Crocodiles are way clever than previously thought, according to new research in India, which found that the "shrewd hunters" use strategic moves to lure their prey.
The study by Vladimir Dinets from the University of Tennessee is the first to observe two crocodilian species - muggers and American alligators - using twigs and sticks to lure birds, particularly during nest-building time.
Dinets' research is the first report of tool use by any reptiles, and also the first known case of predators timing the use of lures to a seasonal behaviour of the prey - nest-building.
Dinets first observed the behaviour in 2007 when he spotted crocodiles lying in shallow water along the edge of a pond in India with small sticks or twigs positioned across their snouts.
The behaviour potentially fooled nest-building birds wading in the water for sticks into thinking the sticks were floating on the water. The crocodiles remained still for hours and if a bird neared the stick, they would lunge.
To see if the stick-displaying was a form of clever predation, Dinets and his colleagues performed systematic observations of the reptiles for one year at four sites in Louisiana, including two rookery and two nonrookery sites.
A rookery is a bird breeding ground. The researchers observed a significant increase in alligators displaying sticks on their snouts from March to May, the time birds were building nests.
Specifically, the reptiles in rookeries had sticks on their snouts during and after the nest-building season. At non-rookery sites, the reptiles used lures during the nest-building season.
"This study changes the way crocodiles have historically been viewed," said Dinets.
"They are typically seen as lethargic, stupid and boring but now they are known to exhibit flexible multi-modal signalling, advanced parental care and highly coordinated group hunting tactics," said Dinets.
The observations could mean the behaviour is more widespread within the reptilian group and could also shed light on how crocodiles' extinct relatives - dinosaurs - behaved.
"Our research provides a surprising insight into previously unrecognised complexity of extinct reptile behaviour," said Dinets.
"These discoveries are interesting not just because they show how easy it is to underestimate the intelligence of even relatively familiar animals, but also because crocodilians are a sister taxon of dinosaurs and flying reptiles," Dinets said.
The research was published in the journal Ethology, Ecology and Evolution.
