Research Note Microhabitat Association of Blanding s Turtles in Natural and Constructed Wetlands in Southeastern New York TANESSA SUZAN HARTWIG, 1,2 Bard College Graduate School of Environmental Studies, Annandale-on-Hudson, NY 12504, USA ERIK KIVIAT, Hudsonia Ltd., P.O. Box 5000, Annandale-on-Hudson, NY 12504, USA ABSTRACT We studied Blanding s turtle (Emydoidea blandingii) microhabitat in natural s and s constructed for the turtles in Dutchess County, New York, USA. Investigation of these topics can provide information on ways to increase the extent of Blanding s turtle habitat, improve its quality, and assure that conservation or restoration managers do not overlook key habitat characteristics. Microhabitat was determined by radiotracking individuals to their exact locations and recording habitat variables. Blanding s turtles were associated with shallow water depths (x ¼ 30 cm), muck substrates, and areas of abundant vegetation (total cover x ¼ 87%). Buttonbush (Cephalanthus occidentalis) had the greatest mean total cover (29%). In the constructed s, Blanding s turtles were associated with significantly less cover and warmer water than in the natural s. Blanding s turtles appeared to be using the constructed s to bask and forage in the spring and early summer but moved to deeper s in late summer when the constructed s dried up or became too warm. For Blanding s turtles, new habitat should contain abundant emergent vegetation (including buttonbush in Dutchess County and other areas where the turtles are known to use buttonbush swamps), basking areas, muck, floating plant material, and submerged aquatic vegetation. Blanding s turtle s use of constructed s highlights the value of a complex of connected habitats in providing for the varied needs of the turtle. (JOURNAL OF WILDLIFE MANAGEMENT 71(2):576 582; 2007) DOI: 10.2193/2005-619 KEY WORDS conservation, Emydoidea blandingii, habitat restoration, mitigation, radiotelemetry, threatened species, s. Blanding s turtle (Emydoidea blandingii) is a threatened species in New York State, where it occurs only in Dutchess County (southeastern New York, USA), Saratoga County (one known population; east-central New York), the eastern Ontario Lake Plain (one known population), Cattaraugus County (western New York), and the St. Lawrence River valley (northern New York). The turtle s range centers on the Great Lakes in the United States and Canada (Ernst et al. 1994). Habitat loss is a major threat to the Blanding s turtle and is a key factor in population declines (Kofron and Schreiber 1985, Kiviat 1997, Piepgras and Lang 2000, Standing 2000). Researchers know little about microhabitat use by Blanding s turtles or their response to constructed s. Investigation of these topics can provide information on ways to increase the extent of Blanding s turtle habitat, improve its quality, and assure that conservation or restoration managers do not overlook key habitat characteristics. We investigated Blanding s turtle microhabitat association and the effects of a recent freshwater construction project on the turtles over 3 years. 1 E-mail: hartwig@bard.edu 2 Present address: Hudsonia Ltd., P.O. Box 5000, Annandale-on- Hudson, NY 12504, USA STUDY AREA The study site (Fig. 1) consisted of approximately 6 ha of natural s used as core habitat (regularly used s, particularly in the winter and early spring) by Blanding s turtles and 1.4 ha of constructed s built to compensate for a Blanding s turtle destroyed as part of a school-expansion project (Kiviat et al. 2004). The 3 natural s were shrub s dominated by buttonbush (Cephalanthus occidentalis). Maximum water levels varied from 1.0 m to 1.5 m and sediments were deep (x ¼ 0.7 m; max..1 m) and organic. The 3 constructed s contained trees (Acer rubrum, Fraxinus pennsylvanica, and Ulmus americana) and shrubs (Cornus amomum, Ilex verticillata, Rosa palustris, Vaccinium corymbosum, and Viburnum dentatum) salvaged from the filled, as well as planted buttonbush. Purple loosestrife (Lythrum salicaria) was very common in the constructed s. Maximum water depths in the constructed s were 1.0 m to 1.2 m, and sediments varied between a mineral substrate and pockets of