Spatial Ecology of the Threatened Eastern Indigo Snake (Drymarchon couperi) in a Subtropical Coastal Landscape in the Southern Extent of its Range
A Thesis
Presented to
The Faculty of the College of Arts and Sciences
Florida Gulf Coast University
In Partial Fulfillment
of the Requirement for the Degree of
Master of Science
By
Matthew Fox Metcalf 2017
APPROVAL SHEET
This Thesis is Submitted in Partial Fulfillment of
The Requirements for the Degree of Master of Science
______
Matthew Fox Metcalf
Approved:
______
John Herman, Ph.D.
Committee Co-Chair
______
Edwin Everham III, Ph.D. Committee Co-Chair
______
Billy Gunnels, Ph.D.
Committee Member
______
Paul Andreadis, Ph.D. Committee Member
______
Kara Lefevre, Ph.D. Committee Member iii
Acknowledgements
There are so many people to thank for their contributions to this project. First, I want to thank my advisors John Herman, Win Everham, Billy Gunnels, Paul Andreadis, and Kara Lefevre for their unwavering dedication to not only this project but to my education and advancement in this field. Each of you provided unique support ranging from - but definitely not limited to - novel field techniques, honing writing skill sets, other research endeavors, or just grabbing a beer with me to keep me
(somewhat) sane after a strenuous day in the field, lab, or classroom. I particularly want to thank John
Herman for taking a chance on me and coercing me to work under his leadership at FGCU. John, you were and continue to be instrumental as I move on in my career as a herpetologist. I cannot thank you enough for your guidance and friendship over the years and look forward to many more herping adventures!
I would also like to thank Jill Schmid at the Rookery Bay NERR for her patience and assistance with ArcGIS analyses for this project. I thank Ian Bartoszek and others at the Conservancy of Southwest
Florida for providing field support and insight. Thank you Dave Ceilley, FGCU’s IERG Lab, and FGCU’s
Animal Behavior Group for all of your words of wisdom and advice while working with this phenomenal species and particularly throughout the writing process. Additionally, I would like to thank the numerous undergraduate and graduate students from FGCU that assisted with this project. Finally, I thank my great friends and family for supporting me through this entire process! This project would not be possible without the contributions made by the network of these amazing people and organizations.
There are not enough words to express how grateful I am for all of your help and support, and I look forward to sharing and implementing the knowledge we have gained from this project to advance the conservation of the Eastern Indigo Snakes and other herpetofauna in southwest Florida!
iv
Abstract
The Eastern Indigo Snake (Drymarchon couperi) is a large, non-venomous snake endemic to the southeastern Coastal Plains of the United States. Due to habitat loss, fragmentation, and collection for the pet trade, this species is listed as federally threatened under the Endangered Species Act. Several studies have looked at D. couperi movement and life history throughout the central and northern portions of their range, but we lack ecological information in regards to the southernmost populations. South Florida differs drastically in climate and habitat features from more northern parts of the state and may require varying management approaches for D. couperi conservation. The present research uses radio telemetry to study D. couperi home range sizes, seasonal variations, habitat and refugia utilization, detectability patterns, and general behavior.
The study took place at Rookery Bay National Estuarine Research Reserve along the Gulf coast of southwest Florida. The Reserve comprises a myriad of habitats including mangrove swamps, upland pine hammocks, and coastal scrubland. Rookery Bay Reserve is a protected area with minimal anthropogenic disturbances; however, it is bordered by growing development.
Four snakes (one female and three males) were tracked between August 2015 and April 2017. Home ranges varied from 113 – 233 hectares. There were no significant differences in home range size between the breeding/dry season and the non-breeding/wet seasons. D. couperi in the Rookery Bay Reserve prefer upland habitats that feature various forms of refugia. These snakes also disproportionally use areas near roads and trailways. Detectability patterns for D. couperi in this reserve trend toward midday activity despite high ambient air temperatures, and had a higher detection probability during the breeding season.
Compared to previous studies in the northern and central part of their distribution, D. couperi in the Rookery Bay Reserve demonstrate unique trends in home range sizes, seasonal activity, habitat and refugia usage, detectability patterns and general behavior. Unique habitat utilization and behavior of the species in its southernmost range highlights the need for different management strategies in southwest Florida. Understanding the ecological needs of this threatened species is imperative to their survival, particularly in south Florida as increasing human development continues.
v
Table of Contents
Page
Acknowledgements iii
Abstract iv
Table of Contents v
List of Figures viii
List of Tables ix
Chapter 1:
Introduction 1
- Taxonomy 3
- Status 4
- Range 4
- Habitat 4
- Description 5
- Feeding 5
- Refugia 5
- Reproduction 6
- Home Ranges 6
- Research Objectives 7
Chapter 2:
Study Site and Methodology 8
- Study Site 8
- Capture 10
- Transmitter Implantation 10
- Radio Tracking 10 vi
- Timeline 11
- Data Analysis 11
Objective 1: Home Ranges 11
Objective 2: Habitat Selection 11
Objective 3: Refugia 12
Objective 4: Detectability 12
Chapter 3:
Results 13
- Objective 1: Home Ranges 13
- Objective 2: Habitat Selection 24
Road Proximity 30 - Objective 3: Refugia 33
- Objective 4: Detectability 37
Chapter 4:
Discussion 39
- Objective 1: Home Ranges 39
- Objective 2: Habitat Selection 42
Road Proximity 43 - Objective 3: Refugia 45
- Objective 4: Detectability 47
Chapter 5:
Conclusion 49
- Management Implications 50
- Future Work 51
vii
Chapter 6:
Observational Notes 54
- Dietary Observations 54
- Potential Breeding Observations 54
- Mortalities 55
- Fecal Samples 56
Literature Cited 57
Appendix
- Appendix Table 1: Home Range Study Comparisons 70
- Appendix Table 2: D. couperi Morphometrics 70
- Appendix Table 3: Snake Species Surveyed 71
viii
List of Figures
Page
2.1 D. couperi Distribution and Study Area Map 9 3.1 All Home Ranges 14 3.2a Total Home Range and Kernel Density Estimates for RB1 15 3.2b Seasonal Breakdowns for RB1 16 3.3a Total Home Range and Kernel Density Estimates for RB2 17 3.3b Seasonal Breakdowns for RB2 18 3.4a Total Home Range and Kernel Density Estimates for RB4 19 3.4b Seasonal Breakdowns for RB4 20 3.5a Total Home Range and Kernel Density Estimates for RB5 21 3.5b Seasonal Breakdowns for RB5 22 3.6 Habitat Designation within Home Ranges 24 3.7 Habitat Selection vs. Reproductive Season for RB1 26 3.8 Habitat Selection vs. Reproductive Season for RB2 27 3.9 Habitat Selection vs. Reproductive Season for RB4 28 3.10 Habitat Selection vs. Reproductive Season for RB5 29 3.11 Road Proximities Located within 10m 31 3.12 Road Proximities Located within 20m 32 3.13 Proportion of Total Refugia 34 3.14 Proportion of Refugia for RB1 35 3.15 Proportion of Refugia for RB2 35 3.16 Proportion of Refugia for RB4 36 3.17 Proportion of Refugia for RB5 36
ix
List of Tables
Page
2.1 Common Plant Species 8
3.1 Home Range Areas 23
3.2 Reproductive Season Home Ranges 23
3.3 Hydrologic Season Home Ranges 23
3.4 Chi-Square of Habitat Locations 25
3.5 Coefficients for Season, Temperature, and Time of Day 38
3.6 Coefficients for Season and Time of Day 38 1
Chapter 1
Introduction
The Eastern Indigo Snake (Drymarchon couperi) is a federally threatened species endemic to the southeastern Coastal Plains of the United States. These large snakes exhibit some of the largest home ranges for any terrestrial snake species (Breininger et al. 2011, Hyslop et al. 2014). Across its range, D. couperi is experiencing loss of viable habitat due to alterations, development, and fragmentation. Populations of D. couperi in south Florida encounter a unique landscape and climate that is distinct from central and northern parts of the species’ range (Steiner et al. 1983). Many landscapes in south Florida predominantly feature freshwater marshes and mangrove forests, with the largest extent of mangroves in the United States occurring in Lee, Collier, Monroe, and Dade counties, Florida (Odum et al. 1982). These mangrove forests are geographically restricted by lack of tolerance to freeze events (Odum et al. 1982, Doyle et al. 2003). Mangrove forests are distinctive to coastal south Florida, and represent a unique habitat for Eastern Indigo Snakes. Additionally, south Florida represents an optimal landscape for the establishment of exotic species. D. couperi may be competing with sympatric exotic species such as the Burmese Python (Python bivittatus) for resources. Moreover, since individual Eastern Indigo Snakes maintain large home ranges, there are increased opportunities to encounter exotic species as well as novel pathogens introduced by these exotics (Reed 2005).
