The Smithsonian Secretary in the 70s, S. Dillon Ripley, was an ornithologist and thought the owls could hunt the rats attracted to the new garbage cans on the National Mall. He named them Increase and Diffusion—a nod to the Smithsonian’s mission of “the increase and diffusion of knowledge”—and they lived in the building’s west tower.

The pair hatched three owlets in the spring of 1977. One of those new owlets fell out of the tower, but was recaptured and brought safely inside by a staff member. After raising their family, the owls departed and never returned.

This Smithsonian Institution Archives photo shows one of the pair refusing to take a message.

(Not to be confused with the previous Castle owl residents, who were known to crash into windows and swoop down on guards on the National Mall at night, and whose extensive droppings caused the collapse of the floor of a tower. They remain nameless.)

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In honor of International Owl Awareness Day