shallow organic muck (x ¼ 0.2 m; max. ¼ 0.5 m) recovered from the original. Managers completed the constructed s in May 1997, which they designed to contain both core habitat for adult Blanding s turtles and shallow areas for juveniles. METHODS We hand-captured (May and June 2000 2002) or livetrapped (May 2000 2002) Blanding s turtles (hereafter, turtles) in hoop traps placed in open-water areas near shrubs or small trees in the site s constructed and natural s. We attached radiotransmitters (Advanced Telemetry Systems, Isanti, MN, and Sirtrack, Havelock North, New Zealand) to the rear third of the carapace using a fast-drying epoxy and released the turtles. We radiotracked turtles daily in May and June and less frequently afterward. For the microhabitat surveys, we radiotracked turtles to their exact location using a CE-12 receiver (Custom Electronics, Urbana, IL) in 2000 and an R-1000 receiver (Communications Specialists, Orange, CA) in 2001 and 2002 with a handheld Yagi antenna. Once we located the turtle, we surveyed microhabitat use by sampling a 3 3 3-m plot centered on the turtle. This plot 576 The Journal of Wildlife Management 71(2)
Figure 1. Blanding s turtle study area in the town of La Grange, Dutchess County, New York, USA, 2000 2002. Drawn by K. A. Schmidt. size made turtle-centered plots comparable to previously established random plots in the study area. We identified vegetation to the species level when possible. Scientific names of plants follow Gleason and Cronquist (1991). We visually estimated aerial cover of each plant species and we recorded the species nearest to the turtle. We also measured water depth to the nearest centimeter, recorded substrate type, estimated coarse woody debris (downed wood more than 10 cm diam 3 100 cm long) cover, and measured water temperature to the nearest degree Celsius (2001 and 2002 only). We categorized substrate type as muck (organic hydric soil), mud (mineral hydric soil), hummocks (usually sedge tussocks), mineral (non-hydric soil; sand or gravel), dead leaves, roots, logs, or needle spikerush (Eleocharis acicularis). We sampled turtle-centered plots in constructed and natural s from May to August in 2000, May to September in 2001, and April to October in 2002. To avoid duplication, we did not sample a plot if it overlapped with a plot previously sampled within a season. We also sampled random plots (3 3 3 m) each September in the constructed and natural s. We located the plots in a stratified random design based on an analysis of plant communities using aerial photography. We recorded coarse woody debris cover and vegetation composition and estimated aerial cover by species. Our plot sizes were comparable to those used to sample vegetation (Dunn and Sharitz 1987) and turtle microhabitat (Carter et al. 1999) in other studies. Turtle-centered plots did not duplicate random plots. We tested sex differences in use of constructed and natural s with a v 2 test. We used Spearman rank correlations to compare variables in turtle-centered plots with time of year (2002 data only). We compared differences in mean microhabitat attributes of turtle-centered plots in constructed and natural s using Student s t- tests with separate variance estimates and a Bonferroniadjusted significance level of a ¼ 0.003. We also compared random plots in constructed and natural s using t- tests with separate variance estimates and the same adjusted significance level. We examined whether microhabitat use differed within natural versus constructed s. Because we surveyed turtle-centered plots and random plots at different times of the year, we could not directly compare the variables with t- tests. Instead, we computed bootstrapped 90% confidence intervals on the differences in turtle-centered plots between natural and constructed s. We did the same for the differences in the random plots from natural and constructed s for each variable. When the bootstrapped confidence intervals for the differences between natural and constructed s for the turtle-centered versus random plots did not overlap, we considered this evidence of significant differences in turtle association with habitat in the 2 types of s and not a