Introduction

Over the last one hundred years the hydrology of the Everglades has been greatly altered by mankind. Efforts to repair the functioning of the ecosystem are using a multicomponent model, the Across Trophic Level System Simulation (ATLSS), to predict the response of native flora and fauna to alternative water delivery scenarios. This study was designed to provide information on the natural history and population functioning of the American alligator in the Everglades for construction of an ATLSS American alligator population model and to investigate restoration needs and status of the alligator in the Everglades ecosystem.

We initiated a five year study on the home range, daily movement, habitat use, thermoregulation, and body temperature patterns of alligators in Shark Slough, Everglades National Park, and Water Conservation Area (WCA) 3A North. A total of 66 alligators were captured and surgically implanted with radio-transmitters. This poster discusses a portion of this study concerning home range and movement patterns of alligators in the Everglades.

Objectives:

• To determine daily and seasonal movements of varying age/size and habitat (canal, interior marsh) classes of Everglades alligators.
• To relate the above objectives to the dynamic hydroperiod of the Everglades.

Methods

Capture

• Sixteen alligators in Water Conservation Area 3A North (WCA) and 15 alligators in Everglades National Park - Shark River Slough (ENP) were captured from an airboat using capture darts and snares.

Surgery The animals were sedated with a Medetomidine injection and Isoflurine gas (D. Gross, University of Florida). An AVM model SB2 transmitter in the 166-170 MHz range was sterilized and surgically implanted intramuscularly anterior to the hind limb. Alligators were then given a dose of Atipamezole Hydrochloride to reverse the initial dosage of Medetomidine.

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Home Range

• Alligators were located on a weekly basis.
• Weekly location data were used to calculate home range size by a 95% adaptive kernel model.
• An ANOVA was used to test for differences in home range size between genders, habitats (marsh vs. canal), study areas (WCA vs. ENP), and seasons.

Daily Movement Daily movement was estimated from 4 weeklong intensive tracking samples conducted during each season from 7 November 1997 to 31 July 1998 in WCA and ENP. Locations were obtained approximately twice per day over each weeklong intensive sample. Ranges V (Institute of Terrestrial Ecology, Wareham, United Kingdom) was used to estimate the minimum linear daily movement (m/24-hr). An ANOVA was used to test for differences in daily movements between genders, habitats, study areas, and seasons.

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Results

Home Range

• Home range size for alligators located in WCA and ENP were not significantly different (F_{1, 28} = 0.03; P = 0.860).

• Annual home range size for male alligators was significantly greater than females (F_{1, 28} = 6.30; P = 0.018).

• Male alligators had significantly longer (F_1,29 = 5.32; P = 0.029) and wider home ranges (F_1,29 = 3.07; P = 0.090) than females.

• Alligators located in canals had more linearly shaped home ranges than marsh alligators (F_1,29 = 3.66; P = 0.065).

• Female (F_1,10 = 1.10; P = 0.32, R² = 0.12) and male (F_1,20 = 0.10; P = 0.11, R² = 0.05) alligator home range size tended to decrease with an increase in total body length.

Mean annual and seasonal home range size for radio-tagged alligators in Water Conservation Area 3A North and Everglades National Park from 1 July 1997 to 21 September 1998. [click on individual images below for larger version]
Male vs. Female
Canal vs. Marsh

Alligator home-range polygons (each color represents an individual alligator) in Everglades National Park, Florida. [larger image]

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Movement

• Movement for alligators located in WCA and ENP were not significantly different (F_1,84 = 1.07; P = 0.305).

• Male alligators moved significantly more in a 24-hour period than female alligators (F_1,11 = 25.60; P = 0.0004).

• No significant differences were found in the mean daily movements of marsh and canal alligators (F_1,86 = 1.94; P = 0.167).

Mean annual and seasonal minimum daily movement for radio-tagged alligators in Water Conservation Area 3A North and Everglades National Park from fall 1997 to summer 1998. [click on individual images below for larger version]
Male vs. Female
Canal vs. Marsh

Annual movements of an adult male alligator in Water Conservation Area 3A North. [larger image]

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Conclusions

• Alligator movement increases with increased water level.
• The spring breeding season was the most critical period for adult male alligators.

  - Greater movements.
  - Larger home range.

• The summer nesting season was the most critical period for adult female alligators.

  - Smallest movements.
  - Smaller home range.

• Seasonal and hydrological effects defined alligator movements in the Everglades.

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Acknowledgements This research was supported in significant part by DOI's Critical Ecosystem Studies Initiative, a special funding initiative for Everglades restoration administered by the National Park Service; and in part by USGS's Florida Caribbean Science Center. T. Foster assisted in formatting the poster.

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1 FFWCC Joe Budd Wildlife Field Office 5300 High Bridge Rd. Quincy, FL 32351
2 USGS-BRD Everglades National Park Field Station 40001 S. R. 9336 Homestead, FL 33034
3 USGS-BRD FL. Co-op Fish and Wildlife Research Unit University of Florida Gainesville, FL 32611

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Related information:

SOFIA Project: Across Trophic Level System Simulation (ATLSS) - Alligators submodel

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