How much stress will it take to shatter a priceless gem? In this case, the gem is an ancient, original prairie.  

Below are stories of both a degradation and a recovery. The drama begins when, from love and curiosity, we did some science. We of the North Branch Prairie Project were now stewards of one of the finest black-soil tallgrass prairies surviving. (Really? See Endnote 1.)

Our story features defenseless ecosystems, innocent animals, the shooting of deer, and evolving ethics. Also: compelling data on both the deer and plants at Somme Prairie.

Many good people oppose eating meat, or wearing fur, or leather, because those materials signify death to an animal that did us no harm. Other good people hunt. Some vegetarians and some hunters work to save endangered species and ecosystems. When we conservationists protect nature from capitalist developers, quite a few folks cheer. Others damn us for killing jobs. 

When we rescue out-of-balance ecosystems by shooting deer, hardly anybody cheers. That’s too bad, because without that culling, numerous defenseless plants (and many animals that depend on those plants) are being deleted by deer from the gene pools of the universe. Public opinion, though divided, makes it difficult for agencies to execute deer control programs, especially in metro areas. 

Sarah Palin campaigned in support of hunting. Was she the ecosystem’s ally?

A former Vice-presidential candidate became the archetype of the hunter. We associate Sarah Palin with shooting wolves out of airplanes and standing proudly over bloody bodies of a big-antlered vegetarian caribou. Her politics, to some, corroborate the evil of hunting. Politically, Palin was very much on the wrong side of history. But as a hunter, does she have a redeeming virtue? 

Biodiversity conservation scientists and agencies support deer control programs (see Endnote 2). Many folks’ preference would be for the ecosystem to have enough wolves and mountain lions to do the job without the apparent ethical pollution of macho human killers, and, indeed, I’m not one to vote for the macho. But it’s important for some humans to regain our station as predators, in principle and practice. 

At Somme (and so many sites) degradation by out-of-balance deer became severe in the early nineties. For millions of years white-tailed deer (a very old species) were natural members of savanna and woodland communities. Then, prior to the 1980s, deer were gone from Somme for nearly a century. Hungry settlers had eaten the last of them in Illinois, hard to believe as that seems today. But their numbers soared once they returned, and by 1992 at Somme, they had reached about ten times (that is 1,000% of) their natural, sustainable numbers. 

They are precious, as all animals and plants are precious. They are nature.
But more is not always better.

Aerial surveys of Somme by Forest Preserve biologist Chris Anchor showed a deer population of more than 160 per square mile. Scientists were reporting that 7 to 15 per square mile would be a natural, balanced population. Before we had caught on to what was happening, many thriving populations of the prairie lady-slipper (Cypripedium candidum) were wiped out at Somme, never to be seen again. Belatedly, we caged a few survivors, which are with us still. 

Our large yellow lady-slipper (Cypripedium calceolus) was eaten, and we’ve not seen one since. Many species were reduced to such low numbers that they likely lost some of their genetic robustness. Some wildflower species didn’t bloom for decades. “So what?” you may ask. One “what” is that pollinators and other species that depended on those specific blossoms or seeds are now also gone, likely for good, short of highly-challenging research and restoration. It’s too bad. 

How heavy was the depredation? At first we had no numbers to measure it, but simple observations were painful and shocking. On many occasions when I walked into 85-acre Somme Prairie Grove in the early evening I would count 25 to 30 deer on a short walk. Across the river in 70-acre Somme Prairie, I’d count 10 or 20 deer, heavily concentrated in the two little Grade A acres. I know what deer like. They like Grade A prairie. They voted with their feet and mouths, clearly preferring the best remnant area to the surrounding degraded landscape, and even to the 10 acres of “Grade B” remnant nearby. Two acres is very small to feed so many deer. On the basis of 15 per square mile – the sustainable number that 2 acres would support is 0.047 deer rather than 10 or 20. The rare prairie remnant was deer candy. Highly palatable rare plants (shooting stars, prairie lilies, alumroots, valerians) were there in large numbers at that time – and nowhere else on the site.     

 

This old photo – from before the deer explosion – shows an impressive density of conservative plants. Prominent here are cream false indigo, hoary puccoon (orange), shooting star (white), downy phlox (pink), and prairie dock (the big leaves). 

Prairie species stood up to the grazing of wandering herds of bison and elk for millennia. But they can’t tolerate high numbers of predator-free resident deer. Fortunately, both the Village of Northbrook and the Forest Preserve District began culling deer in 1993. (Is “culling” the right word? See Endnote 3), and deer numbers since have been very much lower. But have they been low enough? Has the prairie recovered? 

The graphic below tells a powerful story. It compares three sets of vegetation sampling (for the years 1987, 1992, and 2011) – before, during, and after the population explosion. 

