HABITAT SELECTION OF BLANDING’S TURTLE (EMYDOIDEA BLANDINGII): A RANGE-WIDE REVIEW AND MICROHABITAT STUDY
A Thesis Submitted to the Faculty of the Graduate School of Environmental Studies
by Tanessa Suzan Hartwig
in Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE IN ENVIRONMENTAL STUDIES
Bard College Annandale-on-Hudson, New York
May 2004
BARD COLLEGE
GRADUATE SCHOOL OF ENVIRONMENTAL STUDIES
TANESSA SUZAN HARTWIG
______
We, the Thesis Committee for the above candidate for the Master’s Degree, hereby recommend acceptance of the thesis.
Erik Kiviat, Advisor Bard College ______
Charles D. Canham Institute of Ecosystem Studies ______
Jeffrey W. Lang University of North Dakota (Emeritus) ______
K. Lorraine Standing Environment Canada ______
The thesis is accepted by the College
______Michele Dominy Dean of the College
______Robert Martin Vice President for Academic Affairs and Dean of Graduate Studies
May 2004
ii
Abstract of the thesis
Habitat selection of Blanding’s turtle (Emydoidea blandingii):
a range-wide review and microhabitat study
by
Tanessa Suzan Hartwig
Master of Science in Environmental Studies
Graduate School of Environmental Studies
Bard College
May 2004
The Blanding’s turtle is rare throughout most of its range. Habitat loss is considered a key factor in population declines. To conserve a species, habitat selection at all levels of scale must be considered. Much is known about Blanding’s turtle habitat at the landscape scale; however, little is known about range-wide or microhabitat requirements. Therefore, this study consisted of an extensive literature review to determine range-wide habitat characteristics and a field study to determine microhabitat characteristics at a site in Dutchess County, New York.
I conducted a literature review of Blanding’s turtle habitat throughout its range to determine similarities and differences in habitats at the range-wide, landscape, and microhabitat scales. Throughout their range, Blanding’s turtles select wetland complexes with shallow (< 2.5 m) water depths, organic substrates, areas of open water, and abundant vegetation. Wetland complexes consist of deeper wetlands for overwintering or drought refuge and a variety of shallow wetlands for feeding and thermoregulation. In the
iii Great Lakes region Blanding’s turtles tend to use ponds with abundant vegetation or herbaceous wetlands while in the Northeast turtles often use shrub swamps. Nova Scotia turtles use bays and floodplain wetlands with a mix of herbaceous and shrubby vegetation. Juvenile turtles tend to use shallower areas than adult turtles - either in the same wetlands that adults use or different wetlands. Water quality and seasonal movements vary by site, although long distances (> 1000 m) are traveled for nesting and other reasons range-wide. Because Blanding’s turtles are very mobile and use a variety of wetlands during an individual’s lifetime, they are susceptible to loss of individual wetlands and landscape connectivity. Management recommendations include conservation of wetlands in groups, 1 km buffer zones around a Blanding’s turtle wetland complex, and corridors between complexes or known habitats beyond the 1 km zone.
I studied Blanding’s turtle microhabitat in wetlands constructed for the turtles and reference (pre-existing) wetlands to assess Blanding’s turtle microhabitat selection and the suitability of the constructed wetlands as habitat for the turtles. Microhabitat was determined by radio-tracking individuals to their exact location and recording habitat variables. Blanding’s turtles selected shallow water depths (x = 30 cm), muck substrates, and areas of abundant vegetation (total coverx = 87%). Buttonbush (Cephalanthus occidentalis) was most important, with mean cover 29%. In the constructed wetlands,
Blanding’s turtles selected significantly less cover and warmer water than they did in the reference wetlands. Blanding’s turtles appeared to be using the constructed wetlands to bask and forage in the spring and early summer, but they moved to deeper wetlands in late summer, when the constructed wetlands dried up or became too warm. The turtles also overwintered in the reference wetlands. Habitat constructed for Blanding’s turtles iv should contain abundant emergent vegetation (including buttonbush in Dutchess County
and other areas where the turtles are known to use buttonbush swamps), muck substrates,
deep pools and shallow water areas, floating plant material, and submerged aquatic
vegetation. Because the constructed wetlands do not provide core habitat for the turtles, destruction or damage to essential habitat for Blanding’s turtles should be avoided.
Construction of new habitat near essential habitat should, however, be considered, particularly where habitat has already been fragmented or destroyed. Many other wetland animals use multiple wetlands to fulfill their life history requirements and similar management considerations may apply.
v
EXPLANATION OF ALTERNATE THESIS FORMAT
This thesis follows Bard College’s alternate thesis format, in which the thesis is written as one or more articles to be submitted to scholarly journals. The thesis consists of two chapters: a literature review to determine range-wide habitat characteristics and a field study to determine microhabitat characteristics at a site in Dutchess County, New York. Each chapter will be submitted as a separate article to a scholarly journal. The literature review, “A Review of Habitat Use by Blanding’s Turtle (Emydoidea blandingii) and Implications for Management,” will be submitted to the journal Chelonian Conservation and Biology. The field study, “Microhabitat Selection by Blanding’s Turtles in Natural and Constructed Wetlands in Southeastern New York,” will be submitted to the Journal of Wildlife Management. Although the work is my own, both papers are co-authored with my advisor, Erik Kiviat.
vi TABLE OF CONTENTS
Abstract of the Thesis iii
Explanation of Alternate Format vi
Table of Contents vii
List of Tables viii
List of Figures ix
Literature Review: A Review of Habitat Use by Blanding’s Turtle 1 (Emydoidea blandingii) and Implications for Management Abstract 1 Introduction 2 Literature 4 Discussion 21 Conclusions 36 Acknowledgements 44 Literature Cited 45
Field Study: Microhabitat Selection by Blanding’s Turtles in 77 Constructed and Natural Wetlands in Southeastern New York Abstract 77 Introduction 78 Methods 82 Results 88 Discussion 93 Conservation and Management Implications 101 Acknowledgements 103 Literature Cited 104
vii LIST OF TABLES
Literature Review: A Review of Habitat Use by Blanding’s Turtle (Emydoidea blandingii) and Implications for Management Table 1. Blanding’s turtle status in states and provinces throughout its range 65 Table 2. Blanding’s turtle habitat use in the Great Lakes region 66 Table 3. Blanding’s turtle habitat use in the Northern United States and Nova Scotia 69 Table 4. Acreage of wetlands used by Blanding’s turtles and home ranges and activity 70 centers of Blanding’s turtle Table 5. Water quality and characteristics in Blanding’s turtle wetlands 72 Table 6. Long distance movements not related to nesting 74 Table 7. Blanding’s turtle hibernation patterns 75
Field Study: Microhabitat Use by Blanding’s turtle in Constructed and Natural Wetlands in Southeastern New York Table 1. T-test results comparing reference and constructed plots for Blanding’s 111 turtle-centered plots and random plots separately for each year, Dutchess County, New York, USA, 2000 - 2002 Table 2. Number of female, male and subadult Blanding’s turtle observations in 113 constructed and reference (natural) wetlands in Dutchess County, New York, USA, 2001 – 2002 Table 3. Shrub and buttonbush cover in constructed wetland plots, Dutchess County, 114 New York, USA, 2000 – 2002
viii
LIST OF FIGURES
Literature Review: A Review of Habitat Use by Blanding’s Turtle (Emydoidea blandingii) and Implications for Management Figure 1. Patterns of habitat use 76
Field Study: Microhabitat Use by Blanding’s turtle in Constructed and Natural Wetlands in Southeastern New York Figure 1. Scatterplots of habitat variables in turtle-centered plots versus Julian date for 115 Blanding’s turtles in Dutchess County, New York, USA, years 2001 and 2002 Figure 2. Scatterplots of habitat variables in turtle-centered plots versus time of day for 116 Blanding’s turtles in Dutchess County, New York, USA, years 2000 – 2002 Figure 3. Confidence intervals on the differences in means for variables that did not 117 overlap in 2002, plus buttonbush confidence intervals that overlapped slightly, for constructed and reference wetlands in Dutchess County, New York, USA
ix
A Review of Habitat Use by Blanding’s Turtle (Emydoidea blandingii) and Implications for Management
Tanessa Suzan Hartwig Hudsonia Ltd., Bard College Graduate School of Environmental Studies PO Box 5000 Annandale, NY 12504 845-758-7274 (phone) 845-758-7033 (fax) [email protected]
Erik Kiviat Hudsonia Ltd. PO Box 5000 Annandale, NY 12504
Abstract - We conducted a literature review of Blanding’s turtle habitat throughout its range to determine similarities and differences in habitats at the range-wide, landscape, and microhabitat scales. Throughout their range, Blanding’s turtles select wetland complexes with shallow (up to 2.5 m) water depths, organic substrates, areas of open water, and abundant vegetation. Habitat complexes consist of deeper wetlands for overwintering or drought refuge and a variety of shallow wetlands for feeding and thermoregulation. Although there are exceptions, in the Great Lakes region Blanding’s turtles tend to use ponds with abundant vegetation or herbaceous wetlands while in the
Northeast turtles often use shrub swamps. Nova Scotia turtles use bays and floodplain meadows with a mixture of herbaceous and shrubby vegetation. Juvenile turtles tend to use shallower areas than adult turtles - either in the same wetlands that adults use or in different wetlands. In the Great Lakes, upland areas are generally sand, while in the
Northeast they are gravelly or sandy loam. Water quality and seasonal movements varied by site, although long distances (> 1000 m) are traveled for nesting and other reasons
10 range-wide. Difference in wetland type and upland soils are probably related to climatic differences. Because Blanding’s turtles are very mobile and use a variety of wetlands during an individual’s lifetime, they are susceptible to loss of individual wetlands and landscape connectivity. Global warming may also put these north-temperate turtles at risk. Management recommendations include conservation of wetlands in groups, 1 km buffer zones around a Blanding’s turtle habitat complex, and corridors between complexes or known habitats beyond the 1 km zone.
Key Words – Reptilia; Testudines; Emydidae; Emydoidea blandingii; turtle; conservation; habitat fragmentation; habitat selection; landscape; management; microhabitat; range-wide; rare species; threatened species; endangered species; Canada;
USA.
The Blanding’s turtle (Emydoidea blandingii) is listed as threatened or endangered in most of the states and provinces within its range (Table 1), which is centered on the Great Lakes region in North America (Ernst et al., 1994). Isolated relict populations exist in eastern New York, eastern Massachusetts, southern New Hampshire, southern Maine, and southern Nova Scotia (Ernst et al., 1994; A. Breisch, pers.comm).
The Blanding’s turtle is also listed in the United States of America as a federal species of concern and is considered federally threatened in Nova Scotia (Farrar, 2003;
NatureServe, 2003; Wilder, 2003). It has been extirpated from several states (Table 1).
Habitat loss is considered a major threat to the Blanding’s turtle and appears to be a key factor in population declines (Kofron and Schreiber, 1985; Congdon and Gibbons, 1996;
Kiviat, 1997; Piepgras and Lang, 2000; Standing, 2000; Blanding’s Turtle Recovery
Team, 2003).
11 Habitat selection at all scales, from habitat range-wide to habitat use within wetlands, must be understood to conserve a species. Storch (1997) demonstrated this concept for a large game bird, the capercaillie Tetrao urogallus. As the capercaillie declined, conservation efforts focused on microhabitat features--areas within the home range that the capercaillie depended on for reproductive, sheltering, or feeding purposes.
Storch showed, however, that while the capercaillie had specialized microhabitat needs, it also required large areas of rather undeveloped land. Fragmentation in the region led to increased predation and larger home range size, which probably increased energy demands (Storch, 1997). Habitat features at the landscape scale, such as fragmentation, must also be considered in order to prevent the decline of this species.
Blanding’s turtle habitat can also be evaluated on several scales: microhabitat, landscape, and range-wide (similar to Johnson, 1980). Microhabitat selection describes the habitat the turtles use within a wetland, for example feeding and basking areas or hibernation sites. Landscape selection denotes the wetland ecosystems and surrounding areas that a population of turtles uses throughout the individual turtles’ lives. Range-wide selection is defined as the geographical range of the species and describes features such as climate or surficial geology associated with habitats throughout the range.
Blanding’s turtle habitat has been studied on a landscape scale in some areas, but little is known about microhabitat or range-wide requirements. The Blanding’s turtle is a very mobile and fragmentation-sensitive turtle species (Ernst et al., 1994; Power et al.,
1994; Dorff, 1995; Sexton, 1995; Kiviat, 1997; Linck and Moriarty, 1997; Piepgras and
Lang, 2000; Standing, 2000; Joyal, 2001; Rubin et al., 2001). As development encroaches upon wetlands and other habitats used by Blanding’s turtles, it is essential to understand
12 spatial, temporal, and wetland characteristics needed to maintain viable populations. The
purpose of this review is to analyze available habitat information at the microhabitat,
landscape, and range-wide scale for adult and juvenile Blanding’s turtles throughout their range. We synthesize available habitat information and provide management recommendations so that researchers and managers can better protect, restore, and create habitat for Blanding’s turtles. This paper is organized in 6 categories: habitat types, vegetation characteristics, upland and wetland soils, water characteristics, juvenile and hatchling habitat, and patterns of habitat use.
LITERATURE
Habitat Types
At the landscape scale, Blanding’s turtles selected a complex of wetland and upland habitats throughout their range (Power, 1989; Ross and Anderson, 1990; Rowe and Moll, 1991; Sexton, 1995; Butler, 1997; Kiviat, 1997; Linck and Moriarty, 1997;
Kingsbury, 1999; Hall and Cuthbert, 2000; Piepgras and Lang, 2000; Joyal, 2001; Rubin et al., 2001; Lang, 2003; Wilder, 2003; Hamernick and Lang, in prep). Wetlands used included: lakes, ponds, marshes, creeks, wet prairies, “sloughs,” shrub swamps, intermittent woodland pools, forested wetlands, bogs, and sluggish streams (Tables 2 and
3). “Slough” is interpreted differently in various regions of the United States. Mitsch and
Gosselink (2000) defined “slough” as “an elongated swamp or shallow lake system, often adjacent to a river or stream.…” Johnson (1981), Vogt (1981), Butler (1992), and Ernst
13 et al. (1994), cited in this paper, appeared to be referring to similar habitat. The number of wetlands used by an individual turtle varied; in Maine and Minnesota, individuals used from 1 to 6 wetlands annually (Piepgras and Lang, 2000; Joyal, 2001). This appears to be similar to other studies; however most studies did not specify the number of wetlands used by individual turtles. Size of individual wetlands ranged from 0.1 to 327 ha (Table
4). Home ranges and home range lengths also varied among sites and among individual turtles, from 0.1 to 292 ha and 90 to 5183 m, respectively (Table 4). Different methods of calculating home range size yield different results from the same data (Piepgras and
Lang, 2000; Hamernick and Lang, in prep). Therefore, the home range acres cited above are approximate. Each turtle also occupied its own activity center - from 0.15 to 2.7 hectares - defined as an area of concentrated movement in a wetland, which changed through the year and sometimes overlapped with other turtles’ centers (Table 4).
Great Lakes Region. –– In the Great Lakes region (including midwestern states, northwestern New York, Ontario, and Québec), Blanding’s turtle wetlands were often open marshes, ponds, or lakes containing herbaceous emergent vegetation. Of 42 references from the Great Lakes region, 38 mentioned lakes, ponds, or marshes
(herbaceous wetlands) as Blanding’s turtle habitat (Table 2). Cahn (1937) and Dancik
(1974) referred to “swampy floodplains.” Due to the lack of vegetation data, it is unclear whether these papers described herbaceous or wooded wetlands. Several references depicted shrub swamps as habitat. Other Blanding’s turtle habitat in the Great Lakes region included streams and ditches, temporary pools, bogs and swamps, “backwater sloughs,” and shallow, slow-moving rivers (Table 2).
14 Because the Blanding’s turtle is a very mobile species, the landscape surrounding
the wetlands is an important aspect of its ecology, providing nesting habitat, corridors for travel, and cool or warm upland areas to escape unfavorable water temperatures. In the
Great Lakes region, the upland landscape varied from forested and prairie to bare sand, often constituting a mixture of landscape features (Table 2). Many sites were associated with wetlands along shores of the Great Lakes or with river floodplains.
Northeast and Nova Scotia. –– In the northeastern United States (Maine, Massachusetts,
New Hampshire, and eastern New York; hereafter referred to as the Northeast),
Blanding’s turtle wetlands were often shrub swamps with moats or ponded areas (Table
3). Turtles in Nova Scotia were associated with the bogs and vegetated coves of large lakes and tributary streams and rivers (Table 3). In Dutchess and Saratoga Counties
(eastern New York), Maine, and Massachusetts many of the shrubby wetlands contained buttonbush (Cephalanthus occidentalis; scientific names of plants follow Gleason and
Cronquist, 1991).
In Massachusetts, one population primarily used a riverine marsh (Graham and
Doyle, 1977). Other habitats used in the Northeast were “sloughs” and oxbow marshes, temporary pools, bogs, flooded or forested swamps, floodplain ponds and wetlands, and farm ponds (Table 3). In Dutchess County, New York (hereafter referred to as Dutchess
County) Blanding’s turtles also occasionally used slow-moving woodland streams
(Hudsonia Ltd, unpubl. data). Upland habitat always included forested land, but could also include bare sand, shrubby areas, and meadows or meadow-like areas (Table 3).
Several sites were on floodplains or very close to rivers.
15 Vegetation
Great Lakes Region. –– The flora of the marsh habitats in the Great Lakes region included algae, stonewort (Chara), bladderworts (Utricularia spp.), common coontail
(Ceratophyllum demersum), water scorpion-grass (Myosotis scorpioides), jewel-weed
(Impatiens), water-willow (Decodon verticillatus), water-lilies (Nymphaea and Nuphar), water-cress (Rorippa nasturtium-aquaticum), white water-crowfoot (Ranunculus longirostris), arrow-arum (Peltandra virginica), common arrow-head (Sagittaria latifolia), cat-tails (Typha spp.), lesser and greater duckweeds (Lemna minor and
Spirodela polyrhiza), grasses (Poaceae), pickerel-weed (Pontederia cordata), pondweeds
(Potamogeton spp.), rushes (Juncus spp.), sedges (Carex spp.), soft-stem bulrush (Scirpus
tabernaemontani), northern water-nymph (Najas flexilis), and water-weed (Elodea)
(Gibbons, 1968b; Wilbur, 1975; Ballinger et al., 1979; Petokas, 1979; Kofron and
Schreiber, 1985; Ross, 1987; Ross and Anderson, 1990; Rowe and Moll, 1991;
Kingsbury, 1999; Hall and Cuthbert, 2000; Pappas et al., 2000). All 11 references
mentioned coontail or cat-tail, with coontail often a dominant species and cat-tail
sometimes dominant. Submerged vegetation was mentioned in 8 references. One that did
not mention it (Ballinger et al., 1979) was not detailed enough to exclude the possibility
that those wetlands also contained submerged vegetation. Shrub wetlands in the Great
Lakes region contained floating liverworts (Ricciocarpus natans [reported as Riccia
lutescens]), cat-tails, sedges, alder (Alnus), buttonbush, various-leaved swamp-
cottonwood (Populus heterophylla), water-parsnip (Sium suave), willow (Salix), and
16 yellow water-crowfoot (Ranunculus flabellaris) (Evermann and Clark, 1920; Piepgras
and Lang, 2000; F. Schueler field notes, 1972-2003).
