In this August 1, 2014 photo provided by the National Park Service are male caribou antlers in the Oolah Valley, likely the result of a grizzly kill as he migrated south for the winter at the Arctic National Park and Preserve in Alaska. The nation's northernmost national park says its new management plan will have to consider the effects of a new industrial road to the mining district of Ambler, the first road that would be constructed within its Maryland-sized boundaries. (Photo by Cadence Cook/AP Photo/National Park Service)

The first seal pup to be born this season at a major colony of grey seals on the Farne Islands sits beside its mother on Brownsman Island, England on September 30, 2015. (Photo by Owen Humphreys/PA Images)

This photo provided by Netflix/naturepl.com and WWF-International shows an African Elephant (Loxodonta africana) in front of double rainbow, in Masai Mara, Kenya, included in the Netflix natural history series, “Our Planet”, in collaboration with Silverback Films and WWF. The eight-part series debuts in 2019. (Photo by Andy Rouse/Naturepl/WWF-International/Netflix via AP Photo)

A visitor falls down as they run away from a wave caused by a tidal bore which surged past a barrier on the banks of Qiantang River, in Hangzhou, Zhejiang province, China, October 28, 2015. (Photo by Reuters/China Daily)

An Zi, is squashed amongst other commuters in a subway train on his way to work in Beijing, China, November 12, 2015. An, a movie producer, moved to Dongsanqi village in Changping this year. His commute to work can take about 2 hours, with transportation costs topping 200 yuan a month, or about a fifth of his monthly rent. (Photo by Jason Lee/Reuters)

A couple hugs while standing near a Christmas tree made out of plastic bins and plastic hampers outside the Museum of History in Monterrey, Mexico, December 4, 2015. The humble Christmas tree has a rich history, from evergreen trees used to symbolise eternal life in Ancient Egypt to tree worship among pagan Europeans. The modern version has its origins in Germany, where the song “O Tannenbaum” is still a festive favourite. Today the traditional tree with lights and decorations appears in cities including Washington, Moscow and Beirut. Alternative constructions range from recycled rubbish in Mexico City to old window frames in Rakvere, Estonia. Whatever the shape or size, the message is the same: Merry Christmas. (Photo by Neil Hall/Reuters)

A worker stack bricks on his head at a brick factory in Lalitpur January 12, 2015. (Photo by Navesh Chitrakar/Reuters)

A makeshift cart with containers is seen at a suspected drug tunnel under construction during a media tour by Mexican Army in Tijuana April 7, 2015. Mexican soldiers foiled the construction of a suspected drug tunnel underneath a house near the U.S. border, arresting nine people and impounding a truck used to clear debris, the Army said on Tuesday. Wired with lights, the tunnel was being built next to the Tijuana border crossing, south of San Diego, California, and near a Mexican air force installation as well as a regional federal police facility. (Photo by Reuters/Stringer)