Herpetofaunal populations are dramatically declining across the globe due to habitat degradation, overharvesting, disease, wanton persecution, and climate change (Garber and Burger 1995, Gibbons et al. 2000, Araújo et al. 2006). Unfortunately, despite the ecological importance of herpetofauna, habitat loss and degradation in the United States has attributed to the decline of more than 97% of these groups (Wilcove et al. 1998). Additionally, population data are lacking for many species because of the inability to accurately detect reptiles using traditional field techniques and declining snake populations typically garner less attention than more charismatic herpetofauna such as frogs and turtles (Meylan and Ehrenfeld 2000, Norris 2007). Habitat alterations drastically reduce wildlife populations and further complicate conservation management of imperiled species. In the southeastern United States, Longleaf Pine (Pinus palustris) and Wiregrass (Aristida stricta) habitats once dominated the landscape before European colonization. In post-Columbian times, these habitats have been reduced from approximately 30 million to 0.6 million hectares with remnants existing primarily in isolated fragments (Frost 2006). Fragmentation and loss of crucial habitats are leading causes of population declines and decreased fitness for many taxonomic 2
groups. Large areas of Florida have been converted for agricultural and urban expansion in response to a rapidly growing human population (BEBR 2001, Kautz 1998). The effects of such anthropogenic factors have dominated the attention of conservationists. One approach to mitigating habitat fragmentation is to increase and preserve habitat connectivity via wildlife corridors, as has been implemented for large ranging mammals like the Florida Black Bear (Ursus americanus floridanus; Larkin et al. 2004, Dixon et al. 2006) and the Florida Panther (Puma concolor coryi; Kautz et al. 2006). However, management strategies for single umbrella species may be inadequate, or may even be in conflict with, the conserving of other imperiled taxa (Graham 1990, Simberloff 1998). Wide-ranging snakes pose additional conservation challenges. They are more difficult to monitor and consequently sufficient population data is lacking for many snake species (Durso et al. 2011, Turner 1977, Shoemaker et al. 2009). Moreover, habitat destruction and fragmentation may more severely affect snakes due to low densities, limited dispersal abilities, and persecution (Webb and Shine 1998, Breininger et al. 2012). Additionally, urbanization negatively affects snakes by fragmenting habitats as well as creating movement obstacles such as roads. Road construction significantly altered genetic structures, connectivity, and gene flow among Timber Rattlesnake (Crotalus horridus) populations (Clark et al. 2010). Despite behavioral characteristics that disproportionately expose them to traffic hazards (i.e., basking on road surfaces/edges during busy traffic hours, elongated body forms, and slow movement rates), snakes are understudied in road mortality research (Sullivan 1981, Seigel 1986, Jochimsen et al. 2004, Andrews and Gibbons 2005, Jochimsen et al. 2014). However, low-trafficked roadways may share similarities with nonlethal edges, such as forest-field ecotone. Some snakes select habitats near this non-lethal interface because of its thermoregulatory benefits (Row and Blouin-Demers 2006) and greater prey availability (Blouin-Demers and Weatherhead 2001, Patrick and Gibbs 2009).
In addition to these range-wide impacts, populations at a species’ range limit (peripheral populations) are generally reduced and at greater risk of extirpation (Brown 1984). Individuals located at their species range limits inhabit a unique ecological niche, and increased attention on geographic distribution is needed to accurately forecast anthropogenic alterations to the climate and localized habitats (Sexton et al. 2009). For peripheral populations, multiple factors may affect range limitations. For example, peripheral populations exhibit reduced gene flow and are subject to more intense limiting factors such as climate differences (Sexton et al. 2009). Moreover, peripheral populations may inhabit suboptimal landscapes (Brown 1984) which reduce populations to decreased connectivity with source populations (Thomas et al. 2001, Squires et al. 2012). Unique challenges a species encounters at the peripheral range limits has been long recognized (Darwin 1859, Merriam 1894, MacArthur 1972). 3
Peripheral populations may also become more susceptible to parasitic infection when physiologically stressed (Briers 2003) leading to decreased survivability. Despite the unique fitness of peripheral individuals, these populations are often under-sampled compared to those near the range center (Sagarin & Gaines 2002).
Recently, surges in biological invasion studies across the globe have provided novel insights to range dynamics. Florida has become a hot spot for exotic introductions, notoriously hosting more established herpetofauna than any other state or nation (Meshaka et al. 2004, Kraus 2009). With reptilian invaders from Africa, Asia, and South America, south Florida represents a global melting pot for exotic introductions and continues to challenge conservation management (Enge et al. 2004, Reed & Kraus 2010, Engeman et al. 2011). For native species, evolutionary adaptations to exotic species presence has been documented. The Green Anole (Anolis carolinensis) has shown rapid evolution of toe pad size to move to higher perches in response to the established presence of the Cuban Brown Anole (Anolis sagrei) (Stuart et al. 2014). This adaptation, or “niche evolution”, at invasion fronts is comparable to population stress at peripheral ranges (Lee 2002, Cox 2004). As Earth’s climate begins to shift, multiple studies have concluded exotic species in south Florida can potentially expand their distribution further north (Smith et al. 2004, Reed and Rodda 2009, Rodda et al. 2009, van Wilgen et al. 2009).
Taxonomy:
The Eastern Indigo Snake (Drymarchon couperi) is a large, non-venomous colubrid species endemic to the southeastern United States. Although there are no morphological synapomorphies that distinguish members of the superfamily Colubroidea (Cadle 1987), evidence supports cohesive groups exists within this superfamily (Lopez and Maxson 1996). The generalized non-venomous snakes are lumped together into the family Colubridae. The family Colubridae can be dissected further, with Eastern Indigo Snakes being grouped with similar species (racers and rat snakes) into the subfamily Colubrinae. John Edwards Holbrook first described the species in 1842 as Coluber couperi (Holbrook 1842). In 1917, Steineger and Barbour (McCranie 1980) designated the current genus, Drymarchon. Previously, there were two described sub-species endemic to the southeastern United States: the Eastern Indigo Snake (Drymarchon corais couperi) and the Texas Indigo Snake (Drymarchon corais erbennus) (Hyslop 2007). In 2001, the Eastern Indigo Snake was raised to full species status as Drymarchon couperi by the Society for the Study of Amphibians and Reptiles (Crother et al. 2001) and 4
there is current debate on splitting the species even further based on morphological and molecular data (Krysko et al. 2016).
Status:
The species was listed as federally threatened in March of 1978 according to the Endangered Species Act due to habitat loss, pet trade collection, and mortality from the gassing of Gopher Tortoise (Gopherus polyphemus) burrows for rattlesnake round-ups (U.S. Fish and Wildlife Service [USFWS] 1978). A more recent assessment reiterated its imperiled status based on increased habitat alteration, fire suppression, and agricultural development (Stevenson 2006, USFWS 2008).
Range:
Drymarchon species occur throughout tropical regions of the Americas from the southeastern United States to northern regions of Argentina. Currently, there are two species endemic to the United States: the Texas Indigo Snake (Drymarchon melanurus erebennus) and the Eastern Indigo Snake (Drymarchon couperi), being distinguished by allopatry and consistent variation in head scalation (Collins 1991). Historically, D. couperi distribution ranged from coastal Mississippi and Alabama, throughout Florida, southern Georgia, and possibly the southernmost coastal regions of South Carolina (Carr 1940, Diemer and Speake 1983, USFWS 2008, Enge et al. 2013). However, today their distribution is limited to southeastern Georgia and peninsular Florida (Lawler 1977, Moler 1985a, USFWS 2008), although efforts are being conducted at Conecuh National Forest in southern Alabama to reintroduce the species (Wines et al. 2015, Steen et al. 2016) as well as a recent introduction project in Apalachicola at The Nature Conservancy’s Apalachicola Bluffs and Ravines Preserve.
Habitat:
The Coastal Plains region of the southeastern United States historically featured Longleaf Pine (Pinus palustris) forest ecosystems. This unique habitat contains the highest diversity of herpetofauna in the United States (Gibbons et al. 1997). Although this area contained approximately 30 million hectares of Longleaf Pine habitat pre-European settlement, less than 3% of the original extent persists today mostly in isolated fragments (Landers et al. 1995, Frost 2006). Drymarchon couperi frequent Longleaf Pine forests but due to the varying climatic range of the species, different populations utilize multiple habitat types. In cooler climates, such as Georgia and northern Florida, D. couperi can be found in xeric sand ridge habitats dominated by Longleaf Pine and Turkey Oak (Quercus laevis) forests, which host an abundance of burrow refugia created by Gopher Tortoises (Gopherus polyphemus) (Wharton 1977, 5
Hyslop et al. 2012). Most of D. couperi populations are found in peninsular Florida, which includes a more diverse landscape. Eastern Indigo Snakes have been observed in xeric pinelands, tropical hardwood hammocks, citrus groves, upland scrubs, wet prairies, and mangrove swamps (Lawler 1977, Humphrey et al. 1992). Overall, D. couperi has shown preferences for drier areas adjacent to bodies of water (Ernst and Barbour 1989). However, due to climatic differences, the more southern populations of the species are considered more flexible in habitat preferences than their northern counterparts (USFWS 2008).
Description:
Drymarchon couperi is a large, non-venomous colubrid snake with a uniform black to dark blue coloration with varying red and cream pigmentation along their gular scales (Layne and Steiner 1996). The species can reach lengths of 2.63 meters with average lengths around 1.9 to 2.6 meters, making them the longest native snake to North America (Conant and Collins 1998, Stevenson et al. 2009, Enge et al. 2013). Males are typically longer and larger than the females and exhibit a slight keel on one to five mid-dorsal scale rows (Layne and Steiner 1984). All other scales are smooth, large and hexagonal in shape.
Feeding:
D. couperi is known as a diet generalist, foraging on a wide variety of vertebrate prey (Humphrey et al. 1992, Stevenson et al 2010). However, Eastern Indigo Snakes are strongly ophiophagous, even able to consume sympatric venomous snake species. These snakes are not constrictors, but are active hunters and will subdue their prey by sheer jaw strength (Moulis 1976, Stevenson et al. 2010). Stevenson et al. (2010) compiled extensive vertebrate prey records for D. couperi including fish, salamanders, Anurans, snakes, juvenile gopher tortoises, lizards, birds, and mammals. Interestingly, the same study identified unique prey items such as a crocodilian, carrion feeding upon a shark, and cannibalism (Smith 1987, Stevenson et al. 2010).
