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Back in 2010 Deborah and I hiked the length of the Baker Trail here in Western Pennsylvania. The Baker Trail is by most accounts 132 miles long (although the mileage varies depending on which source you consult). We did the hike in 8 or 9 mile segments and made note of the trees, plants, and animals that we saw along the way. I have written about this hike on my Western Pennsylvania hiking web site (“Between Stones and Trees”) and also in an article for the Pittsburgh Post-Gazette. I also have a detailed narrative of the trail from its start at the Freeport Bridge all the way to its terminus in the Allegheny Forest that is available upon request (if anyone wants to know the specifics of some particular section of the trail).
We saw many things on our hike and put together some interesting hypothesis about the historical ecology of Western Pennsylvania. We also made some interesting observations on the ecology and possible ongoing evolution of some of the animals we saw on the trail. I have told my students that asking yourself “did I really see that?” is an excellent way to get started in the process of science! One of our “did we really see that?” speculations from our weeks on the Baker Trail concerned the white-tailed deer (Odocoileus virginianus).
In 1900 it was estimated that there were only 500,000 white-tailed deer left in North America. Intense hunting pressures and massive deforestation through the Nineteenth Century had decimated their numbers and made them a species only rarely seen in our forests. The sighting of a deer, in fact, could make front page news in some of the rural newspapers of northwestern Pennsylvania! Today, however, there are estimated to be over 15,000,000 white-tailed deer in North America! Forest regeneration, elimination of natural predators, and strict hunting laws have allowed this species to reach population numbers and densities that far exceed those even of the pre-European settlement forest ecosystems!
White-tailed deer are both a charismatic species of our eastern forests and a major problem. The sight of a deer emerging from a stand of trees or brush is breathtakingly beautiful, but the damage they do to tree seedlings and forest understory plants (not to mention gardens, shrubs and ornamentals) is devastating. Some foresters, in fact, refer to white-tailed deer as “tree locusts,” and forest ecologists worry that the consequences of deer browsing on tree seedlings might include the disruption of forest succession and renewal throughout the northeast! Fern-lands and moor-lands could possibly replace our diverse hardwood forests if deer are allowed to consume the next successional generation of trees!
But let’s get back to our observations of white-tailed deer. The Baker Trail takes a hiker through a wide range of habitats and landscapes. You walk through suburban neighborhoods, down country roads, through farms and around fields, through old industrial and mining sites, and also through some almost pristine forest. You see the whole range of what is possible in Western Pennsylvania (with the exception of, say, the city canyons of downtown Pittsburgh). In almost every one of the habitats and landscapes we walked through we saw white-tailed deer. The deer in these different places, though, were not at all the same.
In suburban neighborhoods it seemed to us that the deer were larger, and that the does almost always had twin fawns with them. These “city” deer were also much less concerned with us as potential threats or predators. Their “flight initiation distances” (FID’s) were greatly reduced, and they allowed us to walk up quite closely to them!
In the most “natural” of our hiking habitats, though, we felt that we saw a very different type of deer. The adults seemed smaller than their “city” counterparts, and the does seemed to almost always have only one fawn. Further, these “country” deer did not tolerate us to approach very closely. Their FID’s, then, were quite large, and they were very alert and quite wary.
Over these past few years I have frequently looked through some of scientific literature that discusses deer behavior to see if anyone else has had these kinds of observations or impressions, and I think that I have finally found a few.
For example, a study at Georgia Gwinnett College found that “urban” deer were larger and better fed than their more “rural” counterparts. The diversity and abundance of often non-native landscaping plants in the suburban ecosystem provided the deer with a diet that was richer in calories and possibly even richer in nutrients than the wild foods of the surrounding rural ecosystems. Further, they noted that these “city” deer were protected from both natural predators and also human hunters.
A study in Minnesota (in the city of Minnetonka) indicated that “city” deer have a very high survival rate and that ‘city” does have a 93% pregnancy rate typically with twin and even triplet fawns.
In Indiana a study as part of a Master’s thesis at Ball State (T. Carter 2016) measured fawn survival rates to 32 weeks of 70% in urban areas (primary cause of fawn deaths were cars) but only 44% in rural areas (primary cause of fawn deaths were coyotes).
In Massachusetts Gaughan and DeStefano found that urban deer had ranges that were one tenth of those of rural deer, indicating a much higher quality of habitat and, possibly, a reduced probability of chance encounters with either cars or predators (their paper published in Urban Ecosystems in 2005).
Urban and suburban environments, then, greatly favor the growth, survival and reproductive success of white-tailed deer. The deer are bigger (due to more and, possibly better quality food, and also due to the reduction of stress and the necessity of giving up feeding time to watch for or run away from potential threats). The fawn survival rate is higher due to an absence of predators (this was probably why it seemed that all of our “city” deer on the Baker Trail had twins!). A “city” white-tailed deer, then seems like a different animal than its “rural” counterpart!
One last piece of information from the literature: In his book Urban Wildlife Management (3rd edition, 2016) Clark Adams cites a 2011 United Nations study that indicates that 82% of the white-tailed deer in the United States live in urban areas. I have not been able to find this study to read it for myself, but, if true, this is a remarkable statistic that, I think, shows that white-tailed deer are becoming primarily an urban species. It is evolution occurring right before our eyes!