While the rest of us are sleeping, freshwater turtles (龟) from Central America to Asia are getting out of the water and basking (月光浴) at night. There have been reports of this behavior before, but now a new study is the first to document the widespread occurrence. The findings suggest this may be a common and almost entirely overlooked aspect of many species' ecology.
Dr. Donald McKnight, one of the researchers, said he and a colleague first observed freshwater turtles night basking at the Ross River in Townsville, Australia. "We think it's related to temperature. The water is staying so warm at night that it's actually warmer than the turtles like to be and they can cool down by coming out of the water," says McKnight.
For the study, researchers put cameras to watch the night activity of as many freshwater turtle species as possible. The cameras were set up in 25 locations. They were programmed to take a photo every two minutes. They collected data on 29 species of freshwater turtles.
It would be lovely to think the turtles are just enjoying some leisure time when things are quiet. But the researchers note that in most cases, the turtles got out of water when the water was too warm and the air was cooler. Given the warming planet, that's admittedly a bit depressing. However, not all of the nighttime baskers were escaping too-warm water. According to the study, turtles in India exhibited more basking on cooler nights, rather than warmer nights, and those in Africa spent more time basking at night in winter than in summer. The reasons for these differences are unclear. It may be that at some sites or seasons, turtles are escaping unfavourably warm water temperatures, while at others, they are taking advantage of the warm air to increase their body temperature and escape unfavourably cold water.
Regardless of the "why" behind different species' reasons for midnight basking, it's a fascinating look at behaviors not previously documented by scientists. And it is at least encouraging to know that turtles are figuring out important behaviors tied to climate change.
