A zookeeper feeds a hippopotamus with a watermelon in its enclosure in Belgrade's zoo, Serbia, July 20, 2015. Temperatures in Serbia have risen up to 40 degrees Celsius (104 degrees Fahrenheit), according to official meteorological data. (Photo by Marko Djurica/Reuters)

Newborn sea lion “Kaya” crawls at the enclosure at the zoo in Wuppertal, Germany July 23, 2015. Kaya was born on July 4, 2015 in the zoo, officials said. (Photo by Ina Fassbender/Reuters)

A spider monkey eats a mango at the Paraguana zoo in Punto Fijo, Venezuela July 22, 2016. Some 50 animals have starved to death in the last six months at one of Venezuela's main zoos due to chronic food shortages that have plagued the crisis-stricken South American nation. (Photo by Carlos Jasso/Reuters)

At the beginning of the 20th century, Edward S. Curtis set out to document what he saw as a disappearing race: the Native American. From 1907 to 1930, Curtis took more than 2,000 photos of 80 tribes stretching from the Great Plains to the Pacific Northwest and Alaska. He then published and sold these photos, along with narrative text, in 20 volumes of work known as “The North American Indian”. It is one of the most significant collections of its kind, “probably the most important photographic document of its age and its topic,” said Jeffrey Garrett, associate university librarian for Special Libraries at Northwestern University. (Photo by Edward S. Curtis)

A Muslim bride waits for the start of a mass marriage ceremony in Mumbai, India, January 27, 2016. A total of 12 Muslim couples took their wedding vows during the mass marriage ceremony organised by a Muslim voluntary organisation, organisers said. (Photo by Danish Siddiqui/Reuters)

Associated Press photographer Wong Maye-E tries to get her North Korean subjects to open up as much as is possible in an authoritarian country with no tolerance for dissent and great distrust of foreigners. She has taken dozens of portraits of North Koreans over the past three years, often after breaking the ice by taking photos with an instant camera and sharing them. Her question for everyone she photographs: What is your motto? Their answers reflect both their varied lives and the government that looms incessantly over all of them. (Photo by Wong Maye-E/AP Photo)

A pair of giant pandas play in their enclosure at the Beijing Zoo on June 5, 2012 in Beijing, China. With an estimated 1,600 living in the wild, the endangered giant panda dwell in a few mountain ranges in central China, in Sichuan, Shaanxi, and Gansu provinces. (Photo by Lintao Zhang)