Spatial Ecology of the American Crocodile (Crocodylus acutus) and American Alligator (Alligator mississippiensis) in the Greater Everglades

Science Center Objects

Satellite/GPS tags help USGS researchers understand the movements of American Alligators and American Crocodiles in the Greater Everglades.

Spatial Ecology of the American Crocodile and American Alligator in the Greater Everglades

American crocodile

The Science Issue and Relevance: Crocodilians are present throughout virtually all Everglades freshwater wetlands and estuarine areas. Everglades National Park (ENP) has undergone a number of changes that cause concern for the health of this ecosystem. Ongoing efforts for improving water delivery into South Florida freshwater marshes and estuaries may change salinities, water levels, and availability of nesting habitat in receiving bodies of water. Crocodiles and alligators are among top predators within the Greater Everglades ecosystem, and biological impacts of hydrologic operations are concerns for all life stages. Responses of crocodilians are directly related to suitability of environmental conditions and hydrologic change. The previously funded crocodile and alligator Monitoring and Assessment Plan (MAP) involved monitoring and research to measure the responses of these crocodilians to changes associated with the Comprehensive Everglades Restoration Plan (CERP). Studies of movements that quantify home ranges are vital to understand spatial requirements for individuals within the population. Therefore, as a compliment to MAP, we are assessing the home range and core-use areas for crocodiles in Northeast Florida Bay and Cape Sable, and for alligators within the Shark River estuary of ENP. 

Methodology for Addressing the Issue: We have deployed 17 satellite/GPS tags on crocodiles (http://www.seaturtle.org/tracking/?project_id=580) and four on alligators (http://www.seaturtle.org/tracking/?project_id=677). We created kernel density estimates (KDE) with site-fidelity tests to quantify spatial habitat-use patterns over time. This information is important for understanding population processes and life history characteristics, and for designing effective conservation and management strategies. Tracking periods ranged from 3 days to over 406 days. We found that habitat-use patterns of several individuals included areas not previously surveyed during MAP activities. Individual crocodiles traveled relatively short distances from capture and tagging sites, with 5.3 km mean displacement. Overall home ranges (95% KDE) ranged from 23.4-113.5 km 2 (mean= 66.8±33.3 SD), and core-use areas (i.e., 50% KDE) ranged from 3.5 to 22.0 km2, and were within the boundaries of ENP. For alligators, mean core-use area was 10.9 km2 (range 1.8 – 28.7 km2), and mean home-range size (i.e., 95% KDE) was 45.4 km2 (range 10.1 – 105 km2).

Spatial Ecology of the American Crocodile and American Alligator in the Greater Everglades

Satellite/GPS tag on the back of an American alligator. 

Future Steps: Future efforts include the continuation of satellite tracking to increase the sample size of satellite-tagged individuals. Continued tracking of crocodiles and alligators within the estuaries of ENP will result in a better understanding of areas used intensively by crocodilians in the Greater Everglades. In addition, we will summarize data related to growth, survival, and condition from the five year joint MAP project. 

Additional Related Product(s):

Comprehensive Everglades Restoration Plan (CERP): American Alligator Density, Size, and Hole Occupancy and American Crocodile Juvenile Growth & Survival

Fujisaki I, Hart KM, Cherkiss MS, Mazzotti FJ, Beachamp JS, Jeffery BM, Brandt LA (Accepted) Spatial and temporal variability in estuary habitat use by American alligators. Estuaries and Coasts.

Rosenblatt AE, Nifong JC, Heithaus MR, Mazzotti FJ, Cherkiss MS, Jeffery BM, Elsey RM, Decker RA, Silliman BR, Guillette Jr. LJ, Lowers RH, Larson JC (2015) Factors affecting individual foraging specialization and temporal diet stability across the range of a large “generalist” apex predator. Oecologia, DOI 10.1007/s00442-014-3201-6.

Beauchamp, JS (2014) Spatial ecology of the American crocodile, Crocodylus acutus, in Everglades National Park. A thesis presented to the University of Florida 48 pp.

Spatial Ecology of the American Crocodile and American Alligator in the Greater Everglades

Crocodile and alligator spatial ecology

Mazzotti FJ, Hart KM, Jeffery BM, Cherkiss MS, Brandt LA, Fujisaki I, Rice KG (2010) American alligator distribution, size, and hole occupancy and American crocodile juvenile growth and survival. 2004-2009. Final Summary Report for Cooperative Agreement Number 1434-05HQRU1544/244 U.S. Army Corps of Engineers and University of Florida. Fort Lauderdale, FL: University of Florida Fort Lauderdale Research and Education Center. 95 p.

Beauchamp JS, Cherkiss MS, Rochford MR, Mazzotti FJ (2009) A recent capture of a large American crocodile (Crocodylus acutus) in Florida. Florida Field Naturalist 37(4):149-150.

Brien ML, Cherkiss MS, and Mazzotti FJ (2008) American crocodile, Crocodylus acutus, mortalities in southern Florida. Florida Field Naturalist 36(3):55-82.

Mazzotti FJ, Brandt LA, Moler P, Cherkiss MS (2007) American crocodile (Crocodylus acutus) in Florida: recommendations for endangered species recovery and ecosystem restoration. Journal of Herpetology 41(1):122-132.

Cherkiss MS, Parry M, Mazzotti FJ (2007) Crocodylus acutus (American crocodile): migration. Herpetological Review:38(1):72-73.

Cherkiss MS, Bass OS, Mazzotti FJ (2006) Crocodylus acutus: geographic distribution. Herpetological Review 37(4):491.