Burrowing owl chicks gaze out from among flowers near Pawnee National Grassland in Colorado (© Roberta Olenick/Alamy)

Laburnum (golden chain) trees and purple alliums in bloom at VanDusen Botanical Garden, Vancouver (© Greg Vaughn/Alamy)

Travertine terraces of Pamukkale, Turkey (© bybostanci/Getty Images)

Mandarin duck hen with ducklings in South Korea (© VDCM image/Getty Images)

Wadi Rum, Jordan (© Thomas Coex/AFP via Getty Images)

Tree in blue agave field in the tequila producing region near Atotonilco, Jalisco, Mexico (© Brian Overcast/Alamy)

A path winding through a forest of bluebells in Hertfordshire, England (© JayKay57/Getty Images)

Swedish antenna at La Silla ESO Observatory, Chile (© Alberto Ghizzi Panizza/Getty Images)

Koala mother and 8-month-old joey, Queensland, Australia (© Suzi Eszterhas/Minden Pictures)

View of Göreme from an observation deck, Göreme National Park, Cappadocia, Turkey (© Anton Petrus/Getty Images)

Spring forest, Gros Morne National Park, Newfoundland and Labrador (© Don Johnston EC/Alamy Stock Photo)

The village of Oia on the island of Santorini, Greece (© Zebra-Studio/Shutterstock)

Nurses serving with the American Red Cross in Paris, France, in May 1919 (© Universal History Archive/Universal Images Group via Getty Images)

A close-up of a tulip from the Canadian Tulip Festival in Ottawa (© Sandy Thompson/Alamy Stock Photo)

Windmills, Kinderdijk, Netherlands (© Achim Thomae/Getty Images)

Panoramic view of the Bernina Range with blood moon, Eastern Alps, Engadin, Switzerland (© Bernd Zoller/Shutterstock)

Salt ponds of Maras in Peru's Sacred Valley of the Incas (© Fotofeeling/Westend61 on Offset/Shutterstock)

Museum at Prairiefire, Overland Park, Kansas (© Bernard P. Friel/Universal Images Group via Getty Images)

Glass bridge of Zhangjiajie, Hunan, China (© MediaProduction/Getty Images)

Honeybee flying over crocuses in the Tatra Mountains, Poland (© Mirek Kijewski/Getty Images)

Albion Falls, Hamilton, Ontario (© Alexander Sviridov/Shutterstock)

A Burchell's zebra and a cattle egret at the Rietvlei Nature Reserve in South Africa (© Richard Du Toit/Minden Pictures)

Florida red-bellied turtle in Rainbow Springs, Rainbow Springs State Park, Florida (© Michel Roggo/Minden Pictures)

Kornati National Park, Croatia (© Anton Petrus/Getty Images)

Alhambra in Granada, Andalucia, Spain (© Armand Tamboly/Getty Images)

Hanging bridge in Monteverde Cloud Forest, Costa Rica (© Dmitriy Burlakov/Getty Images)

Golden Gate Bridge and Marin Headlands photographed from Golden Gate Overlook in San Francisco, California (© Jeff Lewis/Tandem Stills + Motion)

Bungle Bungle Range in Purnululu National Park, Australia (© Francesco Riccardo Iacomino/Getty Images)

Adult female grizzly bear and cub in the Great Bear Rainforest, B.C. (© Jack Chapman/Minden Pictures)

Sunset lights up Mount Fryatt as the Athabasca River flows over Athabasca Falls in Jasper National Park, Alberta, Canada (© Robert Postma/Getty Images)

Scarlet macaw in Costa Rica (© Harry Collins/Getty Images)