Polar bear twins make their first public appearance with their mother “Freedom” at Ouwehands Zoo Rhenen, in Rhenen, The Netherlands, 19 February 2015. The twins, who were born in November 2014, have not been named because their gender has not yet been determined. (Photo by Bart Maat/EPA)

Indonesian mahouts clean their Sumatran elephant in a river near the zoo in Medan, North Sumatra, Indonesia, 12 December 2014. According media reports, the smallest of the Asian elephants, Sumatran elephant (Elephas maximus sumatrensis) is facing serious pressures arising from illegal logging and associated habitat loss and fragmentation in Indonesia. The population has come under increasing threat from rapid forest conversion to plantations. (Photo by Dedi Sahputra/EPA)

A man carries a blood stained stretcher in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria January 10, 2016. (Photo by Bassam Khabieh/Reuters)

A man dressed as one of the Three Kings greets people during the Epiphany parade in Gijon, Spain January 5, 2017. (Photo by Eloy Alonso/Reuters)

A mouse rides on the back of a frog in floodwaters in the northern Indian city Lucknow June 30, 2006. (Photo by Pawan Kumar/Reuters)

Goat herder Dana McGregor's goats Pismo, left, and Goatee surf at San Onofre State Beach, Calif, on July 11, 2012. McGregor started taking Pismo's mother Goatee to the beach, and it wasn't long before she was on a surfboard. When Pismo was born, McGregor put her on a board too, and she was a natural, he says. (Photo by Rod Veal/The Orange County Register via AP)

A quartet of showgirls in costume sit at an outdoor table and drink from mugs at Disneyland amusement park, Anaheim, California, 1955. (Photo by Loomis Dean/The LIFE Picture Collection/Getty Images)

European bisons (also known as Wisent) at the Bison farm in Muczne, southeastern Poland, 30 December 2018. The Bison farm is a continuation of bison breeding in Bieszczady, which was started in 1963. Here visitors can admire the bison of Bialowieza-Caucasian line, also called the mountain race. The European Bison is the national animal of Poland. (Photo by Darek Delmanowicz/EPA/EFE)