An accumulation of scientific research suggests that there’s a lot more to the social lives of reptiles.
Ned and Sunny stretch out together on the warm sand. He rests his head on her back, and every so often he might give her an affectionate nudge with his nose. The pair is quiet and, like many long-term couples, they seem perfectly content just to be in each other’s presence.
The couple are monogamous, which is quite rare in the animal kingdom. But Sunny and Ned are a bit scalier that your typical lifelong mates — they are shingleback lizards that live at Melbourne Museum in Australia.
In the wild, shinglebacks regularly form long-term bonds, returning to the same partner during mating season year after year. One lizard couple in a long-term study had been pairing up for 27 years and were still going strong when the study ended. In this way, the reptiles are more like some of the animal kingdom’s most famous long-term couplers, such as albatrosses, prairie voles and owl monkeys, and they confound expectations many people have about the personalities of lizards.
“There’s more socially going on with reptiles than we give them credit for,” said Sean Doody, a conservation biologist at the University of South Florida.
Social behavior in reptiles has been largely overlooked for decades, but a handful of dedicated scientists have begun unraveling reptiles’ cryptic social structures. With the help of camera traps and genetic testing, scientists have discovered reptiles living in family groups, caring for their young and communicating with each other in covert ways. And they aren’t only doing this because they love lizards. Currently, one in five reptile species are threatened with extinction; researchers say learning more about reptile sociality could be crucial for conservation.
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Humans have a long history of animosity toward reptiles, and influential twentieth century scientists added to the idea of reptiles as cold, unintelligent beasts. In the mid-1900s, Paul MacLean, a neuroscientist at Yale and then the National Institute of Mental Health, began developing the triune brain hypothesis. He theorized that the human brain contained three parts: the reptilian R-complex, which governed survival and basic instinctual behaviors; the paleomammalian complex, which controlled emotional behavior; and the neomammalian cortex, which was responsible for higher functions like problem-solving and language.
Dr. MacLean’s ideas were popularized in Carl Sagan’s “The Dragons of Eden” in 1977, and they are deeply rooted — the idea of the “lizard brain” as a center for basic survival instincts is still widely believed, even though it is not based on actual facts.
“It’s pretty much totally bogus,” said Stephanie Campos, a neuroethologist at Villanova University.
Gordon Burghardt, an ethologist at the University of Tennessee, Knoxville, who has studied animal behavior for more than 50 years, said that many scientists, even herpetologists, were blinded by their biases, believing that social behaviors “can’t occur in these animals, therefore you’re not seeing what you’re seeing.”
Even without our cultural biases, reptiles can be difficult to study.
“A lot of them are pretty shy,” said Allison Alberts, a conservation scientist and co-founder of the Iguana Specialist Group at the International Union for Conservation of Nature. She added that “They’re so sensitive to when a person’s there. They just freeze — they will not do some of their normal social interactions when a person’s around.”
Many forms of interaction between reptiles are also invisible.
“Chemical communication plays a huge role,” said Julia Riley, a behavioral ecologist at Mount Allison University in New Brunswick, Canada. “And that’s something you can’t even see and it’s very hard to sample from the environment as well.”
Yet despite these prejudices and difficulties, researchers are starting to unveil the complex social worlds of these creatures.
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One of the most fascinating discoveries of reptile social behavior — long-term monogamy in shingleback lizards like Ned and Sunny — happened entirely by accident.
Michael Bull, the Australian biologist who made the discovery, was initially less focused on lizards and more interested in studying the different species of ticks that lived on them. Beginning in 1982, he would capture shinglebacks, mark them, take various measurements, then release them. After several years (and thousands of lizards), he noticed that each spring, after months apart, the same males and females would somehow manage to find each other.
Shingleback courtship is perhaps not the most romantic by human standards.
“The male will trail the female around for a number of weeks, often a few months, and defend that female from any other male that tries to encroach,” said Jane Melville, senior curator of terrestrial vertebrates at Museums Victoria in Australia. Males have also been seen allowing their mates to eat first, she said.
Actually, this last behavior is a good move for males of a number of species. Another lizard species, the Central American whiptail, has been observed offering a potential partner a lovely dead frog to eat before mating.
But shingleback love stories don’t always have happy endings. “It’s very tragic,” said Martin Whiting, a behavioral ecologist at Macquarie University in Sydney, Australia. “Occasionally, they get squashed on the road and the other one will be nudging it. And then it’s very difficult for them to pair up again.”
Dr. Whiting said the lizards can remain with their dead partners for quite some time, continuing to nudge their lifeless bodies. Could this be similar to the quasi-mourning behaviors observed in primates and cetaceans?
While we can’t definitively say that these lizards grieve, Dr. Whiting said, “I would certainly say we can’t discount that certain species that have that strong pair bond might.”
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Despite the bond between mating pairs, shinglebacks are not the most attentive parents. Shinglebacks give live birth to two or three enormous babies (which can weigh nearly half a pound each, while adults top out at around 2 pounds), and shortly afterward, mother and offspring go their separate ways.
Other species are more caring parents. In many species of crocodilians for example, females will guard their nests, keeping their eggs safe from predation. Some baby crocodilians begin to vocalize even before hatching, and scientists think this may cause the mother to dig up the nest and carry the babies to the water.
