Out of sight or in too deep: Effect of visual barriers and water depth on agonistic behaviour and growth in hatchling saltwater crocodiles (Crocodylus porosus)
Publication Type: |
Journal Article |
Year of Publication: |
2014 |
Authors: |
Matthew L. Brien, Christopher M. Gienger, Grahame J. Webb, Keith McGuinness, Keith A. Christian |
Publication/Journal: |
Applied Animal Behaviour Science |
Keywords: |
agonistic behaviour, crocodylus porosus, growth, hatchlings, visual barriers, water depth |
ISBN: |
0168-1591 |
Abstract:
This study tests the role of visual barriers and water depth on levels of agonistic behaviour and growth in hatchling Crocodylus porosus within the first 3 weeks of life. Ninety-six individuals from four separate clutches hatched over 2 days were divided across three treatments containing two groups with 16 individuals each: shallow water with no visual barrier (SW), shallow water with visual barriers (VB), and deep water with no visual barrier (DW). Body mass (BM, g) was measured at introduction and after 21 days, and was used as an index of growth. Behaviour was described and quantified in the night (17:00–08:00 h), when there is an innate peak in behavioural interactions, for three consecutive nights on two occasions (days 9–11 and 18–20 post-hatch). Visual barriers in open shallow water (VB: mean 0.7 interactions/night) nearly eliminated agonistic behaviour relative to SW (mean 10.8 interactions/night; P < 0.05). DW did not reduce the frequency of agonistic interactions relative to SW, but did affect the outcome of interactions (P < 0.05), with both individuals swimming off slowly. The distribution of hatchling growth after 21 days was highly bimodal regardless of treatment, with a group of slow growing (−3.6 to <6 g change in BM) and fast growing hatchlings (6–15 g increase in BM). Although this made statistical comparisons difficult, there was no clear effect of any treatment (P < 0.05) on mean growth rates. The results of this study suggest that there may be utility in providing hatchling and juvenile C. porosus in captivity with a more complex raising environment in order to reduce negative social interactions, but it is not clear whether this improves growth and survival.