ESTIMATING DENSITY OF FLORIDA KEY DEER A Thesis by CLAY WALTON ROBERTS Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2005 Major Subject: Wildlife and Fisheries Sciences ESTIMATING DENSITY OF FLORIDA KEY DEER A Thesis by CLAY WALTON ROBERTS Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved as to style and content by: Roel R. Brown (Member) (Head of Department) May 2005 Major Subject: Wildlife and Fisheries Sciences iii ABSTRACT Estimating Density of Florida Key Deer. (May 2005) Clay Walton Roberts, B., Texas A&M University Chair of Advisory Committee: Dr. Roel Lopez Florida Key deer (Odocoileus virginianus clavium) were listed as endangered by the U.
Fish and Wildlife Service (USFWS) in 1967. A variety of survey methods have been used in estimating deer density and/or changes in population trends for this species since 1968; however, a need to evaluate the precision of existing and alternative survey methods (i., road counts, mark-recapture, infrared-triggered cameras [ITC]) was desired by USFWS. I evaluated density estimates from unbaited ITCs and road surveys. During this same period, 11 ITC stations (1 camera/42 ha) collected 5,511 deer exposures.
Study results found a difference (P < 0.001) between methods with road survey estimates lower (76 deer) than ITC estimates (166 deer). Comparing the proportion of marked deer, I observed a higher (P < 0.001) proportion from road surveys (0.266) than from ITC estimates (0. Lower road survey estimates are attributed to (1) urban deer behavior resulting in a high proportion of marked deer observations, and (2) inadequate sample area coverage. I iv suggest that ITC estimates are a reliable and precise alternative to road surveys for estimating Key deer densities on outer islands.
I also evaluated density estimates from 3 road survey methods. Road survey methods (n = 100) were conducted along a standardized 31-km route where mark- resight, strip-transect, and distance sampling data were collected between June 2003– May 2004. I found mark-resight estimates to be lower ( x = 384, 95% CI = 346–421) than strip-transect estimates ( x = 854, 95% CI = 806–902) and distance estimates ( x = 523, 95% CI = 488–557). I attribute low mark-resight estimates to urban deer behavior resulting in a higher proportion of marked deer observations along roadways.
High strip-transect estimates also are attributed to urban deer behavior and a reduced effective strip width due to dense vegetation. I propose that estimates using distance sampling eliminate some of these biases, and recommend their use in the future. v DEDICATION I dedicate this to my Mom and Dad who taught me that the journey is more important than the destination; and, to my Grandmother and Stepmother who always have time to share a cup of coffee. Also, to my Brother who shares my passion for the outdoors and history.
vi ACKNOWLEDGMENTS I would like to thank the members of my committee, Roel Lopez and Nova Silvy, for their guidance through my graduate school experience. The lessons I learned from them, many of which had nothing to do with scholastic improvement or Key deer biology, will not soon be forgotten. They understand the value and concepts of working hard, having fun, and promoting positive energy with colleagues. Additionally, I would also like to thank Professors M.
Whisenant who helped drag me kicking and screaming up to a higher standard of understanding of various aspects of ecology and research. Secondly, I would like to express my appreciation to my fellow graduate students in the Department of Wildlife and Fisheries Sciences (WFSC) at Texas A&M University, colleagues at the National Key Deer Refuge, The Nature Conservancy, Mosquito Control, and Mote Marine Institute, many of whom are friends, hunting buddies, spear fishing buddies, rum drinking buddies, co-authors and co-conspirators; all of whom made my experience at A&M and in the Keys unforgettable. Special thanks have to be extended to the TAMU student interns, Americorps volunteers, and other volunteers who assisted in the collection of field data. Funding was provided by TAMU System, Rob and Bessie Welder Wildlife Foundation, Florida Fish and Wildlife Conservation Commission, and USFWS (Special Use Permit No.
