Nile crocodiles threatened by alien weed

ratio of females to males in our sample of the adult population," said Leslie. "We are not sure what happens to nesting females that abandon overgrown nest sites. They possibly 'dump' their eggs in the water or continue looking for a suitable site, eventually nesting in 'secondary' nesting sites due to lack of suitable ones."

Leslie and Spotila found that nests shaded by trifid weed were 5 to 6 degrees Centigrade cooler, on average, than nests in preferred unshaded habitat, ensuring that the hatchlings were heavily skewed toward females, if they were viable at all. They also conducted trifid-weed removal experiments, and found that nesting females made use of this reclaimed nesting habitat.

Trifid weed was originally introduced into South Africa in the form of seeds in packaging material on board a ship in Durban Harbor in the last 60 years. It has since spread rapidly throughout southern South Africa, and has recently been reported at Hluhluwe and Umfolozi Game Parks as well. The full extent of this problem is not known, but the threat is clear and the authors hope to raise awareness and encourage management measures throughout the Nile crocodile's range.

"A management plan was put into action at St. Lucia 1997, involving the manual removal of C. odorata from identified nesting sites every year," said Leslie. The plan was based on the promising removal experiments conducted by Leslie and Spotila. "The management plan is being carried out. However, with an incredibly limited budget I dare not say how efficiently."

Nile crocodiles bring a bounty of ecological benefits to African wetlands, from nutrient recycling to keeping fish populations in check, and the loss of these predators would take a tragic toll on the ecosystem. Dr. Leslie is continuing her research on Nile crocodiles in Botswana's renowned Okavango Delta, along with Dr. Hannes Van Wyk of the University of Stellenbosch and Earthwatch volunteers on Crocodiles of the Okavango.


Contact: Dr. Alison Leslie
Earthwatch Institute

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