In 1987 we had laid out a 170-meter transect, marked by metal stakes at fifty meter intervals. We stretched the meter tape between stakes and monitored the plants in ¼ m² circular quadrats, every five meters along that line. Within each quadrat, we recorded which plant species were present and how much of the ground was shaded by their leaves (their “cover”). We repeated the sampling in 1992 and 2011. 

Table 1 shows cumulative results for the 63 species with the highest total vegetative cover in the twenty Grade A quadrats – shown in rank order starting with the highest “Sum Cover.” 

In 1992, when the deer numbers were so high, eleven species had plummeted. These eleven species are among the most “conservative” (see Endnote 4) and therefore the most significant of the remnant. Their trajectories are indicated by colored lines. 

Prairie dock (Silphium terebinthinaceum) had a total cover (again, the amount of total leaf surface recorded in the 20 quadrats) of 272 in 1987. That value dropped to 68 in 1992 – one quarter of the original value. 

Two classic prairie species that are a bit more “conservative” are golden Alexanders (Zizia aurea) and alumroot (Heuchera richardsonii). The Alexanders plunged from 75 to 11. The alumroot plunged from 67 to 10.

Three even-more-conservative (and thus more significant) species did yet worse. Heart-leaved Alexanders (Zizia aptera) dropped from 35 to 4. Even after nineteen years of deer control, it had recovered only to 9. Prairie phlox (Phlox pilosa) dropped from 42 to 9 and then disappeared from the table. As a tweet might say, “Sad.” Cream false indigo (Baptisia leucophaea) dropped similarly from 19 to 2 to gone. As we know from other sites, long-term over-grazing wipes out species permanently. 

To consider the (mostly weedy) species that increased, see Endnote 5.

These statistics represent a bad wound to one of the planet’s best prairie remnants. Our squeamishness about being predators caused this. It was an abdication of our responsibility not to start culling sooner. But it was an act of political courage on the part of the Forest Preserve District that culling began as soon as it did. 

Deer control at that time was also supported by police departments in surrounding communities, which recognized the problem differently. As deer wandered out of depleted preserves looking for food, numbers of deer/automobile collisions soared. People were injured; some died. Diseases related to deer were rising.  

Village police and forest preserve staff both requested and received authorization to shoot deer to reduce numbers after public debate, confusion and ill-feelings. (See Endnote 6.) By 2018, the strife has died down. But much more public engagement and consensus is needed. This is especially true for our few, very-high-quality remnants. 

This data also deserves better analysis than my simple-minded colored lines approach. Is there perhaps someone with a math and science background who might be interested in participating in (or taking charge of) writing that paper? (See Endnote 7.)

  

Endnotes

Endnote 1

A study by the Illinois Natural Areas Inventory in the 1970s found Somme Prairie to be one of the best in Illinois. In the 1990, a study by Marlin Bowles of the Morton Arboretum found it to be one of the two best in the Chicago area. 

This is the kind of treasure people used to call a “virgin” prairie. Virgin? Awash with sex, we now say “original prairie” or “remnant.” Not only is this ecosystem a cauldron of genetic exchange, reproduction, life, competition, and death, but our increasingly “woke” human friends no longer think of so-called “intercourse” as a degradation or diminishment. Language improves. Prairie, rife with complexity, is tender. Vulnerable these days. Fragile, in the face of certain threats. 

We of the North Branch Prairie Project in 1977 were authorized to restore only some badly degraded areas. But within a few years our work was respected enough that we were entrusted with responsibility for clearing brush from and doing the controlled burns for this rare remnant. 

Endnote 2

There is a broad consensus about the need for deer control among Forest Preserve staff, the Illinois Nature Preserves Commission, conservation biologists, and conservation agencies like Audubon and Nature Conservancy. Some have clear explanations on their websites. For one example see: Lake County Forest Preserves. Also check out The Illinois Department of Natural Resources - which authorizes and supervises deer control in this state.

  

Endnote 3

Is “culling" the right word? My first draft repeated the words “executing deer control programs” here. Somehow the suggestive word “execute” seemed to balance the bureaucratic jargon “deer control programs.” In the second draft I replaced the jargon with “shooting deer.” It’s plain and factual. But in context it seemed abrupt and cold-blooded. We feel compassion for individual deer.  

When culling controversies heat up, some people divide into the conservation equivalents of Red States and Blue States. Partisans on one side may refer to shooting deer as “murder.” Partisans on the other may refer to deer as “hoofed rats.” Children are drafted into the fray and are taught, painfully, to see conservationists as heartless “killers.” Language can hurt people and wound the human community. 

To me it seems right to use words like “shoot” and “kill” in some contexts. In others, “cull” or even the dreary “deer control programs” seem better. 