Northeast and Nova Scotia. –– Eastern New York shrub swamp habitats were often
dominated by buttonbush (Kiviat, 1993) or contained buttonbush in sections (Eckler and
Breisch, 1988; Klemens, 1992; A. Breisch, pers. comm). Other shrub species in Dutchess
County were: arrow-wood (Viburnum dentatum), highbush-blueberry (Vaccinium
corymbosum), silky dogwood (Cornus amomum), and winterberry (Ilex verticillata)
(Kiviat, 1997). Herbaceous species included filamentous algae, floating liverworts
(Riccia fluitans and Ricciocarpus natans), beggar-ticks (Bidens spp.), bladderworts,
purple loosestrife (Lythrum salicaria), spiny coontail (Ceratophyllum echinatum), water-
lilies (Nymphaea and Nuphar), yellow water-crowfoot, duckweeds (Lemna minor,
Spirodela polyrhiza, Wolffia), grasses, and pondweeds (Eckler and Breisch, 1988;
Klemens, 1992; Kiviat, 1997). Cat-tail, common reed (Phragmites australis), sedges, and
willows were sometimes present but rarely covered large areas (Kiviat, 1997).
Less information has been reported on vegetation in other parts of the Northeast.
The marsh used as habitat in Massachusetts contained pondweed, free-flowered water- weed (Elodea nuttallii), and common coontail (Graham and Doyle, 1977). Turtles in
Maine used wetland pools surrounded by shrub borders, sphagnum mats, or herbaceous emergent borders (Joyal, 1996). Common species included Sphagnum, sedge and three way sedge (Carex spp. and Dulichium arundinaceum), yellow water-lily (Nuphar sp.), buttonbush, highbush-blueberry, and winterberry (Joyal et al., 2000).
In Nova Scotia, vegetation in the floodplain meadows and bays inhabited by
Blanding’s turtle included Sphagnum, blue-joint grass (Calamagrostis canadensis),
17 freshwater prairie cord-grass (Spartina pectinata), pickerel-weed, pondweeds, sedges
(Carex spp.), spike-rushes (Eleocharis spp.), three way sedge, water-bulrush (Scirpus subterminalis), bladderwort, pickerel-weed, pitcher plant (Sarracenia purpurea), pondweeds, sundew (Drosera rotundifolia), water-lilies (Nuphar sp. and Nymphaea odorata), water-shield (Brasenia schreberi), blueberry, leatherleaf (Chamaedaphne calyculata), red maple (Acer rubrum), rhodora azalea (Rhododendron canadense), speckled alder (Alnus incana), sheep-laurel (Kalmia angustifolia), and sweet gale
(Myrica gale) (Herman et al., 1989; McMaster and Herman, 2000; McNeil, 2002).
Upland and Wetland Soils
Throughout their range, Blanding’s turtles occupied wetlands with organic substrates, often relatively firm (Gibbons, 1968b; Graham and Doyle, 1977; Petokas,
1979; Ross, 1990; Klemens et al., 1992; Power et al., 1994; Kiviat, 1997; J. Moriarty, pers. comm.). Some wetlands in Nova Scotia also contained sandy substrates (Power,
1989).
Most of the Blanding’s turtle range lies north of the glacial maximum; populations in Nebraska, Iowa, central Illinois, and central Indiana are south of the maximum. In the Great Lakes region, upland soils were almost always sands (Evermann and Clark, 1920; Cahn, 1937; Schmidt, 1938a; Breckenridge, 1944; Adams and Clark,
1958; Ballinger et al., 1979; Kofron and Schreiber, 1985; Ross, 1989; Kingsbury, 1999;
Pappas et al., 2000; Piepgras and Lang, 2000; Hamernick and Lang, in prep). One
Indiana account described part of the upland area as gravelly sand (Evermann and Clark,
18 1920). In Minnesota the largest populations occurred in wetlands associated with “sandy outwash or alluvium deposits” (Dorff, 1995). In the Northeast, turtles were found in areas with upland gravelly loam soils (Kiviat et al., 1998), sandy soils (Butler, 1995), coarse sandy loam, or mixed sand and clay (Butler and Graham, 1995). In Nova Scotia, upland soils were sandy loam (Power, 1989).
Water Characteristics
There was no apparent difference in water quality and characteristics of
Blanding’s turtle wetlands between the Great Lakes, Northeast, and Nova Scotia regions
(Table 5). Blanding’s turtles were found in eutrophic water in some areas, but oligotrophic water in other areas. Wetland acidity also varied throughout their range, from alkaline to acidic. Blanding’s turtles occupied wetlands with shallow water depths, generally up to 2.5 m throughout their range. There was also no characteristic water color that prevailed throughout the turtle’s range; at some sites the water was clear, while at others it was dark or tea-colored.
Juvenile and Hatchling Habitat
Hatchlings and juveniles preferred shallower, more densely vegetated areas than adults at most sites. In Massachusetts, hatchlings sought hibernacula in wetlands that were more densely vegetated than those adults were usually found in, and the entry points were moderately to heavily shaded and contained Sphagnum and muck (Butler and
19 Graham, 1995). In a Nova Scotia study, however, hatchling movements were random with respect to water and no single habitat feature was sought (Standing et al., 1997), even during manipulative experiments that placed hatchlings near or far from water
(McNeil et al., 2000). Hatchlings in Nova Scotia may use a random dispersal strategy for survival reasons and may overwinter in terrestrial as well as aquatic hibernacula
(Standing et al., 1997), although in the laboratory Blanding’s turtle hatchlings could not withstand temperatures below –6.0 ºC (Packard et al., 2000). In addition, the open lake habitat at the Nova Scotia nest site may have been less preferred by hatchlings than the vegetated wetlands near the Massachusetts nest site (McNeil et al., 2000).
Hatchlings used a variety of forms to rest in after emergence. Forms were in: haircap moss (Polytrichum), Sphagnum, royal fern (Osmunda regalis) root clumps, little bluestem (Schizachyrium scoparium) tussocks, basal rosettes of spotted knapweed
(Centaurea maculosa), leaf litter beneath sweetfern (Comptonia peregrina), brambles
(Rubus sp.), leaf litter, beach cobble, roots and logs, and short-tailed shrew (Blarina brevicauda) burrows (Butler and Graham, 1995; Standing et al., 1997). Sphagnum was a preferred form substrate for hatchlings in Massachusetts (Butler and Graham, 1995).
Vegetation in an emergent wetland and calcareous fen used by hatchlings in Indiana included large areas of Sphagnum, a robust forb community, dense shrubs (Salix spp. and
Cornus spp.), poison-sumac (Toxicodendron vernix), red-osier dogwood (Cornus sericea), rushes (Juncus spp.), sedges (Carex spp.), shrubby cinquefoil (Potentilla fruticosa), swamp-rose (Rosa palustris), and water-lilies (Nuphar) (Kingsbury, 1999).
Two yearlings in the fen spent most of their time in dense mats of bladderwort
20 (Kingsbury, 1999). Several yearlings in Nova Scotia were found in dense Sphagnum, and
several in shallow, muddy, unvegetated aquatic habitat (Standing et al., 2000).
Juveniles in Nova Scotia were found in riparian wetlands with Sphagnum, sweet gale, and leatherleaf (McMaster and Herman, 2000) and in certain areas within a lacustrine bog used by adult turtles (McNeil, 2002). In southeast Michigan, small juveniles used a wetland with bottlebrush sedge (Carex comosa) and speckled alder hummocks, while larger juveniles used sedge and open water edges, and the largest were in open water dominated by sago-pondweed (Potamogeton pectinatus) and duckweed
(Pappas and Brecke, 1992). At a site in Dutchess County, juveniles were often captured near tussock sedge (Carex stricta), purple loosestrife, and young red maple (K. Munger, pers. comm.). Joyal et al. (2000) suggested that in Maine juveniles may be located in forested wetlands or shrub swamps, which were more heavily vegetated than the open water pools with a vegetated fringe where adults were found. In Indiana, juveniles were more likely to be in forested and shrub areas or sedge and cat-tail-sedge areas, while adults were found more often in sedge, water-lily, and floating mat areas (Kingsbury,
1999). In Nebraska, Bury and Germano (2003) found that while both adults and juveniles used small ponds and marshes, only adults used larger lakes. In Minnesota, wetlands that
supported juveniles had relatively small proportions of open water compared to emergent
vegetation (Dorff, 1995). At another site in Minnesota, juveniles were found in the same
habitats as adults but had fewer and larger activity centers than adults and were less likely
to move between wetlands (Piepgras and Lang, 2000). Piepgras and Lang (2000) did not
find a difference between adult and juvenile habitat; however, turtles were considered
juvenile if their carapace length was < 210 mm. Juvenile turtles in studies that noted a
21 difference in adult and juvenile habitat had carapace lengths of less than 155 mm (Pappas
and Brecke, 1992; Kingsbury, 1999; Joyal, 2000).
With one exception (McMaster and Herman, 2000) water depth tended to increase
as the turtle became older. In Indiana, yearling and hatchling turtles were typically found
in shallow water less than 20 cm deep, juveniles were found in areas with 20 - 40 cm
water, and adults used even deeper waters (Kingsbury, 1999). In Minnesota, juveniles
occurred in water depths of 5 - 50 cm, compared with 30 - 210 cm for adults (Pappas and
Brecke, 1992). At a site in Dutchess County, small juveniles were often found in shallow
waters 30 – 50 cm deep, while larger juveniles were found in waters up to 80 cm deep (K.
Munger, pers. comm.). Congdon et al. (2000) noted that Blanding’s juveniles captured during a study on the E.S. George Reserve in southeastern Michigan were caught in shallow areas of wetlands occupied by adults. Butler (1992) also noted that Blanding’s juveniles used shallower water than adults. McMaster and Herman (2000) attributed lack of body size - water depth correlation in Nova Scotia to lack of water depth heterogeneity in juvenile habitat at their study site.
Patterns of Habitat Use
Wetland complex use
Blanding’s turtles used wetland complexes in several ways at different sites: as a
core - seasonal pattern, winter - summer pattern, or a mixture of the two. At several sites,
wetland complexes consisted of core wetlands and seasonal wetlands (Ross and
Anderson, 1990; Rowe and Moll, 1991; Kiviat, 1997; Barlow, 1999; Joyal, 2001; Wilder,
22 2003; B. Butler, pers.comm). Core wetlands were a set of regularly used wetlands of similar habitat typically occupied during the winter, spring, early summer, and fall. They were deep enough to remain unfrozen at their bottoms, contained abundant aquatic vegetation, and ranged from ponds to emergent marshes or flooded shrub swamps with areas of deep water. Core wetlands functioned as overwintering, foraging, and thermoregulation habitat. Seasonal wetlands were used from early spring through late summer. Seasonal wetlands usually contained at least some standing water, and included deep ponds or lakes, forested wetlands, streams, ditches, and woodland pools. They apparently provided food during times of scarcity in core wetlands or peak productivity in seasonal wetlands, reduced competition, refuge from undesirable water temperatures or levels, and shelter for nesting females and traveling males.
At other sites, the majority of Blanding’s turtles exhibited a winter - summer pattern of habitat use (Power, 1989; Sexton, 1995; Lang, 2001, 2002, 2003; McNeil,
2002; J. Lang, pers. comm.). Turtles moved into overwintering wetlands in the late fall, and then quickly left them in the spring and spent the rest of the year in summer habitats.
Overwintering wetlands included shrub swamps, streams, and lakes while summer wetlands included streams or stream mouths, marshes, swamps, and ponds.
Overwintering wetlands provided unfrozen bottom areas, while summer wetlands provided foraging and thermoregulation habitat.
In other studies, the turtles showed a mixed pattern of habitat use, with some turtles exhibiting a core - seasonal pattern and some exhibiting a winter - summer pattern
(Linck and Moriarty, 1997; Piepgras and Lang, 2000; C. Hall, pers. comm.; J. Lang, pers. comm.). In either the core - seasonal or winter - summer model, some individual turtles
23 may exhibit the alternate pattern. In studies lasting more than one year, individuals
sometimes switched between habitat use patterns (Hudsonia Ltd, unpubl. data; J. Lang,
pers. comm.). In addition, Blanding’s turtles are flexible and will use wetlands differently
as the wetlands change through the years. In Dutchess County, for instance, a seasonal
wetland’s hydrology was altered so that it was flooded more deeply and for a longer
period. Within a year, the turtles began using the wetland as core habitat (Hudsonia Ltd, unpubl. data). At the Weaver Dunes in Minnesota, turtles quickly took advantage of a rare flooding event to occupy wetlands in flooded fields (J. Lang, 2002).
Movement Patterns
Throughout their range, Blanding’s turtles engaged in two different types of
movement: annual home range movement and long distance sojourns (Power et al.,
1994; Butler, 1995; Kiviat, 1997; Sajwaj et al., 1998; Hall and Cuthbert, 2000; Rubin et
al., 2001; Hamernick and Lang, in prep). Annual home range movement included
movements that occurred regularly on a yearly basis, such as travel within and between
wetlands and nesting migrations by females. It was related to seasonal selection of
habitats, such as finding suitable water temperatures or levels, foraging areas,
reproductive strategies, overwintering sites, and possibly seeking refuge from
competition, and could include long distance movements, particularly by females during
nesting season. In fact, movements exceeding 1000 m were common in a Massachusetts
population (Butler, 1997). Long distance sojourns occurred on a less - than - annual basis,
were typically greater than 1000 m, and appeared to be associated with reproductive
strategies or habitat complexes becoming unsuitable for an individual. Although we have
distinguished between these two movement patterns for ease of discussion, a population
24 of turtles may exhibit a continuum of movement patterns from normal annual movement
to long distance movements.
Long Distance Sojourns
Blanding’s turtles are capable of traveling long distances, which allows them to
select suitable habitats within a landscape as habitats or social dynamics change. Whereas
long distance movements by females were common during the nesting season, both male
and female Blanding’s turtles often traveled long distances unrelated to nesting activity
(Table 6). Mobile Blanding’s turtles established residency in new wetlands (Rowe and
Moll, 1991; Power et al., 1994; Butler, 1995; Hall and Cuthbert, 2000; Hudsonia Ltd.,
unpubl. data), mated (Joyal et al., 2000), or eventually returned to their previous home
ranges (Rowe and Moll, 1991).
Annual Home Range Movement
Spring. –– In the spring, Blanding’s turtles emerge from hibernation and require habitats
with plentiful food and opportunities for thermoregulation, such as basking sites and
maximum periods of sunlight. Throughout their range, Blanding’s turtles generally
become active mid-March to mid-April (Vogt, 1981; Herman et al., 1989; Rowe and
Moll, 1991; Kiviat, 1993; Pappas et al., 2000; Piepgras and Lang, 2000; McNeil, 2002).
Depending on the opportunities for thermoregulation and foraging or water temperatures,
Blanding’s turtles spend most of their time in core wetlands, shallow seasonal wetlands,
or on land. In southwestern Minnesota, Weaver Dunes, Minnesota, and Valentine
National Refuge, Nebraska, turtles spent most warm days on land, sometimes in leafless
woods greater than 100 m from water (Lang, 2001; J. Lang, pers. comm.). In Dutchess
County, the turtles spent much of the spring in leafless buttonbush pools (Kiviat, 1997).
25 In Illinois, turtles at the Fox River site inhabited small ponds with sparse vegetation in
May and June (Rowe and Moll, 1991; J. Rowe, pers. comm.). On the St. Lawrence River
in northern New York, turtles occupied shallow water habitat from early spring to late
June (Petokas, 1985). Blanding’s turtles often visited intermittent woodland pools in the
springtime or early summer, probably to take advantage of abundant macroinvertebrates
and amphibian larvae in a relatively small area or to bask in shallow, warm waters
(Herman et al., 1989; Butler, 1995; Kiviat, 1997; Linck and Moriarty, 1997). In Dutchess
County, some turtles spent time in an acidic bog (Kiviat, 1997). At Kejimkujik Lake in
Nova Scotia, turtles moved downstream from their hibernation sites, probably to benefit
from the warmer waters at lake margins (Power, 1989; Herman et al., 1989).
Basking is a significant component of thermoregulation for many species of
turtles, including Blanding’s turtles, which bask often during the spring and summer.
Basking sites are an important component of springtime habitats because water and air
temperatures are cooler than in summer. In Minnesota, for example, many turtles basked
in April and May while fewer basked through the remainder of the season, based on daily internal body temperatures and water temperatures (Sajwaj and Lang, 2000). In Nova
Scotia, turtles were observed basking as early as March 20 (McNeil, 2002). Blanding’s turtles bask in or out of the water. Basking perches tend to be plentiful in Blanding’s turtle habitat, although their actual composition varies. Throughout their range,
Blanding’s turtles basked on land, on shore within 2 m of water, steep banks of dikes and ditches, stumps, logs, piles of driftwood, matted stick piles, cat-tail debris, floating vegetation mats, sedge tussocks, Sphagnum hummocks, muskrat lodges, and even turtle traps (Conant, 1938; Dobson, 1971; Froom, 1976; Gilhen, 1984; Kofron and Schreiber,
26 1985; Rowe and Moll, 1991; Butler, 1992; Kiviat, 1993; Ernst et al., 1994; Joyal, 1996;
Linck and Moriarty, 1997; Sajwaj and Lang, 2000; McNeil, 2002; Wilder, 2003; Hartwig
and Kiviat, unpubl. obs.). Blanding’s turtles also rested under leaf litter or vegetation on
land to escape cool waters (Rowe and Moll, 1991; Joyal, 2001), sometimes up to 40 m
from the nearest wetland (Joyal, 2001). When basking in the water, the turtles remained
partially submerged in neuston -- the floating layer of living and dead plant material on
the water’s surface (Kofron and Schreiber, 1985; Butler, 1992; Kiviat, 1993). Blanding’s
turtles at Camp Ripley preferred sheltered basking sites; for example, sedge mats or
protected openings (Sajwaj and Lang, 2000).
