CORVALLIS, Oregon. – Research by a graduate student at Oregon State University’s College of Science has turned conventional wisdom on its head that for a century falsely guided the study of a toad classified as endangered in part of its range.
Anne Devan-Song used spotlighting – shining light in a dark place and looking for eye reflections – to find large numbers of the Eastern Spadefoot Toad. The study illustrates how confirmation bias – a tendency to interpret new information as ratifying existing theories – can hinder the discovery and development of better theories.
Their results, which show that the toad spends much more time above the earth than is commonly believed, were in the Journal of Herpetology.
Known for bright yellow eyes with elliptical pupils and, as the name suggests, a spade on each hind foot, the eastern spadefoot toad ranges from the southeast corner of the United States to the Atlantic coast to New England. Scientifically known as Scaphiopus holbrooki, it is a species of concern in the northern foothills of its territory.
Devan-Song, a Ph.D. Student of integrative biology, grew up in Singapore, where she learned to look for reptiles and amphibians with spotlights. The eastern toad is critically endangered in Rhode Island, where she did her Masters and then worked as a research fellow at the university.
One rainless night, Devan-Song’s headlights spotted one eastern spade after another while looking for amphibians on a project in Virginia. This surprised her, because it was believed that the toads were only detectable on a few rainy nights each year, when they emerged from underground caves to mate in wetlands.
She kept looking for eastern spade feet and found them even on dry nights, including in highland forests that are not near humid areas. Spade feet stay in the spotlight, making it easy for Devan-Song to approach the eye lights and clearly identify the toads.
“They have to walk across the ground to hunt insects and build energy stores for mating,” she said. “That’s why we found them when and where conventional wisdom said we shouldn’t find them.”
Back in Rhode Island, she tried spade feet; It only took her 15 minutes to find one. The success led to a 10-night survey at two locations last summer that found 42 sightings – almost twice as many eastern toad sightings in Rhode Island over the past seven decades.
Devan-Song also learned that she wasn’t the first to question the notion that the eastern spade was so “secret” that it almost always went undetected. As early as 1944, Devan-Song said, it was suggested in the scientific literature that the toad could be found outside of rain-induced migration and breeding aggregates. And in 1955, researchers used spotlighting to discover large numbers of eastern spade feet in Florida; inexplicably, the technique was then no longer used.
“Verification errors perpetuated the error of when the eastern spade was found,” said Devan-Song. “During our investigations, there were no breeding events or migrations, and we found thousands of toads in Virginia and dozens in Rhode Island. The majority of these were subadults, a demographic category that has mostly been overlooked in the literature. Progress in learning about the toad, its ecology and its protection has been severely hampered by a misunderstanding that persisted even when evidence to the contrary was presented. “
The ease with which many toads could be found during breeding, combined with the lack of data on toads in highland habitats, helped add to confirmatory biases in this case, she said.
“Everyone assumed they were underground most of the time, so no one really looked for them most of the time,” said Devan-Song. “Our research shows they can be seen year-round, although they’re rare in Rhode Island. But probably not as rare as the scientific community thought. “
The National Park Service supported this research through a collaboration agreement with the University of Rhode Island.