Abstract

The mean contribution by mass of individual prey items to the diets of large (> 152 cm) alligators has been determined by examining stomach contents of 253 animals from 1995 through 1997. Prey items that comprise more than 4% of the mean dietary mass are (%): snakes (33), birds (25), mammals (15), turtles (12), fish (10), and amphibians (5). Collecting samples of each prey item and determining individual nutrient and contaminant concentrations were used to estimate total nutrient and contaminant contributions by a prey item to the diet of the alligator. Mean nutrient and contaminant contributions by a prey item were the product of the fractional mass contribution of the prey item to the diet and the concentration of the component in the prey item.

The average prey diet for everglades alligators on a dry weight basis contains 63% protein, 17.9% fat, 18.6% ash and approximately 4,500 cal per kg. The average prey diet on a dry weight basis contains 250 ppm Fe, 120 ppm Zn, 4 ppm Cu, < 0.5 ppm Se, 3.3 ppm Hg, <3.5 ppm Cd, < 7 ppm Cr, < 4 ppm Pb, < 4 ppm Ni, and <0.75 ppm As. Protein contributions to the diet by prey items are (%): birds (30); snakes (26); mammals (16); turtles (12); fish (7); and amphibians (4). Fat contributions by prey items to the diet are (%): birds (50), mammals (20), turtles (14), snakes (10), fish (3), and amphibians (1). Ash contributions by prey items to the diet are (%): snakes (43), birds (25), mammals (13), turtles (12), fish (6), and amphibians (3). Energy contributions by prey items to the diet are (%): birds (38), snakes (21), mammals (18), turtles (13), fish (6), and amphibians (3).

Mercury was the only metal component of the diet detected at levels considered potentially toxic. The mercury concentration of prey items was (ppm): (%): snakes (2.5), turtles (0.37), fish (0.24), amphibians (0.15), birds (0.064), and mammals (0.036). Mercury contributions by individual prey items to the diet are (%): snakes (89), turtles (4), fish (3), birds (2), amphibians (0.8), and mammals (0.6). Snakes were the only prey item that contained mercury at a concentration of > 0.5 ppm and they contribute most (89%) of the mercury in the diet of the large everglades alligator.

Acknowledgements

This work was supported by funds from the U. S. Geological Survey.