Follow the Crowd and Keep Chewing

The story says that in 1832 a scientist found a deer tooth in a Virginia cave. After close examination, he noticed that the tooth was hollow. That simple observation allowed the scientist to name this animal Odocoileus virginianus. Odocoileus comes from a combination of the Greek words for “tooth” (odontis) and “hollow” (koilos).

Up Close

Up Close

White-tailed deer are distributed throughout eastern North America. It’s these “hollow” teeth that chew up vegetation as they spend a lot of time browsing, which can become extremely heavy in some areas. Their niche, or role, in the ecosystem is replaced by mule deer or blacktail deer in the west. These deer occupy a wide range of habitats, but the main ecological drivers are food and cover.

In North Carolina, white-tails have very little population pressures, and therefore, multiplying is not a problem. Based on 2015 harvest numbers, it is estimated that there are 30-44 deer per 640 acres (1 square mile) in Iredell county. According to the U.S. Forest Service, a deer density of 15 to 28 deer per 640 acres is ideal for forest regeneration. Anything less than 10 deer per 640 acres would cause an overgrown understory. Anything higher than this ideal range would be detrimental for the vegetation. Iredell county falls on the high end.

We are interested in how deer in Iredell county are using city greenway spaces and the adjoining land. For the past three fall semesters, our lab group at Mitchell Community College has utilized trail cameras to estimate white-tailed deer population size at one of these urban greenway spaces. This particular space and the immediate land surrounding it total 657 acres. We used this area as our study site. We set up and deployed cameras from September through November during 2014, 2015, and 2016 using the methods put forth by Texas Parks and Wildlife. As part of these methods, the students set up cameras along transects a specified distance apart. At the end of each camera-trapping period, researchers tallied the total number of doe pictures, fawn pictures, and buck pictures. The researchers also determined how many individual bucks were caught on camera. Sample data for 2016 look like the following:

Total # of deer photographed = 742
     Bucks = 112 (Individual bucks = 8)
     Does   = 668
     Fawns = 32 

Students then used the individual bucks identified (8) and divided by the total number of bucks caught (112) to determine the population estimate multiplier.

Population estimate multiplier = 8 bucks/112 total buck pictures = 0.07

The deer population is estimated using this multiplier.

Bucks =                         8
Does =  668 x 0.07 =  2.24
Fawns = 32 x 0.07 =  46.76
_____________________
Total deer =                57

The student researchers used this exact method for the same study site all three years.

Figure 1. White-tailed Deer Data, 2014-2016

Figure 1. White-tailed Deer Data, 2014-2016

The data from 2014-2016 is shown in Figure 1. We realize that there can be fluctuation in deer numbers from year to year since deer are constantly moving in search of food and cover. Our study site is almost completely surrounded by major roads and/or developed neighborhoods. If 28 deer per 640 acres is ideal, that amounts to 22.9 acres per deer. Figure 1 shows that in 2016, there were 11.5 acres per deer at our site. That represents a very dense population.

Why are these numbers much higher than ideal deer population numbers? Why is the deer density in this space more than the average density in Iredell country? The data could indicate that deer density is greater in areas surrounded by urban development simply because the deer are squeezed into these spaces. There isn’t much food or cover available on interstates on in neighborhoods. The density could also be high at this particular site because nearby residents feed the deer. That would certainly seem to attract more individuals. The next question we wanted to answer was, “How does a higher than ideal deer density impact deer behavior and activity?” Are they active and feeding when deer are suppose to feed (like the books suggest) or do they feed for longer periods of time? What does this mean for understory vegetation.

Figure 3. Deer Activity Patterns

Figure 2. Deer Activity Patterns

Figure 2 shows deer density plotted over time (24 hr). Out of this sample of 471 pictures, deer activity drops off sharply before mid-day, or 12 p.m. The data indicate that the deer in this space are most active around sunrise and sunset, which is typical for this particular species. According to Figure 2, the higher density has not caused the individual deer to change the times in which they are active. However, the deer in this area are putting a tremendous amount of pressure on the vegetation. Simply put, they are eating plants faster than the plants can grow. Walk through just about any patch of forests in the county, and you will notice this.  This may, in fact, have negative impacts not just on vegetation but also those species that rely on that vegetation. In future years, students will collect and analyze data from vegetation plots to quantify vegetation loss and again better understanding of how these deer are impacting this ecosystem.

Foraging or Hiding?

Foraging or Hiding?

White-tailed deer look like they are here to stay in large numbers as they crowd into developed areas. Deer management policies and practices have yet to be successful. Hunting has not been able to put a dent into the population. The deer have no real predators (coyotes don’t really count). Maybe its time to reintroduce a large feline carnivore to North Carolina.

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