Population Biology of the American Crocodile

Abstract

The population biology of the American crocodile (Crocodylus acutus) was studied in southern Florida during 1977-1982. Crocodiles occur primarily in inland mangrove swamps protected from wave action. Females use the open waters of Florida Bay only for access to nesting sites. Individuals have large (86-262 ha), overlapping activity areas. Nesting occurs in spring and summer, avoiding the cold and the wet seasons, either of which can affect incubation. Clutches averaging 38 eggs were laid both in mounds and in holes in the ground, either singly or communally. Available data cannot support the view that the number of nests has decreased in recent years. Hatching failure occurred as a result of infertility, predation, and embryonic mortality from desiccation and flooding. Hole and creek nests were most susceptible to embryonic mortality. Seventy-eight percent of nests hatched some young. We found no evidence of adults defending nests or young, but nest opening by adults was essential for hatching. Disturbance at nest sites caused females to abandon the site. All expected age classes occurred in the population. Size at maturity was 2.25 m TL for females. Documented mortality of adults and subadults of approximately 2 crocodiles per year was predominantly human-caused. At least 45 crocodiles have been released into southern Florida in 17 years. We estimate the southern Florida population to be about 220 ? 78 adults and subadults. The northernmost population of the American crocodile (Crocodylus acutus) occurs on the extreme southern tip of the Florida peninsula, USA. The range of this tropical species has always been limited, probably by temperature constraints (Kushlan and Mazzotti, 1989). Early reports of crocodiles in Florida are notices and discussions of its occurrence (Wyman, 1870; Hornaday, 1891; Smith, 1896; Barbour, 1923); Moore (1953) provided the first detailed account of its status. Ogden (1978) documented aspects of its nesting biology. More recently, Gaby et al. (1985) reported on the population biology of a small number of crocodiles living in a power plant cooling system. 3 Present Address: Department of Wildlife and Range Sciences, University of Florida, 3245 College Avenue, Davie, Florida 33314, USA. st population of the Ameriil ( ocodylus acutus) oc urs on the e tip of the Florida peninsula, e of this tropical species has alli ite , probably by temperature ( s la and az ot i, 1989). Early iles in Florida are notices and its occurrence ( yman, 1870; ; S ith, 1896; Barbour, 1923); ) ided the first detailed ac ount . e (1978) documented aspects i iolog . ore recently, Gaby et te on the population biology er of crocodiles living in a powli s ste . ess: epart ent of Wildlife and s, iversity of Florida, 3245 College Many crocodilian populations are endang red because their effective population sizes h ve been reduced by human-related factors such as as hunting and habitat loss. Small poplations, particularly when isolated, risk extirpation because of the action of natural or artificial forces that erode their numbers. The Florida population of the American crocodile is thought to be of limited size (Ogden, 1978), and therefore susceptible to chance and human inerference. As a result it has long been considred to be endangered (Barbour, 1923; Hines et al., 1984). Unfortunately, limited information has inhibited understanding of its population biology, and therefore of its true status or appropriate conservation needs. In this paper we discuss the population biology of the the American crocodile based on a five-year study of the population in the core of its northernmost range, northeastern Florida crocodilian populations are endanbecause their e fective opulation sizes een reduced by human-related factors as as hunting and habi at loss. Small popi s, particularly when isolated, risk extiri because of the action of natural o arti7 This content downloaded from 157.55.39.162 on Thu, 11 Aug 2016 05:12:47 UTC All use subject to http://about.jstor.org/terms J. A. KUSHLAN AND F. J. MAZZOTTI Bay. Where appropriate, we compare information from studies conducted simultaneously and cooperatively with our own on other segments of the population (Gaby et al., 1975; P. Moler, pers. comm.). Other aspects of our overall study program are discussed elsewhere (Behler, 1978; Hall et al., 1979; Dunson, 1982; Lutz and Dunbar-Cooper, 1984; Stoneburner and Kushlan, 1984; Kushlan, 1988; Mazzotti et al., 1988; Kushlan and Mazzotti, 1989).