We assessed the reproductive ecology of the American crocodile (Crocodylus acutus) on Coiba Island, Panama from January–December 2013. We examined nest site characteristics from January–April and hatchling survivorship from April–December. Ten nests were examined at three nesting localities where 30% of the nests were found under forest canopies and 70% were exposed to sunlight (distance to nearest tree = 280 ± 110 cm). Half of the nests were built closer to the sea and the other half closer to bodies of freshwater (700 ± 360 cm). The nest dimensions were 17.5 ± 7.8 cm from the top of the clutch to the surface, 42.9 ± 9.9 cm from the bottom of the clutch to the surface, and 35.9 ± 3.6 cm wide at the top of the nest cavity. The average soil conditions in the nests consistently had high concentrations of potassium (69.3 mL/L) and manganese (9.2 mg/L), moderate concentrations of phosphorus (6.6 mg/L) and iron (3.7 mg/L), and low concentrations of zinc (0.5 mg/L) and copper (0.0 mL/L). Cation exchange capacity showed consistently high concentrations of calcium (2.2 cmol/kg), moderate of magnesium (1.1 cmol/kg), and low in aluminum (0.1 cmol/L). Volumetric water content was about 25.0 ± 2.6% at the bottom and 22.8 ± .3% in the middle of the clutches. Hatching success was 88.9%, of which 68.3% hatched by themselves or with the mother's aid and 20.6% hatched with our aid. Mean size of the mother was 219 ± 6.2 cm total length (TL) and 115.9 ± 3.0 cm snout-vent length (SVL). The incubation period was estimated to be 85–88 days. TL and SVL growth rate of those individuals were 0.03–0.16 cm/day and 0.00–0.09 cm/day, respectively. Population size was estimated to be 218.6 hatchlings in 22.4 km2; the hatchling population declined 65.7% after the first 2 months (May and June) and 95.9% by July, leaving only 0.5% remaining by December. This is the first study to assess nest-site characteristics and estimate hatchling survival in a Pacific population of American crocodiles.
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