Special thanks are extended to the staff of the National Key Deer Refuge, Monroe County, Florida. Last, but certainly not least, thank you to the ladies in the WFSC office that kept me in line all those years. vii TABLE OF CONTENTS Page ABSTRACT. vi TABLE OF CONTENTS.
vii LIST OF FIGURES. ix LIST OF TABLES. xii CHAPTER I INTRODUCTION. 3 II COMPARISON OF CAMERA AND ROAD SURVEY ESTIMATES FOR WHITE-TAILED DEER.
19 III COMPARISON OF 3 METHODS IN ESTIMATING WHITE- TAILED DEER DENSITY. 34 viii CHAPTER Page IV SUMMARY AND SURVEY RECOMMENDATIONS FOR ESTIMATING KEY DEER DENSITY. 69 ix LIST OF FIGURES FIGURE Page 1.1 Range of the endangered Florida Key deer, Monroe County, Florida.1 Road survey route (4-km) and 11 infrared-triggered camera (ITC) stations used to estimate Key deer densities on No Name Key (461-ha), Monroe County, Florida, January 1999-December 2000. Road survey is divided into urban (dashed line, 2.5-km) and rural roads (solid line, 1.
Approximately 79% of total deer observations (n = 3,222) were observed on urban roads compared to 21% for rural roads. The percent of Key deer observations (n = 5,511) by camera station are in parentheses, the star symbol indicates approximate camera station placement. Gray shading represents areas inhabited by deer (upland areas)….2 Florida Key deer density estimates (mean, SE) by season, time of day (sunrise=SR, sunset=SS, nighttime=NT), and method (road survey, infrared-triggered camera estimates [ITC]) for No Name Key (461-ha), Monroe County, Florida, January 1999-December 2000.3 Simpson’s index of evenness for observations from individually marked Florida Key deer (n = 19, n = 12 females, n = 7 males) by method for No Name Key, Monroe County, Florida, January 1999-December 2000. Fish and Wildlife Service 71-km survey route used in estimating Key deer density on Big Pine Key, Monroe County, Florida, (Silvy [1975], Lopez [2001])…………………………….2 Survey route (31-km) used by U.
Fish and Wildlife Service in monitoring Key deer population trends (1975-present) on Big Pine Key, Monroe County, Florida. Arrows indicate the direction of travel (no double counting)….3 Estimated marginal means (Log[Y+1] transformed) by method and season for Florida Key deer, July 2003-May 2004………….4 Florida Key deer density estimates ( x , 1 SE) by season and method (mark-resight, strip-transect, and distance) for Big Pine Key, Monroe County, Florida, July 2003………………………… 31 4.1 Original survey routes (BPK 44-mile, solid and dotted lines; BPK 10-mile, dotted line only; NNK [1998-2001]) used in estimating Key deer density on Big Pine (BPK) and No Name (NNK) keys, 1968-1972 (Silvy 1975), 1998-2001 (Lopez 2001)………………. Fish and Wildlife Service (USFWS) survey route used in monitoring Key deer population trends on Big Pine (BPK) and No Name (NNK) keys, 1975-present………………… 38 4.3 The TAMU/FWS 19-mile route used in estimating Key deer density on Big Pine (BPK), 2003-2004………………………….4 Proposed survey route for future Key deer monitoring by the U. Fish and Wildlife Service (USFWS).
Survey route is slightly modified from the official USFWS route (Figure 2), accounting for recent road closures and high density developments. Arrows indicate the direction of travel (no double counting)…………….5 Relative size comparison of Florida Key deer by sex and age. Head shapes vary between adults (size of egg plant), yearlings (size of papaya), and fawns (size of mango)…………………….6 Body comparison of adult female (top) and male (bottom) Florida Key deer. Note elongated head, rectangular bodies, and, in the case of the males, hardened antlers and swollen neck…………….
49 xi FIGURE Page 4.7 Head comparison of adult female (left) and male (right) Florida Key deer. Note male head shape after dropping antlers………….8 Comparison of body size and head shape for 3 age-classes of female Key deer………………………………………………… 51 xii LIST OF TABLES TABLE Page 4.1 Average Key deer observed by survey route and year, Big Pine and No Name keys, 1969-2001. 40 1 CHAPTER I INTRODUCTION The endangered Florida Key deer, the smallest subspecies of white-tailed deer in the United States, are endemic to the Lower Florida Keys (Hardin et al. Key deer occupy 20-25 islands within the boundaries of the National Key Deer Refuge (NKDR) with the majority of the population (≈75%) found on Big Pine (BPK) and No Name (NNK; Fig.
