Visitors are seen at a birthday celebration for hippopotamus Hugo at the Warsaw Zoo in Warsaw, Poland, on May 29, 2026. As early summer arrives, animals at the Warsaw Zoo spend more time outdoors enjoying the warm weather. (Photo by Jaap Arriens/Xinhua)

Hippopotamus Hugo swims in a pool at the Warsaw Zoo in Warsaw, Poland, on May 29, 2026. As early summer arrives, animals at the Warsaw Zoo spend more time outdoors enjoying the warm weather. (Photo by Jaap Arriens/Xinhua)

A baboon rests in the sunshine at the Warsaw Zoo in Warsaw, Poland, on May 29, 2026. As early summer arrives, animals at the Warsaw Zoo spend more time outdoors enjoying the warm weather. (Photo by Jaap Arriens/Xinhua)

A hippopotamus swims in a pool at the Warsaw Zoo in Warsaw, Poland, on May 29, 2026. As early summer arrives, animals at the Warsaw Zoo spend more time outdoors enjoying the warm weather. (Photo by Jaap Arriens/Xinhua)

Baboons groom each other at the Warsaw Zoo in Warsaw, Poland, on May 29, 2026. As early summer arrives, animals at the Warsaw Zoo spend more time outdoors enjoying the warm weather. (Photo by Jaap Arriens/Xinhua)

A baboon rests outdoors at the Warsaw Zoo in Warsaw, Poland, on May 29, 2026. As early summer arrives, animals at the Warsaw Zoo spend more time outdoors enjoying the warm weather. (Photo by Jaap Arriens/Xinhua)