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)

Mahouts return home with their elephants carrying grass to feed them on the eve of the rhino census in Kaziranga National Park in Assam state, India, 24 March 2015. Kaziranga will be closed to visitors for the next two days for a census of the rhinos commencing 25 March, in a previous census in 2013 in the park the population of the Indian rhinos was 2329. (Photo by EPA/Stringer)

This picture shows a two-year old orangutan seized from a residents house at the provincial Nature Conservation and Agency (BKSDSA) office in Banda Aceh on September 16, 2014. The critically-endangered primates population are dwindling rapidly due to poaching and rapid destruction of their forest habitat that is being converted into palm oil plantations. (Photo by Chaideer Mahyuddin/AFP Photo)

An adult specimen of Nannospalax (leucodon) montanosyrmiensis, a variant of the lesser mole-rat (Spalax leucodon) is pictured near Albertirsa, some 60 kilometers southeast of Budapest, Hungary, 12 May 2018. The critically endangered rodent lives in several isolated populations in the Carpathian Basin. (Photo by Sandor Ujvari/EPA/EFE)

A picture taken on October 5, 2018, shows a general view of Migingo island which is densely populated by residents fishing mainly for Nile perch in Lake Victoria, the continent's largest lake, on the border of Uganda and Kenya. More than 500 people live on the island, which is barely 2,000-square-metres. (Photo by Yasuyoshi Chiba/AFP Photo)

Leo, an orphaned Sumatran orangutan, is taken to the Sumatran Orangutan Conservation Programme rehabilitation centre. Leo will join other orangutans who have been reintroduced to the Pinus Jantho nature reserve. The SOCP has gradually formed a completely new wild population of species that have been threatened with extinction. (Photo by Sutanta Aditya/Barcroft Images)

Smoke billows from the Mt Etna volcano as seen from Linguaglossa, Sicily on Monday, August 9, 2021. Europe's most active volcano remains active scattering ashes around a vastly populated area on its slopes. (Photo by Marco Restivo/Barcroft Media via Getty Images)

A lemur inspects a camera at Tarsus Nature Park in Mersin, Turkey on July 25, 2021. The population of lemurs, one of the inhabitants of Tarsus Nature Park, increases with new births every year. Lemurs are among the most interesting species in the zoo. (Photo by Serkan Avci/Anadolu Agency via Getty Images)