reflection of background habitat differences between constructed and natural s. We performed bootstrapping using Systat (version 9 [1998]; SPSS Corp., Chicago, IL). We performed all other statistical analyses using Statistica (version 6 [2003]; Statsoft, Inc., Tulsa, OK). To determine whether the turtles were associated with the vegetation structure of the microhabitat, we combined species into 8 categories: 1) total plant cover (percent cover of vascular plants, bryophytes, and visible algae); 2) graminoids (grass-like species, especially grasses [Poaceae] and sedges [Cyperaceae]); 3) herbs (forbs and graminoids); 4) shrubs; 5) woody vegetation (trees, shrubs, and woody vines); 6) shrubs and purple loosestrife combined; 7) neuston (the floating layer of plant material, including dead material and algae, on the water s surface); and 8) submerged aquatic Hartwig and Kiviat Microhabitat Use by Blanding s Turtle 577
Table 1. Results of t-tests comparing natural and constructed habitats for Blanding s turtle-centered plots and random plots in 2002, Dutchess County, New York, USA. Natural plots Constructed plots Plot type Variable x SD Min. Max. x SD Min. Max. t 2-sided P a Turtle-centered plots b Total cover (%) 90 34 9 196 54 37 5 141 4.79,0.001 Shrub cover (%) 47 34 0 98 11 21 0 96 6.55,0.001 BB c cover (%) 45 35 0 98 3 6 0 25 9.76,0.001 Non-BB c shrub cover (%) 1 8 0 65 8 21 0 96 1.81 0.079 Neuston cover (%) 6 10 0 51 1 4 0 20 3.60 0.001 Woody cover (%) 48 34 0 102 12 23 0 115 6.28,0.001 Non-BB c woody cover (%) 3 11 0 78 9 23 0 115 1.64 0.109 Shrub-loosestrife cover (%) 49 33 0 98 19 23 0 100 5.39,0.001 Water temp (8C) 20 4 8 27 24 4 14 30 3.76,0.001 Water depth (cm) 26 17 0 100 27 18 0 90 0.23 0.820 Random plots d Shrub cover (%) 47 45 0 133 20 26 0 87 2.35 0.025 BB c cover (%) 35 40 0 99 6 15 0 50 3.32 0.002 Graminoid cover (%) 21 33 0 111 7 6 2 23 2.21 0.035 Water depth (cm) 10 14 0 51 1 2 0 4 3.32 0.002 a Significant results (P, 0.003) are in bold. b We surveyed turtle-centered plots during the active season (May Oct). Natural habitats n ¼ 67, constructed habitats n ¼ 35, except for water temperature: natural habitats n ¼ 60 and constructed habitats n ¼ 29. c BB ¼ buttonbush. d We surveyed random plots in Sep. Natural habitats n ¼ 28, constructed habitats n ¼ 12. vegetation. We combined shrub and purple loosestrife cover to facilitate testing of the hypothesis that loosestrife was acting as a surrogate for buttonbush in the constructed s. We also separately analyzed buttonbush, purple loosestrife, floating filamentous algae, water celery (Vallisneria americana), and floating crystalwort (Riccia fluitans) because examination of nearest species and means of percent cover, and comparison of constructed and natural turtlecentered plots indicated possible microhabitat association of the turtles with these taxa. RESULTS We tracked 21 turtles over the 3 years. We studied 12 turtles (1 subadult, 8 F, 3 M) in 2000, 14 (2 subadults, 9 F, 3 M) in 2001, and 17 (1 subadult, 8 F, 8 M) in 2002. We followed 7 of the females and 2 of the males throughout all 3 years. We sampled 49 turtle-centered plots in 2000 (4 subadult plots, 39 F plots, 6 M plots), 72 in 2001 (11 subadult plots, 43 F plots, 18 M plots), and 102 in 2002 (11 subadult plots, 56 F plots, 35 M plots). We emphasized our 2002 results given the large number of plots and individual turtles sampled during that year. We found 88 plant taxa in turtle-centered plots. Buttonbush was the dominant species, with a mean cover of 29% (SE ¼ 2.3). Other individual taxa, which included arrowwood (Viburnum dentatum), dogwoods (Cornus spp.), highbush blueberry (Vaccinium corymbosum), meadowsweet (Spirea latifolia), swamp rose (Rosa palustris), willows (Salix spp.), winterberry (Ilex verticillata), several tree species, and many herb species, represented,9% of the mean cover each. Throughout the study, turtles in the constructed s were associated with lower levels of total plant cover, shrub cover, and buttonbush cover than turtles in the natural s (Table 1). Shrub cover was not significantly different in constructed and natural turtle-centered plots when we excluded buttonbush cover from this cover type (a ¼ 0.003; Table 1). Turtles used areas of similar depth in the natural (x ¼ 26 cm) and constructed (x ¼ 27 cm) s throughout the study (Table 1). Water depth where the turtles occurred reflected seasonal and annual hydrological trends in the s. Water temperature was 48 C higher in constructed s than in natural s during late June early August 2002 in turtle-centered plots, and it exhibited seasonal patterns (Fig. 2a; Table 1). Muck was the most common substrate type in turtlecentered plots in the natural and constructed s. In the natural s, 77% (112 of 146) of observations were in muck, whereas 49% (37 of 76) of observations were in muck in constructed s. In August and September, we often found turtles in the natural s buried in 2 10 cm of muck, whereas we found only one turtle buried in muck in the constructed s. We found turtles in the natural s most often near buttonbush (38% of observations) or crystalwort (10% of observations; n ¼ 147). We found turtles in the constructed s most often near purple loosestrife (51% of observations) or water celery (10% of observations; n ¼ 72). We often found turtles in areas of abundant vegetation cover; in turtle-centered plots, the average total cover of plants in all s was 87%. Habitat association of females and males differed at the complex scale, but we did not observe a consistent difference at the microhabitat scale. Females were more likely than males to use constructed s in 2001 and 2002 (2001: v 2 ¼ 15.13, df ¼ 1, P 0.001; 2002: v 2 ¼ 88.14, df ¼ 1, P 0.001; Table 2). We found significant Spearman rank correlations (a ¼ 0.05) between certain habitat variables and date, although scatterplots did not indicate temporal trends in those 578 The Journal of Wildlife Management 71(2)
Figure 2. Scatterplots of habitat variables in turtle-centered plots versus Julian date for Blanding s turtles in Dutchess County, New York, USA, 2001 2002. Each dot represents a radiolocation of a single turtle. Open dots represent turtles in constructed s; closed dots represent turtles in natural s. The y-axis represents (a) degrees Celsius, and (b g) percent cover of vegetation. variables. We also found seasonal peaks in association with some variables (Fig. 2). Turtle association with submerged vegetation peaked in late July and August in 2001 and 2002 (Fig. 2b, c). In the constructed s, most submerged Table 2. Telemetry observations of female and male Blanding s turtles in constructed and natural s in Dutchess County, New York, USA, 2000 2002. Yr Wetland type No. of observations F M F:M 2000 Both 467 100 4.7:1 Natural 297 68 4.4:1 Constructed 170 32 5.3:1 2001 Both 633 330 1.9:1 Natural 479 285 1.7:1 Constructed 154 45 3.4:1 2002 Both 727 524 1.4:1 Natural 490 472 1.0:1 Constructed 237 52 4.6:1 Total turtle observations natural (2000 2002) 2,091 Total turtle observations constructed (2000 2002) 690 vegetation was water celery (Fig. 2d), whereas in the natural s, most submerged vegetation was filamentous algae (Fig. 2e). Graminoid cover did not differ significantly between the constructed and natural s (a ¼ 0.003; Table 1). Graminoids were primarily spike-rush and grasses in turtlecentered plots in the natural s. Turtle locations in graminoids peaked during the summer (Fig. 2f, g). We observed diel patterns of association between turtles and neuston, in particular crystalwort, during 1130 1600 hours (Eastern Daylight Time), whereas coarse woody debris use peaked at 1100 hours and decreased to zero by 1650 hours. This pattern occurred throughout the season but was not as apparent in August and September. In the natural s, turtles were positively associated with algal and buttonbush cover, negatively associated with total plant and herb cover, and showed no trend in association with purple loosestrife, shrub loosestrife, or shrub cover (Table 3). In the constructed s, turtles were positively associated with water celery, negatively Hartwig and Kiviat Microhabitat Use by Blanding s Turtle 579