Refugia:
Eastern Indigo Snakes require refugia, or shelter sites, for nesting and reproduction, escape from temperature extremes, retreat from predators, and protection during ecdysis (Speake et al. 1978, Landers and Speake 1980, Hyslop 2007). In particular, the species is closely linked with inhabiting G. polyphemus burrows as overwintering sites (USFWS 2008). Due to extensive use of underground refugia, shelters such as Gopher Tortoise burrows may be an important limiting factor for the species, 6
especially in cooler climates in their northern range (Diemer and Speake 1983, Hyslop et al. 2009a). However, D. couperi will readily utilize a variety of refugia, including mammal burrows, stumps and logs, brush piles, and manmade structures (Lawler 1977, Landers and Speake 1980, Moler 1985b, Stevenson et al. 2003, Jackson 2013, Ceilley et al. 2014, Hyslop et al. 2014).
Reproduction:
As D. couperi is a rare and secretive species, most information about their reproductive habits are limited to captive observations (Hallam et al. 1998). Additionally, with populations spread across varied climate zones, reproductive patterns can be difficult to generalize. Evidence suggests that the breeding season generally begins around October and can last until early April (Groves 1960, Steiner et al. 1983, Hyslop et al. 2012). During this time, males actively search for females and engage in ritualized male-male combat (Stevenson et al 2003, Bauder et al 2016a). Gestation ranges from 100 to 150 days (Smith 1987, O’Connor 1991) resulting in a clutch of 4-12 large eggs (37-89 grams; Moulis 1976, Steiner et al. 1983, Hyslop et al. 2012). Eggs typically hatch between August and September (Groves 1960). Studies suggest birth sex ratios are 1:1 (Moulis 1976, Steiner et al. 1983) and hatchlings measure 340 – 485 mm (Ernst and Barbour 1989). Sexual maturity is reached at a total length of approximately 1,500 mm (Speake et al. 1987, Layne and Steiner 1996) and in a captive study on females, this length was reached in three to four years (Moulis 1976). Both captive and wild-caught surveys indicate that female D. couperi will reproduce annually (Moulis 1976, Bolt 1996).
Home Ranges:
Eastern Indigo Snakes exhibit among the largest home range sizes for terrestrial snake species, with one radio tracked individual maintaining a home range of 1,528 hectares (Breininger et al. 2011, Hyslop et al. 2014, Bauder et al. 2016a). In addition to their secretive nature, low density numbers, and evidence suggesting D. couperi spends approximately 76% of their time underground, documenting and obtaining data for such a wide-ranging species has proven difficult for traditional field techniques such as mark-recapture studies (Parker and Plummer 1987, Hyslop et al. 2009a, Hyslop et al. 2009b). However, radio telemetry has proved to be a successful method for estimating home range sizes for D. couperi and other cryptic species (Speake et al. 1978, Pearson et al. 2003, Dodd and Barichivich 2007, Hoss et al. 2010, Jackson 2013, Bauder et al. 2016b). Early radio telemetry studies on D. couperi relied on relocated and captive-bred individuals with home ranges varying between 4.8 to more than 300 ha (Moler 1985b, Speake et al. 1978, Dodd and Barichivich 2007). Recent studies on wild populations in 7
south Georgia and north-central Florida reported home ranges varying between 12.8 to 1,530 ha (Bolt 1996, Hyslop 2007, Breininger et al. 2011, Bauder et al. 2016b). Projects at Archbold Biological Station in Highlands County, Florida, and the C-44 reservoir in Martin County, Florida, are the southernmost studies on D. couperi home range sizes to date. These studies reported average home ranges of 18.6 to 74.3 ha (Layne and Steiner 1996) and 9.71 to 42.8 ha (Jackson 2013, Ceilley et al. 2014), respectively. However, Eastern Indigo Snake distribution extends yet further south, and data on these southernmost populations are largely lacking.
Research Objectives:
This study looks to enhance the understanding of an increasingly rare and federally protected species occurring in the Coastal Plains of the southeastern United States, the Eastern Indigo Snake (Drymarchon couperi). These data will provide key information from a population in a protected coastal estuarine reserve in southwest Florida that will guide crucial management strategies for this species in its southernmost range. Due to the varying habitat, climatic changes, and increased exposure to exotic species in south Florida, this study looks to highlight novel intraspecific differences not found in previously studied populations of D. couperi throughout its native range. In turn, management for this protected species may need revision to support their conservation needs in south Florida.
1. What are the home range sizes for D. couperi in south Florida? a. Describe the total home ranges sizes for each individual. b. Describe differences in home range sizes by season as defined by hydrological periods and/or reproductive activity. 2. Are D. couperi utilizing various habitat types within their home ranges at random? a. Determine selection or avoidance for specific habitat types (Wetland vs. Upland). b. Determine selection or avoidance of roads or open trails. 3. Describe the refugia utilized by D. couperi in south Florida. 4. Is there a detectability pattern for D. couperi in south Florida? a. Describe any variations based on seasonality. b. Describe any variations based on time of day. c. Describe any variations based on ambient temperature.
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Chapter 2
Study Site and Methodology
Study Site:
This study was conducted in Collier County, Florida at the Rookery Bay National Estuarine Research Reserve (NERR). It is located along the Gulf Coast of Florida, comprising a myriad of diverse habitats including mangrove swamps, upland pine hammocks, and coastal scrub habitats. The Reserve is minimally disturbed from anthropogenic activity with the exception of a low-trafficked paved road and a small public access boardwalk. Portions of the site were once marked for development and the remnant open sandy roads still exist today. On the eastern edge of the Reserve lies Florida state road 951 (Collier Boulevard) that boasts heavy traffic from nearby housing communities including Marco Island. To the north, Henderson Creek is a brackish waterway that serves as a northern barrier for this study. Of the approximately 16,200 hectares of mangrove, fresh water marshes, and upland habitats preserved within the Rookery Bay NERR boundaries, this study site was limited to approximately 900 hectares.
Table 2.1 – List of most common plant species observed in the Rookery Bay Reserve.
COMMON PLANT SPECIES Black Mangrove Avicennia germinans Red Mangrove Rhizophora mangle White Mangrove Laguncularia racemose Buttonwood Conocarpus erectus Cabbage Palm Sabal palmetto Saw Palmetto Serenoa repens Slash Pine Pinus elliottii Live Oak Quercus virginiana Hog Plum Ximenia Americana Wax Myrtle Myrica cerifera Spikerush Eleocharis spp. 9
ROOKERY BAY NATIONAL ESTUARINE RESEARCH RESERVE – COLLIER COUNTY, FLORIDA
Figure 2.1 – The historic and current distribution map of the Eastern Indigo Snake (D. couperi) provided by The Orianne Society. White diamonds represent previous research sites for this species. The yellow star illustrates my research site at the Rookery Bay National Estuarine Research Reserve in Collier County, Florida. To the right is a satellite image with the blue area encompassing Rookery Bay NERR in its entirety. The yellow box indicates the approximate spatial limits of this study area.
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Capture:
D. couperi were opportunistically captured by hand during walking surveys around Shell Island Road and sandy trails in the upland scrub habitats. Upon capture, individuals were assessed for general health then placed in appropriate transportation receptacles. While awaiting transmitter surgery, individuals were kept in isolated containers in a secured room at Florida Gulf Coast University.
Transmitter Implantation:
United States Fish and Wildlife Service permits allowed up to five adult D. couperi to be surgically implanted with radio transmitters. I used Holohil Systems (Holohil Systems Ltd., Carp, Ontario) SI-2T internal transmitters that weighed 13 grams each and had an average battery life of two years. Transmitters were surgically implanted into the coelomic cavity following Reinert and Cundall (1982). While under anesthesia, data were collected on snout-vent length (SVL), total length, mass, ventral scale counts to location of heart, total ventral scale counts, and cloacal probing to determine sex supplemented by examination of keels along the mid-dorsal scales which are indicative of males (Layne and Steiner 1984, Stevenson et al. 2003). Surgeries were conducted by Dr. Darryl Heard at the University of Florida Small Animal Hospital, College of Veterinary Medicine in Gainesville, Florida for Indigos RB1 and RB2, and Dr. Jeff Noble at the St. Francis Animal Clinic in Naples, Florida for Indigos RB3- 5. During recuperation, individuals were held in a secured room at Florida Gulf Coast University for approximately 3 – 5 days before being cleared for release. Implanted snakes were released into G. polyphemus burrows near their original capture site and were tracked one hour after release.
Radio Tracking:
Individuals were typically tracked once per day, three days a week. Radio telemetry equipment included a Communication Specialists (Communications Specialists, Inc., Orange, California) handheld yagi antenna and a car-mounted roof antenna in conjunction with an R-1000 handheld receiver. When an individual was located, a handheld GPS unit recorded coordinates and the time of location. The observer recorded additional information regarding atmospheric conditions, if a visual was confirmed, if the snake was moving, refugia type (if applicable), and any behavioral notes accrued during the encounter. All data were transferred into a Microsoft Excel spreadsheet for analyses.
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Timeline:
Searching for D. couperi at Rookery Bay NERR began in early June of 2014 with the first capture coming in mid-July of 2015. As individuals were hand-captured, implanted and released, duration of sampling varied depending on the individual snake. Data for this study concluded after a complete year of tracking for the last telemetered Indigo released – RB5. At the end of data collection, remaining snakes were retrieved for transmitter removal and then released at their last captured location following post-surgery recovery.
Data Analyses:
Data were organized in Microsoft Excel then imported into multiple software for analyses. Rookery Bay NERR provided GIS habitat designations to overlap our GPS data for habitat selection analysis in ArcGIS 10.3.1. ArcGIS 10.3.1 also provided spatial analyses for home ranges and kernel density maps. All other data were analyzed in R base package 3.4.2 (R Development Core Team 2008) and vcd package (Meyer et al. 2017).
