A murmuration of migrating starlings is seen across the sky in southern Israel December 31, 2015. (Photo by Amir Cohen/Reuters)

A couple who did not give their names walk in downtown Havana, February 2, 2015. (Photo by Alexandre Meneghini/Reuters)

The moon rises behind the skyline and financial district in Toronto, November 25, 2015. (Photo by Mark Blinch/Reuters)

Ukrainian Air Force officers attend a graduation ceremony at the National University of Defence of Ukraine in Kiev, April 24, 2015. (Photo by Gleb Garanich/Reuters)

A competitor participates in the Tough Mudder challenge near Henley-on-Thames in southern England May 2, 2015. (Photo by Eddie Keogh/Reuters)

A helicopter drops water over a wildfire as a firefighter works to contain it in Benahavis, southern Spain, May 19, 2015. (Photo by Jon Nazca/Reuters)

A participant smiles at the annual Christopher Street Day parade on Kurfuerstendamm in Berlin, Germany, June 27, 2015. (Photo by Fabrizio Bensch/Reuters)

Four-month-old fox cubs squaring up to each other in Walthamstow, England on August 7, 2015. (Photo by Greg Morgan/Barcroft Media)