A college girl takes part in the Holi festival celebrations in Bhopal, India, 19 March 2019. Holi is celebrated on the full moon day and marks the beginning of the spring season. Holi will be celebrated as the Hindu spring festival of colors across the country on 21 March. (Photo by Sanjeev Gupta/EPA/EFE)

Fans dressed up in costume await the cast members on the red carpet at the world premiere of the film "The Avengers: Endgame" in Los Angeles, California, April 22, 2019. (Photo by Mario Anzuoni/Reuters)

An actor dressed as Tyrion Lannister, poses for photographers with fake severed head before the screening of final episode of “Game of Thrones” on 20-meter-high screen at RZD Arena in Moscow, Russia on May 20, 2019. (Photo by Maxim Shemetov/Reuters)

Pitch invader Kinsey Wolanski is taken away by security during the Champions League final soccer match between Tottenham Hotspur and Liverpool at the Wanda Metropolitano Stadium in Madrid, Saturday, June 1, 2019. (Photo by Toby Melville/Reuters)

Buyan, a male Siberian brown bear, cools down under a stream of water sprayed by an employee in an enclosure on a hot summer day, at the Royev Ruchey zoo in Krasnoyarsk, Russia on June 14, 2019. (Photo by Ilya Naymushin/Reuters)

In this photo taken on Monday, August 5, 2019, a family watches explosions at a military ammunition depot near the city of Achinsk in eastern Siberia's Krasnoyarsk region, in Achinsk, Russia. Russian officials say powerful explosions at a military depot in Siberia left 12 people injured and one missing and forced over 16,500 people to leave their homes. (Photo by Dmitry Dub/AP Photo)

Kashmiri woman takes part in a physical test of a recruitment rally for the Special Police Officers (SPO) in Jammu and Kashmir Police, in Srinagar on December 6, 2019. As many as 23,000 people have applied for posts in the Special Police Officers (SPO) in Jammu and Kashmir Police and 100 positions will filled in the current phase of recruitment, local authorities said. (Photo by Tauseef Mustafa/AFP Photo)

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)