Northern Diamondback Terrapin Occurrence, Movement, and Nesting Activity Along a Salt Marsh Access Road
ABSTRACT
Northern diamondback terrapins, Malaclemys terrapin terrapin, were tagged with passive integrated transponder tags to mark them and monitor their activity along a road through salt marsh habitat in Tuckerton, New Jersey. A mark-recapture study was conducted to evaluate terrapin movements, nesting frequency, and nest site fidelity. During sampling periods throughout 2 nesting seasons (2004–2005), 300 adult females were tagged. Ninety-two recaptures were made of 54 individual terrapins, with most recaptures (81.5%) occurring within a season (range = 1–45 days, mean = 7.5 days). Some recaptures (18.5%) occurred the following year. Some females crossed the road multiple times during nesting, and nearly half searched for a site within 50 m of the area where they were initially tagged. Nest site selections of all multiple nesters (within and among seasons) varied greatly from approximately 4–1307 m (mean internesting distance = 202.75 m), yet 39% were recaptured within 50 m of their initial tagging location. One-third of yearly nesters showed an internesting distance within 25 m of their initial-year tagging location. These results indicate that some females travel variable distances between nest sites and may demonstrate evidence of nest site fidelity.
As aquatic and upland habitats are developed, modified, or fragmented by human activities (e.g., roads), reproduction of turtles may be increasingly affected as they need to make movements of variable distances overland to find suitable nesting habitat, which may be natural or altered by humans. Nesting females may be attracted to human disturbed sites where little vegetation is present and the ground is open to direct sunlight. These sites can be near houses and fences (Kolbe and Janzen 2002), human-made trails (Feinberg and Burke 2003), edges of power-line rights of way and forest clearcuts (Litzgus and Mousseau 2004), and mowed shoulders of roads (Aresco 2005). Turtles cross roads in agricultural (Reese and Welsh 1997) and residential (Steen and Gibbs 2004) areas and nest along roads near wetland and beach habitat (Seigel 1980a; Wood and Herlands 1997; Standing et al. 1999; Haxton 2000; Joyal et al. 2001; Hoden and Able 2003; Rowe et al. 2005; Szerlag and McRobert 2006). Some aquatic turtles travel great distances through terrestrial landscapes and across roads to nest in fragmented nesting habitat when suitable habitat is limited (Baldwin et al. 2004). Many aquatic turtles, including diamondback terrapins, prefer to nest in areas of sandier soils, little vegetation, and higher elevation (Burger and Montevecchi 1975; Butler et al. 2004). Because marsh roadsides may provide the habitat conditions that are suitable for nesting, substantial turtle mortality also results from vehicular traffic (Wood and Herlands 1997; Hoden and Able 2003; Szerlag and McRobert 2006).
In the family Emydidae, distance traveled during nesting events has been documented for numerous species. Spotted turtles (Clemmys guttata) have been observed to travel an average of 247 m (range, 70–570 m) and Blanding's turtles (Emydoidea blandingii) an average of 633 m (range, 100-1620 m) to nest (Joyal et al. 2001). Standing et al. (1999) tracked one Blanding's turtle for approximately 3 km en route to her nesting site. Painted turtles (Chrysemys picta marginata) have been observed traveling up to 435 m to a nest site from water and up to 758 m between nest sites (Rowe et al. 2005). Western pond turtles (Actinemys marmorata) have been observed nesting up to 400 m from water (Holland 1991, 1994; Rathbun et al. 1992; Reese and Welsh 1997).
Diamondback terrapins appear to exhibit site fidelity and travel short distances to their nest sites. Terrapins have been recaptured numerous times over several years within a 100-m section of the same creek (Gibbons et al. 2001). Roosenburg (1994) found that most nesting routes were < 10 m and that < 1% of terrapins moved great distances of approximately 200 m. Burger and Montevecchi (1975) also found short nesting routes of < 100 m. Cook (1989) suggested females may nest within 200 yards of water, while Feinberg and Burke (2003) found nesting areas of terrapins a maximum of 250 m from water.
Long-distance movements by terrapins have been reported as limited (Gibbons et al. 2001), but they observed 1 female that completed a round-trip distance of 5.5 km after leaving her home range, nesting on a dune, and then returning. Butler (2002) found some tagged terrapins returned to specific creek areas ∼ 5–10 km from their nesting sites, and Hurd et al. (1979) observed 1 female that traveled approximately 8 km to nest.
Despite nesting movements that have already been documented for terrapins, little attention has been directed to the extent of habitat females may utilize along roadsides and how distances may vary between nests. Therefore, this study focused on habitat use, movement, nesting activity, and mortality along a salt marsh road.
