Abstract
We examined agonistic behaviour in seven species of hatchling and juvenile crocodilians held in small groups (N = 4) under similar laboratory conditions. Agonistic interactions occurred in all seven species, typically involved two individuals, were short in duration (5–15 seconds), and occurred between 1600–2200 h in open water. The nature and extent of agonistic interactions, the behaviours displayed, and the level of conspecific tolerance varied among species. Discrete postures, non-contact and contact movements are described. Three of these were species-specific: push downs by C. johnstoni; inflated tail sweeping by C. novaeguineae; and, side head striking combined with tail wagging by C. porosus. The two long-snouted species (C. johnstoni and G. gangeticus) avoided contact involving the head and often raised the head up out of the way during agonistic interactions. Several behaviours not associated with aggression are also described, including snout rubbing, raising the head up high while at rest, and the use of vocalizations. The two most aggressive species (C. porosus, C. novaeguineae) appeared to form dominance hierarchies, whereas the less aggressive species did not. Interspecific differences in agonistic behaviour may reflect evolutionary divergence associated with morphology, ecology, general life history and responses to interspecific conflict in areas where multiple species have co-existed. Understanding species-specific traits in agonistic behaviour and social tolerance has implications for the controlled raising of different species of hatchlings for conservation, management or production purposes.
Highlights
Agonistic behaviour plays an important role in determining access to resources such as food, shelter and mates, and in establishing dominance status in a wide range of mammals [1] [2], birds [3] [4], fish [5] [6], reptiles [7] [8], amphibians [9] [10], and invertebrates [11] [12]
Observed agonistic interactions occurred in open water, with none observed on land
Agonistic Behaviour Many of the behaviours observed during agonistic interactions among juvenile crocodilians in this study have been reported among adults [22] [18] [24], which suggests that agonistic behaviour, as with other behaviours in crocodilians [19], may be hard wired from birth and stereotypical for most species
Summary
Agonistic behaviour plays an important role in determining access to resources such as food, shelter and mates, and in establishing dominance status in a wide range of mammals [1] [2], birds [3] [4], fish [5] [6], reptiles [7] [8], amphibians [9] [10], and invertebrates [11] [12]. Agonistic behaviour is often present shortly after birth or hatching, and can vary widely in terms of the nature and ontogeny, both within and among species [13]. This variability is often associated with differences in the ecology, morphology, or general life history of a particular species or population, which can have an evolutionary or adaptive significance [14] [15]. Detailed information on agonistic behaviour among hatchling and juvenile reptiles is limited, due to the often small, cryptic and secretive nature of many species during this early life stage [21]. All appear subject to species-specific variation in the way they are expressed in different contexts and the way they change ontogenetically
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