A Radiotelemetric Study of Activity and Movements of the Blanding's Turtle (Emydoidea blandingi) in Northeastern Illinois

Abstract

-Seasonal and daily activity of a population of Blanding's turtle (Emydoidea blandingi) inhabiting a marsh-fen ecosystem in northeastern Illinois were investigated by capture-recapture and radiotelemetric techniques. Turtles emerged from dormancy by late March and were observed active at water temperatures of 10 C and feeding at 14 C. Trapping success peaked in June at water temperatures of 18-29 C, then declined in July when water temperatures exceeded 30 C. Nesting occurred in late May and June. Turtles entered winter dormancy between 19 October and 22 November. Emydoidea were primarily aquatic in this study. Terrestrial activity occurred chiefly in the spring, including brief daily sojourns from a single pond, long and short treks between ponds, and long distance treks by females for nesting. Activity centers of individuals were relatively uniform, seldom exceeding two hectares, and were occasionally interrupted by sojourns of both long and short duration. Emydoidea were active diurnally between 0530 and 2230 h. Trapping data suggested a bimodal feeding pattern with peaks in the morning and evening, although telemetry information indicated greater morning activity. For all months combined, females were equally active throughout the day while males were active more in the morning than in afternoon or evening. Daily aquatic movements within activity centers ranged from 1 to 230 m/day and males moved significantly greater distances per day than females. The Blanding's turtle (Emydoidea blandingi) is widely distributed in eastern and central United States and Canada and is found in ponds, lakes and marshy habitats (Ernst and Barbour, 1989). Within the past two decades, several comprehensive studies have been made on the ecology of this turtle (Gibbons, 1967; Graham and Doyle, 1977; Congdon et al., 1983; Kofron and Schreiber, 1985; Ross and Anderson, 1990); however, daily and seasonal patterns of activity and movement are not well documented. Congdon et al. (1983) described movements associated with reproduction in females, and Ross and Anderson (1990) examined movements associated with seasonal activity and habitat use, and estimated minimum daily movements in a Wisconsin population. Thorough documentation of seasonal activity and movements of other turtle species are rare (Sexton, 1959; Moll and Legler, 1971; Plummer and Shirer, 1975; Obbard and Brooks, 1981; Morreale et al., 1984; Pluto and Bellis, 1988), and detailed information on daily activity or movements are even fewer (Moll and Legler, 1971; Ernst, 1971, 1986; Obbard and Brooks, 1981). Daily and seasonal activity and movement information can be important when asking ' Present Address: School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68858-0118, USA. questions about total energy budgets. In reptiles, energy acquisition can be limited by absolute resource availability, as well as by maximum harvest and process rates of individuals (Congdon, 1989). Harvest rates can be influnced by time spent on activities other than resource acquisition (i.e., social and basking activities), and both harvest and process rates can be influenced by biophysical limitations (i.e., temperature and rainfall) imposed on a daily or seasonal basis (Congdon, 1989). Information on daily and seasonal activity and movements are essential in identifying potential constraints on energy acquisition. We studied a population of Blanding's turtles in northern Illinois to more precisely determine seasonal and daily patterns of activity and movement. MATERIALS AND METHODS Capture-recapture and radiotelemetric techniques were used from late March to November, 1986 at Chain of Lakes State Park in Lake and McHenry counties of northern Illinois. Daily activity investigation began 12 May and continued though 23 August. Information was gathered intermittently in the fall of 1986. Turtles were collected with baited hoopnets (Legler, 1960) and by hand. Hoopnets were checked four times daily (0600-0900, 0900-1300, 1300-1700 and 1700-2100 h), with air and water temperatures and weather conditions recorded at these times. Shell measurements were obThis content downloaded from 157.55.39.162 on Thu, 11 Aug 2016 05:26:51 UTC All use subject to http://about.jstor.org/terms ACTIVITY IN THE BLANDING'S TURTLE tained and all turtles were permanently marked by notching the marginal scutes using the code system of Cagle (1939). Sex was determined by the presence of a concave plastron and greater preanal tail length in males (Ernst and Barbour, 1972; Graham and Doyle, 1977). We placed single-stage radio transmitters (Custom Electronics, Urbana, Illinois) on 12 Emydoidea (6 males, 5 females, and 1 juvenile) at the onset of the study. Transmitters were enclosed in paraffin or beeswax, encased in dental acrylic (x = 26.2 g, N = 4) or Bondo? (x = 30.0 g, N = 4), and wired to the rear of the carapace. Turtles were released at the site of capture and radio-located at least four times per week and 0-49 times per day. All locations were plotted on large scale maps prepared from aerial photographs. Weather conditions, air and water temperatures were recorded at each relocation. The reproductive status of females was monitored periodically by palpating the inguinal pocket for shelled eggs. Range length and activity center size were calculated for individuals studied for at least two months of the summer. Ross and Anderson (1990) defined activity centers in Emydoidea as areas within a habitat type used by turtles for a minimum of five days. In this study, an individual's activity center was defined by the distribution of plotted radiolocations of its movements throughout the season. Activity centers were characterized by movements within a pond, marsh or portions thereof where discrete localizations of movements could be detected (clusters of dots). Maximal straight-line distances traveled per day were less than 100 m, and there were typically multiple core areas within an activity center. Movement patterns that lacked localization of movements such as brief sallies away from and movements between activity centers were considered transient. Activity centers were plotted using the minimum polygon method (Mohr, 1947), and their areas calculated using a compensating polar planimeter. Range length was calculated as the distance between the two most extreme points of location of an individual (Pluto and Bellis, 1988). Movements of females associated with nesting were not included in activity center and range length estimates. Daily activity was obtained by direct observation, trapping records and radiotelemetry. For convenience, the total daily activity period (ca. 18 h) was divided into three six hour blocks: 0600-1200; 1200-1800; and 1800-0000 h. Turtles with three or more radiolocations per day were tallied as active or inactive for each of the above periods and an individual's percent activity was calculated for each period for each month (active observations/total observations x 100). TABLE 1. Monthly trapping success and recorded pond temperatures for Blanding's turtles at the Fox River site, 1986.