Field experiments on foraging in free-ranging water snakes Enhydris polylepis (Homalopsinae)
Section snippets
Study area and species
The wet–dry tropics of northern Australia are hot year-round (mean monthly temperature 27.0°C) but exhibit intensely seasonal precipitation regimes, with 78% of the 1394-mm mean annual precipitation falling during the brief (4-month) ‘wet-season’ (December–March: Brown & Shine 2004). These monsoonal rains cause widespread flooding, especially in relatively flat low-lying floodplains. We worked at Fogg Dam 60 km east of the city of Darwin in the Northern Territory. This site has been used for
Results
We gathered data on 5 nights (26 February to 2 March 2003). Snake numbers were dramatically lower immediately before and after this time, so our study encompassed the main period during which Enhydris were present in large numbers at the dam wall in 2003. Hourly mean water temperatures at foraging sites spanned a narrow range, from 27.5°C (recorded predawn) to 30.0°C (recorded midafternoon). During the time we gathered data (1900–2300 hours), mean hourly water temperatures remained between 28.0
Discussion
Most of the snakes that we approached ignored our presence, continued to forage, and reacted to experimental stimuli with feeding rather than defensive behaviours. This result suggests that experimental studies on foraging in free-ranging snakes will be feasible with other taxa such as North American natricines (Nerodia, Thamnophis, etc.) that forage in similar ways in similar habitats to Enhydris (personal observation). We predict that many (independently evolved) similarities with Enhydris
Acknowledgments
We thank C. Shilton, E. Cox, S. Dusty, M. D'Aquirie and the staff of Beatrice Hill Farm for their assistance. Shine and Elphick wish to record their appreciation for Brown's accuracy and speed with a slingshot, which drove away a 4.5-m saltwater crocodile intent on conducting its own foraging study with us as the subjects. Funding was provided by the Australian Research Council.
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