Genko Stoykov fires a rifle as he and other men prepare for the traditional “Horo” dance on Epiphany Day in the icy winter waters of the Tundzha river on January 6, 2022 in Kalofer, Bulgaria. As part of the tradition, a priest throws a cross in the river and it is believed that the one who retrieves it will be healthy throughout the year. Today, cultures throughout Christendom mark the Feast of the Epiphany, when Jesus was revealed to the Magi as God incarnate. (Photo by Hristo Rusev/Getty Images)

A Kashmiri Shiite Muslim mourns as he flagellates himself during a Muharram procession in Srinagar, Indian controlled Kashmir, Thursday, July 27, 2023. Muharram is a month of mourning for Shiite Muslims in remembrance of the martyrdom of Imam Hussein, the grandson of the Prophet Muhammad. (Photo by Dar Yasin/AP Photo)

Macaques huddle together for warmth at a hot spring in Nagano, Japan in the last decade of December 2023. Known as snow monkeys, the animals soak in the 40°C water every day during cold weather, spending their bathtime grooming, snoozing and playing on visitors’ camera tripods. (Photo by David Lazar/Animal News Agency)

Bangladeshi laborers unload watermelons from a boat at the Buriganga River in Dhaka, Bangladesh, 03 April 2024. Watermelon is in harvesting season and is filling the city markets as it arrives from the southern part of Bangladesh. According to the Department of Agriculture Extension (DAE), Barishal has set an ambitious goal to expand watermelon cultivation to 54,002 hectares across six high-yielding districts in the division, which is 14 percent higher than last year. (Photo by Monirul Alam/EPA/EFE)

Vehicles move past a man resting on a taxi, as he waits for passengers, along a road in Karachi, Pakistan, May 5, 2015. (Photo by Akhtar Soomro/Reuters)

Female of pygmy hippopotamus called Malaya from Netherlands in zoo in Dvur Kralove nad Labem, Czech Republic, February 22, 2016. (Photo by David Tanecek/CTK via ZUMA Press)

People protest at the Boston Free Speech Rally in Boston, USA on August 19. 2017. With the Boston Free Speech rally was closed to the media (despite the Boston Common being a public space), a lot of the media’s coverage centred on the tensions within the larger counter-protest. (Photo by Stephanie Keith/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)