A migrant smokes a cigarette as he waits among others to cross the Croatian border near the village of Berkasovo, Serbia October 19, 2015. Thousands of migrants clamoured to enter European Union member Croatia from Serbia on Monday after a night spent in the cold and mud of no-man's land, their passage west slowed by a Slovenian effort to impose limits on the flow to western Europe. (Photo by Marko Djurica/Reuters)

A Russian ground staff member signals to the pilot of a Sukhoi Su-25 fighter jet at the Hmeymim air base near Latakia, Syria, in this handout photograph released by Russia's Defence Ministry October 22, 2015. (Photo by Reuters/Ministry of Defence of the Russian Federation)

A ring-tailed lemur is pictured at Zoom Torino, a zoological park in Cumiana near Turin, on April 22, 2015. Zoom Torino is a new immersive zoological park, where animals can be seen without bars or cages, only natural barriers ensure the visit. (Photo by Marco Bertorello/AFP Photo)

Children react after what activists said was shelling by forces loyal to Syria's President Bashar al-Assad near the Syrian Arab Red Crescent center in the Douma neighborhood of Damascus May 6, 2015. (Photo by Bassam Khabieh/Reuters)

A mine worker is seen outside “The Progreso” gold mine near La Paz, November 13, 2014. According to local media, the president of the Central Bank of Bolivia (BCB) Marcelo Zabalaga said on Thursday that the falling price of oil and minerals in the international market will not affect the national economy. (Photo by David Mercado/Reuters)

A house built on a rock on the river Drina is seen near the western Serbian town of Bajina Basta, about 160km (99 miles) from the capital Belgrade May 22, 2013. The house was built in 1968 by a group of young men who decided that the rock on the river was an ideal place for a tiny shelter, according to the house's co-owner, who was among those involved in its construction. (Photo by Marko Djurica/Reuters)

A serviceman walks near an APC while a helicopter flies on the position of the Ukrainian troops in Donetsk region on August 9, 2014. Fighting with pro-Russian separatists in eastern Ukraine has left 13 troops dead in the last 24 hours, Ukraine's military said Saturday. (Photo by Anatolii Stepanov/AFP Photo)

In this Saturday, August 16, 2014 photo, Mandy Stokes stands with her daughter Molly Kate Stokes next to a large alligator weighing 1011.5 pounds measuring 15-feet long is pictured in Thomaston, Ala. The alligator was caught in the Alabama River near Camden, Ala., by Mandy Stokes and family. (Photo by Sharon Steinmann/AP Photo/Al.com)