The six-months-old female koala cub holds on to the back of zoo keeper Lena at the zoo in Duisburg, Germany, 23 October 2015. The yet unnamed baby weighs 580 grams. (Photo by Roland Weihrauch/EPA)

Young stag deer clash antlers during the annual rut in Richmond Park in west London, Britain, October 16, 2015. The Royal Park has had Red and Fallow deer present since 1529, and early autumn sees the rutting or breeding season begin amongst the herd of over six hundred animals. (Photo by Toby Melville/Reuters)

Students in Aone’s elementary school during break in between the class on April 9, 2015. The school has only six students, two of whom are from the same family. Similarly small schools can be found throughout Japan. (Photo by Ko Sasaki/The Washington Post)

A small section of the expanding remains of the Veil Nebula, a massive star that exploded about 8,000 years ago. The entire nebula is 110 light-years across, covering six full moons on the sky as seen from Earth, and resides about 2,100 light-years away in the constellation Cygnus, the Swan. (Photo by Reuters/NASA/ESA/Hubble)

Bo, a 55-day-old baby Echidna known as a puggle, rests in the hands of vet nurse Annabelle Sehlmeier at Taronga Zoo in Sydney November 1, 2012. The puggle was brought to the zoo after it being found by itself on a walking track north of Sydney and will be fed by hand until it is weaned at about six months of age. (Photo by Tim Wimborne/Reuters)

Tsetse, six-year-old daughter of Dukha herder Erdenebat Chuluu, sits among her family's reindeer in a forest near the village of Tsagaannuur, Khovsgol aimag, Mongolia, April 21, 2018. Nyamaa is an ethnic Darkhad, herders of northern Mongolia who have historically inhabited the steppe that borders the Taiga forests. (Photo by Thomas Peter/Reuters)

Robots serve trays with food to customers waiting at the Robot theme restaurant in Bangalore, India, 17 August 2019. Six robots are deployed as waiters at the the robot-themed Robot restaurant where each table is equipped with a tablet to place one's order. (Photo by Jagadeesh N.V./EPA/EFE)

Six month- old baby elephant “Clear Sky” is kept afloat with the help of a harness during a hydrotherapy session at a local veterinary clinic in Chonburi Province on January 5, 2017. After losing part of her left foot in a snare in Thailand, baby elephant 'Clear Sky' is now learning to walk again – in water. (Photo by Roberto Schmidt/AFP Photo)