Objective 1: Home Range
GPS points for each individual snake were imported into ArcGIS 10.3.1 to create minimum convex polygons to estimate home range sizes. ArcGIS also created kernel density estimations to determine high activity areas within the given home ranges. Kernel density estimates provide visual representation for high activity areas, measuring the frequency for an individual sampled per square meter. This analysis generates a color gradient map for GPS locations showing red for areas of higher probable use and green for lower probable use. Seasonal home ranges were created with kernel densities to show land use during varying seasons. Breakdown of seasons included a dry (November – April) and wet (May – October) season, as well as a breeding (October – March) and non-breeding (April – September). Due to these seasons mostly overlapping, further analyses solely focused on the breeding and non-breeding seasons.
Objective 2: Habitat Selection
The staff at Rookery Bay Reserve provided GIS habitat maps to overlay individual D. couperi GPS location points to determine habitat selection. Once corresponding GPS locations were assigned a habitat type, these habitats were grouped into two categories, upland and wetland, based off hydrological and floral components. I performed a chi-square test to assess preferential selection 12
between the wetland and upland habitats for individual snakes. The statistical package “R” 3.4.2 was used to analyze habitat selection during the breeding and non-breeding season. Binomial tests were run to determine if D. couperi were located more often than expected near road edges and open trail ways within 10 and 20 meter proximity buffers than non-edge habitats.
Objective 3: Refugia
This study looked to describe refugia use by D. couperi within the Rookery Bay Reserve. Refugia were grouped into seven categories: active Gopher Tortoise burrows, inactive Gopher Tortoise burrows, mammal burrows, grass, root systems, anthropogenic features, and no burrow type. The proportion of burrow type were analyzed in “R” 3.4.2 for each individual as well as compiled proportions for overall burrow use.
Objective 4: Detectability
At each location, snakes were scored as either “Seen” or “Hidden”. Ambient air temperatures were gathered from metadata collected by Rookery Bay Reserve and linked to the corresponding times of snake detection. Once an individual was detected, the time of day was recorded and categorized as “Morning” (< 1000), “Midday” (1000-1400), and “Afternoon” (> 1400). Data were analyzed in the statistical package “R” 3.4.2 to determine activity patterns in relation to air temperature, time of day, and seasonality.
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Chapter 3
Results
Five Eastern Indigo Snakes were tracked between 20 July 2015 and 11 May 2017: one female and four males (Table 3.1, Appendix Table 2). Of these, three individuals were sampled over 100 times; the female, RB1, was located 151 times and the males, RB4 and RB5, were located 102 and 128 times, respectively (Table 3.1). Tracking of RB2 lasted from 12 November 2015 to 11 October 2016 and was recorded on 61 points. The smallest male, RB3, was located a total of 18 times from 2 January 2016 to 20 February 2016. However, due to such a restricted time frame, RB3 was not included in statistical analyses. Both RB2 and RB3 were found deceased during the study timeline (see Ch. 6).
Objective 1: Home Ranges
Home range polygons were created using minimum bounding geometry for each individual snake (Figure 3.1). The total home range sizes for this study ranged from 113 ha to 233 ha (Table 3.1). The only female in the study, RB1, comprised the smallest home range of 113 ha (Table 3.1, Figure 3.2a), while the largest home range of 233 ha belonged to RB2 (Table 3.1, Figure 3.3a). The home ranges for RB4 encompassed 223 ha (Table 3.1, Figure 3.4a) and 207 ha for RB5 (Table 3.1, Figure 3.5a).
Breeding season was determined to be between the months of October and March, in accordance with previous literature and personal observations (Stevenson et al. 2009, Hyslop et al. 2014, Bauder et al. 2016b). The smallest home range recorded during the breeding season was by RB5 at 75 ha (Table 3.2, Figure 3.5b), while the largest during this season was by RB2 at 224 ha (Table 3.2, Figure 3.3b). RB1 encompassed a range of 107 ha in the breeding season (Table 3.2, Figure 3.2b) and RB4 a home range of 158 ha (Table 3.2, Figure 3.4b). For the non-breeding season from April to September, RB2 exhibited the smallest home range at 33 ha (Figure 3.3, Table 3.2)
14
Figure 3.1 – Minimum Convex Polygons (MCP) for all telemetered D. couperi created in ArcGIS 10.3.1.
15
Figure 3.2a – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the female D. couperi, RB1. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green.
16
Breeding Non-Breeding
Dry Wet
Figure 3.2b – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the female D. couperi, RB1, based on seasonality. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green. KDE for the reproductive seasons (Breeding and Non-Breeding) are shown on top, while KDE for hydrologic seasons (Dry and Wet) are shown at the bottom. 17
Figure 3.3a – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the male D. couperi, RB2. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green. 18
Breeding Non-Breeding
Dry Wet
Figure 3.3b – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the male D. couperi, RB2, based on seasonality. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green. KD for the reproductive seasons (Breeding and Non-Breeding) are shown on top, while KDE for hydrologic seasons (Dry and Wet) are shown at the bottom. 19
Figure 3.4a – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the male D. couperi, RB4. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green.
20
Breeding Non-Breeding
Dry Wet
Figure 3.4b – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the male D. couperi, RB4, based on seasonality. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green. KDE for the reproductive seasons (Breeding and Non-Breeding) are shown on top, while KDE for hydrologic seasons (Dry and Wet) are shown at the bottom. 21
Figure 3.5a – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the male D. couperi, RB5. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green.
22
Breeding Non-Breeding
Dry Wet
Figure 3.5b – Kernel Density Estimates (KDE) heat map showing probability of occurrence of the male D. couperi, RB5, based on seasonality. The yellow outline highlights the total home range for this individual. Within this home range, the KDE heat map illustrates high use areas in red and low use areas in green. KDE for the reproductive seasons (Breeding and Non-Breeding) are shown on top, while KDE for hydrologic seasons (Dry and Wet) are shown at the bottom. 23
Table 3.1 - Home ranges for all subjects that are located at least 61 times throughout the study. All data points calculated in ArcGIS 10.3.1 to create home range size polygons by minimum bounding geometry. Snake ID Sex # of Locations Total Home Range (hectares) RB1 FEMALE 151 113 RB2 MALE 61 233 RB4 MALE 102 223 RB5 MALE 128 207
Table 3.2 - Breeding vs. Non-Breeding seasonal breakdowns of individual Eastern Indigo Snakes.
Snake Sex Breeding Breeding Season Non-Breeding Non-Breeding Range ID Season Points Range (ha) Season Points (ha) RB1 FEMALE 82 107 69 75 RB2 MALE 37 224 24 33 RB4 MALE 54 158 48 151 RB5 MALE 65 75 63 166
Table 3.3 - Dry vs. Wet seasonal breakdowns of individual Eastern Indigo Snakes.
Snake Sex Dry Season Dry Season Wet Season Wet Season Range ID Points Range (ha) Points (ha) RB1 FEMALE 72 110 79 62 RB2 MALE 39 232 22 17 RB4 MALE 58 170 44 149 RB5 MALE 67 108 61 178
24
Objective 2: Habitat Selection Four individuals, one female and three males, were sampled throughout the year for analysis of habitat selection. Habitats are designated from ArcGIS maps created by the Rookery Bay Reserve.
Habitat types were categorized as either “wetland” or “upland” based on hydrological and floral components. Wetland habitats included mixed mangrove systems and freshwater marshes while upland habitats were comprised of pine scrubland, xeric oak scrub, and manmade features such as roads. Habitats within the total home ranges (MCP) for each snake were categorized according to the criteria above. All male snake habitats included larger proportions of wetland habitats while the female’s home range included proportionally more upland habitat (Figure 3.6). A chi-square test was run to determine preferential selection of habitat between wetland and upland habitats for individual snakes. Each snake significantly selected for the upland habitat compared to wetlands (Table 3.4).
RB1 RB2
RB4 RB5
Figure 3.6 – Habitat (wetland or upland) designation for individual D. couperi within corresponding home ranges (MCP). 25
Table 3.4 – Wetland vs. Upland points and chi-square results for individual snakes. Snake ID Sex % Upland Upland % Wetland Wetland p-value Habitat Points Habitat Points RB1 FEMALE 59 128 41 23 < 0.001 RB2 MALE 45 53 55 8 < 0.001 RB4 MALE 45 76 55 26 < 0.001 RB5 MALE 34 87 66 41 < 0.001
Habitat selection was analyzed in comparison to seasonality. Herein, only reproductive seasons were included; hydrological seasons were comparable and therefore excluded for the purpose of this analysis.
RB1 and RB2 both showed a significant affinity for wetland habitats during the Breeding season and a significant avoidance of wetland habitats during the Non-Breeding season (Figure 3.7 and Figure 3.8).
RB4 and RB5 showed no significant selection or avoidance of particular habitats during either reproductive season (Figure 3.9 and Figure 3.10).
