May 18 is Endangered Species Day, an annual holiday introduced by the U.S. Senate in 2006 to raise awareness of endangered plants and animals and "promote species conservation worldwide."

Honoring species on the brink of extinction may sound like a bummer, but Endangered Species Day isn't meant to bring us down. Instead, the goal is to help us appreciate that we have a concept of "endangered species" at all — a notion that was on few people's radars 100 years ago, even as humans were wiping out ancient animals like passenger pigeons, Caspian tigers, Zanzibar leopards and thylacines.

Such loss of wildlife finally began to weigh on world governments by the early 20th century, leading to landmark conservation laws like the United States' Lacey Act of 1900 and the Migratory Bird Treaty Act of 1918. The U.S. Endangered Species Act later set a new standard of protection in 1973, and it's largely credited with saving iconic creatures such as American alligators, bald eagles, brown pelicans and red wolves.

Endangered Species Day doesn't overlook the ongoing problems for endangered species, though; it merely aims to stir up optimism that we can still save them, even if the outlook is bleak. It's celebrated at a wide range of U.S. parks, wildlife refuges, zoos, aquariums, botanical gardens and schools, with official events ranging from tours and field trips to festivals, film screenings and community cleanups.

And while Endangered Species Day began in America, it fits into a global tradition of dedicating one day a year to endangered species, both to reflect and build on past successes. The U.N.'s International Day for Biological Diversity, for example, falls just a few days after Endangered Species Day on May 22.

Regardless of how or when you observe these holidays, here are 15 photos to help you appreciate our planet's less fortunate flora and fauna (scroll down for all credits):

Amur leopard (Panthera pardus orientalis)

Range: Russia, North Korea

Status: Critically endangered

Threats: Poaching, habitat loss, climate change

A white axolotl with black-blue eyes and pink frills

Axolotl salamander (Ambystoma mexicanum)

Range: Mexico

Status: Critically endangered

Threats: Habitat loss, invasive species

Grandidier's baobab tree (Adansonia grandidieri)

Range: Madagascar

Status: Endangered

Threats: Habitat loss, overharvesting for timber

Amazon River dolphin

Amazon River dolphin (Inia geoffrensis)

Range: Brazil, Peru, Ecuador, Colombia, Venezuela

Status: Endangered

Threats: Pollution, overfishing, boat traffic, habitat loss

California condors

California condor (Gymnogyps californianus)

Range: Western U.S., Mexico

Status: Critically endangered

Threats: Poaching, lead poisoning, DDT poisoning, power lines, habitat loss

Mountain gorilla (Gorilla beringei beringei)

Range: Democratic Republic of Congo, Rwanda, Uganda

Status: Critically endangered

Threats: Poaching, habitat loss, disease, war and armed conflict

Scalloped hammerhead shark

Scalloped hammerhead shark (Sphyrna lewini)

Range: Coastal waters in temperate or tropical regions

Status: Endangered

Threats: Overfishing, primarily for shark fin soup

Leatherback sea turtle (Dermochelys coriacea)

Range: Nearly global

Status: Critically endangered

Threats: Chemical pollution, plastic pollution, bycatch in fishing nets

Sumatran orangutan (Pongo abelii)

Range: Indonesia

Status: Critically endangered

Threats: Poaching, habitat loss

Red wolf (Canis lupus rufus)

Range: Southeastern U.S.

Status: Critically endangered

Threats: Habitat loss and fragmentation, predator-control killing

North Atlantic right whale

North Atlantic right whale (Eubalaena glacialis)

Range: North Atlantic Ocean

Status: Endangered

Threats: Whaling, ship strikes, ship noise, entanglement in fishing gear

Monarch butterfly (Danaus plexippus)

Range: Southern Canada to northern South America

Status: Near threatened

Threats: Invasive species, climate change

Gharial crocodile (Gavialis gangeticus)

Range: India, Nepal

Status: Critically endangered

Threats: Habitat loss, entanglement in fishing gear

Tasmanian devil (Sarcophilus harrisii)

Range: Australia (Tasmania)

Status: Endangered

Threats: Habitat loss, invasive predators, road mortality, infectious disease

Whooping crane (Grus americana)

Range: Eastern and central U.S.

Status: Endangered

Threats: Habitat loss, hunting

Also on MNN:

Photo credits

  • Amur leopard: Tobias/Flickr
  • Axolotl salamander: Ulmus Media/Shutterstock
  • Grandidier's baobab: Frank Vassen/Flickr
  • Amazon River dolphin: guentermanaus/Shutterstock
  • California condor: Steve Cukrov/Shutterstock
  • Mountain gorilla: Joachim Huber/Flickr
  • Scalloped hammerhead: NOAA National Marine Fisheries Service
  • Leatherback sea turtle: Scott R. Benson/National Marine Fisheries Service
  • Sumatran orangutan: Maritime Aquarium at Norwalk/Flickr
  • Red wolf: Stephen Nakatani/Flickr
  • North Atlantic right whale: NOAA
  • Monarch butterfly caterpillar: Sid Mosdell/Flickr
  • Gharial crocodile: Matěj Baťha/Wikimedia Commons
  • Tasmanian devil: J.J. Harrison/Wikimedia Commons
  • Whooping crane: U.S. Fish and Wildlife Service

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Happy Endangered Species Day
In honor of Earth's less fortunate flora and fauna, this collection of awe-inspiring photos illustrates endangered wildlife from all over the planet.