Ecology and Physiology of Nesting and Early Development of the American Alligator

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Abstract
Ambient temperatures were significantly correlated with alligator (Alligator mississippiensis) nesting activity. Nesting occurred earliest when March-April-May ambient temperatures were highest. Rainfall had no significant relationship with time of nesting activity although water levels did affect the degree of nesting. The bulk of the nesting took place within a 2-week period each year. Nesting chronology and factors affecting nesting were investigated at Rockefeller Refuge from 1964 through 1987. Courtship activities generally began in early April and progressively intensified until early June. From late May through the first week of June courtship and copulation were intense, the females ovulated, and the high point of spermatogenesis occurred. Factors which seriously affected nesting success were floods, droughts, and predation. Salinity levels affected nesting densities along the coast. Nesting success (% of nests which produced live hatchlings) averaged 68.3% for 266 nests followed during a 4-yr study. Hatching success (% of eggs which hatched) averaged 58.2% for 154 nests followed during two nesting seasons. Habitat selection, home ranges, and daily movements were delineated for adult males and females. Courtship occurs in deep open water during springtime. Adult females selectively seek out dense vegetation adjacent to isolated ponds for nesting during the summer. Adult and sub-adult males tend to prefer open water all year round and only occasionally venture into the more secluded and heavily vegetated areas used by the females. Home range sizes and daily movements were much larger for adult males than for adult females. Laboratory studies evaluated the effects of four different egg incubation temperatures on hatching success, sex determination, size at hatching, and growth rates to 18 mo of age. The results indicate that incubation temperature can have a profound effect on sex ratios, hatchling size, and post-hatching growth. No significant differences were observed in hatching success at the four different temperatures.

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