26
Indigo 1 (RB1) Habitat
Upland Wetland
Breeding
Reproduction
Breeding
- Non
Figure 3.7 – Habitat selection (Upland or Wetland) in comparison to reproductive season (Breeding or Non-Breeding) for female D. couperi, RB1. The height of each bar represents the Pearson’s residual. Pearson’s residuals above 1 or below -1 indicate significance. The width of each bar represents the number of samples for each pair of categories. This graph illustrates RB1 was located more often than expected in the Wetlands during the Breeding season, but was located less often than expected in the Wetlands during the Non-Breeding season. 27
Indigo 2 (RB2) Habitat
Upland Wetland
Breeding
Reproduction
Breeding
- Non
Figure 3.8 – Habitat selection (Upland or Wetland) in comparison to reproductive season (Breeding or Non-Breeding) for male D. couperi, RB2. The height of each bar represents the Pearson’s residual. Pearson’s residuals above 1 or below -1 indicate significance. The width of each bar represents the number of samples for each pair of categories. This graph illustrates RB2 was located more often than expected in the Wetlands during the Breeding season, but was located less often than expected in the Wetlands during the Non-Breeding season. 28
Indigo 4 (RB4)
Habitat Upland Wetland
Breeding
Reproduction
Breeding -
Non
Figure 3.9 – Habitat selection (Upland or Wetland) in comparison to reproductive season (Breeding or Non-Breeding) for male D. couperi, RB4. The height of each bar represents the Pearson’s residual. Pearson’s residuals above 1 or below -1 indicate significance. The width of each bar represents the number of samples for each pair of categories. This graph illustrates RB4 did not select either habitat type more often than expected for either reproductive season. 29
Indigo 5 (RB5) Habitat
Upland Wetland
Breeding
Reproduction
Breeding
- Non
Figure 3.10 – Habitat selection (Upland or Wetland) in comparison to reproductive season (Breeding or Non-Breeding) for male D. couperi, RB5. The height of each bar represents the Pearson’s residual. Pearson’s residuals above 1 or below -1 indicate significance. The width of each bar represents the number of samples for each pair of categories. This graph illustrates RB5 did not select either habitat type more often than expected for either reproductive season. 30
Road Proximity: To evaluate D. couperi selection or avoidance of trails and roadways, I used ArcGIS to create 10 and 20 meter buffers around these features of the study site (Figure 3.11 and Figure 3.12). Of the total
442 GPS locations recorded, 61 were found within the 10 m buffer (Figure 3.11; 14%) and 135 within 20 m (Figure 3.12; 31%) of roads and trails. However, the 10 and 20 m buffers only accounted for 21 and
42 ha, respectively. Snakes were found more often than expected near roads and trails (binomial test:
10 m from road p < 0.001 and 20 m from road p < 0.001), even though these habitats accounted for only
5% of the available habitat at 10 m from the road and 10% of habitat at 20 m from the road. The total range for these four individual snakes encompassed an area of 417 ha. 31
Figure 3.11 – D. couperi locations within 10 meters of designated roads and trail ways. The white shaded areas indicate the 10 meter buffer from the roads and trails. Blue dots represent D. couperi locations found within the buffer zone. 32
Figure 3.12 – D. couperi locations within 20 meters of designated roads and trail ways. The white shaded areas indicate the 20 meter buffer from the roads and trails. Blue dots represent D. couperi locations found within the buffer zone. 33
Objective 3: Refugia Overall refugia use was examined for all D. couperi (Figure 3.13) as well as for individual snakes: the female (RB1: Figure 3.14), and the three males (RB2: Figure 3.15, RB4: Figure 3.16, RB5: Figure 3.17).
Refugia types were split into seven distinct categories: active and inactive Gopher Tortoise burrows, mammal burrows, grass, roots, anthropogenic features, and no refugia. The anthropogenic features included manmade structures such as concrete piles and building materials. No refugia type was attributed if the snake was sighted in the open, such as during basking behavior, or if the signal indicated the snake was actively moving across the landscape but no visual was obtained. All other data were obtained throughout the year, encompassing multiple season changes.
Collectively, D. couperi were recorded on the surface either actively moving, basking, or hunting for 38% of the locations. Eastern Indigo Snakes took advantage of Gopher Tortoise burrows on 33% of the total recorded locations. The second most utilized burrow type consisted of mammal burrows, 22%, while grass, roots, and anthropogenic features combined for less than 10% of verified refugia.
Individually, the female, RB1, shared similar patterns of refuge use with males RB4 and RB5.
41% and 42% of recordings show the female and two males above ground, not in any burrow type, respectively. Gopher Tortoise burrow use showed similar patterns: 9-10% at active burrows and 22-26% in inactive burrows. Mammal burrows were used approximately 20-25% for all individuals. Grass patches were used sparingly for RB1 (1%), RB4 (5%), and RB5 (2%), but served a significant feature for
RB2 (20%). Root systems were rarely utilized for all individuals, less than 3% for every snake and no recordings of use of roots by RB5. RB2 was the only snake to be located in anthropogenic features, for
10% of his locations. 34
Figure 3.13 – Relative proportion of the refugia types used by all telemetered D. couperi at the Rookery Bay Reserve. “No Refugia” indicates that the subject was above ground at the time of recorded location.
35
Figure 3.14 – Relative proportion of the refugia types used by the female D. couperi, RB1, at the Rookery Bay Reserve. “No Refugia” indicates that the subject was above ground at the time of recorded location.
Figure 3.15 – Relative proportion of the refugia types used by the male D. couperi, RB2, at the Rookery Bay Reserve. “No Refugia” indicates that the subject was above ground at the time of recorded location. 36
Figure 3.16 - Relative proportion of the refugia types used by the male D. couperi, RB4, at the Rookery Bay Reserve. “No Refugia” indicates that the subject was above ground at the time of recorded location.
Figure 3.17 – Relative proportion of the refugia types used by the male D. couperi, RB5, at the Rookery Bay Reserve. “No Refugia” indicates that the subject was above ground at the time of recorded location. 37
Objective 4: Detectability Visual confirmation of snakes was not associated with the air temperature (Table 3.5; Backwards
Stepwise Logistic Regression; p= 0.97). Once temperature was removed from the model, both season and time of day showed significant associations with the detectability of snakes (Table 3.6; Backwards
Stepwise Logistic Regression; Season p = 0.004; Time of Day p = 0.014). The likelihood of seeing an
Eastern Indigo Snake during the breeding season was 92% higher compared to the non-breeding season
(Odds Ratio = 0.52). Additionally, Eastern Indigo Snake were 84% more likely to be seen during the midday hours when compared to other times of day (Odds Ratio = 1.84).
Mark-recapture methods are traditionally used to estimate population size (Pradel 1996, White and Burnham 1999, Hines and Nichols 2002). However, this method may be inaccurate for cryptic and secretive taxa, such as snakes (Durso et al. 2011). Walking and driving surveys throughout the Rookery
Bay Reserve accounted for approximately 284 hours of search effort. If these times are fixed based on search effort (number of field assistants x hours spent searching), then the adjusted search time would amount to 656 hours. This undertaking recorded 13 snake species (Appendix Table 3). These surveys yielded nine individual D. couperi observed over the course of this study. When applicable, morphometrics were taken for each individual D. couperi encountered (Appendix Table 2). Of those observed, one was a dead yearling that was too decomposed for its sex to be determined. Another was an adult male found dead on the road. Of the remaining seven, one was female and six were male.
38
Table 3.5 – Coefficients for Backwards Stepwise Logistical Regression for Season, Temperature, and Time of Day analyses.
ESTIMATE STD. ERROR Z VALUE P-VALUE
INTERCEPT -1.07294 0.77183 -1.39 0.1645
SEASON: NON-BREEDING -0.647138 0.265534 -2.437 0.0148*
TEMP C -0.001015 0.031132 -0.033 0.974
TIME OF DAY: MIDDAY 0.610327 0.248263 2.458 0.014*
TIME OF DAY: MORNING 0.116034 0.30124 0.385 0.7001
* denotes statistical significance
Table 3.6 – Coefficients for Backwards Stepwise Logistical Regression for Season and Time of Day analyses.
ESTIMATE STD. ERROR Z VALUE P-VALUE
INTERCEPT -1.0972 0.2107 -5.207 1.92E-07
SEASON: NON-BREEDING -0.6517 0.2257 -2.887 0.00389*
TIME OF DAY: MIDDAY 0.6096 0.2474 2.465 0.01372*
TIME OF DAY: MORNING 0.1177 0.2971 0.396 0.69206
* denotes statistical significance
39
Chapter 4
Discussion
This project sought to determine home range sizes, habitat and refugia utilization, as well as detectability patterns for D. couperi throughout various seasons of the year in southwest Florida. These data highlight novel information gathered for this species in the southernmost portion of its range. The southwest Florida region possesses a unique climate and habitats dissimilar to core areas of D. couperi’s distribution. Over the course of this study, from July 2015 to April 2017, a total of nine D. couperi were observed in the Rookery Bay Reserve (see Ch. 6, Appendix Table 2). Of these, five adults (one female and four males) were implanted with radio transmitters. However, only the female and three of the males were successfully tracked for a sufficient amount of time to include in analyses. These four individuals were tracked two to three times per week for 334 to 546 days (Appendix Table 1). Due to permit restrictions and the cryptic nature of this species, population level conclusions may be limited by the small sample size. However, future investigations and conservation management in south Florida may be able to make inferences from these data.
Small sample size studies of threatened species is almost inevitable for permitting and practical reasons. Generalizations on these species can develop from reviews of multiple studies. In addition, longer term studies of smaller populations tend to illuminate individual differences rather than focus on species’ averages. This recognition of variation might be critical to conserving species with reduced populations, such as the Eastern Indigo Snake.
Objective 1: Home Ranges
Home ranges from this study are larger than all other studies except one (Appendix Table 1).
The largest home ranges recorded for D. couperi were in a military reservation located in southeastern 40
Georgia, with males averaging 538 ha and females averaging 126 ha (Hyslop 2007). Hyslop (2007) found one male controlling a home range of 1,530 ha, which represents the largest home range for a native snake in North America. Another study conducted in central Florida (Brevard, Highlands, and Polk
Counties) recorded congruent results to our study with an average home range of approximately 202 ha for males and 76 ha for females (Breininger et al. 2011).