Nesting Season. –– In May and June (and sometimes early July), female Blanding’s
turtles travel long distances to lay their eggs, often using wetlands or terrestrial sites as staging, or resting, areas. The females nested in a variety of soils, but generally chose well-drained sunny soils (Petokas, 1986; Kiviat, 1997; Linck et al., 1999; Standing et al.,
1999; Lang, 2001; Blanding’s Turtle Recovery Team, 2003; Lang, 2003). Blanding’s turtles traveled between 100 m and 2900 m to lay their eggs (Linck et al., 1989; Ross and
Anderson, 1990; Rowe and Moll, 1991; Herman et al., 1994; Butler, 1997; Kiviat, 1997;
Joyal, 2000; Piepgras and Lang, 2000; McNeil, 2002; Farrar, 2003). Nesting females used dense vegetation or leaf litter on land, intermittent woodland pools, wooded swamps, shallow marshes, deep marshes, ornamental ponds, and open water areas as staging or rehydrating areas before and after nesting (Eckler and Breisch, 1988; Rowe and Moll, 1991; Kiviat, 1997; Sajwaj et al., 1998; Standing et al., 1999; Congdon et al.,
2000; Piepgras and Lang, 2000; McNeil, 2002; Hudsonia Ltd., unpubl. data).
27 Summer. –– During the summer, Blanding’s turtles move between wetlands while
searching for food, and often travel to drought refuge habitat that provides escape from
the heat or falling water levels. Drought refuges were usually ponds or lakes, or deeper
portions of core wetlands (Petokas, 1985; Ross, 1987; Kingsbury, 1999; Rubin et al.,
2001; J. Rowe, pers. comm.). In Dutchess County, these refuges were 250-900 m from the nearest springtime habitats (Kiviat, 1997). In Nova Scotia, turtles on smaller streams moved to the stream mouths on Kejimkujik Lake and spent most of their summer in the mouths, while turtles on larger rivers rarely used the lake (Herman et al., 1994); probably the smaller streams became too warm or too shallow. Another population in Nova Scotia moved upstream to an unvegetated pool and remained in channels under the bank; at this site the cove at the stream mouth dried up (McNeil, 2002).
Blanding’s turtles may increase inter-wetland movements during the summer to search for suitable foraging areas (Ross and Anderson, 1990). Turtles at a Minnesota site left their overwintering wetland, Beckman Lake, by mid-June and moved to shallower wetlands (Hall and Cuthbert, 2000), probably to feed on tadpoles and invertebrates (C.
Hall, pers. comm.). Movement and foraging activity may also decrease or cease during hot periods (Kofron and Schreiber, 1985), as the turtles become inactive to escape warm waters or drought conditions. Blanding’s turtles remained inactive for periods of 6 hours to 21 days under herbaceous vegetation, shrub thickets, fallen logs, or leaf litter on land; or in the sediments of dry wetlands, in the silt substrate of a creek, under matted cattails, in deep pools, and in the water in red maple swamps (Ross and Anderson, 1990; Rowe and Moll, 1991; Joyal, 1996, 2001; Linck and Moriarty, 1997; Hudsonia Ltd, unpubl. data).
28 Hibernation and Winter. –– In the fall, the turtles moved to suitable overwintering sites, although in Dutchess County some late-fall overland movement occurred during warm spells (Hudsonia Ltd., unpubl. data). Date of hibernation, water temperature, and water depth at hibernacula were quite variable through the geographic range (Table 7).
Blanding’s turtles often hibernated in deeper areas of a core wetland or in large ponds
(Ross and Anderson, 1990; Rowe and Moll, 1991; Kiviat, 1993; Sajwaj and Lang, 2000;
Kingsbury, 1999; Hall and Cuthbert, 2000). Streams were used in Nova Scotia, southwest
Minnesota, and Wisconsin (Herman et al., 1989, 1994; Ross and Anderson, 1990; Lang,
2003; Wilder, 2003). In Nova Scotia, seasonally isolated pools or backwaters were also used (Power, 1989). In addition, turtles in Wisconsin hibernated in a beaver flowage at the mouth of a creek and in borrow pits (Wilder, 2003), some turtles in Massachusetts hibernated in intermittent woodland pools (B. Butler, pers. comm.), and at McGowan
Lake in Nova Scotia turtles overwintered in a wooded swamp and in certain areas of their summer bog (McNeil, 2002). At some sites, Blanding’s turtles chose the deepest water available (Ross and Anderson, 1990) while at other sites the turtles chose hibernacula in shallower water than was available (Kofron and Schreiber, 1985; Rowe, 1987; Sajwaj et al., 1998).
During hibernation, Blanding’s turtles lay exposed on the substrate, sometimes under shrubs or undercut stream banks, or buried themselves in sediment, vegetation, or debris (Cahn, 1937; Carr, 1952; Kofron and Schreiber, 1985; Herman et al., 1989; Ross and Anderson, 1990; New York State Department of Environmental Conservation, 1991;
Rowe and Moll, 1991; Kingsbury, 1999; McNeil, 2002). Turtles also occasionally used muskrat burrows (Cahn, 1937; Ross, 1985). Graham and Butler (1993) reported that the
29 turtles buried in sediment in marshes but maintained a more exposed position in ponds.
They suggested that this behavior could be related to water depth; in deeper waters
burrowing to avoid freezing or predation may not be necessary. In Missouri, for instance,
sediment cover was up to 15 cm in 9.5 – 21 cm of water (Kofron and Schreiber, 1985).
This behavior was not universal, however; in Dutchess County turtles hibernated exposed in 30-60 cm of water (Hudsonia Ltd., unpubl. data).
DISCUSSION
Habitat Types
At the landscape scale, there was a strong preference for herbaceous, marshy wetlands in the Great Lakes region and wetlands with shrub components in the Northeast and Nova Scotia. Several authors have presented evidence that Blanding’s turtles inhabited prairie regions in pre- and post-Wisconsin eras and relict populations are remnants of a prairie fauna that survived glaciation in a southwestern refuge and then migrated eastward via a “Prairie Peninsula” that formed during an arid, warm
(Xerothermic) climatic period (Schmidt, 1938b; Smith, 1957; Preston and McCoy, 1971).
Relict populations in Nebraska prairies and western fossil records also suggest that
Blanding’s turtle was originally a prairie marsh-pond species (J. Harding, pers. comm.).
In addition, a late Pleistocene record from southern Ontario is described as marsh-pond habitat (Churcher et al., 1990). Current distribution records suggest that the largest population of Blanding’s turtles may be in the prairie wetlands of the Valentine National
30 Wildlife Refuge in Nebraska (Farrar, 2003), suggesting that this may be favorable
habitat.
However, an alternate hypothesis postulated that Blanding’s turtles had a pre-
Wisconsin distribution in eastern North America and survived glaciation in an Atlantic coastal plain refuge (Bleakney, 1958). Recently discovered Pleistocene records from the southeastern states supported this view (Jackson and Kaye, 1974; Parris and Daeschler,
1995). Evidence that Blanding’s turtle populations in the Northeast and Nova Scotia are closer genetically to each other than to populations in the Great Lakes region (S.
Mockford, pers. comm) may also support this hypothesis, because genetic differentiation in turtles appears to occur slowly (Starkey et al., 2003). The dorsalis-picta split in
Chrysemys, for instance, may have occurred 3.5 to 2.7 million years ago; the last ice sheets retreated less than 20,000 years ago (Starkey et al., 2003).
If prairie marshes were the ancestral habitat of Blanding’s turtles and they migrated to eastern North America via a prairie peninsula, the northeastern turtles are relicts of a previous climate and vegetation. As the climate cooled and the Northeast and
Nova Scotia was reforested, the turtles probably declined in number or shifted their distribution towards the Great Lakes region, isolating eastern populations. Blanding’s turtles may have then adjusted their habitat use to shrub swamps due to thermal strategies described below. An analysis of United States wetland maps indicated that Blanding’s turtles did not simply adapt to shrub swamps because they were more prominent in the
Northeast; shrub swamps cover more surface area than emergent wetlands in both the
Northeast and the Midwestern states (Wilen and Tiner, 1993). Comparable information for Canadian wetlands was not available. If Blanding’s turtles inhabited northeastern
31 North America before the Wisconsin glaciation, it is possible that they either have occupied shrub swamps in the Northeast and Nova Scotia since pre-Wisconsin times or that the Northeast’s climate and vegetation were significantly different than today, encouraging use of marshy habitats. Unfortunately, we could not find information on pre-
Wisconsin Blanding’s turtle habitat or flora in the Northeast. Although the fact that the largest population in the Great Lakes region uses prairie wetlands may be indicative that these wetlands are Blanding’s turtle’s ancestral habitat, there many factors are involved in the health of a population and more paleoecological evidence is needed for this hypothesis to be conclusive.
Thermoregulation factors determined by climatic differences may strongly influence which wetland type Blanding’s turtles occupy. The Northeast receives fewer hours of sunlight than the United States portion of the Great Lakes region in May, although during other times of the year the Northeast receives the same or more sunlight than the Great Lakes region (NCDC, 2000). May, however, was an important time of the year for active thermoregulation at Camp Ripley, Minnesota (Sajwaj and Lang 2000). In areas that do not receive high amounts of sunshine or that are cooler in the spring,
Blanding’s turtles may prefer wetlands that warm quickly. In the shrub ponds of Maine,
Joyal (1996) found that Blanding’s turtle wetlands received more hours of sunlight than other wetlands. In Dutchess County, restricted or no surface water flow into wetlands, leafless buttonbush and tree fringe, abundant neuston, and upland gravelly soil may contribute to rapid warming of the water surface in the spring (Kiviat, 1997). Buttonbush and other shrub swamps also provide protected basking areas in shallower waters than herbaceous marshes or ponds before the shrubs leaf out.
32 In the Great Lakes region, Blanding’s turtles also used shrub swamps as an
important component of habitat in portions of the St. Lawrence River valley, at Camp
Ripley, Minnesota, and in portions of Ontario (Petokas, 1985; Piepgras and Lang, 2000;
Sajwaj and Lang, 2000; F. Schueler, pers. comm.). In Ontario, many of these swamps were also buttonbush-dominated (F. Schueler, pers. comm.). While studying the thermal ecology of Blanding’s turtles, Sajwaj and Lang (2000) determined that shrub swamps, important habitat in Camp Ripley, provided significant diversity of thermal environments for the turtles. These areas are all at the northern periphery of the Blanding’s turtle range at approximately the same latitude, and presumably have cool spring climates compared to more southerly populations; climate maps indicate a general cooling trend in the spring as latitude increases (Thomas, 1953; NCDC, 2000). In addition, Ontario also appears to receive fewer hours of sunlight in May than the rest of the Great Lakes region (Thomas,
1953; NCDC, 2000). However, interpretation of sunshine hours in Canada versus the
United States is difficult due to different methodologies: Canada uses a sunshine recorder to record “bright sunshine,” while the U.S. computes the “hours of sunshine observed.”
Blanding’s turtles in the interior of Ontario also occupied more open, marshy wetlands
(M. Oldham, pers. comm.) as well as shrub swamps. Analysis of microclimate at sites
where Blanding’s turtles primarily use shrub swamps versus sites where marshes are
mostly occupied would be useful.
Blanding’s turtles were found in prairie or grassland, forested, or mixed
landscapes. About half of the references to landscape (Tables 2 and 3) described a mixed
landscape containing forested areas and bare soil or grassland conditions. Blanding’s
turtles require areas of sparse vegetation for nesting, such as prairies, grasslands,
33 disturbed areas, maintained lands, or agricultural fields. Forested areas, however, may
provide important corridors for movement; adults and hatchlings traveled through
forested areas to and from nest sites or wetlands (Butler, 1995; Standing et al., 1997;
Hudsonia Ltd., unpubl. data). Forested areas also provide turtles with cool, shaded, and
moist terrestrial sites in which to remain inactive during drought or high water
temperatures, and warm areas to bask or escape cool waters in spring. Leaf litter from
trees is an important component of detritus, the base of the food web in wetlands (Mitsch
and Gosselink, 2000), and also an important food resource for the aquatic insects that
may comprise 10 to 20% total volume of the turtles’ diet (Lagler, 1943; Rowe, 1992). A
mixed landscape of disturbed or open, and forested, upland, therefore, may provide
optimal Blanding’s turtle habitat in some regions.
Many Blanding’s turtle sites were in the floodplains or within travel distance of large rivers or lakes (Tables 2 and 3). In Illinois, Blanding’s turtle populations were often closely associated with the Mississippi and Illinois Rivers, in Indiana – the Pigeon River, in Iowa – the Des Moines River, in Minnesota – the Mississippi River, in northern New
York – the St. Lawrence River, in Nova Scotia – Kejimkujik and other lakes, in Ohio –
Lake Erie, and in Ontario – the Great Lakes. In New England, the turtles were generally found in association with the Merrimack River and its major tributaries (Butler, 1997).
River valleys and lake basins provide aquatic travel corridors, and are also potentially locations of milder climates and more wetlands. Blanding’s turtles may use these aquatic systems as travel corridors when establishing new habitat complexes or moving to and from activity centers. Cahn (1937) mentioned that Blanding’s turtles spent time in the
Illinois River. Sajwaj et al. (1998) suggested that the Crow Wing and Mississippi rivers
34 may be travel corridors at Camp Ripley, Minnesota, noting a sighting of a basking turtle on the Mississippi. At the Weaver Dunes in Minnesota, turtles often traveled along the edges of the Mississippi River (Lang, 2002). Movement across the Nashua River by breeding females was commonplace (Butler, 1995). Blanding’s turtle populations in Ohio were mostly associated with the marshes of Lake Erie; however, the turtles (including a hatchling) were found on islands in the lake as far as 13,500 m from the mainland
(Conant, 1938; Langlois, 1964; Cormack and Cormack, 1975; King, 1988).
River and lake corridors are also less likely to have human-created barriers and are probably less dangerous than upland corridors, which often contain roads, fences, and other barriers. Therefore, Blanding’s turtle populations may be surviving near major waterbodies whereas they have been extirpated in many areas without aquatic corridors.
In addition, low topography, as is generally present in river valleys and lake basins, favors formation of wetlands and their contiguity (Weakley and Schafale, 1994; Tiner,
1998). Finally, Bleakney (1958) indicated that Kejimkujik Lake provided a thermal buffer at night, providing extra warmth to Blanding’s turtle eggs at the northern periphery of their range. Numerous wetlands, easily accessible travel corridors, and moderated nighttime temperatures should provide favorable habitat for Blanding’s turtles in any part of their range.
Vegetation
Common genera or species found in Blanding’s turtle habitat in the Great Lakes region and the Northeast includes cat-tails, duckweeds, grasses, sedges, smartweeds,
35 bladderworts, coontails, and water-lilies. Nova Scotia shares bladderworts, sedges, and water-lilies with the Great Lakes region and the Northeast. In all regions, submerged vegetation seems to be prominent in wetlands occupied by turtles. Sexton (1995) noted that Blanding’s turtles were often located in areas of submerged vegetation. He speculated that plants such as common coontail, leafy pondweed (Potamogeton foliosus), stoneworts, and water-crowfoots provided mats strong enough to support the turtles
(Sexton, 1995). In particular, coontail may be a preferred shelter for Blanding’s turtles, or support and shelter invertebrates or other prey. It was a dominant plant in the Great Lakes region habitats, and was also found in some of the northeastern habitats. Several studies have noted a preference for coontail by Blanding’s turtles. In Illinois, the turtles were seen foraging within coontail mats and stayed in coontail mats from July or August until dormancy (Rowe, 1987; Rowe and Moll, 1991). In Indiana, the turtles also exhibited a preference for large coontail mats, especially in the fall (Kingsbury, 1999). At the
Weaver Dunes in Minnesota, rooted submerged aquatics (species not noted) and emergent vegetation were selected for (Hamernick and Lang, in prep). However, coontail was not present in turtle habitat in Nova Scotia, but other submerged aquatics were abundant (Power, 1989; McMaster and Herman, 2000) and in Dutchess County, turtles showed no affinity for coontail over other submerged vegetation (Hartwig, 2004).
Throughout the Blanding’s turtle’s range, abundant submerged aquatic vegetation is selected for; species may vary between sites or regions although coontail appears to be important in the center of the Blanding’s turtle range.
36 Upland and Wetland Soils
Organic soils are found in wetlands used by the Blanding’s turtle throughout its range. Organic soils probably provide greater food resources for turtles than sandy wetland soils. Organic materials, especially fine particulate matter, are an important food and habitat resource for invertebrates (Evans et al., 1999). Turtles in ponds with organic substrates grew faster than those in ponds with sandy bottoms, possibly due to increased production of certain aquatic insects (Quinn and Christiansen, 1972; Moll, 1976).
Organic wetland soils may also provide more stable and warmer environmental temperatures.
In the Great Lakes region, Blanding’s turtles were found mainly in areas with sandy upland soils, while in the Northeast upland soils were often sandy loam or gravelly loam. For instance, in Dutchess County Blanding’s turtle populations are associated with till-outwash soils (Kiviat, 1997). This difference may be an artifact of availability; glacial deposits of sand and silt are more prevalent in the Great Lakes region, while glacial till is more prevalent in the Northeast (Hunt, 1986). In the Great Lakes region, Blanding’s turtle populations were mostly located in sand and alluvial silt areas rather than loess, a wind deposited silt, or other surficial deposits. Loess is very fine grained, and may not have favorable thermal, moisture, or structural characteristics for turtle nests. Loess is also very productive farmland; turtle habitat may have declined in loess regions due to agricultural drainage.
The characteristics of upland soils may be an important component of Blanding’s turtle habitat. Maternal selection of nest site was an important factor in the survival and
37 fitness of turtle hatchlings (Wilson, 1998; Kolbe and Janzen, 2001), and was more
important than physical characteristics - such as egg size or carapace length - of snapping
turtle (Chelydra serpentina) hatchling survival (Kolbe and Janzen, 2001). Blanding’s turtles discontinued using a nesting site in Nova Scotia when the substrate size was reduced for human recreation (Blanding’s Turtle Recovery Team, 2003); they appear to avoid sandy sites in Nova Scotia (Power, 1989).
One of the key characteristics of sandy and gravelly soils is that they make a poor growing medium for plants (Miller and Donahue, 1995), creating sparsely vegetated potential nesting sites. Sandy and gravelly soils also warm rapidly (Miller and Donahue,
1995), presumably warming the eggs in the nest. Warm eggs develop and hatch faster
(Sajwaj et al., 1998), giving hatchlings more time to find overwintering areas and to acclimatize to their new surroundings before winter. Blanding’s turtles in Nova Scotia, which often nested in cobble beaches, were probably choosing their nest sites to maximize warming at the northern periphery of their range (Standing et al., 2000).
