The Duchess of Cambridge pulls a pint with the Duke of Cambridge during their visit to Belfast Empire Hall for an informal party to celebrate inspirational young people who are making a real difference in Northern Ireland as part of their two day visit to Northern Ireland on February 27, 2019. (Photo by Aaron Chown/PA Wire Press Association)

An art wall painting representing performance artist Marina Abramovic by Italian artist Maurizio Cattellan to publicize his upcoming exhibition The Artist is Present, in Shanghai, China, is displayed on a facade of a building, in Milan, Italy, Wednesday, September 19, 2018. (Photo by Luca Bruno/AP Photo)

Olena Korzeniuk, a 15-year-old girl poses on the stairs during a bid to set the national record for the longest hair on a child in Kiev, Ukraine on March 12, 2019. During a ceremony, the experts of the National Register of Records found the blonde hair of the Ukrainian Rapunzel to be 2.35m (6.5ft) long. (Photo by Tarasov/Ukrinform/Barcroft Images)

Relatives of community leader Josemano “Badou” Victorieux, one of the victims of clashes with the Police, cry during his funeral in Port-au-Prince, Haiti, 16 October 2019. The protest movement in Haiti completes a month with no sign of remitting and without the President, Jovenel Moise, yielding to the voices that require him to resign. (Photo by Orlando Barria/EPA/EFE)

Women members of the national police take part in a parade during a graduation ceremony in Bogota, Colombia on November 7, 2019. (Photo by Juan Barreto/AFP Photo)

George Harrison of the Beatles sits cross-legged with his musical mentor, Ravi Shankar of India, a sitar virtuoso, in Los Angeles, August 3, 1967, as Harrison explains to newsmen that Shankar is teaching him to play the sitar, a 25-stringed guitar-like instrument. Harrison said “Indian music makes God come through in a spiritual way”. (Photo by AP Photo)

A man in “Red Army” garb hits the pavement during a simulated attack during a re-staging of part of the Long March in Jinggangshan September 14, 2017. The scene brings alive an extraordinary chapter in China's history that established the supremacy of Chairman Mao Zedong and the Communist Party. Deep in the mountains of Jinggangshan in the southeastern province of Jiangxi, a classroom of bank tellers participates in an ideological boot camp that plays into Chinese President Xi Jinping's drive to further consolidate his grip on power. (Photo by Thomas Peter/Reuters)

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)