The veil between this world and the next feels much thinner at this time of year, with Halloween focusing attention on death: the friends, leaders, and loved ones we have lost and, perhaps, the species humans have driven into extinction.

While we mourn and celebrate the dead, perhaps we can learn something from these former life-forms as well. That's the seasonal goal of the Smithsonian Institution's National Zoological Park in Washington, D.C., which has included a graveyard for extinct species among its Halloween decorations. The display includes headstones for dozens of mammals, birds and reptiles that have disappeared due to of human activities, mostly over the past century. These species include the Ryukyu wood pigeon (Columba jouyi), wiped out by hunting and deforestation; the Caucasian wisent (Bison bonasus caucasicus), poached into extinction; and the slender-billed grackle (Quiscalus palustris), which disappeared after its marshy Mexican habitat was drained.

"Zoos around North America have been doing this for decades," says Don Moore, associate director of animal care sciences at the National Zoo. "We try to make fun events that engage and inspire the public and have a strong educational message. In this case," he says, talking about the graveyard, "the conservation message is really strong."

Moore says the graveyard, which he has helped to organize for several years, resonates with zoo visitors. "People relate to a graveyard. They know if you go into the ground, you have a headstone and you're gone forever." The message isn't completely downbeat, though: the zoo also has a separate, year-round ride called the Conservation Carousel, which represents the conservation work it does to preserve endangered species such as the giant panda, clouded leopard and common cuttlefish.

The zoo holds events throughout the year that don't necessarily address conservation, but Moore says events and displays like this showcase the zoo's mission of saving species. He adds: "The extinction graveyard is another tool in our tool kit to educate the public about the need for conservation."

One species the National Zoo has committed to help conserve is the Asian elephant, which led Moore to wonder why the related North American mammoth wasn't represented in the graveyard. Before we spoke, he spent a few minutes looking in the Smithsonian database to see what elephant or mammoth materials they had in their collection and came up with a recently discovered 13,000-year-old bone fragment with a picture of a mammoth carved into it. He hopes to use the early art in future educational outreaches about extinct species. This direct link to the past through the broader Smithsonian "family" is something that many other zoos don't have, he says. "It's pretty invigorating some days to know how much science and information we can bring to the table at the zoo through the Smithsonian."

Moore says he does have one regret about this year's graveyard: it includes no headstones for extinct insects or other invertebrates, many of which have also disappeared because of humans. "We do have a couple of spiderwebs hanging about it," he muses. "Maybe that gets the message out about invertebrates."

Photos by environmental storyteller John Messeder, who was kind enough to let me know about the extinct species graveyard and offered the use of his photographs for this article

Explore further: You can find photographs of many other extinct species graveyards online, including images from the Bronx Zoo (which probably had the first of these displays nearly 50 years ago), San Francisco Zoo, Mesker Park Zoo and Botanic Garden, Como Park Zoo and Conservatory, and El Paso Zoo.