To capture the essence of a migratory animal, such as the monarch butterfly, a photographer must become migratory, too.

Over nearly two decades, photographer and National Geographic Explorer Jaime Rojo has followed monarch butterflies on their epic, multigenerational journey across North America.

He’s shivered with the insects as they clustered on oyamel trees within the Monarch Butterfly Biosphere Reserve in Michoacán, Mexico, and wilted under the sun with them as they winged their way north through Texas, Oklahoma, Kansas, Iowa, and Minnesota.  

Alexa Keefe, managing photography editor and selector of this year’s best wildlife photos, kept coming back to just how much time and dedication each photographer showed in the pursuit of their shots. 

For instance, she points to Michael Forsberg’s image of whooping cranes stopping for the night in a Nebraska wetland: “He would spend hours, sometimes days, observing from a blind waiting for the right moment to press the shutter.”

Likewise, to create the “Into the Amazon” special issue, photographer and National Geographic Explorer Thomas Peschak spent 396 days in the field to capture their aquatic realm in all its glory.

Whether it was Jennifer Hayes’ harp seals or Acacia Johnson’s brown bears, so many of these entries represent vast catalogues of photographs built from years of familiarity with their subjects.