Blanding’s turtles may also prefer cobble, gravel, or mixed sand areas in the
Northeast and Nova Scotia for hydrologic reasons; the substrate may allow water to percolate more quickly than sand due to its larger pore sizes (Miller and Donahue, 1995), not drowning the eggs. Mean annual precipitation in the Great Lakes region is 51 to 76 cm, while in the Northeast it is 102 cm and in Nova Scotia it is 116 cm (Visher, 1954;
GreenLane, 2004). Herman et al. (1989) also hypothesized that Blanding’s turtles may choose gravel or cobble substrate in Nova Scotia due to its greater stability, making nest construction easier. Nests constructed in sand in Nova Scotia collapsed before the turtle could deposit her eggs (L. Standing, pers. comm.). However, in at least some areas of
38 Massachusetts Blanding’s turtles chose “sandy” soil (but not fine sand) for nesting
substrate (Linck et al., 1989; Butler and Graham, 1995; Butler, 1997).
Water Quality
Blanding’s turtles are often found in eutrophic water, sometimes in organic-
polluted situations. For example, a Blanding’s turtle marsh in Massachusetts received
most of its water from a sewage treatment plant; algal blooms were typical and indicated
cultural eutrophication (Graham and Doyle, 1977). Although there was a less polluted
pool in the same marsh, Blanding’s turtles were typically found in the pool receiving the
effluent (Graham and Doyle, 1977). In some areas, Blanding’s turtle wetland complexes
were surrounded by farmland or suburban land uses and included farm ponds (Dancik,
1974; Kofron and Schreiber, 1985; Rowe and Moll, 1991; Kiviat, 1997; Linck, 1997).
These land uses were probably adding excess nutrients and other pollutants to the system.
Blanding’s turtles may be able to tolerate certain types of pollution, especially organic pollution from sewage or livestock, but not the extreme amount that is associated with urbanization. Habitat fragmentation associated with residential development has been shown to adversely affect Blanding’s turtles (Dorff, 1995; Linck and Moriarty, 1997;
Rubin et al., 2004). Urban and suburban situations provide more opportunities for collectors, increased exposure to automobiles, and greater habitat fragmentation. These may be more important factors than water quality in the decline of Blanding’s turtles in urban and suburban situations.
39
Juvenile Habitat
In much of the literature, an apparent scarcity of juvenile Blanding’s turtles has been noted (Gibbons, 1968a; Graham and Doyle, 1977; Kofron and Schreiber, 1985;
Ross, 1989). Juvenile Blanding’s turtle habitats were often wetlands not occupied by adults or shallow, vegetated sections of occupied wetlands that adults did not frequent.
Juvenile turtles of other species used shallower waters than adults of their species, possibly due to distribution of appropriate or abundant food resources, avoidance of fish and adult turtle predators, swimming abilities, difference in thermal preferences, and social interactions (Congdon et al., 1992; Bodie and Semlitsch, 2000). Fish, however, may not be as important predators of hatchling turtles as has previously been thought; a few studies have indicated that largemouth bass do not prey substantially on hatchling turtles (Semlitsch and Gibbons, 1989; Britson and Gutzke, 1993). Because smaller turtles are subject to higher mortality rates (Iverson, 1991), natural selection may favor young turtles that take advantage of shallow vegetated waters with abundant food resources to grow quickly (Bodie and Semlitsch, 2000). Juveniles may stay in shallow waters until body size decreases their ability to hide or vegetation density impairs their ability to escape predators (Congdon et al., 1992). Juvenile Blanding’s turtles probably have life history requirements similar to other juvenile turtles. As an example, Pappas and Brecke
(1992) attributed Blanding’s juveniles’ use of shallow water and complex vegetation habitats to reduced competition with larger turtles and protection from predators. Care should be taken to include nearby shallow, vegetated wetlands or wetland sections not
40 associated with adult habitat when searching for juveniles or determining the impacts of
development on Blanding’s turtle populations.
We found few references to Sphagnum in the literature on adult habitat, yet it may
be a crucial plant for juveniles, at least in the Northeast and Nova Scotia. McMaster and
Herman (2000) considered Sphagnum along with overhead vegetation cover optimal
habitat for juveniles in Nova Scotia, while Butler and Graham (1995) found that
hatchlings only entered wetlands in areas that contained Sphagnum. Sphagnum was also
the preferred form substrate for hatchlings in Massachusetts (Butler and Graham, 1995).
Because it can cover large areas, is flexible enough for a small turtle to move through but
dense enough to provide cover, and stays moist, Sphagnum can provide optimal habitat
for a young Blanding’s turtle. An exception to juvenile affinity for Sphagnum was in
Indiana, where two yearlings were associated with dense mats of bladderworts
(Kingsbury, 1999). Sphagnum was only available in small patches at this site, and the hatchlings may have preferred the larger area covered by the bladderwort. Younger turtles may be selecting for large areas of dense, flexible submerged vegetation in shallow water rather than a particular species.
Patterns of Habitat Use
Wetland Use
Core-seasonal and winter-summer patterns were not related to any pattern in
climate or surficial geology at the coarse scale available to us on maps (Hunt, 1986;
NCDC, 2000). Nor did we detect differences in wetland complexes or habitat use in the
literature that explained these different habitat use patterns. Blanding’s turtles were
41 probably responding to differences at a finer scale than can be discerned from the
literature. One possibility is that in core-seasonal scenarios, core wetlands warmed
quickly in the spring, allowing the majority of the turtles to make use of these wetlands
for a longer period of time. At sites that exhibit winter-summer patterns, the
overwintering wetlands probably did not warm as quickly, and the turtles promptly
moved to warmer waters or spent time on land. Other possible explanations include food
resources or social behavior.
Movement Patterns
Long Distance Sojourns
Figure 1 is a representation of Blanding’s turtle seasonal and long-term movement
patterns. Long distance movements, either non-annual sojourns or annual nesting
movements, allow Blanding’s turtles to leave unsuitable or overcrowded habitat, find
mates, and increase genetic diversity. While wetland complexes may originally meet food
and shelter requirements, they can eventually become overcrowded or environmentally
unsuitable, causing a few turtles to disperse long distances to other wetland complexes.
Plummer and Shirer (1975), for instance, suggested that the softshell turtle (Trionyx muticus) explored new habitats when its home range became unsuitable. Female
Blanding’s turtles traveled long distances when nesting or sometimes mating, possibly to avoid overcrowding their home range, to establish new habitat, or to effect gene flow.
While many females returned to familiar nesting grounds, others occasionally pioneered new areas. For example, Congdon et al. (1983) observed that while 8 turtles remained faithful to previous nest sites, 3 turtles nested as far as 1300 m from their previous nest
42 sites. In Nova Scotia, certain females nested as far as 1800 m and 2000 m from their
previous nesting site (Standing et al., 2000; McNeil, 2002).
These movement patterns link local populations of Blanding’s turtles, creating a
metapopulation structure. In a Massachusetts study, Butler (1995) found that the
“frequency of movement between wetlands ... suggest(s) that Blanding’s turtles ... comprise a single, more or less freely interbreeding meta-population as opposed to several distinct population units.” Genetic analysis of two populations in Nova Scotia also suggested a metapopulation structure; movements between the populations were common enough to maintain genetic variation but were sufficiently rare to make the two populations genetically distinguishable (Blanding’s Turtle Recovery Team, 2003). In
Dutchess County, adults from several populations mingled in drought refuges or used the same nesting areas (Hudsonia Ltd, unpubl. data). The random movement of hatchlings exhibited in Nova Scotia may also be related to metapopulation maintenance. This has implications for conservation, emphasizing landscape scale features such as land use patterns and habitat fragmentation.
Annual Home Range Movement
Annual home range movement is also important to the conservation of this
species. Inhibiting movement between habitats within a complex may be as harmful to an
animal as actually destroying a wetland (Harris, 1988). Animals that require
heterogeneous habitats, such as Blanding’s turtles, are particularly sensitive to loss of
connectivity in the landscape (Lehtinen et al., 1999; Pope et al., 2000). In fact, wetlands
surrounded by barriers (e.g., major roads, railroads, solid fences) often became unsuitable
for Blanding’s turtles (Dorff, 1995). Aquatic corridors providing connectivity may
43 include streams and ditches (Hall and Cuthbert, 2000; Lang, 2002), and culverts under roads (Lang, 2000; Rubin et al., 2001; T. Hartwig, pers. obs). Terrestrial corridors include undeveloped, or at least roadless, forested or open areas. To allow access to resources and nesting sites and maintain contact between local populations, terrestrial and aquatic travel corridors must be intact.
Mobile animals may increase their home range size in response to development or fragmentation to meet nutritional and shelter needs (Storch, 1997). It is not clear whether this is the case for Blanding’s turtles. Development increases exposure to risks or creates barriers such as roads, curbs, solid fences, or walls. A study of turtles in two suburban preserves in the Chicago metropolitan area found that home range sizes were significantly less in the smaller preserve in late summer, probably due to a lack of natural wetland habitats as the turtles were moving longer distances to inhabit drought refuges
(Rubin et al., 2001). Blanding’s turtles at the Valentine National Wildlife Refuge in
Nebraska had larger home ranges than those in more populated areas (Farrar, 2003). In addition, maximum distances (not related to nesting or home range change) from the literature showed Blanding’s turtles moving longer distances at less developed sites (e.g.,
1500 m at Kejimkujik National Park in Nova Scotia [T. Power, pers. comm.]; 2900 m at
Camp Ripley [Sajwaj et al., 1998]; 2050 m in Maine [Joyal et al., 2001]) than they did at more developed sites (900 m in Dutchess County [Kiviat, 1997]; 722 to 1000 m in
DuPage County, Illinois [Rubin et al., 2001]).
The maximum distances traveled, however, were also from the northern periphery of the range, where soils and waters may be less fertile and food less concentrated.
Longer distances may be traveled in order to fulfill nutritional requirements in these
44 northern areas (e.g., Piepgras and Lang, 2000). In addition, a study of habitat in Weaver
Dunes, Minnesota, found that Blanding’s turtles had larger home ranges in a fragmented section of the Dunes than in an unfragmented section (Hamernick and Lang, in prep). In this case, however, fragmentation of habitat was caused by a lock and dam system, which decreased vegetation productivity and therefore fragmented good habitat, rather than roads and suburban development. Blanding’s turtle home ranges in Camp Ripley,
Minnesota, where habitats are widely dispersed, were larger than in other parts of their range, but were not different from a nearby population in a rapidly developing area
(Piepgras and Lang, 2000 and references cited therein). Blanding’s turtle home ranges are probably larger in areas where widely spaced resources are equivalent to habitat fragmentation, but it is not clear whether suburban development increases or decreases home range size yet. Larger home ranges may require the turtles to expend more energy to meet nutritional or habitat requirements and risk road mortality, while smaller home ranges may decrease nutritional and shelter opportunities or reduce gene pool size and genetic diversity.
CONCLUSIONS
Although Blanding’s turtle habitat complexes are different in the Great Lakes region, Northeast, and Nova Scotia, they perform similar functions. Deep pools (>1 m) provide hibernacula and cool water during summer heat. Shallow waters with abundant emergent and submerged vegetation offer shelter from predators and nutrition for food resources. Organic wetland soils supply nutrients to the wetland system and may warm
45 the waters quickly in spring, while infertile, coarse-textured upland soils provide nesting
sites. Open areas (moats, ponds, leafless shrubs, herbaceous wetlands) provide basking
sites, and basking perches are supplied by emergent or submerged vegetation or fallen
trees from the woody fringe. Undeveloped upland areas provide estivation sites and travel
corridors between wetlands.
Conservation of the Blanding’s turtle must be considered at all habitat scales if
the species is to persist amid human-induced pressures. At the microhabitat scale,
Blanding’s turtles require feeding areas, basking sites, refuge sites for periods of inactivity (deep pools, dried wetlands, terrestrial sites), and overwintering sites. Juveniles and yearlings require shallow vegetated areas. Drainage or altered hydrology (through, for example, agricultural practices or residential development) may eliminate deep pools and change the chemical characteristics of the wetland. Removal of a surrounding fringe of trees may reduce basking sites or allow water temperatures to reach intolerable levels.
Any human activities that affect the chemical, vegetation, or hydrologic conditions in
Blanding’s turtle wetlands should be avoided.
At the landscape scale, landscape complementation effects as well as conservation of landscape corridors must be considered for species showing metapopulation dynamics
and requiring the use of several habitat types (Pope et al., 2000). Landscape
complementation is a measure of the availability of all critical habitats needed for a
species to complete its life cycle (Dunning et al., 1992; see also Taylor et al., 1993).
Critical habitat for Blanding’s turtles constitutes overwintering habitat (which varies by
site), a diversity of nearby wetlands available for seasonal use, and upland areas for
nesting and other life history requirements. Blanding’s turtles require wetlands with
46 organic substrates and abundant vegetation, generally marshes or ponds in the Great
Lakes region, shrub swamps in the Northeast, and the lower reaches of rivers and bays of
lakes in Nova Scotia. These habitats cannot exist in isolation; rather they must be part of
a wetland complex with habitats that provide drought refuge, seasonal food resources,
juvenile habitat, and thermoregulation opportunities. Upland areas surrounding the
wetland complex must provide nesting sites, travel corridors between wetlands and to
nest sites, cool sites for periods of inactivity when wetlands are dry or too warm, and
warm sites for basking when waters are cold.
Residential development in or near Blanding’s turtle habitat complexes alters
chemical and hydrologic wetland regimes, increases road mortality, exposes turtles to
collectors, isolates populations, and degrades or eliminates upland habitat. Development
also “subsidizes” many predators of turtle eggs and hatchlings, increasing predator
densities and predation rates (Mitchell and Klemens, 2000). Raccoons are known to be a
major predator of eggs in Nova Scotia (Power, 1989). Although it is thought that many of
these predators - including skunks (Mephitis mephitis, Spilogale putorius), crows (Corvus
spp.), opossum (Didelphis virginiana), and foxes (Vulpes vulpes, Urocyon cinereoargenteus) - have detrimental effects on turtle populations, only ravens (Corvus spp.) and raccoon (Procyon lotor) have been studied to date (Mitchell and Klemens,
2000).
Several studies have documented detrimental effects of development on
Blanding’s turtle populations (Dorff, 1995; Linck and Moriarty, 1997; Rubin et al., 2001,
2004). Roads kill turtles, create barriers to gene flow, provide collectors and vandals easy access to wildlife, and increase development density (Boarman et al., 1997; Wood and
47 Herlands, 1997; Findlay and Bourdages, 2000; Trombulak and Frissell, 2000). (See
Trombulak and Frissell (2000) for a detailed description of these and other affects.)
Development and road construction near known Blanding’s turtle habitat should be restricted or avoided, or at least planned with the turtles in mind. Where development has already encroached upon Blanding’s turtle habitat, management or mitigation may be required (Joyal, 2001), with the goal of increasing or maintaining both adult survival
(Congdon et al., 1993; Rubin et al., 2004) and juvenile survival (Iverson, 1991; Rubin et al., 2004). While juveniles of long-lived species are often considered less important for conservation than adults (Congdon et al., 1993), Rubin et al. (2004) argued that in threatened populations in suburban Chicago, where adult mortality was extremely low and apparently natural but populations were small, conservation of juveniles was also important.
Joyal (2001) suggested that an upland matrix surrounding a complex of wetlands is required to protect Blanding’s turtle populations. Buffer zones of at least 100 m are recommended for general wildlife and water quality protection (Environmental Law
Institute, 2003); however, for a wide-ranging species like the Blanding’s turtle 100 m is clearly insufficient. For the Blanding’s turtle, a 1000 m buffer zone surrounding a wetland complex of regularly-used wetlands, rather than individual wetlands, would encompass the average home range length in most populations (Table 4). A 1000 m buffer will include most or all of the habitats used by an adult even if that individual’s home range only slightly overlaps the known habitats of the complex. We advise implementing a 1000 m buffer zone for unstudied populations throughout the geographic range. If a population can be radio-tracked for at least 2 years, this buffer zone can then
48 be adjusted to the actual activity areas, and aquatic and terrestrial connections to other known populations or occupied wetlands can be incorporated. If long-term studies are not possible, a 1000 m zone may represent the best compromise between scientific conservation and economic activities. Current wetland regulations do not adequately protect Blanding’s turtles. Buffer zones are not required for federally regulated wetlands in the United States, and buffer zones for state regulated wetlands in many states, including New York and Massachusetts, do not usually exceed 31 m (Montella, 1991;
Riexinger, 1991; Butler, 1997; Schneider et al., 2002). In suburban areas where wetlands have been destroyed, additional wetland construction may be necessary to satisfy the turtles’ life history requirements (e.g., Kiviat et al., 2000).
Within a buffer zone, development should be avoided or planned carefully and mitigated for, and landowners should be educated about Blanding’s turtle ecology and conservation. Buffer zones need not necessarily be free of human influence; however, erring on the side of caution is appropriate. Allowing even low-impact human recreation
(hiking and fishing) within the area occupied by a wood turtle population was clearly shown to detrimentally affect the turtles (Garber and Burger, 1995). New development
(including road construction), for example, should be avoided within the buffer zone. If this is not possible, development should be avoided within 200 meters of a wetland complex to prevent destruction of upland habitats used for basking and summer inactivity periods. Development should also be avoided between regularly-used wetlands and between regularly-used wetlands and other habitats, including nesting areas and drought refuges. Development in other areas within the buffer zone should be planned carefully.
New and existing roads should be fenced and have wide culverts so that the turtles can
49 cross the road safely (e.g., Lang, 2000; Farrar, 2003). In addition, “Rare Turtle Crossing” signs can be erected during nesting season, when adult females are most at risk (e.g.,
Lang, 2000; Farrar, 2003), curbs can be angled at 45° so that turtles, including hatchlings, can climb them rather than following them to certain death in storm drains (Piepgras et al., 1998), storm drains can be screened to keep hatchling out, and planners can consider gravel roads, lower speed limits, or speed bumps to slow down traffic. Females, however, may be at risk if they attempt to nest on gravel road surfaces. Developments should be planned to create as little increased pavement area as possible and to avoid destruction or alteration of wetlands regardless of their size. Homeowners or public agencies should refrain from using herbicides or weed harvesting in ponds or wetlands, because aquatic vegetation is an important component of Blanding’s turtle habitat. Public education, in the form of a poster campaign or a mailing, should also be implemented within the buffer zone (e.g., Herman et al., 1998; McNeil, 2002). A poster or packet could include information on actions homeowners can take to protect Blanding’s turtles (e.g., looking under cars during nesting season, fencing swimming pools, covering pitfalls such as window wells, watching carefully when mowing, leaving brush piles or creating shrub thickets for resting turtles). Posters and mailings are also an efficient way to collect additional information on Blanding’s turtle habitats (Herman et al., 1998; McNeil, 2002).