The most recent population estimate indicates approximately 500 Key deer on BPK and NNK (Lopez 2001), an increase from the estimated 30–50 deer in the late 1940s. The need for wildlife managers to obtain reliable population estimates is paramount in the field of wildlife ecology. Managers need practical, field-tested techniques that are repeatable and can be used by a variety of field personnel (Koenen et al. Estimating abundance or density of an animal population is important for developing proper conservation policy and management protocols (Gelatt and Siniff 1999, Swann et al.
2002), particularly with threatened or endangered species like the Florida Key deer. Annual population monitoring is mandated in the current Key Deer Recovery Plan (U. Fish and Wildlife Service [USFWS] 1999). Traditional methodologies such as drive, strip, aerial, thermal/infrared counts, and mark-capture techniques can be expensive, labor intensive, or limited to habitats with high visibility and lack of dense cover (Lancia et al.
1994, Jacobson et al. Since 1968, spotlight counts have been conducted on the Florida Key The format and style of this thesis follows Journal of Wildlife Management. Efforts to estimate population density (deer/unit area), however, have been limited to mark-resight efforts conducted in 1968-1972 and 1998-2001 (Silvy 1975, Lopez 2004). Use of mark-resight methodologies are labor intensive and expensive, and may be impractical in the annual monitoring of Key deer by USFWS biologists.
A need to evaluate alternative methods of estimating Key deer density is necessary, particularly methods that are easy to implement, precise, and economical. Furthermore, methods that provide USFWS biologists with annual density estimates rather than population trends (e., index from spotlight counts) would be preferred. OBJECTIVES The objective of my thesis was to evaluate 2 alternative methods to estimate population density for the endangered Florida Key deer. First, I evaluated the use of infrared-triggered cameras (ITC) in estimating deer numbers (Kucera et al.
1995, Jacobson et al. 1997, Koerth and Kroll 2000) compared to traditional mark-resight methods to assess the applicability of ITCs in estimating Key deer densities on outer islands. Alternative methods of estimating Key deer densities on outer keys where the lack of roads precludes traditional road counts are needed. Second, I compared distance sampling (Buckland et al.
1993, Corn and Conroy 1998, Tomas et al. 2001, Forcardi et al. 2002a, Koenen et al. 2002, Swann et al.
2002, Ransom and Pinchak 2003), strip- transect (Burnham and Anderson 1984, Johnson and Rutledge 1985, Hiby and Krishna 2001), and mark-resight methodologies to evaluate the usefulness of these methods in future monitoring efforts with Key deer. My thesis is divided into 3 chapters: 3 1. Use of infrared-triggered cameras in estimating Key deer (Chapter II). Comparison of distance sampling, strip-transects, and mark-resight methods in estimating Key deer (Chapter III).
Final recommendations for estimating Key deer (Chapter IV). STUDY AREA The Florida Keys extend 200 km from the southern tip of peninsular Florida (Fig. Soils vary from marl deposits to bare rock of the oolitic limestone formation (Dickson 1955). Typically, island areas near sea level (maritime zones) are comprised of red mangrove (Rhizophora mangle), black mangrove (Avicennia germinans), white mangrove (Laguncularia racemosa), and buttonwood (Conocarpus erecta) forests.
With increasing elevation, maritime zones transition into hardwood (e., gumbo limbo [Bursera simaruba], Jamaican dogwood [Piscidia piscipula]) and pineland (e. Two islands, BPK (2,548 ha) and NNK (461 ha), were selected in my study because (1) the majority of the Key deer population (≈ 75%, Lopez 2001, Lopez 2004) reside on these 2 islands, and (2) long- term population survey data have been collected on these 2 islands (Silvy 1975, Lopez 2004).