How Zebras use their stripes to stay cool

In a first, scientists have found that zebras can manipulate their black stripes to control their body temperatures.

The research, published in the Journal of Natural History, shows that it is the special way zebras sweat to cool down and the small-scale convection currents created between the stripes which aid evaporation.

They also found that zebras can erect their black stripes -- further aiding heat loss.

These three elements are key to understanding how the zebras' unique patterning helps them manage their temperature in the heat, according to a UK-based biology technician, Alison Cobb and her zoologist husband, Dr Stephen Cobb.

The duo, who have spent many years in sub-Saharan Africa directing environmental research and development projects, assessed zebras in their natural habitat for the first time to investigate the role of stripes in temperature control.

"My early attempts forty years ago at testing this hypothesis involved comparing the temperatures of water in oil drums with differently coloured felt coats, but it seemed to me that this was not a good enough experiment, and I wanted to see how the stripes behaved on live zebras," said Alison Cobb, lead author of the study.

"The solution to the zebra's heat-balance challenge is cleverer, more complex and beautiful than we'd imagined. Of course, there is much more work to be done to gather evidence and fully understand how the stripes help zebras control temperature," Cobb said.

The researchers collected field data from two live zebras, a stallion and a mare, together with a zebra hide draped over a clothes-horse as a control, in Kenya.

The data revealed a temperature difference between the black and white stripes that increases as the day heats up.

Whilst this difference stabilises on living zebras during the middle seven hours of the day, with the black stripes 12-15 degrees Celsius hotter than the white, the stripes on a lifeless zebra hide continue to heat up, by as much as another 16 degrees Celsius.

This indicates there is an underlying mechanism to suppress heating in living zebras.

It is therefore the way the zebra stripes are harnessed as one part of their cooling system, rather than just their contrasting coat colour, that is key to understanding why these animals have their unique patterning.

The researchers propose that the differential temperatures and air activity on the black and white stripes set up small-scale convective air movements within and just above the stripes, which destabilise the air and the water vapour at the tips of the hairs.

During the field research, the researchers also observed that zebras have an unexpected ability to raise the hair on their black stripes while the white ones remain flat.

The researchers said that the raising of black hairs during the heat of the day, when the stripes are at different temperatures, assists with the transfer of heat from the skin to the hair surface.

Conversely, when the stripes are at the same temperature in the early morning, and there is no air movement, the raised black hairs will help trap air to reduce heat loss at that time.

-PTI