Researchers at ETH Zurich, the Swiss Federal Institute for Forest, Snow and Landscape Research, and SPYGEN have developed a drone that can autonomously collect so-called environmental DNA samples from tree branches. The samples can be used by ecologists to determine which species are present in a certain area.
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.
However, not all branches are the same, varying in thickness and elasticity. Branches also bend and rebound when a drone lands on them. Programming the aircraft in such a way that it can still approach a branch autonomously and remain stable on it long enough to take samples presented the roboticists with a significant challenge. ‘Landing on branches requires complex control,’ said Stefano Mintchev, a professor of environmental robotics at ETH Zurich.
Initially, the drone doesn’t know how flexible a branch is, so the researchers fitted it with a force-sensing cage that allows the drone to measure flexibility and incorporate it into its flight manoeuvres.
The researchers tested the device on seven tree species. In the samples, they found DNA from 21 distinct groups of organisms, including birds, mammals and insects. ‘This is encouraging, because it shows that the collection technique works,’ said Mintchev.
The researchers now want to improve their 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, Mintchev and his team are currently working in 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.
For this event, however, the collection device must become more efficient and mobilise more rapidly. In the tests in Switzerland, the drone collected material from seven trees in three days; in Singapore, it must be able to fly to and collect samples from ten times as many trees in just one day.
Collecting samples in a natural rainforest, however, 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 said.
The research has been published in Science Robotics.