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)

People visit a frozen waterfall illuminated by colorful lights at Dadunxia sceneic area on December 25, 2022 in Linxia Hui Autonomous Prefecture, Gansu Province of China. (Photo by Shi Youdong/VCG via Getty Images)

Japanese macaques, also known as snow monkeys, play as they soak in a hot spring in Jigokudani valley in Nagano Prefecture, northwest of Tokyo Saturday, March 6, 2021. (Photo by Kiichiro Sato/AP Photo)

A day-old lamb exploring new surroundings on the vernal equinox, considered the first day of spring, on March 20, 2019 at Coombes Farm in Lancing, England. (Photo by Andrew Hasson/Getty Images)

A grey seal basks under a rainbow on a beach on the Lincolnshire coast, England on November 21, 2017. (Photo by Sean Weekly/Caters News Agency)

An ostrich is seen at Woburn Safari park before its opening as coronavirus disease (COVID-19) restrictions begin to ease, in Woburn, Britain on April 11, 2021. (Photo by Andrew Boyers/Reuters)

A killdeer (Charadrius vociferus) chick on sand dunes in Pacific Grove, California, US on June 21, 2023. The killdeer gets its name from its shrill, loud call. (Photo by Rory Merry/ZUMA Press Wire/Rex Features/Shutterstock)

Bangladeshi artists wear floral attire as they join celebrations of the spring festival “Basanta Utsav” at the Faculty of Fine Arts of the University of Dhaka, in Bangladesh, 14 February 2024. The Bashanta Utshab, or Spring Festival, is a local traditional festival which marks the beginning of the Spring Season while young people also celebrate it along with Valentine's Day. (Photo by Monirul Alam/EPA/EFE)