A student wearing a face mask prays before the start of the annual college entrance examination amid the coronavirus pandemic at an exam hall in Seoul, South Korea, Thursday, December 3, 2020. South Korean officials are urging people to remain at home if possible and cancel gatherings as about half a million students prepare for a crucial national college exam. (Photo by Kim Hong-Ji/Pool Photo via AP Photo)

People pose for pictures on the banks of Yangtze River on New Year's Eve in Wuhan, in China’s central Hubei province on December 31, 2020. (Photo by Noel Celis/AFP Photo)

Police officers detain a Navalny supporter during a protest in St. Petersburg, Russia, Tuesday, February 2, 2021. A Moscow court has ordered Russian opposition leader Alexei Navalny to prison for more than 2 1/2 years on charges that he violated the terms of his probation while he was recuperating in Germany from nerve-agent poisoning. Navalny, who is the most prominent critic of President Vladimir Putin, had earlier denounced the proceedings as a vain attempt by the Kremlin to scare millions of Russians into submission. (Photo by Dmitri Lovetsky/AP Photo)

A classic American car is wrapped in plastic to prevent sea salt from corroding it in Havana, Cuba, Tuesday, March 2, 2021. Vintage cars in Cuba are part of daily life with most classic cars being used as taxis and to transport tourists. (Photo by Ramon Espinosa/AP Photo)

A driver pulls a handgun on protesters after they broke his trucks lights on March 28, 2021 in Salem, Oregon. The protesters clashed with occupants of vehicles that had participated in an American flag-waving car caravan, despite law enforcements efforts to to keep the groups separate. (Photo by Nathan Howard/Getty Images)

Tourists enjoy blooming cherry blossoms at China Pharmaceutical University on March 22, 2021 in Nanjing, Jiangsu Province of China. (Photo by Yang Bo/China News Service via Getty Images)

Eva Longoria Farmer Visits "The Tonight Show Starring Jimmy Fallon" at Rockefeller Center on November 24, 2015 in New York City. (Photo by Theo Wargo/NBC/Getty Images for "The Tonight Show Starring Jimmy Fallon")

Behaviour: Mammals category. Giant Gathering by Tony Wu, USA. Dozens of sperm whales mingled noisily off Sri Lanka’s northeast coast, stacked as far down as Tony could see. This was a congregation of dozens of social units, like a gathering of the clans. Aggregations like this could be a critical part of the whales’ rich social lives but are rarely reported. Some two thirds of the population was wiped out before commercial whaling was banned in 1986. This kind of major gathering could be “a sign that populations are recovering”, says Tony. (Photo by Tony Wu/Wildlife Photographer of the Year 2017)