麻豆传媒

In the rivers and creeks of Belize, turtles swim together in armoured squads. The turtles are the first known to casually group together, rather than socialising to reproduce or feed. The findings add to an emerging understanding of the true complexity of reptilian social lives.

Central American river turtles (Dermatemys mawii) 鈥� known in Belize as 鈥榟icatees鈥� 鈥� live in the river systems of parts of Mexico, Belize, and Guatemala. They are totally aquatic, never basking in the sun and only leaving the water to lay eggs.

at the Savanna Field Station in Belize and his colleagues were studying the turtles, tracking them to better understand their movement patterns. But they noticed that the reptiles often moved closely together in pairs, says McKnight.

鈥淥r a whole group of turtles would be together in one spot one day and then they鈥檇 be in another spot the next day,鈥� he adds.

The researchers tweaked their study to assess how the carapaced animals were clustering. They captured 19 hicatees and attached sonic transmitters to their shells. From a canoe, the team then tracked the turtles鈥� movements with a receiver. After calculating the distances between hicatees, they compared the turtles鈥� positions relative to one another with what a computer model would expect if the turtles were moving randomly through their environment rather than in groups.

鈥淚n all the simulations we ran, the random turtles generated by the computer were never as close together as our actual turtles were in that environment,鈥� says McKnight. 鈥淚t鈥檚 not related to mating, it鈥檚 not related to some food that they鈥檙e all clustered around. It鈥檚 just choosing to be near each other.鈥�

To the researchers鈥� knowledge, this is the first documentation of turtles huddling in this way. The findings add to an expanding view of turtles鈥� social behaviours. Some species, for example, are now known to establish dominance hierarchies and maintain social networks. In recent years, says McKnight, researchers have found that most turtles will make vocalisations, sometimes to each other. Female Arrau turtles (Podocnemis expansa) down from the beach so they can meet in the river.

Among reptiles, it鈥檚 not just turtles being increasingly recognised for their social complexity.

鈥淲e already know of some Australian skink species that live in long-term, stable family groups,鈥� says at the University of Bern in Switzerland.

However, at the University of South Florida thinks more research is needed to confirm that hicatees are truly living in groups. The turtles may only behave like this during part of the year, for instance.

In the future, McKnight is interested in investigating whether hicatees have a preference for buddying up with relatives, or if any turtle will do.

It will also be worth exploring if there are evolutionary benefits to the hicatees鈥� lifestyle. One possibility is that a flotilla of turtles provides a safety-in-numbers effect against predators, such as crocodiles.

There are conservation considerations, too. Hicatees are critically endangered; they represent one of the most imperilled turtle species in the world, says McKnight, largely because of overconsumption by humans.

鈥淭he strategy that may have evolved for anti-predatory behaviour may actually be backfiring,鈥� he says, since poachers can find turtle clusters and harvest dozens in a single night.