Table 3. Bootstrapped confidence intervals on the differences in means for selected variables in 2002 for constructed and natural Blanding s turtle sin Dutchess County, New York, USA. Variable Plot type Natural x Constructed Natural x constructed x Lower CI Upper Natural Association a Constructed Total cover Random 107 117 10 35 19 Negative Negative Turtle centered 90 54 36 25 50 Herb cover Random 15 65 50 54 33 Negative Negative Turtle centered 7 16 9 14 3 Shrub-loosestrife cover Random 48 53 5 28 15 Neutral Negative Turtle centered 49 19 30 21 40 Algae cover Random 0 0 0 0 1 Positive Positive Turtle centered 13 4 9 4 14 Purple loosestrife cover Random 2 33 31 40 21 Neutral Negative Turtle centered 2 8 6 8 2 Water celery cover Random 0 0 0 0 0 Neutral Positive Turtle centered 0 12 12 19 5 Buttonbush cover b Random 35 6 29 12 38 Positive Negative Turtle centered 45 3 42 35 50 Shrub cover Random 47 20 27 5 42 Neutral Neutral Turtle centered 47 11 36 26 44 a These columns are our interpretation of turtle association (positive, negative, or neutral) with each variable in natural and constructed s. b Buttonbush confidence intervals overlapped slightly. associated with herb, total, and purple loosestrife cover, and showed no trend in association with shrub cover (Table 3). DISCUSSION Our data indicated that, during the active season, Blanding s turtle microhabitat at our study site consisted of muck substrates, water depths of 1 110 cm, and dense buttonbush, submerged vegetation, or neuston. The turtles also favored shallow, warm water with abundant aquatic vegetation and nearby cover. In addition, we discovered that Blanding s turtles responded to the constructed s in part by using them to bask particularly during the spring and early summer and to rehydrate or rest during nesting movements. Kiviat et al. (2004) previously found that Blanding s turtles at this site were associated with buttonbush. Blanding s turtles in the Northeast may prefer buttonbush to other shrubs because its late leaf-out provides protected basking areas in the early spring, and its dense, low cover provides shade and shelter in the summer. Other shrubs in these s leaf out earlier and are more widely spaced. Buttonbush can survive with its roots and stems submerged, in contrast to other shrubs that grow on elevated substrates or where the hydroperiod is shorter. In other parts of their range, Blanding s turtles were mostly associated with dense herbaceous, rather than shrubby, vegetation (Piepgras et al. 1998, Barlow 1999). Thermoregulation dynamics may make shrub s preferable to herbaceous s in areas of the turtles range that experience cooler springs or less sunshine (Hartwig 2004). Blanding s turtles in New York appeared to shift their preference from buttonbush to graminoids in late summer. As water levels decreased in the shallower shrub areas, turtles probably moved to the deeper emergent areas to take advantage of cooler water. Blanding s turtles may be associated with filamentous algae and other submerged vegetation because they provide food, a warmer microclimate, or cover from predators. Submerged vegetation and filamentous algae are known to harbor high densities of macroinvertebrates (Elwood et al. 1981, Evans et al. 1999, Yozzo and Diaz 1999), which are a primary food for Blanding s turtles (Lagler 1943, Rowe 1992, Blanding s Turtle Recovery Team 2003). We often found turtles in natural s in beds of algae at the edge of buttonbush patches. In constructed s, turtles often used water celery beds near large pieces of coarse woody debris (T. Hartwig, Hudsonia Ltd., personal observation). These edge areas appeared to provide cover adjacent to basking areas and food. Blanding s turtles in Dutchess County basked on logs in early morning and in neuston by late morning as the sun warmed the water surface; turtles in Minnesota, USA, exhibited a similar pattern (Sajwaj and Lang 2000). Neuston, primarily crystalwort and duckweed (Lemna minor; Kiviat et al. 2004) at our site, may provide camouflage for Blanding s turtles, similar to the camouflage provided by duckweeds alone (Lemnaceae; Ross and Lovich 1992). In addition, duckweeds are an important habitat for macroinvertebrates (Gaston 1999); crystalwort may also host macroinvertebrates. While in neuston, Blanding s turtles may conserve energy by simultaneously basking and foraging (E. Kiviat, Hudsonia Ltd., personal observation). Blanding s turtles were apparently using the new s for basking in the spring and early summer; they were associated with less vegetation cover and warmer water in constructed s at that time. Constructed s provided good basking habitat due to shallower water, less tree cover, and abundant basking logs compared to the natural s. In addition, females moved into constructed s before and after nesting, and we found them in these s more often than males. Many nest 580 The Journal of Wildlife Management 71(2)