Initially, according to Vladimir Dinets, a zoologist at the University of Tennessee, Knoxville, human observers misunderstood this behavior. “It was originally thought that crocodiles and alligators were incredibly dumb,” he said. When the females dug up the babies and took them “into their jaws, they assumed that they were just cannibalizing them.”
Crocodilians continue to vocalize after hatching, emitting “contact calls,” which may help facilitate group cohesion. Hatchlings also produce distress calls, which attract mothers, presumably for protection.
Another much-maligned creature, the rattlesnake, may also display surprising social habits and family ties: Genetic analysis has revealed that pregnant females prefer to associate with kin, hinting at the potential importance of family groupings. Parental care, at least initially, seems to be important as well.
“Rattlesnakes give birth to live young,” said Melissa Amarello, executive director of Advocates for Snake Preservation. “The females and the babies stay together at least until the babies start shedding their skin for the first time, which seems to happen one to two weeks after they’re born.”
While the mother’s presence alone is likely a deterrent for predators, Ms. Amarello said she had also observed instances of mother snakes exhibiting defensive behavior when potential threats approached her offspring. Research has also shown that pygmy rattlesnakes are more responsive to threats when they are with their offspring when compared with females without babies.
Ms. Amarello said that when female snakes spend their pregnancy together, the one who is still pregnant may stay close to the offspring of the snake who has already given birth. “After seeing this now over so many years with the Arizona black rattlesnakes, it’s usually the younger females that are stuck being pregnant and ‘babysitting,’” she said.
Family living also occurs in a handful of lizards in the Scincidae family, or skinks (which includes shingleback lizards like Ned and Sunny). A three-year-long imaging study only recently revealed the devotion of Cunningham skink mothers. In one case, a female skink was basking with her family when a snake appeared near their crevice.
The female, according to Dr. Riley, “runs forward, grabs the Eastern brown snake, shakes it, and then makes sure it goes away from the crevice.”
She added, “Now that is clearly an act of parental care,” one that is a great personal risk on the mother’s part, as Eastern brown snakes have one of the most toxic venoms of any snake on the planet.
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Social abilities have other benefits. Many species have demonstrated their ability to learn from one another, a phenomenon called social learning. Even the red-footed tortoise, a species which is thought to be largely solitary, can learn how to obtain a food reward by watching a fellow tortoise perform the task. Some reptiles, such as the Italian wall lizard, also can learn from other species.
Does this seem like it might be too much for a tiny lizard brain? Scientists like Dr. MacLean gave lizard intellect a bad rap, but reptile brains and mammal brains really aren’t all that different.
When comparing reptile and mammal brains, “a lot of the regions are very similar to what we have,” said Dr. Campos, who studies chemical communication in lizards. Many of the brain regions that are important for social behavior in mammals, she says, are also involved in reptile interactions.
In mammals, vasopressin and oxytocin play important roles in social behaviors, and reptiles have structurally similar hormones called vasotocin and mesotocin. Although the reptilian versions have received relatively little attention, there are intriguing early studies about how they regulate reptile sociality.
Dr. Campos’s research indicates that vasotocin may alter chemical communication between green anole lizards, and other researchers found that mesotocin may be related to courtship behaviors in brown anoles. When researchers blocked the activity of vasotocin in pygmy rattlesnake mothers, they strayed farther from their babies, suggesting this hormone may influence maternal behavior.
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Learning more about reptiles’ social structures could be essential for saving species from the brink of extinction.
For example, headstarting programs are attempting to bolster wild populations of critically endangered Caribbean rock iguanas by raising baby iguanas in captivity and releasing them when they’ve grown large enough to avoid being eaten by invasive predators like cats and mongooses.
While some factors involved in the success of such programs have been well-studied, Dr. Alberts said, social factors have been relatively overlooked. That leads to questions like, “How many should we release at the same time? Should they all be released at the same site?” she said. “This is where I feel like some of these social considerations and understanding them better could go into improving the success of the program.”
Social information also may be important for rattlesnake reintroductions. Early research suggests chemical cues from other snakes may be very important for guiding behavior. Timber rattlesnakes, for example, can follow the scent trails of fellow rattlesnakes out of a maze, and they have been shown to select prey ambush sites based on the smell of a snake that had recently fed.
Jeff Smith, director of research at Advocates for Snake Preservation, said the social information these smells provide may aid survival. “The way that the scents can be written on the landscape provides juveniles with kind of a cheat sheet for navigating the world,” he said, adding that smells potentially helping young snakes find places to hunt, to hide from predators or to spend the winter.
Understanding reptiles’ capacity for sociality also could be helpful in other ways. “Reptiles in general face great persecution — snakes in particular, but also crocodilians and a lot of lizards as well,” Dr. Riley said.
People may develop more empathy for these animals if they come to understand that they are social creatures, too.
“If we can open this secret social world of reptiles to people, maybe people will think twice about killing a snake or a lizard and maybe will find some value in these animals that people oftentimes just discount as creepy, or worse,” Dr. Riley said.
In simple terms, she added, “we don’t conserve what we don’t care about.”
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