Methods
Fieldwork was conducted along Great Bay Boulevard in Tuckerton, New Jersey. The site is a relatively pristine salt marsh of the 2168-ha peninsula of Great Bay Wildlife Management Area. Great Bay Boulevard is an 8.1-km paved along the centerline of the marsh (Fig. 1). Five bridges cross over subtidal creeks.
Citation: Chelonian Conservation and Biology 6, 2; 10.2744/1071-8443(2007)6[295:NDTOMA]2.0.CO;2
Surveys of Great Bay Boulevard were conducted during the terrapin nesting seasons of 2004 and 2005. Roadside sampling began when terrapins were first sighted (late May–early June) and lasted until the last terrapin was encountered (end of July). Adults were generally absent from the road all other times of the year (Hoden and Able 2003). Eight to 10 daily surveys were completed 5–6 days per week by car or bicycle. Surveys were typically conducted between 0800 and 1700 hours. An additional 12 surveys were conducted after dark between 2100 and 2400 hours each season. Parameters recorded for each encounter included date, location found (GPS coordinate), and whether the individual was alive, dead, or tagged for each encounter.
In this study, if a recapture was recorded after 17+ days during the same nesting season or during the following year, it was considered a “long-term” recapture and a multiple nester. Multiple nesters within a nesting season were based on previous studies finding an approximate 17-day internesting interval for terrapins (Klemens 1993; Feinberg and Burke 2003).
Three hundred adult female terrapins (100 in 2004 and 200 in 2005) were tagged during the first week(s) of nesting using passive integrated transponder (PIT) tags (12 × 2.1 mm, Biomark Inc., Boise, ID). Tagging methods followed Buhlmann and Tuberville (1998) and adhered to field standards developed by the American Society of Ichthyologists and Herpetologists (2004).
Tags were inserted under the skin in soft tissue just caudal and medial to the bridge, pointed in the direction of the head, anterior to the right hind limb. The skin was cleansed with 70% isopropyl alcohol and the tip of the injector swabbed with an antibiotic ointment with an analgesic, praxomine hydrochloride (Johnson & Johnson Consumer Companies Inc., New Brunswick, NJ). Liquid bandage tissue adhesive (Prestige Brands, Inc., Irvington, NY) was applied after injection. The animal was checked for adverse reactions or discharges from the injection site and then scanned with a PIT-tag pocket reader (Biomark) to verify the tag number. Terrapins were released back in the marsh in the same direction they were traveling when captured.
Straight-line internesting distances and distance between road crossings were determined using the GPS positions obtained for each terrapin location using ArcView GIS (v. 3.3; ESRI, Redlands, CA). Data were projected using ArcView to Universal Transverse Mercator units in meters to allow calculation of these distances.
Results
A total of 299 surveys were conducted from May to July 2004 and 272 surveys from May to July 2005. We tagged 300 adult female terrapins; 54 (18%) were recaptured a total of 92 times. We found no visible evidence of infection from the injected PIT tags.
During the 2004 nesting season, we documented 25 recaptures of 16 females, and in 2005 there were 50 recaptures of 38 individuals (Table 1). Additionally, 17 recaptures of 15 individuals from the 2004 tagged group were recorded in 2005 (Tables 1 and 2). We observed 2 tagged terrapin mortalities by automobiles, one in each year.
Time between recaptures varied, ranging from the same day of tagging to up to 45 days later within a season (mean = 7.5 days) (Fig. 2). Two modes were observed in the recapture intervals: one mode occurring within 0–9 days and another mode within 13–45 days. “Long-term” recaptures (probable multiple nesters 17+ days after initial tagging in a season or the following year) were observed within and among seasons (Tables 1 and 2).
Citation: Chelonian Conservation and Biology 6, 2; 10.2744/1071-8443(2007)6[295:NDTOMA]2.0.CO;2
Terrapins were recaptured crossing the road multiple times each season while searching for suitable nest sites. Distances between road crossings (excluding “long-term” seasonal recaptures) ranged from 4 to 934 m, with a mean of 140.2 m, but 47.3% of terrapins continued to search for a suitable nest site within 50 m of their initial tagging location.
Terrapins that probably nested more than once within a season ("long-term” recaptures, n = 15; 6 in 2004 and 9 in 2005) had a mean internesting distance of 171.8 m with a range of 4–916 m. Of these, 6 (40%) were recaptured nesting within 50 m of their original nesting site.
We found a mean internesting distance of 239.3 m (range = 6.8–1307.4 m) for 15 terrapins that were tagged in 2004 and recaptured nesting in 2005. Of these, 6 (40%) were recaptured within 50 m of their original nesting site, and of those, 5 (33%) were within 25 m of their original nesting site.