sites were near (approx. 10 m) constructed s, and we frequently observed females basking in the spring. Spring basking may facilitate egg development before nesting (Standing et al. 1999, Blanding s Turtle Recovery Team 2003). However, there was no difference in spring basking behavior of females and males in Minnesota, although females basked more than males in the fall, when egg production may also occur (Sajwaj and Lang 2000). Purple loosestrife may provide shrub-like habitat structure similar to buttonbush because loosestrife has robust stems that persist through winter, and both plants develop late in the growing season. We often observed turtles beneath fallen-over purple loosestrife stems (see also Kiviat et al. 2004). As loosestrife becomes dominant in a, however, it often becomes very dense. Turtles may not be able to maneuver in dense stands of loosestrife, or they may prefer more open areas for thermoregulation purposes and consequently avoided loosestrife stands in the constructed s. Loosestrife was less dense in the natural s, and turtles did not appear to avoid it. The constructed s were 3 years old when this study began, and they are rapidly changing. It will require many more years of monitoring to determine their long-term value to this population of Blanding s turtles. MANAGEMENT IMPLICATIONS Wetland management for Blanding s turtles should include enhancing emergent and submerged vegetation, edge habitat between emergent vegetation and open water, basking areas, and deep muck substrates (70 cm). Although purple loosestrife control where loosestrife has become dense might benefit Blanding s turtles, managers should not disturb submerged vegetation. Movement of turtles into constructed s to bask underscores not only the value of providing basking substrates for the turtles, but also the importance of a complex of connected habitats to provide a variety of resources to meet the turtles needs. Blanding s turtles use a diversity of s in habitat complexes rather than single isolated s ( Joyal et al. 2001, Hartwig 2004), and new s, even if they do not function as core habitat, can increase the capacity of the landscape to support Blanding s turtles by augmenting and diversifying available resources. Wetland restoration and construction may be particularly useful in suburban areas, where increased availability of resources near core s may decrease the turtles need to travel long distances (see also Piepgras and Lang 2000, Hamernick 2001) and hence their exposure to human-related hazards such as roads and developments. ACKNOWLEDGMENTS We are grateful to many individuals for field assistance, editing, and data management, especially H. K. Bock, D. Goodfriend, J. Hazard, and K. Munger. AmeriCorps; Arlington Central School District; Guinness Water of Life; Geoffrey Hughes Foundation; New York State Office of Parks, Recreation, and Historic Preservation; the Society for Ecological Restoration Project Facilitation Award; United States Environmental Protection Agency (grant CD992776-01-0 to New York State Office of Parks, Recreation, and Historic Preservation); and individual donors funded our work. All opinions and conclusions are those of the authors. This paper is part of the senior author s thesis for the Master of Science in Environmental Studies degree at Bard College. We thank C. D. Canham, J. W. Lang, and K. L. Standing for sitting on the thesis committee and providing editorial review. We are especially grateful to C. D. Canham for extensive assistance with statistical procedures. This is Bard College Field Station Hudsonia Contribution 95. LITERATURE CITED Barlow, C. E. 1999. 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