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Ever seen an elephant yawn? You can if you get up early enough, as zookeeper at the San Diego Wild Animal Park found, when he spotted a yawning elephant for the first time shortly before 5 am.

The elephants in this video, Ranchi and Devi, are among 18 caught on camera in 12 zoos as part of an investigation by and of the University of California, Davis.

The sightings suggest that the early morning is the best time to catch the animals in the act. The team think a wake-up yawn could help elephants cool down their brain, which tends to heat up at night when their brain-cooling system is less active. The same theory has been proposed to explain yawning in humans – one experiment found that people were less likely to yawn when a cold pack was placed on their head.

Next, the team wants to find out whether elephant yawns are contagious. This behaviour is not unique to humans: chimps have been observed catching yawns from dominant males,while budgies can make each other yawn, suggesting that they are capable of empathy.

were presented on 13 June at the in Anchorage, Alaska.