Editor’s note: This photo gallery is an edited version of the article “Meet the Sentinels,” which appeared in the November 20, 2017, edition of Chemical & Engineering News. Please see the original article for more in-depth descriptions of the remarkable role these creatures play in helping to protect the planet.

In the movie “Arrival,” a team of scientists takes along a canary in a cage when visiting an alien spaceship. The purpose of the canary is never disclosed, but one assumes it serves as a sentinel — as the bird once did in coal mines — to alert the team if environmental conditions in the spaceship turn unfavorable.

Scientists have identified dozens of animals and plants that can function as sentinel species — harbingers of danger to human health and the environment. They have used sentinels to track persistent organic pollutants, to check for toxic metals, and to look at changes in nitrogen and phosphorus nutrients as well as dietary shifts that could be the result of climate change or invasive species.

Sentinel species aren’t a replacement for other types of sampling or lab research. However, they go further by providing physical evidence of how pollutants are damaging ecological systems.

New technologies are changing how scientists monitor sentinel species. For example, researchers are now using microsensors fitted to the backs of honeybees to analyze their ability to pollinate. Others are using drones to snatch snot samples from the blowholes of whales at sea to evaluate their well-being.

Click through the photos above to learn about a few key sentinel species and how they are helping us monitor the health of our environment.