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Southeast Ecological Science Center


Thermoregulation of the American Alligator in the Everglades

H. F. Percival1, S. R. Howarter2, K. G. Rice3, C. R. Morea4,
C. L. Abercrombie5, K. Portier6, A. G. Finger7

1U.S. Geological Survey, Florida Cooperative Fish and Wildlife Research Unit
University of Florida, Building 810, Gainesville, FL 32611

2Lacassine National Wildlife Refuge, 209 Nature Rd, Lake Arthur, LA 70549

3U.S. Geological Survey, University of Florida Field Station,
3205 College Ave, Ft. Lauderdale, FL 33314

4FFWCC, Joe Budd Wildlife Field Office,5300 High Bridge Rd., Quincy, FL 32351

5Wofford College, 429 N. Church St., Spartanburg, SC 29303

6University of Florida, Department of Statistics, Gainesville, FL 32611

7The Institute of Environmental and Human Health, Department of Toxicology
Texas Tech University, Lubbock, TX

Presented at the Greater Everglades Ecosystem Restoration Conference, Naples, FL.  December 2000.

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ABSTRACT

Fourteen adult alligators (Alligator mississippiensis) from two study sites in the Florida Everglades, 10 from Water Conservation Area (WCA) 3A North and 4 from Shark River Slough, Everglades National Park, were implanted intraperitoneally with data loggers that recorded core body temperature (Tb) simultaneously at 72 minute intervals. Alligators were recaptured one year later and data loggers removed.  Alligator Tb's were high and stable in summer. Fall Tb decreased corresponding to a decrease in ambient temperatures. Winter Tb remained low, occasionally elevating to activity levels. In spring, daily minimum Tb increased as ambient temperatures increased.  However, unlike fall, spring Tb was elevated to activity levels on nearly a daily basis. The increased frequency of elevated Tb in spring corresponds with both the breeding season and the peak of the dry season.  Elevated Tb is likely to aid sperm and egg production, as well as prey digestion.  Since the Everglades is normally a nutrient poor environment, increasing the rate of digestion while prey are concentrated in pools by the decreased water levels, would allow acquisition of energy. Further examination of annual Tb patterns of Everglades alligators across seasonal hydropatterns may reveal information about their physiology and ecology.

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INTRODUCTION

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Range of the American Alligator - click to enlarge
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In South Florida, alligators face ambient temperature patterns unlike elsewhere in their range. The consistently high temperatures lead to increased metabolic cost.

Alligator mortality - click to enlarge

Alligators in the Everglades have reduced length to weight ratio, reduced total length, and  delayed onset of sexual maturity compared with other parts of their range. The reason for this poor condition is currently suspected to be a combination of low food availability and sustained high temperatures.

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METHODS

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Snare Capture Method - click to enlarge

Alligators were captured from airboats at night using snares or toggle darts.  About 50% of animals equipped with data loggers were recaptured in the same manner, except implanted radio transmitters enabled researchers to target study animals.  Innate wariness of alligators makes recapture quite difficult.

Data recording device - click to enlarge
Temp Logger - click to enlarge

Technological advances have allowed miniaturization of temperature data logging devices so that continuous data collection is now possible.  Tidbit Stowaway Temperature Loggers manufactured by Onset Computer Corporation were programmed to synchronously record temperature from a range of -5 to 37 oC with an accuracy of +/- 0.2 oC every 72 minutes, allowing 396 days of continuous data collection.

Surgical implant team - click to enlarge

Both data loggers and radio transmitters were implanted intraperiotoneally into alligators.  The veterinary team led by Drs. Timothy and Denise Gross (USGS, Florida Integrated Science Center) employed novel anesthesiology which is more compatible with large reptiles than previously available techniques.

Alligators implanted with radio transmitters were then able to be tracked by plane or airboat - click to enlarge
Alligators implanted with radio transmitters were then able to be tracked by plane or airboat - click to enlarge
Alligators implanted with radio transmitters were then able to be tracked by plane or airboat - click to enlarge

Alligators implanted with radio transmitters were then able to be tracked by plane or airboat.

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RESULTS

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Graph 1 - click to enlarge

Seasonal, weekly, daily, and within-day components of body temperature of a typical alligator from WCA 3A North.

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Graph 2 - click to enlarge

A comparison of seasonally smoothed body temperatures for 10 alligators from WCA 3A North.  Body temperatures were recorded simultaneously at 72 minute intervals.

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Graph 2 - click to enlarge
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The typical pattern of body temperature of an alligator from WCA 3A North for 1 year (1997-1998).  Due to a large amount of data (20 intervals/day), the above smoothing is necessary for analysis.

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CONCLUSIONS

  • Spring is metabolically the most important season for alligator populations in the Everglades due to breeding cycles and feeding on concentrated food supplies during the dry season.
     
  • Due to consistently high temperatures and decreased food supplies, summer is metabolically expensive.
     
  • In fall alligator body temperatures decline with decreasing ambient temperature.
     
  • Winter reduces body temperature to levels that inhibit activity, but do not allow efficient hibernation.
     
  • Canals provided a thermal refuge for alligators.
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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 Integrated Science Center.
     
  • Among numerous individuals, the following were instrumental to this project: M. Anderson, S. Bass, L. Brandt, M. Cherkiss, M. Chopp, B. Fesler, T. Foster, P. George, D. Gross, T. Gross, L. Hord, D. Hughes, M. Jennings, F. Mazzotti, B. McNab, C. Morea, S. Shrestha, S. Snow, C. Tucker, C. Weiser, C.Westall, and A. Woodward.
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