Certain military activities and small-scale agricultural practices within a
Blanding’s turtle buffer zone may be more compatible with turtle conservation than suburban developments, creating disturbed land for nesting females and preserving undeveloped land (e.g., Petokas, 1986; Linck et al., 1989; Butler, 1995, 1997; Piepgras and Lang, 2000; Lang, 2003). Farm ponds may also provide habitat for Blanding’s turtles
50 (Linck, 1988) if not overly polluted. Farm or military machinery, however, may crush eggs or turtles, pesticides may damage embryos, wetlands may be drained for agricultural purposes, and agricultural or military activities may increase erosion, adding mineral sediments to the wetlands. These land uses can be either a sink or a source for Blanding’s turtle populations, depending on how they are managed. Wildlife managers should work with farmers and military bases to minimize risk to eggs or turtles during critical times of the year, generally June – September, and to avoid siltation or other damage to the wetlands. Purchase of Development Rights (PDR) programs in many states buy development rights to agricultural lands, ensuring that they remain open space. Because farms have the potential to both damage and sustain turtle and other animal populations,
PDR and similar programs should take into greater consideration the affect of specific farming practices on local wildlife when accepting applications.
The Blanding’s turtle range lies generally within the 4.4ºC – 10ºC normal annual mean temperature range (Thomas, 1953; Visher, 1954). Reptiles and amphibians tend to have low dispersal rates and high sensitivity to moisture and temperature fluctuations, and may be particularly at risk of extinction under global warming conditions (Hall and
Cuthbert, 2000). As the climate warms, Blanding’s turtles may be unable to tolerate temperature fluctuations beyond their current temperature range. In areas where mean annual temperature is expected to increase, Blanding’s turtles may be particularly at risk due to their low critical thermal maximum (Hutchison, 1966). Blanding’s turtle as a species is at least 5.5 million years old (Lang, 2001); and has survived global climate changes in the past. The current warming trend, however, is occurring rapidly and temperatures may increase even more quickly in the future (Cox and Moore, 1993).
51 Turtles may not be able to adapt or migrate quickly enough, considering current landscape fragmentation in North America (see Williams et al., 1998). Because development leads to fewer and more isolated wetlands and more roads, it decreases an animal’s ability to migrate from unfavorable environments (Findlay and Bourdages,
2000; Gibbs, 2000; Trombulak and Frissell, 2000). Large-scale corridors should be incorporated into land use planning now in order to prevent the need for more drastic measures, such as transporting populations to better habitat or keeping individuals in zoos, in the future.
It has been argued that habitat selection at coarser scales (i.e. range-wide) reflects the most important factors for an animal’s survival (Rettie and Messier, 2000). Selection at finer scales (i.e., landscape, microhabitat) will continue to reflect these factors until the next most important factors become more relevant (Rettie and Messier, 2000). If we compare Blanding’s turtle habitat range-wide, we find certain features appear in all populations studied: wetland complexes that include a variety of wetlands and open or disturbed upland areas, and sandy or gravelly soils. Wetland complexes contain: open deep pools (m 1 m) or ponds; shallow vegetated areas (at least 0.1 m) within wetlands, basking sites (which vary by location), and organic wetland soils. In addition, to remain viable, populations require minimum habitat fragmentation and road construction, or possibly mitigation measures such as culverts to compensate for prior development.
Blanding’s turtle complexes that are unable to meet these requirements will require the turtles to expend more energy at finer scales to compensate, leading to decreased fitness and exposing individuals to higher risks (e.g., Rettie and Messier, 2000). As an example, if organic soils become silted in a Blanding’s turtle wetland, food resources may decrease
52 and the turtles will spend more time searching for food or may need to leave the wetland to search for more suitable habitat.
At the landscape scale, wetland complexes vary by region, and by site, to meet range-wide needs on a local basis. Wetland type, landscape, preferred vegetation, upland soils, water quality and characteristics, and patterns of habitat use all vary by region or by site. While certain wetland types or soils tend to dominate in each region, there is enough variability to justify caution in generalizing these habitat patterns to specific populations without prior research. At the microhabitat scale, basking, inactivity, drought refuge, nesting, feeding, and overwintering sites vary by location and by season or year.
Therefore, temporal as well as spatial scales must be considered when studying the ecology of this species. Protection of a specific population ideally requires long-term study of that population or nearby populations judged by local experts to be using similar habitat. Two years of research, one during a dry year and one during a wet year, are probably the minimum required to gain an understanding of any population of Blanding’s turtles.
ACKNOWLEDGEMENTS
Our work was funded in part by the Geoffrey C. Hughes Foundation. This paper is part of the senior author’s thesis for the Master of Science in Environmental Studies degree at
Bard College. Charlie Canham, Jeff Lang and Lorraine Standing were members of the thesis committee and provided editorial review. We thank Krista Munger, Raymond
Saumure, and Lorraine Standing for earlier reviews. We also thank Jaime Hazard for editorial assistance. Finally, we thank Al Breisch, Brian Butler, Carol Hall, James
53 Harding, Tom Herman, Jeff Lang, Steve Mockford, James Moriarty, Krista Munger,
Mike Oldham, Terry Power, James Rowe, Cory Rubin, Lorraine Standing, and Fred
Schueler for their communications and insights. This is Bard College Field Station-
Hudsonia Contribution 94.
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73 Table 1. Blanding’s turtle status in states and provinces throughout its range. State or Province
Status: E = Endangered, T = Threatened, SC= Special Concern or in need of conservation. National
Heritage Status: S = Subnational; 1 = critically imperiled, 2 = imperiled, 3 = vulnerable to extirpation or extinction, 4 = apparently secure. National Heritage status is from NatureServe (2003).
State or Province State or National Reference for State or Province Listing Province Status Heritage Status USA Illinois T S3 Center for Reptile and Amphibian Research, 2004 Indiana E S2 Center for Reptile and Amphibian Research, 2004 Iowa T S3 Center for Reptile and Amphibian Research, 2004 Maine E S2 Maine Department of Inland Fisheries and Wildlife, 2004 Massachusetts T S2 Natural Heritage and Endangered Species Program, 2004 Michigan SC S3 Center for Reptile and Amphibian Research, 2004 Minnesota T S2 Center for Reptile and Amphibian Research, 2004 Missouri E S1 Center for Reptile and Amphibian Research, 2004 Nebraska SC S4 Farrar, 2003 New Hampshire SC S3 New Hampshire Department of Environmental Services, 2004 New York T S2, S3 New York State Department of Environmental Conservation, 1991 Ohio SC S2 Center for Reptile and Amphibian Research, 2004 Pennsylvania extirpated S1 Pennsylvania Department of Conservation and Natural Resources, 2004 Rhode Island extirpated Standing, 2000 and pers. comm. cited therein South Dakota T S1 Natural Source, 2004 Wisconsin T S3 Center for Reptile and Amphibian Research, 2004 Canada Nova Scotia E S1 Standing, 2000 and pers. comm. cited therein Ontario No status; S3? Ontario Ministry of Natural Resources, 2004; recommended T Standing, 2000 Québec No status; S1 Herman et al., 1994; L. Standing, pers. comm. candidate
74 Table 2. Blanding’s turtle habitat use in the Great Lakes region
Location Aquatic Habitat Upland Landscape Reference Illinois Illinois River, tributary streams Fields, woods, Cahn, 1937 or adjacent swampy areas prairies, sandy areas Illinois, Des Plaines Overflow swamps, mudflats Forested Dancik, 1974 River Illinois, Fox River, Man-made ponds, lowland marsh Deciduous forest, Rowe, 1987 Chain O’ Lakes State areas prairie, farmland Park Illinois, Pratts Wayne Marshes, flooded timber, sedge Suburban, Rubin et al., 2001 Woods and West meadows, wet prairies, ponds, agricultural Chicago Prairie and lakes Indiana Drainage ditches, swampy -- Grant, 1936 ground, shallow grassy pond Indiana, Jasper-Pulaski Wet prairie and sedge meadow Oak forest, Brodman et al., and Willow Slough Fish savannah, and sand 2002 and Wildlife Areas prairie Indiana, Lake Small shallow ponds, marshes, Deciduous Evermann and Maxinkuckee and ditches. Temporary woodlands Clark, 1920 woodland ponds Indiana (northeast), Cat-tail-sedge wetland, forested Deciduous forests, Kingsbury, 1999 Pigeon River Fish and and shrub wetlands Managed prairies, Wildlife Area agricultural fields Michigan Marshes, ponds, and river -- Harding, 1990 backwaters Michigan (southwest), Grass-sedge marsh, eutrophic -- Gibbons, 1968b Sherriff’s Marsh and lake Wintergreen Lake Minnesota Small streams, drainage ditches, -- Breckenridge, marshy places 1944 Minnesota Shallow emergent marshes Grasslands Dorff, 1995 Minnesota, Crow- Wetlands with floating sedge Old fields, planted J. Moriarty, Hassan Reserve mats and peat bottoms, prairies, mesic pers.comm.. mesotrophic lakes woodlands Minnesota, Camp Shrub swamps, deep and shallow Mixed hardwood Sajwaj et al., Ripley marshes, ponds and conifer forest, 1998; Piepgras fields, training and Lang, 2000 ranges Minnesota, Marget Lake Vegetated lakes Old field, farmland, Hall and Wildlife Management woodlots on sand Cuthbert, 2000 Area and Cedar Creek plains Natural History Area Minnesota, Meadowvale Ditches, restored wetlands, -- Lang, 2002 wetlands around ponds and lakes
75 Table 2 continued Location Aquatic Habitat Type Upland Landscape Reference Minnesota, Prairie potholes, ephemeral Dry terraces, Lang, 2003 southwestern wetlands, streams cropland, dairy pasture Minnesota, Weaver Side channels of Mississippi Sand terrace, Pappas et al., Dunes River, eutrophic ponds, marshes, agricultural crops, 2000; Hamernick backwater areas, flooded prairie, oak savanna and Lang, in prep deciduous woods Missouri Preferred: natural marshes, river -- Johnson, 1981 sloughs. Also ponds and drainage ditches Missouri, Mississippi Marsh Grassland, pasture Kofron and River floodplain Schreiber, 1985 Nebraska Lakes Sandhills Hudson, 1942 Nebraska Lakes and marshes Prairie Ballinger et al., 1979 Nebraska, Valentine Small ponds and marshes, edges Sandhills Germano et al. National Wildlife of lakes 2000, Bury and Refuge Germano, 2003 New York (northern), Shrub wetlands, beaver-created dairy farm pasture, Petokas, 1979, St. Lawrence River wetlands and ponds, emergent- forested 1985 shrub marsh New York, St. Isolated coves, weedy bays, -- Department of Lawrence River shallow, marshy waters and Environmental ponds Conservation, 1991 Ohio Ditches, bogs, swamps, marshes Lake plains and till Conant, 1938 associated with lakes plains Ohio, Lake Erie Marshes of Sandusky Bay, -- Cormack and shoreline Cormack, 1975 Wisconsin Open grassy marshes, backwater Mesic prairie Vogt, 1981 sloughs, prairie potholes, shallow slow-moving rivers and shallow lakes Wisconsin Stream, marsh Prairie, oak forest Temple, 1987 Wisconsin, Crex Deep, large, permanent marshes Brush prairie, pine Evrard and Meadows Wildlife Area barrens Canfield, 2000 Wisconsin, Fort McCoy Ponds, borrow pits, streams, -- Wilder, 2003 lakes, ditches, marshes Wisconsin, Pentenwell Ponds with abundant vegetation, Grasslands, forested Ross and Wildlife Area ditches, streams Anderson, 1990 Canada Shallow, marshy waters and -- Froom, 1976 ponds
76 Table 2 continued Location Aquatic Habitat Type Upland Landscape Reference Ontario, Peterborough Beaver ponds, marshes or open M. Oldham, pers. region swamps, ponds, small lakes, bays comm of larger lakes Ontario Creekside shrub swamps, Young forests F. Schueler, pers. buttonbush swamps along creeks, comm. and field ditches, ponds, Typha marshes, notes, 1972-2003. rocky stream Ontario, Arden, Big Wide, shallow, densely vegetated -- Saumure, 1990 Clear Lake tributary stream Ontario, Byron Bog Pond within floating bog Deciduous forest Judd, 1965 Ontario, Long Point Marshy ponds, shallow marsh -- Snyder, 1931 areas Ontario, Long Point, Grass-sedge wetland -- Ashley and Big Creek National Robinson, 1996 Wildlife Area Ontario, Point Pelee Temporary rain pools -- Snyder, 1921 Ontario, St. Lawrence Sedge meadow Deciduous forests, Petokas, 1986 River, Grenadier Island abandoned farm fields
77 Table 3. Blanding’s turtle habitat use in the Northern United States and Nova Scotia Location Aquatic Habitat Upland Landscape Reference Maine Marshes, shrub swamps, slow- -- Graham, 1992 moving rivers and streams, farm ponds, vernal pools Maine, York County Pools with scrub-shrub border Deciduous –coniferous Joyal, 1996; (core), fen complex (core), forest Joyal, 2001 scrub-shrub swamps, forested wetlands, seasonal pools Massachusetts Marshes, sloughs, buttonbush Woodlands Butler, 1992 swamps, temporary pools Massachusetts, Riverine marsh -- Graham and Concord and Sudbury Doyle, 1977 Rivers, Great Meadows National Wildlife Refuge Massachusetts, Marsh-shrub (buttonbush) Woodlands, bare Butler 1995, Nashua River Valley, swamp, floodplain buttonbush disturbed sand, sparse 1997; Butler and Fort Devens, ponds, vernal pools, forested herbaceous vegetation, Graham, 1995 wetlands, borrow pits scrub-shrub vegetation New York, Dutchess Shallow water-lily and Hay and corn fields, Eckler and County buttonbush pond (core) woodlots, residential Breisch, 1988 New York, Dutchess Woodland pond (core), shrub Forest, meadow, Klemens et al., County swamp, buttonbush pond maintained land 1992 New York, Dutchess Buttonbush swamps, Hardwood forests, Kiviat, 1997 County intermittent woodland pools, shrubby abandoned acidic bogs fields, hay, maize, cattle pasture, “waste grounds,” maintained land New York, Saratoga Shallow ponds with buttonbush Sand plains A. Breisch, pers. County comm Nova Scotia, Vegetated coves, bogs and Forested Gilhen, 1984; Kejimkujik National vegetated inlets of Kejimkujik Herman et Park Lake, boggy marshlands al.,1989, Power, associated with tributary rivers 1989; Power et al., 1994; McMaster and Herman, 2000 Nova Scotia, beaver-maintained vegetated cottage development, McNeil, 2002 McGowan Lake bogs and coves of McGowan forest, harvested Lake, riverine sedge-shrub woodlots meadow Nova Scotia, Pleasant open and forested tributary -- Blanding’s Turtle River streams, beaver-maintained Recovery Team, riparian wetlands 2003
78 Table 4. Acreage of wetlands used by Blanding’s turtles and home ranges and activity centers of
Blanding’s turtle. Mean home range lengths are in parenthesis except where mean length was the only data reported.
Location Wetland Home Home Activity Reference Acreage Range (ha) Range Center (ha) (ha) Lenth (m) Illinois, Chain of Lakes -- -- 480 to 870* 0.4 to 2.3 Rowe and State Park Moll, 1991 Illinois, Pratts Wayne -- 0.1 to 9.8* -- -- Rubin et al., Woods and West Chicago 2001 Prairie Indiana, Pigeon River Fish 4.3 to 10.9 0.18 to 16.7 -- 0.15 to 2.7 Kingsbury, and Wildlife Area 1999 Maine, York County > 0.4 -- 90 to 2050 -- Joyal, 2001 (680)** Massachusetts, Nashua 25 ------Butler and River Valley Graham, 1995 Michigan, E.S. George 0.4 to 0.6, ------Congdon and Reserve 5, 7.3 Gibbons, 1996 Michigan, Sheriff’s Marsh 8, 35.6 ------Gibbons, and Wintergreen Lake 1968b Minnesota, Camp Ripley > 6, 18, 371 5.9 to 7.8 208 to 2700 1.5 to 2.6 Piepgras and (835) Lang, 2000 Minnesota, Crow-Hassan < 0.4, 2, 8.4 ------Linck and Park Reserve Moriarty, 1997 Minnesota, Marget Lake and 0.5 to 4, 8, -- 300 to 1000 -- Hall and Beckman Lake 40 (700) Cuthbert, 2000 Minnesota, southwestern 28 ------Lang, 2003 Minnesota, Weaver Dunes 750, 1620 2.2 to 292 370 to 5183 -- Pappas et al., (~1633) 2000; Hamernick and Lang, in prep Nebraska, Valentine 0 to 327 ------Bury and National Wildlife Refuge Germano, 2003 New York, Dutchess County 0.1 to 7.2 ------Kiviat, 1997 New York, Dutchess County 6.8 ------Eckler and Breisch, 1988 New York, Dutchess County 0.6 to 4 ------Kiviat et al., 2000 New York, St. Lawrence 40.7 ------Petokas, 1979 River
79 Table 4 continued Location Wetland Home Home Activity Reference Acreage Range (ha) Range Center (ha) (ha) Lenth (m) Nova Scotia, McGowan 11 0.03 to 3.1 -- -- McNeil, 2002 Lake
Ontario, St. Lawrence River, 70 ------Petokas, 1986 Thousand Islands region Wisconsin, Fort McCoy -- 1.5 to 278 -- -- Wilder, 2003 Wisconsin, Pentenwell < 0.2; -- 260 to 635 0.56 to 0.94 Ross and Wildlife Area ponds (489) Anderson, 1990 *mean distance or acreage, **distance between wetlands