Endnote 4

For a relatively simple explanation of “High Quality” and “conservative species”, see the middle and the endnotes of the post: A Myth Coming True

Endnote 5

Figure 2 is the same basic table as in Figure 1. But in this case, rather than the decreasers, the increasers are highlighted. 

The big winners were wild bergamot (Monarda fistulosa) and the tall prairie grasses, for example big bluestem (Andropogon gerardii), which are common in the average prairie restoration. (Deer leave the grasses to the bison and elk.) So, yes, some win; some lose. But what the precious Grade A area of Somme was losing … was irreplaceable. 

Other increasers include prairie coneflower (Ratibida pinnata), which is commonest in recovering prairies, and the nodding wild onion (Allium cernuum), a conservative plant, but apparently not quality as the deer taste it.

Rattlesnake master (Eryngium yuccifolium) behaved strangely. It initially rose in rank order but dropped a few points in “SumCover.” Then it tripled its cover after deer control began. It is a conservative prairie species and yet one that increases rapidly if there’s extra space for it. I wouldn’t make too much of this odd behavior beyond commenting that there are a lot of shortish-term dynamics at play. And this data set is, of course, a small one.   

Endnote 6

A bit of Illinois and Somme deer history

According to the University of Illinois Extension:

“Reports during the early 1800s indicate that deer were more abundant than when Europeans first began settling the area. The population grew in response to reduced pressure from predators, as people eliminated wolves and cougars, and from an increase in available edge-habitat as forests were cleared to make way for agriculture. The large numbers did not last long. White-tailed deer were virtually eliminated from Illinois by the late 1800's … Even into the 1970s, it was not that common to see deer in Illinois.” 

Bill Valentine, who spent much time during his youth in the Somme Preserves, remembers seeing his first deer there in 1977. That was the first time he saw deer or their tracks. 

We North Branch volunteer stewards found no deer in Miami Woods or other southern North Branch preserves when we began working as stewards in 1977. We were excited to find deer tracks in Miami Woods forest preserve (seven miles south of Somme) starting in 1978. 

We recorded deer as "common" at Somme starting in 1980. Soon we found stashed ladders that led to deer-hunting platforms. One such (in the mighty tree we dubbed the "Deerslayer Oak”) would, in autumn, collect beer cans underneath. As a volunteer crew was collecting seed one day, our ears were suddenly blasted by the largest boom I’d ever heard. We looked at each other, wondering if we should leave. A few minutes later, three young men came out of the brush with sheepish looks on their faces. They tried to act nonchalant. As if to be casual, one said to me, “Hey, where’s your camera.” In those days, I spent a lot of time at Somme alone, taking photos. I’d never seen this person before, but obviously he’d been watching me, from a camouflaged hide. With a loaded gun. It was a bit creepy. All three had beer cans in their hands. To make the case that they were good conservationists, they discussed participation in the local Izaak Walton League, an organization once famous for ethical sportsmanship. At this point, as the deer were increasing and increasing, we were already starting to realize what a threat deer overpopulation could be, which gave us mixed feelings about the tipsy “sportsmen.” But we never saw evidence of them again. 

The Village of Northbrook adopted a resolution committing to deer control in 1991. The Forest Preserve District of Cook County began its program of deer control at Somme in 1993. 

From the Chicago Tribune. Nov. 24, 2010

“For most of the state, archery and firearms hunting seasons, which run October to January, go a long way toward thinning the herds, with more than 189,000 animals harvested last winter…

A secondary means of deer management — and an unfortunate population gauge — are deer-vehicle accidents, which have averaged about 24,000 a year in Illinois for much of the past decade, according to the state Department of Transportation. Cook County tops the state, averaging nearly 1,000 crashes a year.

With hunting not permitted in much of the Chicago area, the Department of Natural Resources launched sharpshooting programs in 1988 to help manage robust urban and suburban herds, where densities in some forest preserves topped 100 deer per square mile ...

Annual deer culling, which runs November through March, has been adopted by Cook, Lake and DuPage county forest preserve districts. A number of North Shore communities have culled periodically, including Glencoe, Northfield, Northbrook, Glenview, Riverwoods, Lincolnshire, Bannockburn and Lake Forest.

Last winter, 14 agencies and communities culled 31 sites, harvesting more than 1,300 deer. Since the late '80s, the program has resulted in more than 400 tons of ground venison donated to food shelters and charities…”

Endnote 7

We should have done more with this apparently unique data back in 2011, but we had (and have) too many irons in the fire. A more technical and complete analysis of this data should be made and published. Indeed there’s a lot more data and a lot more to say about both the deer and the plants. Does anybody happen to have technical experience in this field and a possible interest in partnering on a proper paper, for some conservation journal? 

Acknowledgements

Thanks to Kathy Garness and Eriko Kojima for helpful proofing and edits.