Geographically, the nearest radio telemetry study on D. couperi found the smallest average home ranges of 43 ha for males and 10 ha for females (Jackson 2013). However, that study was the only one conducted in a heavily altered landscape, an abandoned citrus grove containing a large network of canals. The small home ranges recorded by Jackson (2013) may have been a result of habitat quality at this site. This means all D. couperi requirements such as thermoregulatory sites, available prey and water sources, and mate availability are compressed within smaller areas, reducing their need to make large landscape movements. Previous data suggested D. couperi is dependent on Gopher Tortoise burrows for mating, reproduction, and thermoregulation (Diemers and Speake 1983, Alexy 2003, Hyslop
2007); however, Jackson (2013) found D. couperi successfully utilizing a multitude of other refugia despite the absence of a Gopher Tortoise population.
These differences in D. couperi home ranges may represent a unique feature for species existing across various climatic and geographic areas. Peripheral populations may encounter differing limiting factors and ecological challenges than core populations (Vanek and Wasko 2017), such as inhabiting suboptimal landscapes and climates (Brown 1984) and decreased population connectivity (Thomas et al.
2001, Squires et al. 2012). For peripheral populations of D. couperi (i.e. Hyslop 2007 and this study), it may be necessary for snakes to maintain larger home ranges in order to obtain necessary requirements such as food and water, mates, and appropriate refugia (Gibbons and Semlitsch 1987). However, the smallest home ranges in the Jackson (2013) study suggest that peripheral populations may only show this range trend in more naturalized areas. Finally, it is possible that these southernmost populations of 41
D. couperi are not peripheral, but closer to an optimal biogeographic range with the possibility of populations to the south precluded.
The Rookery Bay Reserve provides a distinct landscape at the peripheral edge of D. couperi distribution. Located in coastal southwest Florida, Rookery Bay is bordered by the Gulf of Mexico on the west and large human development such as the cities of Naples and Marco Island on the east, north, and south ends. Multiple factors may influence home range fluctuations throughout the year with varying biotic and abiotic features. These would include hydrological periods, salt water intrusions, climate features, prey availability, and competition for resources with established exotic species (e.g.
Burmese Pythons). Prey items were prevalent throughout the Reserve, with multiple predation events observed and recorded during this study (see Ch. 6). However, availability of fresh water and temperature may have been more important factors influencing the distribution of these snakes.
A study conducted in Georgia with reintroduced D. couperi determined temperature and seasonality to be the strongest factors affecting snake activity (Speake et al. 1987). Southwest Florida typically sees very mild temperature changes in the winter months, which encompass D. couperi breeding season. Warmer temperature congruency throughout the year may be a significant factor in movement patterns for D. couperi in southwest Florida. Colder temperatures greatly decreased the movements of snakes in more northern regions; often restricting them to prolonged stays in refugia for thermoregulatory needs (Hyslop 2007). However, with a more consistent climate in south Florida, snake movement may not be limited based on temperature extremes or seasonality alone. While ectotherms are dependent on the balance between costs and benefits of thermoregulation during various times of year (Brown and Weatherhead 2000, Blouin-Demers and Weatherhead 2001), organisms in more stable climates may not need to prioritize this requirement thus possibly elevating other factors, such as hunting or mating. This may point to more consistent landscape movements for D. couperi and other ectothermic organisms residing in more constant climate regions, such as southwest Florida. 42
I examined differences in home range sizes between varying times of year based on the breeding season. Breeding season for D. couperi is from October to March (Stevenson et al. 2009,
Hyslop et al. 2014, Bauder et al. 2016a). Other snake telemetry studies show that male snakes in particular will make larger landscape movements during breeding seasons, inevitably increasing their mating potential (Waldron et al. 2006, Sperry and Weatherhead 2009, Bauder et al. 2016b). Individual snakes in this study showed varying results for seasonal home ranges. RB1 and RB2 increased their home range sizes during the breeding season. RB4 maintained approximately the same home range size between seasons and RB5 decreased his home range during the breeding seasons. These data suggests breeding season may not significantly influence D. couperi home range in southwest Florida.
Objective 2: Habitat Selection
Rookery Bay is a protected reserve comprising a variety of ecosystems with unique flora and fauna. Located along the Gulf Coast of southwest Florida, the Reserve contains mangrove swamps, upland pine hammocks, and coastal scrublands. South Florida’s climate and floral components are vastly different from the rest of D. couperi distribution; therefore our study examined how various habitats were selected.
Although D. couperi is described as a habitat generalist, these snakes prefer drier areas adjacent to fresh water sources (Lawler 1977, Ernst and Barbour 1989). At Rookery Bay, snakes significantly selected for the upland habitat compared to wetlands (Table 3.4). These data match previous records of
D. couperi selection of drier, more upland features (Steiner et al. 1983, Hyslop 2007). This upland habitat includes necessary burrows and thermoregulatory spots, which together lowers their risk of desiccation in subtropical climates (Bogert et al. 1947, Ernst and Barbour 1989). However, different patterns were observed when compared with the breeding and non-breeding seasons. 43
The female (RB1) and the largest male (RB2) were found significantly more often in wetlands during the breeding season, and were less likely to be found in the wetlands during the non-breeding seasons. The breeding season for D. couperi coincides with the dry season in south Florida. During this time, many of the wetland areas are less inundated with standing water or completely dry. Although these areas will still be more exposed compared to canopied areas near upland features, reduced freshwater availability may aggregate many prey species in search of water and food. RB1 and RB2 occupied much larger home ranges during the breeding season as well. Yet, both males RB4 and RB5 showed no preference for either habitat types between the breeding and non-breeding seasons. These two males had either no change in home range size (RB4) or a greatly reduced home range (RB5) during the breeding season.
Road Proximity
The development of roads and fragmentation of habitats is an ever-growing concern for conservation issues throughout the United States and worldwide (Forman and Deblinger 2000).
Estimates of ecological effects of roads, known as the “road-effect zone”, extend more than 100 meters from the road and affects approximately one-fifth of land area in the United States (Forman 2000).
Effects of roads and highways can be direct (e.g. road mortality) and indirect (e.g. fragmentation).
Additionally, roads can create dispersal barriers which limit gene flow (Clark et al. 2010). Limited gene flow may lead to isolated populations becoming more likely to undergo inbreeding depression, and in turn cause a higher probability of species extinction (Mills and Smouse 1994, Frankham 1995). This road-effect zone can substantially alter individual and population behavior for far-ranging species in particular (Boarman and Sazaki 2006). Roads are especially dangerous for snakes given their elongated body forms, slow movement rates, basking behaviors, and the tendency for persectuion by drivers
(Sullivan 1981, Jochimsen et al. 2014). 44
Individuals in this study stayed within the confines of the Rookery Bay Reserve for the entirety of the project. The Reserve has distinct boundaries that may have restricted their movement. At the eastern edge of the Reserve lies a major roadway and dense housing developments. Although there are wild areas across the major roadway that appear suitable, no individual attempted to cross the four-lane road during this study.
When reviewing the home range and road proximity maps from this study, two important features are worthy of note. All individuals spent a significant amount of time near roads and open trails. This affinity for open areas near roads may point to behavioral adjustments made when encountering roadways. For example, D. couperi are active visual predators that may benefit from open and exposed areas where prey items cross. The thermal gradients of road edges may also play as an important feature for several reptilian species which, coincidentally, make up a large portion of the typical D. couperi diet.
D. couperi in this study appear to recognize the risk between heavily and slightly trafficked roadways. Every individual crossed the smaller and less trafficked road (Shell Island Road) cutting through the Reserve at least once, yet no individual made a known attempt at crossing the heavily trafficked four-lane road (Florida State Road 951). State Road 951 appears to truncate D. couperi movement, edging parallel to every tracked snake’s home range polygon. This limitation suggests that
D. couperi at Rookery Bay can identify and assess the risks of crossing roads with fluctuating traffic loads. However, our study would need a larger data set to accurately test this hypothesis. Although none of our telemetered snakes crossed State Road 951, a male Indigo Snake was unfortunately found road killed on Shell Island Road (see Ch. 6). This incident highlights that despite the possibility that D. couperi can identify hazards involved with crossing roads, for whatever reason they may still take the risk to do so. 45
Many snake species will intentionally avoid crossing roads (Andrews and Gibbons 2005).
However, some low-trafficked roads may share similarities with non-lethal edges that potentially serve thermoregulatory benefits (Row and Blouin-Demers 2006) and greater prey availability (Blouin-Demers and Weatherhead 2009). Reproductive behaviors may be affected by road proximity as well. If nests are located near cleared areas with more sunlit exposure, this results in warmer nests (Shine et al. 2002,
Shine et al. 2004). Such an effect would have major implications for organisms (e.g. crocodilians and most turtles) with temperature-dependent sex determination (Lang and Andrews 1994, Tomillo et al.
2015, Laloё et al. 2016).
Studies also suggest there is an age-dependent impact of roadways with adult Timber
Rattlesnakes (Crotalus horridus) moving parallel to road surfaces (Fitch 1999). In addition, adult
Massasaugas (Sistrurus catenatus) were less likely to cross roads in comparison to neonates (Seigel and
Pilgrim 2002). The impacts of road development will obviously vary according to species-specific behaviors and life history traits. Andrews and Gibbons (2005) found that smaller snake species such as
Ring-necked Snakes (Diadophis punctatus) and Southeastern Crowned Snakes (Tantilla coronata), which have restricted home range and daily movements, are more likely to avoid roadways. Other snake species that retain larger home ranges and daily movements, such as D. couperi, increase their probability of facing the perils of crossing roads.
Objective 3: Refugia
Refugia plays an important role for many fauna especially for poikilothermic species that require thermoregulation. D. couperi are often associated with the presence of Gopher Tortoise burrows, preferring these refugia sites (Layne and Steiner 1996, Hyslop 2007, USFWS 2008). However, D. couperi will readily use a variety of refugia, including mammal burrows, brush piles, stumps, logs, and manmade 46
structures like pipes and septic systems (Lawler 1977, Humphrey et al. 1992, Jackson 2013, Ceilley et al.