80 Table 5. Water quality and characteristics in Blanding’s turtle wetlands.
Location Nutrient Acidity Water Water Reference levels depth (m) color Illinois, Chain of Lakes -- -- 1.5, 2.5 -- Rowe and Moll, State Park 1991 Indiana, Pigeon River -- -- 1.5 -- Kingsbury, 1999 Fish and Wildlife Area Indiana, Lake ------Tea- Evermann and Maxinkuckee colored Clark, 1920 Maine -- -- > 0.5 Dark Graham, 1992; Joyal, 1996 Massacusetts, Great Eutrophic ------Graham and Doyle, Meadows Refuge 1977 Massachusetts, Nashua -- -- 1 to 2 -- Butler and Graham, River Valley 1995 Michigan, Sheriff’s Eutrophic Calcar- -- -- Gibbons, 1968b Marsh and Wintergreen eous Lake Michigan, E.S. George -- -- 1.3 -- Sexton, 1995 Reserve Minnesota, Camp Ripley -- -- 0.1-2; up to Discolored Sajwaj et al., 1998; 4 Piepgras and Lang, 2000 Minnesota, Marget Lake -- -- 1 to 2 -- Hall and Cuthbert, and Beckman Lake 2000 Minnesota, Weaver Eutrophic ------Pappas et al., 2000 Dunes Minnesota, Crow-Hassan Meso- Non- -- -- J. Moriarty, pers. Reserve eutrophic calcareous comm. Minnesota, southwestern -- Calcar- 0.25 to 0.5 -- Lang, 2003; J. eous (stream) Moriarty, pers. comm. Missouri, northeastern ------Clear Kofron and Schreiber, 1985 New York, Dutchess Oligotro- Calcar- 0.5 to 1.2 -- Kiviat, 1993; County phic eous Kiviat, 1997; C. Galik, unpubl. data New York, Dutchess Eutrophic -- 1; up to 4 -- Eckler and Breisch County 1988 New York, St. Lawrence -- -- 2.5* -- Petokas, 1979 River region
81 Table 5 continued Location Nutrient Acidity Water Water Reference levels depth (m) color
Nova Scotia, Kejimkujik Oligotro- Acidic 0.2 to 3 Highly Kerekes, 1975; National Park phic colored Power et al., 1994; Herman, 1997; McMaster and Herman, 2000 Ontario, St. Lawrence -- -- .75 -- Petokas, 1986 River, Thousand Islands Wisconsin, Pentenwell Eutrophic Slightly < 3 Highly Ross, 1985; Ross Wildlife Area acidic (ponds); [ colored and Anderson, (pH=6.9) 0.3 1990 (marshes) *mean depth of creek running through marsh
82
Table 6. Long distance movements not related to nesting
Location Distance (m) Sex Date Reference Illinois 895 – 1400 Female, male Late May to July Rowe and Moll, 1991* Illinois 722 – 1000 Female, male -- Rubin et al., 2001 Maine 1330 Female June or July Joyal, 2000 Massachusetts 1000 – 1600 Female, male -- Butler, 1995 Minnesota 2200 Male July Hall and Cuthbert, 2000* Minnesota, 5632 Male Mid-May Lang, 2001* Weaver Dunes Nebraska, ~3200 Male Late April to early June Farrar, 2003* Sandhills New York, 2600 Female -- Hudsonia Ltd, Dutchess County unpubl. data Nova Scotia 5000 – 11,500 Male -- Power et al., 1994 Wisconsin 900, 1240 Male July Wilder, 2003* *Data for these turtles was only available for one year or the duration of the study was unknown; therefore we cannot be certain these were not annual movements.
83 Table 7. Blanding’s turtle hibernation patterns.
Location Water Depth, Water Temperature, Date Reference cm ºC Illinois -- 5 19 October to 22 Rowe and Moll, November 1991 Indiana 30 – 50 -- -- Kingsbury, 1999 Massachusetts 3 – 110 9 October Graham and Butler, 1993 Minnesota 40-170 -- 15 November Sajwaj et al., 1998 Missouri 10, 20 6.2, 7.5 31 October, 15 Kofron and November Schreiber, 1985 New York, -- -- Mid-fall Kiviat, 1993 Dutchess Cty Nova Scotia 50 – 200 -- Mid-November or later Herman et al., 1989, 1994 Ontario ~100 -- -- Schueler, 1981 Wisconsin 90 10-13 20 September to 22 Ross and Anderson, October 1990
84 Intermittent Woodland Secondary Pools Foraging Habitat Streams
Bogs Juvenile Juvenile Habitat Habitat Streams
Often Long Distance Nesting Core or Winter Deep Habitat Wetlands Pools Drought Habitat Upland
Wetland Habitat
Staging E x
Habitat pl Dry L
o o Wetlands
r n a
g
t o
D r
y i Deep or s
Overwintering Upland E t
a x Shallow
n Habitat Staging c
c ur
Habitat e Water s
D
i o i
s n
p s Streams
e
r s
a
l Key regular movement Wetland occasional movement New Habitat core or winter wetlands Habitat seasonal or summer wetlands Complex upland
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Tanessa Hartwig Hudsonia Ltd., Bard College Graduate School of Environmental Studies P.O. Box 5000 Annandale on Hudson, New York, 12504 845-758-7274; FAX 845-758-7033; Email [email protected]
RH: Microhabitat Use by Blanding’s Turtle • Hartwig and Kiviat
MICROHABITAT ASSOCIATION OF BLANDING’S TURTLES IN NATURAL
AND CONSTRUCTED WETLANDS IN SOUTHEASTERN NEW YORK
Tanessa Suzan Hartwig1, Hudsonia Ltd. and Bard College Graduate School of
Environmental Studies, P.O. Box 5000, Annandale on Hudson, NY, 12504, USA
Erik Kiviat, Hudsonia Ltd., P.O. Box 5000, Annandale on Hudson, New York, 12504,
USA
Abstract: We studied Blanding’s turtle (Emydoidea blandingii) microhabitat in wetlands
constructed for the turtles and natural wetlands in Dutchess County, New York, USA. We
intended to determine Blanding’s turtle microhabitat association and the suitability of the
constructed wetlands as habitat for the turtles. Microhabitat was determined by
radiotracking individuals to their exact locations and recording habitat variables.
Blanding’s turtles were associated with shallow water depths (x = 30 cm), muck
substrates, and areas of abundant vegetation (total coverx = 87%). Buttonbush
(Cephalanthus occidentalis) had the greatest mean total cover (29%). In the constructed
wetlands, Blanding’s turtles were associated with significantly less cover and warmer
water than in the reference (natural) wetlands. Blanding’s turtles appear to be using the
constructed wetlands to bask and forage in the spring and early summer, but move to
deeper wetlands in late summer, when the constructed wetlands dry up or become too
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warm, and in the winter to overwinter. 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), deep pools and shallow water
areas, neuston, and submerged aquatic vegetation. Because the constructed wetlands do
not provide core habitat for the turtles, destruction or damage to core habitat for
Blanding’s turtles should be avoided. Construction of new habitat near core habitat
should, however, be considered, particularly where habitat has already been degraded,
fragmented, or destroyed. Many other wetland animals use multiple wetland types to
fulfill their life history requirements; these comments probably apply to them as well.
JOURNAL OF WILDLIFE MANAGEMENT 00(0):000-000
Key Words: Blanding’s turtle, conservation, constructed wetlands, Emydoidea blandingii,
habitat, microhabitat, mitigation, New York, radiotelemetry, threatened species,
wetlands.
Blanding’s turtle is listed by the New York State Department of Environmental
Conservation as threatened in the 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), and the St. Lawrence
River Valley (northeastern New York). The disjunct Dutchess and Saratoga County
populations are considered relict populations. In eastern North America, other relict populations exist in eastern Massachusetts, southern New Hampshire, southern Maine, and southern Nova Scotia (Ernst et al. 1994:240). The turtle’s range centers on the Great
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Lakes in the USA and Canada (Ernst et al. 1994:240). Habitat loss is a major threat to the
Blanding’s turtle and appears to be a key factor in population declines (Kofron and
Schreiber 1985, Congdon and Gibbons 1996, Kiviat 1997, Standing 2000).
Much is known about Blanding’s turtle habitat selection at the landscape scale - the wetland ecosystems and surrounding areas that the turtles use during their lives
(Hartwig 2004.). Throughout their range, Blanding’s turtles tend to use a habitat complex made up of several wetlands and adjacent or non-adjacent upland areas (Hartwig 2004).
In Dutchess County and in some other parts of their range, wetland complexes used by this species consist of core wetlands and seasonal wetlands (Ross and Anderson 1990;
Rowe and Moll 1991; Kiviat 1997; Barlow 1999; Joyal 2001; B. O. Butler, Oxbow
Wetlands Associates, personal communication). Core wetlands are regularly used by adult turtles, particularly during the winter, spring, early summer, and fall. Many of the core wetlands in the Northeast have been described as shrub swamps or ponds, often composed largely of buttonbush with areas of open water, and function as overwintering, feeding, and thermoregulation habitat (Hartwig 2004).
In contrast, seasonal wetlands are used during early spring through late summer.
Seasonal wetland types are more variable than core wetlands and in Dutchess County they include intermittent woodland pools, riparian wetlands, emergent marshes, wooded swamps, acidic bogs, lakes, and ponds (J. Eckler and A. Breisch. 1988. The Blanding’s turtle (Emydoidea blandingii) in a Dutchess County Nature Conservancy Preserve, New
York Field Office of the Nature Conservancy; Kiviat 1997; Hudsonia Ltd., unpublished data). Seasonal wetlands have many functions. They serve as rehydration or staging areas during nesting migrations, or drought refuges, thermoregulation areas, or feeding areas -
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particularly when the core wetlands become unsuitable. Core wetlands may, for example,
dry up or become overcrowded. Sluggish streams are also occasionally used as refugia
from warm waters and as movement corridors (Hudsonia Ltd, unpublished data).
In many areas, Blanding’s turtle habitat is becoming increasingly fragmented, and
wetlands are being degraded or destroyed. Opportunities to increase extent of Blanding’s
turtle habitat, or improve its quality, should be considered, and where possible integrated
into conservation and restoration programs for this species at risk. Wetland restoration,2 however, often ignores key ecological principles (Zedler 2000), resulting in a success rate of less than 50% and a net loss of wetlands (Mitsch and Wilson 1996, Mitsch and
Gosselink 2000:680-684). Reasons for failure are many, and include improper water levels and hydroperiod (Mitsch and Gosselink 2000:681-684) and habitats dissimilar to those being replaced or inappropriate for the target species (Zedler 2000). Therefore, special attention and caution are required when restoring wetlands for a rare species such as the Blanding’s turtle.
Few published studies have monitored the success of wetland restoration in arresting the decline of rare animal species. Most research has monitored rare birds in restored salt marsh habitats, where results have indicated success (Shuwen et al. 2001), partial success (Haltiner et al. 1997, Boyer and Zedler 1998), or partial failure (Powell and Collier 2000, Darnell and Smith 2001). One study discussed the success of a restored salt marsh in increasing habitat for endangered salmon species (Tanner et al. 2002). Our study investigates the effects of a freshwater wetland restoration project on Blanding’s turtles and their habitat use and association over 3 years.
2used here in its broadest sense, includes wetland construction as well as improvement of degraded wetlands (Kiviat et al. 2000, Zedler 2000)
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As part of a plan to expand its buildings, parking lots, and athletic fields, the
Arlington Central School District in Dutchess County proposed to fill a 0.7-ha wetland used by Blanding’s turtles. The New York State Department of Environmental
Conservation issued a permit to fill the wetland with the condition that 1.4 ha of suitable wetland habitat be created. In 1996, Hudsonia Ltd. (Annandale, NY) designed the wetland mitigation project as habitat for Blanding’s turtles. Part of the rationale behind
Hudsonia’s participation was the opportunity to protect and study Blanding’s turtles and their habitat, and the chance to develop methods that could be used elsewhere to expand and restore habitats for this species (Kiviat et al. 2000). Construction of the new wetlands was completed in May 1997. Hudsonia has monitored the success of the mitigation project for 8 years.
Beginning in 1996, turtles were live-trapped each May in the natural (reference) and the newly created wetlands. Radio transmitters were attached to adult and subadult turtles (minimum carapace length = 174 mm), and turtles were then tracked daily through the nesting season and less frequently afterwards. Vegetation plots in the constructed and reference wetlands were surveyed each fall in 1997 and 1999. Turtle microhabitat was sampled beginning in 1999.
This paper evaluates the success of the mitigation project in creating Blanding’s turtle habitat, describes Blanding’s turtle microhabitat at the Dutchess County site, and compares microhabitat plots in reference and constructed wetlands. Previous observations have led to the development of the following 5 hypotheses: (1) Turtles in southeastern
New York have an affinity for organic substrate, dense vegetation (shrubby or submerged), warm water or sunny exposed areas if water is cold, and shallow water; (2)
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The constructed wetlands provide suitable aquatic habitat throughout the active season;
(3) Microhabitats in constructed and natural wetlands differ in vegetation composition
(due to vegetation differences between the wetlands), but are similar in vegetation structure, water temperature and water depth; (4) Purple loosestrife (Lythrum salicaria) is acting as a surrogate for buttonbush in the habitat structure of the constructed wetlands; and (5) Microhabitat requirements change through the year, and turtles respond by occupying different wetlands throughout the year.
METHODS
Study site
The study site consists of approximately 6 ha of pre-existing reference wetlands used as core habitat by Blanding’s turtles and 1.4 ha of constructed wetlands. The 3 pre- existing wetlands are shrub wetlands, dominated by buttonbush. Corner Swamp has a central red maple (Acer rubrum) swamp surrounded by buttonbush and a deep moat
(maximum water depth 1 m). Southeast Swamp contains buttonbush, purple loosestrife, and other shrubs interspersed with areas of deep water (maximum 0.9 m). North Campus
Pond is a little less than half buttonbush-covered with a dredged pool in its southern end.
Small pools and channels are scattered among the buttonbush. Maximum depth in the dredged pool is 2.7 m; in the non-dredged section water levels can exceed 1.5 m. The three constructed wetlands (A1, A2, and B) contain wetland trees and shrubs salvaged from the filled wetland as well as planted buttonbush. Purple loosestrife is very common.
Maximum water depths in the constructed wetlands are 1.0 to 1.2 m. Constructed wetlands were designed to contain both core habitat for adults and shallow areas for
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juveniles. Kiviat et al. (2000) provided a detailed description of the study site and
restoration project.
Data collection
Blanding’s turtles were collected under New York State Department of
Environmental Conservation Endangered/Threatened Species License ESP03-0167.
Turtles were livetrapped in hoop traps (May) or were hand captured (May and June).
Radio transmitters (Advanced Telemetry Systems, Isanti, Minnesota, USA and Sirtrack,
Havelock North, New Zealand) were attached to the carapace using a fast-drying epoxy,
and the turtles were released. Turtles were radio-tracked to their exact location using a
CE-12 receiver (Custom Electronics, Urbana, Illinois, USA) in 2000, and 2 R-1000
receivers (Communications Specialists, Orange, California, USA) in 2001 and 2002, with
a hand-held Yagi antenna. A turtle’s general location was established by triangulation or
occasionally by sight without the aid of telemetry. The researcher then entered the swamp
and moved towards the signal if using telemetry. When the signal was strong (the turtle was close), the researcher circled the area, using the receiver to determine direction, until the turtle was seen or located. If a turtle appeared to be avoiding the researcher (e.g., signal continuously moved away from researcher) data were not collected. This occurred rarely; typically, the turtle either did not appear to be disturbed by the research activities or dropped down to the bottom sediments when the researcher approached and then swam away after a few minutes. Other researchers have noted this “drop and hide” behavior in Blanding’s turtle (Carr 1952, Gibbons 1968, Dobson 1971, Graham and
Doyle 1977, Vogt 1981, Barlow 1999).
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Once the turtle was located, a 3 x 3 m2 plot was sampled with the turtle at its center to determine microhabitat use. This plot size made turtle-centered plots comparable to previously established random plots in the study area. Vegetation composition was documented, and plants were identified to the species level when possible. Scientific names of plants follow Gleason and Cronquist (1991). Aerial cover of each plant species was visually estimated, and the species nearest to the turtle was recorded. Because structural and physical components of habitat may be more important to turtles than flora (Carter et al. 1999; Hamernick and Lang, in preparation), we also measured water depth to the nearest centimeter, recorded substrate type, estimated exposed soil cover, estimated cover of coarse woody debris (downed wood greater than
10 cm x 100 cm) cover, and measured water temperature to the nearest degree Celsius
(2001 and 2002 only). Water depth was measured using a meter stick and water temperature was measured mid-column with a red liquid thermometer. Because we did not know where in the water column the turtle was before we disturbed it, we felt that mid-column temperature was most representative. These wetlands are generally ≤ 1 m deep, and do not appear to exhibit vertical thermal gradients apart from the neuston layer which may be warmer than the water below. Substrate type was determined visually and categorized as either muck—organic hydric soil; mud—mineral hydric soil; hummocks— usually sedge tussocks; mineral soil—sand or gravel; dead leaves; roots; logs; or a plant identified to species. Turtle-centered plots were sampled in constructed and reference wetlands from May to August in 2000, May to September in 2001, and April to October in 2002. Plots were not sampled if they overlapped with a previous plot within a season.
Nesting season (June) was often underrepresented; we did not sample turtle-centered
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plots due to time constraints and concern about disturbance of the females. We attempted
to standardize the number of plots sampled each week; however, plot sampling was
limited by the demands of the field season and the movements of the turtles into
inaccessible areas, seasonal wetlands, or terrestrial habitats. Although we surveyed
microhabitat in seasonal and terrestrial habitats, we did not include these samples in our
analysis because our primary interest was to compare the constructed wetlands to core
Blanding’s turtle habitat.
Random plots were also sampled each September in the constructed and natural
wetlands to describe the wetlands used by the turtles. The plots were located in a
stratified random design based on an analysis of plant communities using the plans for
the constructed wetlands or aerial photographs of the reference wetlands. Comparable
data collected included coarse woody debris cover and vegetation composition and aerial
cover. Random plots were 3 x 3 m2. Our plot sizes are comparable to those used to
sample vegetation (e.g., 2 x 2 m for shrubs and 0.5 x 0.5 m for herbs [Dunn and Sharitz
1987] and turtle microhabitat (e.g., 3 m diameter circle [Carter et al. 1999]). Turtle-
centered plots did not duplicate random plots.
Data analysis
We used Spearman rank correlations to compare variables in turtle-centered plots
with time of year (2002 data only). Differences in mean microhabitat attributes of turtle-
centered plots in constructed and reference wetlands were compared using Student’s t-
tests with separate variance estimates and a Bonferroni adjusted significance level of α =
0.003. Random plots in constructed and reference wetlands were also compared using t-
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tests with separate variance estimates and the adjusted significance level. Data for many
of the variables did not meet the t-test’s assumptions of normality or homogeneity of
variances. T-tests, however, are fairly robust to non-normal distributions (McBean and
Rovers 1998:179) and separate variance estimates were used to account for heterogeneity
of variances. Adjusting the significance level also helped to correct for effects of non-
normality. Because transformations did not improve data distributions, raw data were
analyzed.
