Scientists know a bit more about contagious yawning – one of science's utter mysteries – than they did a year ago, thanks to a study called No Evidence of Contagious Yawning in the Red-Footed Tortoise, Geochelone carbonaria. The study's authors say their experiments, conducted with seven tortoises, might help eliminate some of the many competing theories as to why humans yawn when they see other humans yawn.

Writing in the journal Current Zoology, Anna Wilkinson, Isabella Mand and Ludwig Huber of the University of Vienna, Austria, and Natalie Sebanz of Radboud University in the Netherlands, explain: "This study aimed to discriminate between the possible mechanisms controlling contagious yawning by asking whether contagious yawning is present in a species that is unlikely to show empathy or nonconscious mimicry: the redfooted tortoise, G carbonaria.

The researchers say that although tortoises have not been known (by humans) to mimic each other, the animals do sometimes respond to things they see around them, making them "ideal subjects for examining this question".

The tortoises, named Alexandra, Moses, Aldous, Wilhelmina, Quinn, Esme and Molly, were not "experimentally naive, but they had never previously been involved in a contagious yawning task or any similar experiment," the study notes.

The researchers trained Alexandra to open her mouth whenever they waved a little red square near her head. "This took six months," they write, and "the resulting behaviour appeared highly similar to a naturally occurring tortoise yawn". Alexandra thus became the "demonstrator", the individual who yawned in plain view of her fellows.

In one experiment, the other tortoises watched as Alexandra yawned a single time. In a second, Alexandra yawned several times in succession. In the third and final experiment, the observer tortoises watched videos of a tortoise (a) yawning and (b) not yawning. The scientists conclude with the suggestion that "tortoises do not yawn in a contagious manner".

The monograph ends with a statement expressing gratitude to their colleagues. Perhaps lacking for warmth, it says, "Acknowledgements: The authors would like to thank the cold-blooded cognition group at the University of Vienna for their helpful comments."

(Thanks to Stefano Ghirlanda for bringing this study to my attention.)

• Marc Abrahams is editor of the bimonthly Annals of Improbable Research and organiser of the Ig Nobel prize