2014).
This study recorded refugia type, if any, snakes were utilizing. For all individuals except male
RB2, Gopher Tortoise burrows (active + inactive) were the most often used refugia site. Mammal burrows provided a similar proportion of refugia. The Rookery Bay Reserve has a tremendous number of both tortoise and mammal burrows (Metzger 2011), making these the most predominant burrow types on the landscape. Only a small proportion of refugia was dedicated to grassy brush piles and root systems. However, these refugia were typically found in either exposed open areas or in often inundated wetlands. These factors likely deter D. couperi from using brush piles and root systems for extended periods of time but may serve as temporary, spur of the moment refugia. Over one-third
(approximately 38%) of overall marked locations represented D. couperi actively moving. Evidence suggest this species spends approximately 24% of their time above ground despite sex or seasonality
(Hyslop et al. 2009a, Hyslop et al. 2014). The results from this study are surprising in comparison, potentially suggesting D. couperi are more active at the surface in south Florida compared to individuals in more northern populations.
Male RB2 had the most diverse and evenly distributed refugia proportions compared to any other individual snake in this study. He was recorded using manmade structures such as concrete rubble piles and discarded PCV pipes (10%) as well as utilizing grassy brush piles 20% of the time.
Unfortunately RB2 was found deceased on 11 October 2016 due to parasitic infection (see Ch. 6). This infection, and any secondary infections, potentially altered RB2’s behavior. The parasite, Kiricephalus coarctatus, has been documented in Eastern Indigo Snakes and most diagnostic symptoms include weight loss and mucoid oral and nasal discharge but can be fleeting (Brock et al. 2012). 47
Refugia are multi-purpose serving as thermoregulatory areas during extreme temperatures, safe-havens from predators, protective spaces for ecdysis, and places for mating. During this study, four of our telemetered snakes (RB1, RB2, RB4, and RB5) used one burrow system on several occasions. The female (RB1) was recorded in this specific burrow system with each of the radio-tagged males (except
RB3) either in the same burrow or nearby. On a few occasions, RB1 was found in this burrow with no radio-tagged male residing with her. Although, it is possible non-tracked snakes shared refugia with telemetered snakes. This burrow was in a clearing near State Road 951 with large powerline towers and remnants of wire fencing and other metal debris. This particular site produced dynamic snake activity despite being close to a busy roadway and having regular disturbance from maintenance trucks and workers.
Objective 4: Detectability
Walking surveys through the Rookery Bay Reserve yielded nine total D. couperi individuals: one female, seven males, and one undetermined (Appendix 2). The biased sex ratio suggests detectability rates may differ between the sexes for D. couperi. Males will combat other males for territory and access to females. It is therefore reasonable to assume males of all age classes will be encountered more often (e.g. subordinate males will be pushed from territories occupied by more dominant males).
Some evidence suggests female snakes move more often during the breeding season (Cardwell 2008,
Row et al. 2012) resulting in a higher probability of finding females during this time. However, the
Bauder et al. (2016b) study on D. couperi showed no increase in movements or home range sizes during the breeding season.
Snakes are especially challenging subjects for field ecology studies due to their cryptic behaviors, especially for species in decline such as the Eastern Indigo Snake. Previous studies have demonstrated varying detection probabilities for snakes based on sex, time of day, and ambient air temperature (Kery 48
2002, Christy et al. 2010, Durso et al. 2011, Willson et al. 2011). For D. couperi in this study, there was no significant correlation with visual encounters and ambient air temperatures. My original hypothesis that this species would be encountered more often during the early morning and late afternoon hours when temperatures were less extreme was not supported. Surprisingly, I was able to make a visual confirmation of D. couperi during the midday hours (1000-1400h) more often than other times, despite higher ambient air temperatures. If temperatures are consistent throughout the day, D. couperi would be less dependent on basking and could use that time to fulfill needs such as hunting and mate searching. These findings may provide more evidence for differing thermoregulatory behavior trends for D. couperi, and possibly other ectotherms, in southwest Florida.
Eastern Indigo Snakes were also more likely to be seen during the breeding season (October –
March) compared to the non-breeding season. These results were expected as male snakes increase their movement during the breeding season to improve their mating success (Waldron et al. 2006,
Sperry and Weatherhead 2009, Bauder et al. 2016b).
49
Chapter 5
Conclusion
D. couperi in the Rookery Bay Reserve demonstrate unique patterns in home range sizes, seasonal activity, habitat and refugia, detectability patterns and general behavior in comparison to similar studies conducted on central to northern populations in the species range. A better understanding of these patterns is essential to the conservation of this federally protected species. For example, the snakes in this radio telemetry study suggest that D. couperi in southwest Florida may require larger home ranges than more central populations. Peripheral populations such as those in this study and South Georgia (Hyslop 2007) potentially reside in less desirable habitats, resulting in larger and more frequent landscape movements compared to individuals within the core of the species distribution. In a nearby site in south-central Florida, Jackson (2013) found the smallest recorded home ranges. However, that study was conducted in an abandoned citrus grove that was heavily modified with canals and disturbed habitats. These modifications potentially condensed the necessary resources
D. couperi requires, decreasing their need to make long distance movements. A deeper understanding of factors that influence habitat use and home range size is needed throughout the range of D. couperi.
South Florida is a unique region with a subtropical climate and distinctive floral compositions.
These habitats differ from elsewhere in the D. couperi distribution as well as vary greatly from previous studies on the species. This study looked at a coastal population in southwest Florida which includes more stable year-round temperatures, hydrological variations, and increased saline environments (e.g. mangrove swamplands). As in previous research, D. couperi preferred to utilize upland features more often, yet would readily use wetland habitats including mangrove swamps. This is of particular interest as D. couperi and other terrestrial species are encountering sea level rise and salinity encroachment into previously held territories. 50
D. couperi can be considered a refugia generalist, readily utilizing various burrow systems.
Although the largest natural burrow systems are produced by tortoises and mammals, Eastern Indigo
Snakes will also take refuge in manmade structures such as pipes, scrap metal piles, and concrete rubble. Historically D. couperi has been closely associated with Gopher Tortoise burrows, yet the
Jackson (2013) study showed even in the absence of tortoise burrow systems, these snakes will exploit any available refugia, and can maintain a robust population. This may lead to a paradigm shift in management for this species, since Gopher Tortoise burrows may not be as limiting a factor as once believed (Diemer and Speake 1983, Hyslop et al. 2009a).
The detection of an organism is imperative to management implications, especially for species of concern that exhibit low detectability rates across its distribution such as the Eastern Indigo Snake.
Our study demonstrates ambient air temperature does not affect visual encounters, but the time of day and season may be stronger indicators for detection. Walking and driving surveys documented several snake species in the Rookery Bay Reserve and the detection probability for D. couperi is comparable to other cryptic species such as the Eastern Diamondback Rattlesnake (Crotalus adamanteus).
Management Implications
Understanding the spatial ecology and resource allotment of a particular species has direct conservation value. This study identified important factors to be considered for management of D. couperi in south Florida. Home range sizes, seasonal variations, and preferred habitats are now baselined in southwest Florida to understand spatial requirements for this species. Conservation plans should take into consideration natural and, potentially, modified landscapes that are open canopied upland systems near wetland features. Although the presence of Gopher Tortoises and their burrows are not required for a population of D. couperi to sustain itself, these large burrow systems are important features of upland habitats in southwest Florida that provide refuge for a plethora of species. 51
To determine the presence of D. couperi in a particular landscape, this study highlights times and seasons for surveys to increase the probability of encountering this species. When performing biological assessments in southwest Florida, biologists should increase search efforts during the midday times
(1000-1400h) and during the breeding season (October – March) in drier, upland features with suitable refugia present, but false negative survey results are likely with this cryptic species.
Future Work
There are many aspects of this project that can be applied to future research. Larger data sets and other populations of D. couperi across southern Florida and into the Florida Keys would provide a more accurate depiction of how this species utilizes unique and peripheral landscapes. I believe similar studies to Jackson (2013) would benefit the species by determining their use of habitats that are heavily altered, such as abandoned citrus groves. The Jackson (2013) study found significantly smaller home ranges for D. couperi in a highly modified habitat. These modifications may provide an almost optimal landscape for Eastern Indigo Snakes, limiting their spatial requirements due to condensed resource allotment. As urbanization continues to encroach on wild spaces, understanding how D. couperi responds to these alterations will be imperative for the species’ future success. Recent reintroductions of the species into once extirpated areas of the Florida panhandle is promising for the species as a whole, but areas with intense modifications as in the Jackson (2013) study should also be considered as potential reintroduction sites.
One of the most unique features of this study site is the abundance of exotically introduced species. Florida is notorious for its established invasive species, particularly herpetofauna (Engeman et al. 2011). Few studies have delved into native reptilian responses to invasions in Florida (Stuart et al.
2014). A multitude of exotic species have been documented in the Rookery Bay Reserve and this site was originally chosen for this research because of the established presence and on-going research on 52
Burmese Pythons (Python bivittatus). The negative effects of Burmese Python introduction are well documented, mostly in regards to mammal and avian species declines in and around the Everglades
National Park (Snow et al. 2007, Dove et al. 2011, Dorcas et al. 2012). Nonetheless, their effects on native reptiles and amphibians are lesser known. The Eastern Indigo Snake is a large, active, federally protected, and sympatric snake species. Burmese Pythons may not be competing against Indigo Snakes solely for prey items, but also for crucial refugia which both need for thermoregulation, ecdysis, reproduction, and protection – as highlighted in this study. With D. couperi maintaining such large home ranges, it is very likely they will encounter exotic species, including novel pathogens brought in by these exotics (Reed 2005). Alternatively, possibly more complex trophic interactions may be occurring.