Another possible problem was the potential lack of independence of our sample
units, which increases the probability of rejecting the null hypothesis when there is no difference (Type 1 error). Between individuals, we believe dependency is a negligible problem because Blanding’s turtles are not known to exhibit territoriality or parent- offspring relations. Within individuals, we reduced autocorrelation by requiring a minimum of two days before re-sampling an individual turtle. Other microhabitat studies of turtles have considered 1 or 3 days between samples adequate to reduce autocorrelation (Nieuwolt 1996, Carter et al. 1999). In addition, lack of independence typically results in underestimating the true variance (Erickson et al. 2001). Our variances are quite large, ranging from 21 to 2087 (Hudsonia Ltd., unpublished data). Our conservative α also helped to prevent Type 1 errors.
We also examined whether microhabitat use differed within reference versus constructed wetlands. We used the difference in a habitat variable between random plots in the reference vs. constructed wetlands to establish the null pattern. When the difference in a habitat variable between turtle-centered plots in the reference vs. constructed wetlands mirrored the null pattern found in the random plots, we concluded
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that there was no evidence of difference in microhabitat association between reference
and constructed wetlands (i.e., that the turtles were simply using the habitats in
proportion to their abundance in the wetlands as a whole). Because turtle-centered plots and random plots were surveyed at different times of the year, we could not compare the variables with t-tests directly; instead, we computed bootstrapped 90% confidence intervals on the differences in turtle-centered plots between reference and constructed wetlands. We did the same for the differences in the random plots from reference and constructed wetlands for each variable. When the bootstrapped confidence intervals for the differences between reference and constructed wetlands for the turtle-centered versus random plots did not overlap, we considered this evidence of significant differences in turtle association with habitat in the two types of wetlands, and not a reflection of background habitat differences between constructed and reference wetlands. We used confidence intervals of 90% because lack of overlap in confidence intervals is considered a conservative method to test for differences. Bootstrapping was performed using Systat
(Version 9 [1998], SPSS Corp., Chicago, Illinois, USA). All other statistical analyses were performed using Statistica (Version 6 [2003], Statsoft, Inc., Tulsa, Oklahoma,
USA).
To determine whether the turtles are associated with microhabitat in relation to vegetation structure we combined species into 8 cover types: (1) total (all plant species, vascular and non-vascular), (2) graminoids (grass-like species, including grasses
[Poaceae], sedges [Cyperaceae], and rushes [Juncaceae]), (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,
96 Hartwig including dead material and algae, on the water’s surface) and (8) submerged aquatic vegetation (submerged rooted vegetation). Shrubs and trees included any species taxonomically considered a tree or a shrub by Gleason and Cronquist (1991). Shrub and purple loosestrife cover was combined to facilitate testing of the hypothesis that loosestrife is acting as a surrogate for buttonbush in the constructed wetlands. Vegetation structure may be more influential than specific plant species in predicting habitat selection for many animals; however, flora may also play an important role (Morrison et al. 1998). Therefore we also analyzed buttonbush, purple loosestrife, floating filamentous algae, watercelery (Vallisneria americana), and the floating liverwort (Riccia fluitans) because examination of nearest species and means of percent cover, and comparison of constructed and reference plots, indicated possible microhabitat association by the turtles for these taxa. Purple loosestrife is also considered an invasive wetland plant in the USA and therefore warrants attention wherever it is present at a research site.
RESULTS
Twelve turtles (1 subadult, 8 females, and 3 males) were studied in 2000, 14 (2 subadults, 9 females, and 3 males) in 2001, and 17 (1 subadult, 8 females, and 8 males) in
2002; a total of 21 turtles were studied over the three years. Seven females and 2 males were studied in all 3 years. Forty-nine turtle-centered plots were sampled in 2000 (4 subadult plots, 39 female plots, and 6 male plots), 71 in 2001 (11 subadult plots, 43 female plots, and 18 male plots), and 102 in 2002 (11 subadult plots, 56 female plots, and
35 male plots). The number of plots in a single month varies from 3 to 35. Because the greatest numbers of plots and individual turtles were sampled in 2002, we have
97 Hartwig emphasized the interpretation of 2002 results, particularly for the statistical and seasonal analyses.
Ninety-two species of plants were found in turtle-centered plots. Buttonbush was the dominant species with a mean percent cover of 29%. Other individual species represented less than 9% each of the mean cover in turtle centered plots. Most (80%) represented less than 1% of the total vegetation cover within each plot.
T-tests indicate that although water depth differed in 1 of 3 years between the reference and constructed wetlands, turtles used areas of similar depth in the reference and constructed wetlands in all years (Table 1). The water in random plots in the reference wetlands was deeper than in the constructed wetlands in 2002, but was non- significantly different in 2000 and 2001 (Table 1). Mean depth in all turtle-centered plots for the 3 years was 30 cm (n = 223, min = 0 cm, max = 110 cm, SD = 22 cm). Mean depth in reference turtle-centered plots was 28 cm (n = 146, min = 0 cm, max = 100 cm,
SD = 20 cm) and mean depth in the constructed turtle-centered plots was 34 cm (n = 77, min = 0 cm, max = 110 cm, SD = 25 cm).
Although turtles occupied areas of similar depth in the reference and constructed wetlands, we noted differences in microclimate association between the turtle-centered plots in the constructed and reference wetlands. Water temperature was higher in constructed wetlands than in reference wetlands from late June through early August
2002 (Figure 1). In 2002, water in turtle-centered plots was significantly warmer in the constructed wetlands than in the reference wetlands (Table 1; n = 29 constructed wetland plots and 60 reference wetland plots). Mean water temperature in turtle-centered plots for both wetland types was 22ºC (n = 134, min. = 8ºC, max. = 35ºC, SD = 5ºC; data collected
98 Hartwig in 2001 and 2002 only). Mean water temperature in reference turtle-centered plots was
21ºC (n = 97, min = 8ºC, max = 35ºC, SD = 5ºC). Mean water temperature in constructed turtle-centered plots was 23ºC (n = 37, min = 13ºC, max = 30ºC, SD = 5ºC).
Muck was the most commonly observed substrate type in both reference and constructed wetlands. In the reference wetlands, muck was the substrate type for 78%
(113 of 146) of observations. In August and September, the turtles were sometimes found half buried to completely buried under 2 to 10 cm of muck in the reference wetlands and once in a constructed wetland. Other substrate types in reference wetlands were: hummocks (10%), mud (5%), dead leaves (5%), roots (2%), and spike-rush (Eleocharis acicularis, 1%). In the constructed wetlands, substrate type was muck for 49% (37 of 76) of observations. In late summer, a turtle was found buried in muck once in a constructed wetland. Other substrate types in constructed wetlands were: mud (30%), hummocks
(9%), mineral soil (7%), logs (3%), dead leaves (1%), and roots (1%).
In the reference wetlands, turtles were found most often in association with buttonbush (38% of observations) or Riccia fluitans (10% of observations; n =147). In the constructed wetlands, turtles were found most often in close association with purple loosestrife (51% of observations) or watercelery (10% of observations; n = 72). Average total cover of plants in both constructed and reference wetlands for all 3 years in turtle- centered plots was 87%.
There was a difference in habitat association by females, males, and subadults at the wetland complex scale but no consistent difference at the microhabitat scale. In 2001, buttonbush cover was greater at the locations of 9 females compared to those of 3 males
(n = 43 observations of females and 18 observations of males, t = 4.04, P [ 0.001). In
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2002, filamentous algae cover was greater at the locations of 8 males compared to those of 8 females (n = 56 observations of females and 35 observations of males, t = 3.45, P =
0.001). These patterns did not occur in other years. At the wetland complex scale, females were more likely to use the constructed wetlands than males. In both 2001 and
2002, the ratio of female to male microhabitat observations was higher in the constructed wetlands than in the reference wetlands (Table 2). Total female to male observations was similar to female to male observations in the reference wetlands, indicating that both sexes spent equal amounts of time in the reference wetlands (Table 2). Year 2000 data were not considered because there were only 6 microhabitat observations of males. Also, because we only had data for two subadults (one individual in 2000 and another individual in 2001 and 2002), we could not compare subadult microhabitat use to adult use. The subadult (CL ≈ 182 mm) we tracked in 2001 and 2002 spent more time in the constructed wetlands than in the reference wetlands (Table 2); we only recorded 4 observations (all in reference wetlands) for the subadult (CL = 174 mm) tracked in 2000.
Although most habitat variables were not significantly correlated with time of year, several variables showed interesting seasonal peaks (Figure 1). Turtle use of submerged vegetation peaked in late July and August in 2001 and 2002 (Figure 1). In
2001, 14 turtles (9 females, 3 males, 2 subadults) were in the reference wetlands during these months; however, in 2002, 14 turtles (7 females, 6 males, and 1 subadult) spent time in the reference wetlands and 5 turtles (4 females, 1 male) spent time in the constructed wetlands (Figure 1). In the constructed wetlands, most of the submerged vegetation was water celery (Figure 1); from 23 July to 31 July 2002, 3 females were
100 Hartwig located in areas of high cover consisting mainly of water celery. In the reference wetlands, most of the submerged vegetation was filamentous algae (Figure 1).
Graminoid use also peaked during the summer (Figure 1). In the reference wetlands, turtles used graminoid cover most often in late July to early August 2001 and in
August 2002. During this time, radioed turtles were not in the constructed wetlands, even though the availability of graminoid cover did not differ significantly between the constructed and reference wetlands (Table 1). Graminoids in turtle-centered plots in the reference wetlands were primarily spike-rush in 2001 and spike-rush and grasses
(Poaceae) in 2002.
For most of the time the turtles were in the constructed wetlands, herb cover was greater than in the reference wetlands (Figure 1). Turtles were associated with neuston, in particular Riccia fluitans, between approximately 1130 h and 1600 h, while coarse woody debris use peaked at approximately 1100 h and then gradually decreased to zero by 1650 h (Figure 2). This pattern occurred throughout the season, but was not as apparent in
August and September. Water depth in turtle-centered plots showed a non-significant decrease throughout the day (Figure 2).
In all 3 years, the turtles in the constructed wetlands consistently used total cover, shrub cover, and buttonbush cover less than turtles in the reference wetlands (Table 1).
However, if buttonbush cover is removed from the shrub cover, shrub cover is no longer significantly different (Table 1); it appears that the turtles were favoring buttonbush, rather than other shrub species. In addition, in 2002, the turtles in the constructed wetlands used neuston, woody vegetation, and shrub-loosestrife cover significantly less than turtles in reference wetlands (Table 1). Woody vegetation, however, is also no
101 Hartwig longer significantly different when buttonbush is removed (Table 1), again indicating an association with buttonbush by the turtles. Based on the random plots, reference wetlands were significantly higher in buttonbush cover for all three years than the constructed wetlands (Table 1).
By comparing confidence intervals and means (Figure 3), we determined that turtle locations:
1. were positively associated with algae and buttonbush in the reference
wetlands
2. were negatively associated with herb cover and purple loosestrife cover in the
constructed wetlands
3. were negatively associated with herb cover in the reference wetlands and
neither negatively or positively associated with purple loosestrife in the
reference wetlands
4. were positively associated with high total cover and high shrub-loosestrife
cover in reference wetlands but were negatively associated with these
variables in constructed wetlands, and
5. were positively associated with water celery in the constructed wetlands.
Although the confidence intervals did overlap slightly for buttonbush cover, indicating no association, we believe the turtles are favoring buttonbush because analyses discussed above also indicated association.
DISCUSSION In Dutchess County, New York, Blanding’s turtles generally are associated with waters between 0 and 110 cm in depth with muck substrates and dense vegetation cover during the active season. Turtles often are associated with vegetation cover consisting of
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buttonbush, submerged vegetation, or neuston. This supports our original hypothesis that
Blanding’s turtles in southeastern New York are found in areas with organic substrates,
dense submerged or shrubby vegetation cover, and shallow waters. Turtles were found in
similar water depths in the constructed and reference wetlands and microhabitat
association changed through the season, as we hypothesized.
We also hypothesized that the turtles seek warm water or sunny exposed areas in
cold water. This idea is supported by our data, although lack of random water
temperature data requires the use of circumstantial evidence. Use of neuston increased at
about the same time during the day that use of coarse woody debris decreased. The turtles
bask on logs in the early morning and then use neuston by late morning as the sun warms
the pool surface. Turtles in Minnesota exhibited a similar pattern; on sunny days the
turtles basked on land during mid-morning, quickly raising their body temperatures, and
then switched from land to water later in the day to maintain a body temperature of
32.5ºC (Sajwaj and Lang 2000). In Dutchess County, this pattern was not as strong in
August and September, probably because the turtles were seeking refuge from the heat in
cool waters or burying in the muck. Similarly, in Minnesota most turtles did not bask in late summer and early fall (Sajwaj and Lang 2000). The neuston, most of which in this study area is the duckweed-like Riccia fluitans, may provide good camouflage for the turtles, similar to the camouflage effect noted for duckweeds (family Lemnaceae; Ross and Lovich 1992). Duckweeds are an important habitat for macroinvertebrates (Gaston
1999), and this might also be true of Riccia. By spending time in neuston, which also includes algae and detritus, Blanding’s turtles may be able to conserve energy by basking and foraging simultaneously (Kiviat, personal observation).
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Piepgras et al. (1998) and Barlow (1999) described Blanding’s turtle habitat association at the microhabitat scale in the Great Lakes region. In Indiana, floating mats of sedges (Carex spp.), rushes (Juncus spp.), and water-willow (Decodon verticillatus) had the greatest relative use by Blanding’s turtles, followed by sedge and waterlily
(Nuphar spp. and Nymphaea spp.) areas (Barlow 1999). In Minnesota, shallow water depths (about 55 cm) and dense vegetation (in particular narrow-leaved cat-tails [Typha angustifolia] and sedges [Carex spp.]) were more abundant in turtle microhabitats than in random plots (Piepgras et al. 1998). The water depth associated with turtles in Duchess
County was shallower for all three years combined (x = 30 cm) than in Minnesota; however turtles at our study site were found in varying water depths (53 cm in 2000, 20 cm in 2001, and 27 cm in 2002) and may partly depend on year-to-year water level variation in the wetlands. In Dutchess County, Blanding’s turtles also appear to prefer dense vegetation cover, usually provided by buttonbush rather than sedges or cat-tails. In late summer 2001 and 2002, graminoid cover as well as buttonbush cover was high in turtle-centered plots (Figure 1). Possibly, water levels were decreasing in the shrubby sections of the wetlands and some turtles moved to the deeper emergent areas, where water may have been cooler and invertebrate densities may have been higher (Voigts
1976, Sharitz and Batzer 1999, Hamernick and Lang in preparation).
Blanding’s turtles may be found in association with certain plants because they provide support and structure, or feeding and thermoregulation opportunities. In
Michigan, for example, Blanding’s turtles remained in areas of submerged vegetation in a shallow pond (maximum water depth 1.3 m) and avoided filamentous algae (Sexton
1995). Sexton speculated that the association between turtles and plants such as coontail
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(Ceratophyllum), leafy pondweed (Potamogeton foliosus), stoneworts (Chara), and white water-crowfoot (Ranunculus longirostris) was because these plants, unlike the filamentous algae, provide mats strong enough to support the turtles (Sexton 1995).
Turtles in Duchess County (this study) do not appear to use these plants as frequently as the turtles in Michigan even though coontail and pondweeds are widely available in wetlands at the study site. The turtles in Dutchess County were associated with filamentous algae in the reference wetlands (Figure 3) and possibly watercelery in the constructed wetlands. The turtles were associated with algae and water celery in shallower areas (mean water depth in plots with algae = 0.32 m, n = 59; mean water depth in plots with watercelery = 0.34 m, n = 26) than may have been available in most of the Michigan pond. In the Dutchess County wetlands, coontail, pondweeds, and stoneworts are often found in deeper water than algae and watercelery (T. Hartwig, personal observation).
In shallow water depths, filamentous algae may offer other benefits for the turtles, such as more food resources, a warmer microclimate, or cover from predators.
Submerged aquatic vegetation is known to harbor high densities of macroinvertebrates
(Yozzo and Diaz 1999, Gaston 1999); snail and other macroinvertebrate densities are also high in filamentous algae (Elwood et al. 1981, Euliss et al. 1999, Evans et al.1999).
Snails and other macroinvertebrates are a primary food source for Blanding’s turtles
(Lagler 1943, Rowe 1992, Blanding’s Turtle Recovery Team 2003), although snails were not a large source in Michigan (Lagler 1943). At our site, turtles in reference wetlands were often found in beds of algae at the edge of buttonbush patches (mean buttonbush cover in turtle-centered plots with algae = 33% [n = 47, min. = 0%, max. = 90%, SD =
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32]; plus T. Hartwig, personal observation). Constructed wetlands in which the turtles
used water-celery did not support large beds of coontail, pondweeds, or stoneworts.
Many of the water-celery beds were also near large pieces of coarse woody debris,
although they were not always in the turtle-centered plots (T.Hartwig, personal
observation). These areas probably provided nearby cover and abundant food resources in
shallow warm waters. In both reference and constructed wetlands, the turtles were
apparently favoring shallow, warm waters, abundant aquatic vegetation with its
associated macroinvertebrates, and nearby cover; association of structure was probably more important to the turtles than association with particular species of submerged vegetation.
In our study, turtles were associated with areas with less vegetation cover and warmer water temperatures in the constructed wetlands. This is contrary to our original hypothesis, which stated that the turtles would be found in areas of similar vegetation structure and water temperature. Blanding’s turtles used the constructed wetlands as basking areas, particularly in the spring and early summer. Other studies (e.g. Sajwaj and
Lang 2000) have also reported Blanding’s turtles basking more in spring and early summer. In our study, turtles were found in areas with less total cover and less shrub- loosestrife cover in the constructed plots (Figure 3). Areas with less total cover and less tall vegetation cover (e.g. shrubs or loosestrife) potentially receive more sunlight and provide basking opportunities for the turtles, as indicated by the fact that turtles in the constructed wetlands were found in areas with warmer water temperatures than turtles in the reference wetlands (Table 1).
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Females basked in the constructed wetlands more often than males, and females moved into these wetlands before and after nesting. Constructed wetlands were near (~
10 m) many nest sites. We frequently observed females basking in the spring. Females at our site may bask more often in the spring to facilitate egg development before nesting, as they also apparently do in Nova Scotia (Standing et al., 1999; Blanding’s Turtle
Recovery Team, 2003). Power (1989) also noted that females may move to warm waters in the spring to complete egg development. Although in Figure 1 a clear difference in water temperature is only seen after Julian date 170 (late June) we feel that this pattern also probably exists in early spring. The reproductive cycles of Blanding’s turtles, however, are not well studied (Ernst et al. 1994) and the timing of egg production is unknown. A Minnesota study found no difference in basking behavior between females and males in the spring but found that females basked more than males in the fall, indicating that egg production may occur then (Sajwaj and Lang 2000).
