Born to be bad: agonistic behaviour in hatchling saltwater crocodiles (Crocodylus porosus)

Abstract

Detailed observations on groups of captive saltwater crocodile (Crocodylus porosus) hatchlings revealed sporadic periods of intense agonistic interactions, with 16 highly distinctive behaviours, in the morning (06:00–08:00 h) and evening (17:00–20:00 h) in shallow water. Ontogenetic changes in agonistic behaviour were quantified by examining 18 different groups of hatchlings, six groups each at 1 week, 13 weeks and 40 weeks after hatching. Agonistic interactions between hatchlings at 1 week of age (mean 7.3 ± 0.65/night) were not well-defined and varied in intensity (low, medium, high), number of individuals that were aggressive, and the outcome, while most interactions involved contact (94.5%). There were also clutch specific differences in the frequency of agonistic interactions. At 13 and 40 weeks, a more hierarchal dominance relationship appeared to be established which primarily involved aggression–submission interactions. Agonistic interactions were more frequent (13 weeks 9.7 ± 0.61/night; 40 weeks 22.2 ± 0.61/night) and intense (medium, high), but shorter in duration, in which the subordinate individual fled in response to an approach by a dominant animal that often gave chase but did not make contact. While the full repertoire of behaviour was displayed by hatchlings at 1 week of age, a smaller subset based on dominance status was displayed among 13- and 40-week-old hatchlings. Agonistic behaviour occurs in C. porosus shortly after hatching and is important in establishing and maintaining dominance hierarchies that are characterised by aggression–submission interactions. This type of interaction appears typical for C. porosus both in the wild and in captivity, and may be important in preventing serious injury in a species equipped with formidable armoury. Dispersal by hatchling C. porosus at around 13 weeks of age appears to be driven by a growing intolerance of conspecifics, while territoriality is apparent at an early age. Consequently, agonistic behaviour and social status may be major contributors to the observed differences in growth rates and survival in captivity.