April 14, 2021


For generations, a herd of wild horses has made their home on a long barrier island at the southern tip of the Outer Banks of North Carolina. Mark Darrough camped among the Shackleford Horses and learned a thing or two about survival (Mark Darrough, April 13, 2021, Bitter Southerner)

Rubenstein explained what first led him to Shackleford as a grad student in 1973, when the field of behavioral ecology -- the study of animals' ability to adapt to ecological pressures such as hurricanes and limited food and water sources on an exposed barrier island -- was in its infancy. 

Because Shackleford horses are protected within a small and isolated environment, they provided Rubenstein "a wonderful laboratory, a lens on animal behavior."

"I was interested in how these horses adapt to a unique, harsh environment. Behavior is a front-line response, is the first response to the problems that animals face, problems posed by nature, right? So, for example, you were hot, you took your shirt off, you got sunburned; that's a behavioral response, probably not too adaptive if you didn't sleep very well. And so if that happened over and over again, you wouldn't be around. ... So your predilection to things is shaped by how well you solve the problems posed by nature."

In the 1970s, the field of behavioral ecology was just beginning, he told me. Instead of simply looking at what animals do as "sort of evolutionary, genetically controlled behavior -- that this group does that and this other group does that," as Austrian zoologist and ethologist Konrad Lorenz viewed animal behavior -- the big question at the time was how genetics affects things such as sociality in animals.

Zoologist Richard D. Alexander, Rubenstein's mentor when he was studying at the University of Michigan, told him there are no automatic benefits for living in groups. But there are automatic costs, such as increased competition for scarce resources and disease transmission, like we saw at the beginning of the coronavirus pandemic. Most social animals attempt to reduce those costs by living with family members.

"What makes horses special is that they're like neolocal modern Western humans: Both sons and daughters leave home to go reproduce. ... As highly social animals, how do they get those benefits [to outweigh] the costs when there's no genetic sharing to reduce those costs? That's what drove me to study the horses," Rubenstein said.

The Banker horses, as these horse populations are called today, adapted to the Outer Banks by learning to dig for springs and find thin layers of fresh water at the surface of saltwater ponds, to graze on marsh and dune grasses, and to retreat to the maritime forest during storms. 

Not all horses survive the fierce hurricanes that thrash the islands most summers. Initial reports presumed the horses of Cedar Island, about 40 miles to the north of Shackleford, survived Hurricane Dorian in 2019, but officials later discovered 28 horses had drowned when a wall of water hit the island. Their bodies washed ashore on nearby beaches while others were lost at sea. Several of the 21 survivors managed to swim to nearby islands.

Other horses across the Outer Banks survived by retreating to dry high ground under sturdy live oak trees, their powerful haunches pointed windward to stabilize against 100-mph gusts. Experts observed groups of horses sensing a change in air pressure and joining other harems -- a rarely observed behavior -- to ride out the coming storm. 

"It is harsh out there. ... If the tide comes up and they're in the wrong place, they can get washed out to sea," Rubenstein said, noting the five wild horses that drowned when Hurricane Isabel swept them off the Rachel Carson Reserve in 2003.

Posted by at April 14, 2021 7:13 AM