If the larger pythons are impacting prey in higher trophic levels, smaller Eastern Indigo Snake prey may be relieved and increase the carrying capacity of the habitat for these native snakes. The introduction of exotic competitions and novel prey is likely to alter food webs in complex ways. Future research is needed to determine the response and extent that D. couperi undergoes while interacting with these exotic species. How D. couperi interacts with invasive species in south Florida could have a rippling effect for populations elsewhere that will potentially compete with these exotic species as their growing populations expand northward (Rodda et al. 2009).
For this population and others near coastal habitats, the threat of climate change and sea level rise is a reality. A warming climate will greatly affect reptilian populations due to physiological processes, making them particularly vulnerable to this phenomenon and will have complex impacts on these communities (Huey et al. 2012, Moreno-Rueda et al. 2012, Dade et al. 2014). Understanding the life history traits of D. couperi in their southernmost range may accurately translate to more northern populations as temperatures rise. Adaptive responses to altered local and regional climates will need to be monitored especially for a species with a distribution that includes several varied climates (Dade et al. 2014). 53
Sea level rise is a major threat to the survivability of this population at Rookery Bay as well.
Many coastal areas in south Florida are already seeing the damaging effects of sea level rise, most notable in the Florida Keys and cities like Miami (Ross et al. 1994, Wdowinski et al. 2016). Many low- lying areas will quickly become inundated, pushing species further inland. For species residing in the
Rookery Bay Reserve, development and a heavily trafficked road (State Road 951) blocks their escape inland. Future studies should map estimated sea level rise in coastal habitats and the connectivity to protected inland habitats for D. couperi and other imperiled species. Although D. couperi in this study often encountered brackish environments such as mangrove swamplands, the species salinity tolerance is currently unknown. Some snake species have shown tolerance to extended exposure to high salinities such as the exotic sympatric species, the Burmese Python (Python bivittatus; Hart et al. 2012), but D. couperi may respond differently and the lack of species-specific information can thwart the development of accurate and effective conservation strategies.
The results of this study add to the evolving understanding of the habitat requirement of this threatened species. A more complex understanding of the ecology of D. couperi across its range will be critical to its survival. In addition, this large, far-ranging species’ ability to adapt to human modified landscapes provides insight to conservation of biodiversity worldwide.
54
Chapter 6
Observational Notes
Throughout the course of this study, many unique observations were made that are worthy of note.
Dietary Observations:
14 November 2015 – 2 days after capture, RB2 defecated identifiable pieces of a hatchling Gopherus polyphemus. 3 February 2016 – RB3 observed consuming a Coluber constrictor. 11 April 2016 – RB1 observed eating an invasive Clarias batrachus (Walking Catfish) in a drying marsh. 21 April 2017 – RB5 regurgitated an intact juvenile Nerodia floridana, as well as the tail of a Coluber constrictor.
Potential Impact
Due to varying habitats, climate, and faunal compositions in southwest Florida, D. couperi diet may differ here than elsewhere in its distribution. Eastern Indigo Snakes in southwest Florida encounter a higher number of exotically introduced species than northern conspecifics, such as recorded observations of predation on C. batrachus (Metcalf and Herman, in press) and P. bivittatus (Paul Andreadis, personal communication). This unique diet may also pressure these southern populations with a higher exposure to novel pathogen and parasitic infections.
Potential Breeding Observations:
RB2 and RB1 in an active tortoise burrow from 12-19 December 2015. RB4 and RB1 in an inactive tortoise burrow from 7-11 March 2016. RB4 and RB1 in a mammal burrow 7 January 2017. RB5 and RB1 in a mammal burrow from 14-24 December 2016. Combat between RB4 and RB5 observed and recorded 19 March 2016.
55
Potential Impact
Although a warmer and more stable climate in south Florida allows for continuous movement of D. couperi throughout the year, the breeding observations from this study do not indicate an adjustment from more northern populations (Bauder et al. 2016b). This may indicate reproductive behavior in D. couperi is independent from environmental factors.
Mortalities:
20 February 2016 - RB3. RB3 was found deceased in an inactive tortoise burrow. During this time of year and being of smaller stature, it is conceivable he succumbed to combat with a larger male. However, upon retrieval he was in an advanced stage of decomposition, making it difficult to accurately assess his cause of death. 11 October 2016 – RB2. RB2 was out in the open grass, near an armadillo burrow complex around which he spent the previous week. Upon retrieval, he was taken to St. Francis Animal Clinic where a necropsy was performed and biopsies were sent to the Florida Department of Agriculture and Consumer Services for analyses. During necropsy, the Pentastomid Kiricephalus coarctatus was found throughout the coelomic body cavity (n=6) and within the lung (n=1). K. coarctatus is sexually dimorphic, resulting in identification of two males and five females in RB2. The mature stage of this native parasite has been documented in D. couperi previously (Foster et al. 2000, Brock et al. 2012), as well as other North and Central American snake species (Montgomery et al. 2006). Eggs of K. coarctatus are non-infectious to snakes, but are transmitted by ingestion of infective nymph stages residing in mammals, amphibians, and lizards (Guidry and Dronen 1980, Riley and Self 1980). Snakes that become the definitive hosts for these parasites will often house them within the lungs and body cavity (Detterline et al. 1984, Foster et al. 2000). Results from the biopsies determined the cause of death of RB2 pertained directly to parasitic infection of Kiricephalus coarctatus. 22 December 2016 – a young D. couperi was found deceased near the site where RB2 died. This individual was dried and had decomposed, so accurate morphometrics and sex were unable to be determined. However, a rough estimate for length was taken – approximately 125 cm. 56
16 July 2017 – an adult Indigo was found dead along Shell Island Road. The individual was probed and determined to be a male, despite having no visible vertebral scale keels. He weighed 1.5 kg and was 172 cm total length.
Fecal Samples
Fecal samples were obtained from RB4 and RB5 upon capture. Florida Gulf Coast University student, Taylor Grimes, used this information for an undergraduate senior research project. Herein are the results of those samples: - RB4 was found to have approximately 104 eggs from hookworms (Kalicephalus sp.) and 4 eggs of the Pentastome Kiricephalus coarctatus. - RB5 was found to have approximately 685 eggs from hookworms (Kalicephalus sp.) and 56 eggs of the Pentastome Kiricephalus coarctatus.
Potential Impact
Understanding the survivability of D. couperi throughout its range is essential to land and conservation management of the species. The recorded presence of a deceased young D. couperi is an indication that the species is reproducing and provides confirmation of a sustained population at the Rookery Bay Reserve. Additionally, we were able to report parasitic infection in one individual (RB2) that resulted in death, as well as two other individuals (RB4 and RB5) with confirmed Hookworm and Pentastomid infection. Due to their secretive and cryptic nature, this information provides a rare insight into internal health risks in wild populations of D. couperi. Additionally, as south Florida becomes ever more developed and urbanized, careful attention should be given to the survivability of this far-ranging species.
57
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Appendix
Appendix Table 1 – D. couperi Home Range Study Comparisons (ordered geographically, north to south)
Average Female Female Average Male Male Tracking Study Location Home Range Size Sample Size Home Range Sample Size Duration (Days) Study Authors (ha) Size (ha)
Southeastern Georgia (Fort Stewart Military 126 14 538 24 89 - 711 Hyslop 2007 Reservation) Levy County, FL ------141 4 unknown Moler 1985
Brevard County, FL 41 18 118 31 unknown Bolt 1996
Highlands County, FL 18.6 7 74.3 12 8 - 197 Layne and Steiner 1996 Brevard, Highlands, and 75.6 21 201.7 23 224 – 1113 Breininger et al. Polk Counties, FL 2011 Martin County, FL 9.71 1 42.8 4 83 – 365 Jackson 2013
Collier County, FL 113.3 1 220.8 3 334 - 546 This Study
Appendix Table 2 – Morphometric Data for D. couperi Found at the Rookery Bay Reserve.
Snake Capture Date Release Date Sex Mass SVL Total Length # Locations Tracking ID (Kg) (cm) (cm) Duration (Days)
RB1 20 July 2015 7 Sept 2015 FEMALE 1.44 149 178 151 546
RB2 12 Nov 2015 27 Nov 2015 MALE 3.07 173 208 61 334
RB3 2 Jan 2016 17 Jan 2016 MALE 1.67 168 200 18 49
RB4 29 Feb 2016 5 March 2016 MALE 2.58 164 193 102 437
RB5 3 March 2016 19 March 2016 MALE 2.54 171 202 128 422
RB6 17 Nov 2016 17 Nov 2016 MALE 0.85 122 151 1 0
RB7 22 Dec 2016 Dead ------125 1 0
RB8 21 Jan 2017 21 Jan 2017 MALE --- 124 152 1 0
RB9 16 July 2017 D.O.R. MALE 1.50 142 172 1 0 72
Appendix Table 3 – Snake species encountered in the Rookery Bay Reserve during surveys
Species Common Name Detections
Coluber constrictor Black Racer 93
Diadophis punctatus Southern Ring-neck Snake 28
Nerodia clarkia Salt Marsh Snake 17
Thamnophis sauritus Ribbon Snake 10
Drymarchon couperi Eastern Indigo Snake 9
Crotalus adamanteus Eastern Diamondback Rattlesnake 8
Pantherophis alleghaniensis Yellow Rat Snake 8
Patherophis guttatus Corn Snake 6
Nerodia fasciata Banded Water Snake 5
Cemophora coccinea Scarlet Snake 2
Nerodia floridana Florida Green Water Snake 2
Storeria victa Florida Brown Snake 1
Boa constrictor* Red-tailed Boa 1
* Non-native species