Tourists sleep as they travel by boat along Li River between Guilin and Yangshuo, China

Mother with child in a baby carrier, Hong Kong

Snorkeler photographing a pod of Sleeping sperm whale (Physeter macrocephalus) Researchers first saw this unusual sleep behavior in sperm whales in 2008. The scientists in that study found that sperm whales dozed in this upright drifting posture for about 10 to 15 minutes at a time, Vulnerable (IUCN). The sperm whale is the largest of the toothed whales. Sperm whales are known to dive as deep as 1,000 meters in search of squid to eat. Dominica, Caribbean Sea, Atlantic Ocean. Photo taken under permit n°RP 16-02/32 FIS-5.

Pod of Sleeping sperm whale (Physeter macrocephalus) Researchers first saw this unusual sleep behavior in sperm whales in 2008. The scientists in that study found that sperm whales dozed in this upright drifting posture for about 10 to 15 minutes at a time, Vulnerable (IUCN). The sperm whale is the largest of the toothed whales. Sperm whales are known to dive as deep as 1,000 meters in search of squid to eat. Dominica, Caribbean Sea, Atlantic Ocean. Photo taken under permit n°RP 16-02/32 FIS-5.

Free diver is swimming over a pod of Sleeping sperm whale (Physeter macrocephalus) Researchers first saw this unusual sleep behavior in sperm whales in 2008. The scientists in that study found that sperm whales dozed in this upright drifting posture for about 10 to 15 minutes at a time, Vulnerable (IUCN). The sperm whale is the largest of the toothed whales. Sperm whales are known to dive as deep as 1,000 meters in search of squid to eat. Dominica, Caribbean Sea, Atlantic Ocean. Photo taken under permit n°RP 16-02/32 FIS-5.

Pod of sperm whale relaxing after a short sleep (Physeter macrocephalus) Researchers first saw this unusual sleep behavior in sperm whales in 2008. The scientists in that study found that sperm whales dozed in this upright drifting posture for about 10 to 15 minutes at a time, Vulnerable (IUCN). The sperm whale is the largest of the toothed whales. Sperm whales are known to dive as deep as 1,000 meters in search of squid to eat. Dominica, Caribbean Sea, Atlantic Ocean. Photo taken under permit n°RP 16-02/32 FIS-5.

Pod of Sleeping sperm whale (Physeter macrocephalus) Researchers first saw this unusual sleep behavior in sperm whales in 2008. The scientists in that study found that sperm whales dozed in this upright drifting posture for about 10 to 15 minutes at a time, Vulnerable (IUCN). The sperm whale is the largest of the toothed whales. Sperm whales are known to dive as deep as 1,000 meters in search of squid to eat. Dominica, Caribbean Sea, Atlantic Ocean. Photo taken under permit n°RP 16-02/32 FIS-5.