Intra- and interspecific agonistic behaviour in hatchling Australian freshwater crocodiles (Crocodylus johnstoni) and saltwater crocodiles (Crocodylus porosus)

Abstract

Abstract. We examined agonistic behaviour in hatchling Australian freshwater crocodiles (Crocodylus johnstoni) at 2 weeks, 13 weeks, and 50 weeks after hatching, and between C. johnstoni and saltwater crocodiles (Crocodylus porosus) at 40-50 weeks of age. Among C. johnstoni, agonistic interactions (15-23 s duration) were well established by two weeks old and typically involved two and occasionally three individuals, mostly between 17 : 00 and 24 : 00 hours in open-water areas of enclosures. A range of discrete postures, non-contact and contact movements are described. The head is rarely targeted in contact movements with C. johnstoni because they exhibit a unique 'head raised high' posture, and engage in 'push downs'. In contrast with C. porosus of a similar age, agonistic interactions between C. johnstoni were conducted with relatively low intensity and showed limited ontogenetic change; there was also no evidence of a dominance hierarchy among hatchlings by 50 weeks of age, when the frequency of agonistic interactions was lowest. Agonistic interactions between C. johnstoni and C. porosus at 40-50 weeks of age were mostly low level, with no real exclusion or dominance observed. However, smaller individuals of both species moved slowly out of the way when a larger individual of either species approached. When medium-or high-level interspecific interactions did occur, it was between similar-sized individuals, and each displayed species-specific behaviours that appeared difficult for contestants to interpret: there was no clear winner or loser. The nature of agonistic interactions between the two species suggests that dominance may be governed more strongly by size rather than by species-specific aggressiveness.

The Good, the Bad, and the Ugly: Agonistic Behaviour in Juvenile Crocodilians

“…For crocodilians, detailed information on agonistic behaviour is available for the adults of three species ( Crocodylus acutus , Crocodylus niloticus , and Alligator mississippiensis ; [22] [23] [24] , and recently, for hatchlings and juveniles of two species ( Crocodylus porosus ; Crocodylus johnstoni ) [25] [26] . The results suggest that some agonistic behaviours are shared by different species whereas others are species-specific.…”

“…Comprehensive studies of hatchling and juvenile C. porosus and C. johnstoni under captive conditions have recently revealed that a full repertoire of species-specific agonistic behaviours are displayed during the first few weeks and months post-hatching [25] [26] . For both species, clutch specific differences were observed in the frequency and intensity of agonistic interactions, but importantly not in the range of behaviours displayed [25] [26] . However, a wide range of other factors (eg.…”

Spatial resolving power and spectral sensitivity of the saltwater crocodile, Crocodylus porosus, and the freshwater crocodile, Crocodylus johnstoni

“…These two crocodiles occupy overlapping geographic habitats, where variations in salinity, competitive ability and nesting methods have created separate ecological niches (Webb et al, 1983;Tucker et al, 1997;Kay, 2005). Crocodylus johnstoni is endemic to Australia's northern regions, is commonly found further upstream, is less aggressive (Brien et al, 2013) and has a much narrower snout than C. porosus (A. Pearcy, Implications of skull shape for the ecology and conservation biology of crocodiles, PhD Thesis, Leiden University, 2011). Although both species are opportunistic feeders, C. johnstoni tends to eat smaller prey items and may hunt a higher proportion of fishes than C. porosus (Webb et al, 1983).…”

Crocodilian perivitelline membrane‐bound sperm detection

“…Despite the presence of sperm in every egg, there were differences in developmental rates. Differences in developmental rates may be a result of social grouping as crocodilians are behaviorally complex (Augustine, Pryes, & Evans, ; Augustine & Watkins, ; Brien, Lang, Webb, Stevenson, & Christian, ; Brien, Webb, Lang, McGuinness, & Christian, , ; Garrick & Lang, ; Garrick, Lang, & Herzog, ; Lang, ; Thorbjarnarson & Hernández, ; Vliet , , ). In captive crocodilian groups, competition for resources leads to the establishment of dominance hierarchies instead of established territories (Brien et al, ) and increased competition leads to agonistic behaviors (Drummond, ; Lovern & Jenssen, ).…”