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. Blanding’s turtles were associated with buttonbush cover in the reference wetlands, as determined by the confidence intervals on the differences in means, which overlapped only slightly (Figure 3). Conversely, the greater overlap in the confidence intervals for the total shrub cover indicates no association with shrub cover by the turtles in the reference or constructed wetlands. In the constructed wetlands, shrub cover has increased over the years (Table 3) and by 2002 there was no difference in shrub cover between reference and constructed wetlands
(Table 1). Buttonbush, which grows slowly, did not show such a large increase in the
107 Hartwig constructed wetlands (Table 3). Interestingly, turtle use of shrubs actually decreased in constructed wetlands but turtle use of buttonbush in constructed wetlands increased slightly in 2002 compared to previous years (Table 3).
We hypothesized that purple loosestrife in the constructed wetlands plays the role that buttonbush does in the reference wetlands because we often saw turtles beneath lodged (fallen-over) loosestrife stems. Although our field observations suggest that the turtles do not entirely avoid loosestrife (turtles were seen under dead loosestrife 7 – 9 times each year), the confidence intervals on the means did not overlap in 2002 (Figure
3), indicating that turtles were not associated with loosestrife in either constructed or reference wetlands. Turtles were often found under overhanging plants, including marsh fern (Thelypteris palustris), purple loosestrife, tussock sedge (Carex stricta), buttonbush, marsh swamp-rose (Rosa palustris), and northern swamp-dogwood (Cornus racemosa).
The turtles may select for cover, either from predators or prey, rather than a particular plant species.
We believed that loosestrife may provide habitat structure similar to buttonbush because both plants develop late in the growing season. Loosestrife also has some shrub- like characteristics, such as robust stems that persist through the winter. These ideas, however, were not supported by our data. As loosestrife reaches a high level of dominance, it becomes very dense. The turtles may not be able to maneuver in dense stands of loosestrife, or they may prefer more open areas for thermoregulation purposes.
In seasonal wetlands, loosestrife may not be detrimental to the turtles as long as it does not reach high densities. In core habitats, however, invasion by loosestrife may signal
108 Hartwig
declining habitat quality because the turtles are not associated with it, while they are
associated with buttonbush.
We hypothesized that the constructed wetlands are providing appropriate habitat
for the turtles throughout most of the active season, but not in winter. Our data indicate that the constructed wetlands provide good habitat during the spring and early summer by providing warm basking areas due to shallower water, less tree fringe cover, and basking logs. This type of habitat is important for thermoregulation, which is an essential part of the species’ life history requirements (Sajwaj and Lang 2000). The constructed wetlands also provide staging or rehydrating areas for nesting females (Hudsonia Ltd., unpublished data) but in most years they become too warm or too shallow by August, and the turtles move to deeper waters elsewhere (Hudsonia Ltd., unpublished data).
The constructed wetlands also do not appear to provide suitable winter habitat.
Only one turtle (a subadult) has been observed overwintering in the constructed wetlands since they were built 7 years ago and this turtle did not return to overwinter in the following years (Hudsonia Ltd., unpublished data). Analysis of substrate types in the turtle-centered plots indicates that the constructed wetlands have a discontinuous muck substrate throughout the wetlands, which Blanding’s turtles appear to prefer to mineral soil throughout their range (Hartwig 2004). If buttonbush cover continues to increase in the constructed wetlands, they may become more similar to the reference wetlands, but the difference in hydrology may preclude them from becoming suitable core habitat.
Constructed wetlands were also built to provide habitat for juvenile Blanding’s turtles; unfortunately we do not have enough data on young turtles to determine whether the constructed wetlands are providing juvenile habitat. Juvenile turtles tend to prefer
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shallow, well-vegetated wetlands compared to adults throughout their range (Hartwig
2004). Previous studies that have noted this difference in habitat use have studied young turtles with carapace lengths of less than 155 mm (Hartwig 2004). Because we studied only two young turtles, and their carapace length was ~ 182 mm, we cannot make any statements about juvenile habitat at our study site.
CONSERVATION AND MANAGEMENT IMPLICATIONS Destruction or damage to core Blanding’s turtle wetlands should be avoided.
Mitigation costs are high (Kiviat et al. 2000) and it is difficult (or impossible) to replace
organic soils and shrubby vegetation. Lack of suitable soils and vegetation and our
limited understanding of the ecology of the Blanding’s turtle and its habitats limited the
success of our project; these factors have also limited success of restoration projects for
rare birds (Haltiner et al. 1997, Boyer and Zedler 1998, Powell and Collier 2000, Darnell
and Smith 2001). The lag involved before constructed wetlands may become suitable as
core habitat or may be considered successful is also an important consideration, as are
other uncertainties in creating core habitat (e.g. habitat requirements of different age
classes and hydrologic conditions). At our study site, although the turtles began using the
constructed wetlands soon after they were built, it will require many more years of
monitoring to determine whether these wetlands will function as core habitat. In addition,
their success in increasing or maintaining the population may not be known until we can
develop life tables and determine demographic changes in the population. This will
require at least 15-20 years of post-construction monitoring because Blanding’s turtles
generally mature at 14-20 years of age (Congdon and van Loben Sels 1993).
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Constructed wetlands can provide good supplements to the habitat complex used
by Blanding’s turtle, but they should not be considered core habitat unless they meet the
needs of the turtles throughout their life cycle and at all seasons. Altering the design of
the constructed wetlands and deliberately planning for the different seasonal needs of the turtles could improve the quality and range of habitat provided by constructed wetlands.
Creating more and deeper pools could provide cool, wet areas throughout the summer and encourage the growth of submerged vegetation and neuston, providing cover and foraging areas. Unfortunately, the muck soils the turtles often bury themselves in during the summer are difficult to create or obtain during wetland restoration. We salvaged muck soils from the filled wetland; however, construction constraints limited our success.
We also do not know how much muck is optimal for the turtles. At this site, reference wetland plots contained an average of 68 cm of muck (2002 data only; n = 27, min = 7 cm, max m 100 cm, SD = 31 cm). Until more is known about the specific role that organic soils play in turtle ecology, wetlands constructed for Blanding’s turtles in the Northeast should probably attempt to imitate these depths. In addition, upland areas surrounding the complex should also be examined to determine if they provide essential habitat such as nesting sites or refugia from hot or cold waters. In our study, nesting sites in the surrounding area were limited and therefore nesting berms were also constructed. While the data are still being analyzed, the results indicate that nesting areas are also difficult to reproduce. Although some turtles have used the nesting berms, most use areas cleared during construction of the wetlands or outside the study site.
Wetland complexes constituting diverse wetland types are required to sustain a
Blanding’s turtle population (Hartwig 2004). Because they are currently providing good
111 Hartwig thermoregulation habitat and because good core habitat exists nearby, it may be desirable for the constructed wetlands to continue to function as seasonal habitat. Blanding’s turtles use a diversity of wetlands in habitat complexes rather than single isolated wetlands (see also Joyal 2001), and new wetlands, even if they do not function as core wetlands, can increase the capacity of the landscape to support Blanding’s turtles by providing high quality seasonal habitat. Construction of wetlands, both core and seasonal, should be considered where Blanding’s turtle wetlands have already been fragmented or destroyed, and is a useful tool for conservation. Construction of terrestrial habitats, such as clearing nesting areas or planting trees and shrubs as refuges from cool or warm waters, and the integration of upland and aquatic habitats, should also be considered. For example, because our constructed wetlands were near nest sites, they served as staging areas for nesting females. Many aquatic animals require multiple wetlands or water bodies, either to sustain metapopulations or individuals (Schneider et al. 2002); these comments probably apply to any species that requires specialized habitat and uses a variety of aquatic systems during its life cycle.
ACKNOWLEDGEMENTS
We are grateful to many individuals for field assistance, editing, and data management, especially H. Bock, D. Goodfriend, J. Hazard, and K. Munger. Our work was funded in part by AmeriCorps; Arlington Central School District; Guiness Water of Life; Geoffrey
C. Hughes Foundation; New York State Office of Parks, Recreation, and Historic
Preservation; the Society for Ecological Restoration Project Facilitation Award
(underwritten by Monsanto); United States Environmental Protection Agency (grant
CD992776-01-0 to New York State Office of Parks, Recreation, and Historic
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Preservation); and individual donors. 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 providing extensive assistance with the statistical procedures, particularly the bootstrapping technique. This is Bard College Field Station-
Hudsonia Contribution 95.
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Table 1. T-test results comparing reference and constructed plots for Blanding’s turtle-centered plots and random plots separately for each year, Dutchess County, New York, USA, 2000 - 2002. Turtle-centered plots were surveyed during the active season each year; random plots were surveyed in September. Significant results (P<0.003) are in bold type. Random plots: reference n=28, constructed n=12. Turtle-centered plots: reference n=26, constructed n=23 (year 2000); reference n=53, constructed n=19 (year 2001); reference n=67, constructed n=35 (year 2002).
Variable Ref- Min Max SD Cons- Min Max SD t-value 2-sided erence tructed P Plot Plot Mean Mean Year 2000 Turtle-centered Total cover 102% 9% 175% 36% 57% 6% 92% 26% 5.07 [ 0.001 plots Shrub cover 49% 0% 99% 31% 17% 0% 65% 21% 4.37 [ 0.001 Button-bush 39% 0% 99% 33% 0% 0% 5% 1% 5.98 [ 0.001 cover Shrub cover 17% 0% 71% 21% 11% 0% 65% 22% 0.99 0.329 without buttonbush Water depth 53 cm 10 cm 90 cm 14 cm 53 cm 18 cm 110 cm 29 cm 0.11 0.911 Random plots Shrub cover 41% 0 % 120 % 42% 2% 0% 7% 2% 5.06 [ 0.001 Buttonbush 30% 0% 95% 36% 1% 0% 5% 2% 4.25 [ 0.001 cover Water depth 32 cm 4 cm 100 cm 21 cm 24 cm 0 cm 71 cm 28 cm 0.93 0.366 Year 2001 Turtle-centered Total cover 117% 38% 267% 46% 75% 4% 159% 49% 3.27 0.003 plots Shrub cover 46% 0% 111% 36% 13% 0% 65% 22% 4.68 [ 0.001 Buttonbush 43% 0% 100% 36% 0% 0% 5% 1% 8.65 [ 0.001 cover Shrub cover 13% 0% 80% 22% 3% 0% 65% 12% 1.84 0.079 without buttonbush Water depth 18 cm 0 cm 100 cm 16 cm 23 cm 0 cm 60 cm 17 cm 1.15 0.259
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Table 1 cont. Variable Ref- Min Max SD Constr Min Max SD t-value 2-sided erence ucted P Plot Plot Mean Mean Random plots Shrub cover 45% 0% 110% 43% 13% 0% 56% 18% 3.33 0.002 Buttonbush 33% 0% 99% 40% 3% 0% 25% 7% 3.78 0.001 cover Graminoid 16% 0% 91% 26% 3% 1% 7% 2% 2.59 0.015 cover Water depth 4 cm 0 cm 76 cm 15cm 2 cm 0 cm 27 cm 8cm 0.47 0.643 Year 2002 Turtle-centered Total cover 90% 9% 196% 34% 54% 5% 141% 37% 4.79 [ 0.001 plots Shrub cover 47% 0% 98% 34% 11% 0% 96% 21% 6.55 [ 0.001 Buttonbush 45% 0% 98% 35% 3% 0% 25% 6% 9.76 [ 0.001 cover Shrub cover 1% 0% 65% 8% 8% 0% 96% 21% 1.81 0.079 without buttonbush Neuston 6% 0% 51% 10% 1% 0% 20% 4% 3.60 0.001 cover Woody cover 48% 0% 102% 34% 12% 0% 115% 23% 6.28 [ 0.001 Woody cover 3% 0% 78% 11% 9% 0% 115% 23% 1.64 0.109 without buttonbush Shrub- 49% 0% 98% 33% 19% 0% 100% 23% 5.39 [ 0.001 loosestrife cover Water 20ºC 8ºC 27ºC 4ºC 24ºC 14ºC 30ºC 4ºC 3.76 [ 0.001 temperature Water depth 26 cm 0 cm 100 cm 17 cm 27 cm 0 cm 90 cm 18 cm 0.23 0.820 Random plots Shrub cover 47% 0% 133% 45% 20% 0% 87% 26% 2.35 0.025 Buttonbush 35% 0% 99% 40% 6% 0% 50% 15% 3.32 0.002 cover Graminoid 21% 0% 111% 33% 7% 2% 23% 6% 2.21 0.035 cover Water depth 10 cm 0 cm 51 cm 14 cm 1 cm 0 cm 4 cm 2 cm 3.32 0.002
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Table 2. Number of female, male and subadult Blanding’s turtle observations in constructed and reference (natural) wetlands in Dutchess County,
New York, USA, 2001 – 2002. Subadult observations were based on 1 turtle and therefore were not included as a ratio.
Number of female Number of male Number of Ratio observations observations subadult (female : observations male) Year 2001 Total 43 18 10 2.4:1 Reference 35 14 3 2.5:1 wetlands Constructed 13 4 12 3.3:1 wetlands Year 2002 Total 57 24 11 1.6:1 Reference 32 31 4 1.0:1 wetlands Constructed 24 4 7 6:1 wetlands
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Table 3. Mean shrub and buttonbush cover in constructed wetland plots, Dutchess County, New York, USA,
2000 – 2002.
Mean percent cover in constructed wetlands 2000 2001 2002 Shrubs in random plots 2 13 20 Buttonbush in random plots 1 3 6 Shrubs in turtle-centered 17 13 11 plots Buttonbush in turtle- 0 0 3 centered plots
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160 160 160
140 140 140 ds ds 120 120 120 noi noi
100 100 n 100
80 80 tio 80 ta e g
60 60 e 60 v cover submerged cover grami cover grami 40 40 40
20 20 20 Percent Percent Percent 0 0 0 80 100 120 140 160 180 200 220 240 260 280 300 320 80 100 120 140 160 180 200 220 240 260 280 300 320 80 120 160 200 240 280 320 100 140 180 220 260 300 Julia n da te 2001 Julia n D ate 2002 Julia n da te 2001
160 160 160
140 a 140 140 i r 120 e 120 120 n gae lis
n 100 100 100 Va ana tio
80 c 80 80 ta e cover al g
e 60 60 60 v cover submerged ameri cover 40 40 40
20 20 Percent 20 Percent Percent 0 0 0 80 120 160 200 240 280 320 80 120 160 200 240 280 320 80 100 120 140 160 180 200 220 240 260 280 300 320 100 140 180 220 260 300 100 140 180 220 260 300 Julia n da te 2002 Julia n da te 2002 Julia n da te 2002
160 160 32 30 140 140 28 n
o 120 120 26
Degrees 24
100 n 100 22 s ure, tio 80 80 iu 20 ta ls
e 18 g Ce cover neust 60 e 60 16 v cover herbaceous 14 40 40
r Temperat 12 e
Percent 20 20 10
Percent 8 0 0 Wat 6 80 100 120 140 160 180 200 220 240 260 280 300 320 80 120 160 200 240 280 320 80 120 160 200 240 280 320 100 140 180 220 260 300 100 140 180 220 260 300 Julia n D ate 2002 Julia n D ate 2002 Julia n D ate 2002
Figure 1. Scatterplots of habitat variables in turtle-centered plots versus Julian date for Blanding’s turtles in Dutchess County, New York, USA, years 2001 and 2002
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180 180
160 155 140 140
120 120
100
90 Riccia fluitans 80 75
57 60 rcent cover neuston e
P 40 40
26 Percent cover 20 13 0 0 7:12 9:36 12:00 14:24 16:48 19:12 21:36 7:12 9:36 12:00 14:24 16:48 19:12 21:36
Time Time
180 110 160 100 140 90 120 75 100 65
80 55 45 60 36 40 27
Water depth, in centimeters 18 rcent cover coarse woody debris
e 20
P 9 0 0 7:12 9:36 12:00 14:24 16:48 19:12 21:36 7:12 9:36 12:00 14:24 16:48 19:12 21:36
Time Time Figure 2. Scatterplots of ha bitat variables in turtle -centered plots ve rsus time of day for Blanding’s turtle s in Dutc hess County, Ne w York, USA, ye ars 2000 - 2002
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Figure 3. Confidence intervals on the differences in means for variables that did not
overlap in 2002, plus buttonbush confidence intervals that overlapped slightly, for
constructed and reference wetlands in Dutchess County, New York, USA. Columns
represent the difference between the constructed and reference plot means for either
random or turtle-centered plots. Error bars represent the bootstrapped confidence intervals for the difference in means. If the confidence intervals did not overlap, the difference between wetland types for turtle-centered plots is considered significant due to habitat association rather than habitat differences. Positive values indicate that reference plot means were greater than constructed plot means; negative values indicate that constructed plot means were greater than reference plot means. Means for each plot type are on the right of each graph. Ref = random reference plots, Con = constructed reference plots, TRef = turtle-centered reference plots, TCon = turtle-centered constructed plots.
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Total Cover 2002 Herb Cover 2002 Ref = 107% Ref = 15% 60 Con = 117% 0 Con = 65% TRef = 90% Ra ndom Turtle-cente re d TRef = 7% 40 -10 TCon = 54% -20 TCon = 15% 20 Total Cover 2002 -30 Herb Cover 2002 0 -40 -20 -50 -40 Random Turtle Centered -60
Shrub-loosestrife Cover 2002 Algae Cover 2002 Ref = 48% Ref = 0% 60 Con = 53% 20 Con = 0% TRef = 49% TRef = 13% 40 TCon = 19% 15 TCon = 4% 20 Shrub-loosestrife 10 Algae Cover 2002 0 Cover 2002 5 -20 0 -40 Random Turtle-centered Random Turtle-centered
Purple Loosestrife Cover 2002 Buttonbush Cover 2002 Ref = 2% Ref = 35% 0 Con = 33% 60 Con = 6% TRef = 2% 50 TRef = 45% -10 Random Turtle-c entered TCon = 8% 40 Buttonbush Cover -20 30 Purple Loosestrife 2002 -30 Cover 2002 20 10 -40 0 TCon = 3% -50 Random Tu rtle-centere d
Water Celery Cover 2002 Ref = 0% 0 Con = 0% TRef = 0% Random Turtle-centered -5 TCon = 12% -10 Water Celery Cover -15 2002 -20 -25
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