A Survey of the Box Turtle Population Density Along the I-69 Corridor in Southern Arkansas
Wildlife & Ecosystems
Research Idea Scope
The United States Congress in 1991 designated certain highway corridors of national significance to be included in the National Highway System under the Intermodal Surface Transportation Efficiency Act (ISTEA). Corridor 18 (I-69) was designated as one of the high priority corridors at that time. I-69 will extend from the Canadian border in Michigan to the Mexican border in the Lower Rio Grande Valley of Texas. Total length of the I-69 corridor is around 1600 miles. One hundred and forty five miles of this corridor will cross all or portions of seven counties in southern Arkansas: Union, Columbia, Ouachita, Calhoun, Bradley, Drew, & Desha. The landscape of this part of Arkansas is classified as West Gulf Coastal Plains except for the eastern part of Drew and Desha Counties. This portion is prime habitat for the Three-toed Box Turtle (Terrapene carolina triungulis), a species listed of special concern by the Arkansas Natural Heritage Commission. The Arkansas Natural Heritage Commission conducted a statewide box turtle survey in 2007 & 2008. To conduct such a vast survey, they partnered with citizen scientists. Results of the 2007 survey were made public while results of the 2008 survey are still being processed. Over 2,500 observations were submitted. Of this total, 2,061 were deemed actual sightings of either the three-toed box turtle or ornate box turtle. Ninety-five percent of the sightings were of live turtles with dead ones accounting for the remaining five percent. Roadways played an important role in the survey. Over half of the live turtles were observed along roadways while 92 percent of the dead turtles had been crushed along roadways. One noticeable problem with the data is that the majority of the sightings came from the populated Little Rock area. In the rural areas there is noticeable lack of data or sightings. Research has found that both the male and female box turtle have a high degree of site fidelity. Home territory can vary in size, depending on numerous factors but varies between three to 100 acres. A study of box turtles at the Jug Bay Wetland Sanctuary in Maryland found that male box turtles had a mean range of 1.2 ha while females had a higher range of 6.2 ha. The larger range in the female territory can be attributed in large part to a search for suitable nesting habitat in the spring. Research has found that the box turtle population is in a serious state of decline. Several factors have contributed to this decline. Loss/fragmentation of habitat has been listed as one of the primary reasons for the decline. However many researchers have listed roadways as the primary reason for the decline. Female box turtles do not reach sexual maturity until they are approximately 13 years old. Research has suggested that female turtles may be more prone to being killed on roads than males due the search for nesting habitat. Results of long-term research indicate that as little as a 2-3 percent annual mortality is more than most turtle species can survive and still maintain positive population growth. Faculty at the State University of New York developed a model that indicates that excessive mortality (greater than 5 percent of individuals) already occurs among land turtles in many regions of the country including Arkansas. In summation, it is recognized that the box turtle population is in a serious decline with roadways being identified as a primary reason. The question arises as to what impacts construction of I-69 across southern Arkansas will have on the current population. To illustrate the lack of information on this issue, the consultants on one of the Environmental Impact Statements (EIS) covering this project in Arkansas was asked a page and half of questions about the potential impacts. Their only reply was “Comments noted”.
Urgency and Payoff
As previously noted three EIS’s were prepared to address the I-69 project in Arkansas. Two have been approved while the third is nearing completion. Only a preferred alignment has been chosen at this time and no roadway design work has been initiated. However, improvements in the nation’s infra-structure have been at the forefront of the government’s economic stimulus movement. Such projects as this can be put on the fast track. This is why such a survey could be beneficial at this time. First is to determine what the population density is in the preferred corridor. This is very important since research has shown that box turtle have a small territorial range. If there is a significant population in the area, fragmentation with the construction of the interstate highway could have serious consequences on the population. In the fall of 2007 researchers removed over 200 turtles from the area where the Inter-county Connector (ICC), an 18.8 mile, six-lane highway that will connect 1-270 and U.S. 1 in Montgomery & Prince George’s counties north of Washington, D.C. will be constructed. There is another important reason to identify the population density along the corridor at this time. Research at the Jug Bay Wetland Sanctuary found that research plots adjacent to wetlands supported significantly more box turtle. These plots have a higher density than plots several hundred meters away from the wetlands. Research has found that the proximity of water and wetlands appear to be important on a local scale for determining turtle habitat selection and home range. Location of potential high density and populations and suitable habitat would be useful to incorporate during the roadway design phase. This is the time when such ideas as passage ways underneath the roadway, changes in the specifications for the type of fencing along the highway, or changes in barrier walls need to be incorporated. Such changes are difficult and usually very expensive to incorporate once a highway project is designed or under construction. Any opportunity to determine if such measures are truly needed and where and how to best implement them would be greatly enhanced by the availability of sound data. The opportunity exists here to possibly help to reduce the decline in the population of a species that everyone is familiar with. This opportunity should be investigated in the other states that the I-69 corridor crosses as well to determine what can be done to mitigate the impacts of road construction on species such as the three-toed box turtle.
Henry W. Langston and Sherry LeBlanc, Arkansas Highway & Transportation Department, Environmental Department