When combining all multiple nesting terrapins, we found similar results, a mean internesting distance of 202.8 m (range = 4.0–1307.4 m) (Fig. 3). These included 31 total recaptures (6 in 2004 and 9 in 2005 that nested more than once in their respective seasons, 15 [tagged in 2004] that were recaptured nesting once the following year [2005], and 1 [tagged in 2004] that was recaptured nesting at least twice the following year [2005]). Of these 31 recaptures, 12 (38.7%) were recaptured nesting within 50 m of their original nesting site (Fig. 3).
Citation: Chelonian Conservation and Biology 6, 2; 10.2744/1071-8443(2007)6[295:NDTOMA]2.0.CO;2
Discussion
Collecting data from tagged animals can lead to a better understanding of general movement and migration patterns, reproductive strategies, population sizes, specific use of habitat, and individual behavior (Balazs 1999). Such information is critical to understanding life-history strategies and conserving terrapin populations. In this study, PIT tags proved to be a reliable method of tagging and identifying individual terrapins.
Our study revealed information on distances and time intervals between recaptures of terrapins crossing the road in search of initial nest sites and multiple nesting terrapins within a season and the following year. “Long-term” within-season recaptures were found 17 or more days after initial tagging and likely represented second nestings (Seigel 1980b; Butler 2002). Feinberg and Burke (2003) also tagged adult females and confirmed individuals nesting for a second time in a season.
Terrapins may search multiple areas before selecting a nest site, similar to Blanding's turtles that arrive at nesting beaches and adjacent roadways several days prior to nesting and make numerous attempts before effectively completing one (Standing et al. 1999). Western pond turtles also make multiple exploratory nesting excursions on land ranging from 2 to 11 trips (Reese and Welsh 1997). Burger (1977) observed terrapins digging up to 10 different nests before selecting the final one. In our study, several individuals were also captured multiple times in relatively short periods of time. Terrapins were observed crossing the road during the same day, the following day, and up to 9 days after tagging, possibly still searching for a suitable nesting site. Nearly 50% of these terrapins searched within 50 m along the roadside for a nest site, while a few traveled well over 300 m.
Turtles returning to nesting sites may be displaying nest site fidelity nest or site philopatry (Roosenburg 1994; Gibbons et al. 2001; Rowe et al. 2005). In our study, terrapins used the same nesting area repeatedly (site fidelity) and are either faithful or restricted to certain nesting sites. Nest fidelity has previously been observed in terrapins, but distances between nest sites have not been reported. Burger (1977) found some terrapins returned to nest over several years on the same dune area (20 × 400-m transect) on Little Beach Island in southern New Jersey. Roosenburg (1991, 1994) documented females returning to the same nesting areas (∼ 0.5 acres) each time they laid a new clutch, across one or more seasons in Maryland. Similar results were also observed in New York (Feinberg and Burke 2003).
In our study, internesting distances of all “long-term” recaptured terrapins along the roadside revealed a variable distance range up to 1307 m, but nearly all (28 of 31 individuals) nested within 450 m of their initial tagging site. Three females moved great distances (> 900 m) between nest sites. Interestingly, many females (nearly 40%) returned to nest in the same general area along the roadside within 50 m of their initial tagging location. Between years, approximately a third nested within 25 m of their initial tagging site. The data collected suggest there may be some evidence of successive nesting near initial nesting sites (site fidelity) along roadsides for some individuals.
These results are similar to what has been observed in other Emydidae. Multiple nesting Blanding's turtles have shown high site fidelity among years, with 73% returning to the same nesting areas (Standing et al. 1999). A painted turtle study reported an average internesting distance of 88.7 m (n = 51; range 5–310 m) among consecutive years and an average of 106.2 m (n = 22; range 6–500 m) within a season (Rowe et al. 2005). The same study considered an internesting distance within 50 m, as some evidence of nest site fidelity and many individuals (∼ 30%) nested within 25 m of the previous year (Rowe et al. 2005). Further studies should be conducted from year to year to confirm if terrapins display nest site fidelity within a certain distance of previous nesting sites.
The results from our study provide some insight for management strategies in this and other areas where terrapins cross roadways. Terrapins making multiple road crossings and repeated nesting efforts are exposed to high risk from vehicular mortality, even though we recorded only 2 of 104 female terrapins killed over the 2 nesting seasons. Fencing along roads has been used to help reduce mortalities of some turtles (Aresco 2005). By identifying nesting sites and heavily used road crossing areas (nesting and road mortality “hot spots"), certain portions of wetlands that are intersected by roads may need more protection than others.
Map of the study site, Great Bay Boulevard within the Great Bay Wildlife Management Area of the Jacques Cousteau National Estuarine Research Reserve in Tuckerton, New Jersey.
Number of terrapins recaptured after initial tagging (day 0) to next recapture day on Great Bay Boulevard.
Internesting distances of all multiple nesting terrapins (within and among seasons) on Great Bay Boulevard.
