Cowboys Wyatt Williams (R) and David Thompson work to restrain a calf in order to give it medicine near Ignacio, Colorado June 12, 2014. The land where the cattle graze is leased from the Forest Service by third-generation rancher Steve Pargin. Several times a year, he and a crew led by his head cowboy, David Thompson, spend a week or more herding cattle from mountain range to mountain range to prevent them from causing damage to fragile ecosystems by staying in a single area too long. (Photo by Lucas Jackson/Reuters)

Arctic wolves in their new enclosure in the wildlife park in Hanau, Germany, 10 February 2015. The pack is one of the park's main attractions, which specializes in local and European breeds. (Photo by Boris Roessler/EPA)

A woman sells fried chicken at the Kyaik-Khauk pagoda festival in the Tanlyin township outside Yangon February 4, 2015. (Photo by Soe Zeya Tun/Reuters)

A Kenyan soldier takes cover as shots are fired in front of Garissa University in Garissa town, located near the border with Somalia, some 370km northeast of the capital Nairobi, Kenya, 02 April 2015. At least 15 people have been killed and some 60 were injured in an attack carried out by Somalia's Islamist militant group al-Shabab, according to local media reports. (Photo by Dai Kurokawa/EPA)

Yaks head towards the Everest base camp in Solukhumbu District April 28, 2014. (Photo by Navesh Chitrakar/Reuters)

Saudi youths demonstrate a stunt known as “sidewall skiing” (driving on two wheels) in the northern city of Tabuk, in Saudi Arabia December 3, 2014. (Photo by Mohamed Al Hwaity/Reuters)

The rear of the Chevorlet Chaparral 2X Vision Gran Turismo concept car at its world debut at the Los Angeles Auto Show in California, November 19, 2014. The annual event is open to the public beginning November 21. (Photo by Lucy Nicholson/Reuters)