Medic James E. Callahan of Pittsfield, Mass., gives mouth-to-mouth resuscitation to a dying soldier in war zone D, about 50 miles northeast of Saigon, June 17, 1967. Thirty-one men of the 1st Infantry Division were reported killed in the guerrilla ambush, with more than 100 wounded. (Photo by Henri Huet/AP Photo)

The National Geographic Photo Ark is a travelling exhibition of photographer Joel Sartore’s quest to create a photo archive of biodiversity around the world. So far, Sartore has captured studio portraits of more than 6,000 species – a number that he hopes to double. On 1 July, the ark will open at Melbourne zoo – the first time it has been exhibited in the southern hemisphere. More than 50 portraits will be on display, including many of Australian endangered animals being protected by programs at the zoo itself. These captions have been edited from text supplied by Melbourne zoo. Here: Barking owl. (Photo by Joel Sartore/National Geographic Photo Ark/The Guardian)

Former Olympic gymnast Nastia Liukin performs a flip while throwing the ceremonial first pitch during a baseball game between the Los Angeles Angels and the Tampa Bay Rays, Friday, July 14, 2017, in Anaheim, Calif. (Photo by Jae C. Hong/AP Photo)

This picture taken on May 21, 2016 shows professional wrestlers fighting each other during the Wrestling City Asia organized by Singapore Pro Wrestling at a stadium in Kuala Lumpur. Kenneth Thexeira is a mild-mannered writer for an interior-design magazine by day, but on certain nights his alter ego bursts forth in golden tights and a baby-blue cape: enter “The Eurasian Dragon”. (Photo by Mohd Rasfan/AFP Photo)

A picture made available on 20 June 2016 shows people praying as they wait to break the fast during the Muslim holy month of Ramadan, in Karachi, Pakistan, 19 June 2016. Muslims around the world celebrate the holy month of Ramadan by praying during the night time and abstaining from eating and drinking during the period between sunrise and sunset. Ramadan is the ninth month in the Islamic calendar and it is believed that the Koran's first verse was revealed during its last 10 nights. (Photo by Shahzaib Akber/EPA)

Bathing suit models are shown listening to the radio on the beach, circa 1940's. (Photo by Bettmann Archive/Getty Images)

Workers clean empty cooking oil containers at a roadside recycling workshop in Kolkata, India, July 13, 2016. (Photo by Rupak De Chowdhuri/Reuters)

Cambodian children sleep on a pavement at a park in Phnom Penh on July 8, 2016. (Photo by Tang Chhin Sothy/AFP Photo)