People stand around a leopard with its head stuck in a vessel in Rajsamand district of Rajasthan state, India, Wednesday, September 30, 2015. The leopard's head got stuck when it attempted to drink water from the pot, according to news reports. Forest officials tranquilized the animal and sawed off the vessel later in the day. (Photo by Kabir Jethi/AP 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)

An exhausted Rohingya refugee woman touches the shore after crossing the Bangladesh-Myanmar border by boat through the Bay of Bengal, in Shah Porir Dwip, Bangladesh, September 11, 2017. (Photo by Danish Siddiqui/Reuters)

The Aurora Borealis (Northern Lights) lights up the sky near the village of Pallas (Muonio region) of Lapland, Finland September 8, 2017. (Photo by Alexander Kuznetsov/Reuters/All About Lapland)

Mave Grace, 11, who had part of her arm chopped off by militiamen when they attacked the village of Tchee, stands with her sister Racahele-Ngabausi, aged two, in an Internally Displaced Camp in Bunia, Ituri province, eastern Democratic Republic of Congo, April 12, 2018. (Photo by Goran Tomasevic/Reuters)

Leon Feingold, right, drops his jeans as his girlfriend Patrizia Calvio looks in her purse on the uptown E Train during the 18th annual No Pants Subway Ride, January 13, 2019, in New York. (Photo by Kathy Willens/AP Photo)

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)