Drones scour tree canopy for DNA samples to monitor biodiversity

Ecologists have been collecting genetic material samples, called environmental DNA (eDNA), to catalogue and monitor biodiversity. Based on these DNA traces, they can determine which species are present in a certain area.

While obtaining samples from water or soil is easy, other habitats such as the forest canopy are more difficult for researchers to access, which makes it harder to track the species that live there.

Researchers at ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, and the company SPYGEN have partnered to develop a special drone that can autonomously collect samples on tree branches.

The drone is equipped with adhesive strips. When the aircraft lands on a branch, material from the branch sticks to these strips. Researchers can then extract DNA in the lab, analyse it and assign it to genetic matches of the various organisms using database comparisons.

The differing thickness and elasticity in branches can make it difficult for drones to assess where to land to collect the strips. Accordingly, the test drone has been programmed to approach a branch autonomously and remain stable on it long enough to take samples without causing damage.

“Landing on branches requires complex control,” explained Stefano Mintchev, professor of environmental robotics at ETH Zurich and WSL.

Initially, the drone does not know how flexible a branch is, so the researchers fitted it with a force-sensing cage. This allows the drone to measure this factor at the scene and incorporate it into its flight manoeuvre.

Researchers have tested their new device on seven tree species. In the samples, they found DNA from 21 distinct groups of organisms, or taxa, including birds, mammals and insects. “This is encouraging, because it shows that the collection technique works,” said Mintchev.

Efforts are now underway to improve the drone further to get it ready for a competition in which the aim is to detect as many different species as possible across 100 hectares of rainforest in Singapore in 24 hours.

To test the drone’s efficiency under conditions similar to those it will experience at the competition, the team are currently working at the Zoo Zurich’s Masoala Rainforest.

“Here we have the advantage of knowing which species are present, which will help us to better assess how thorough we are in capturing all eDNA traces with this technique or if we’re missing something,” Mintchev said.

Collecting samples in a natural rainforest presents the researchers with even tougher challenges. Frequent rain washes eDNA off surfaces, while wind and clouds impede drone operation.

“We are therefore very curious to see whether our sampling method will also prove itself under extreme conditions in the tropics,” Mintchev concluded.