This gentle drone collects loose DNA from swaying tree branches •

by Ana Lopez

Understanding the biodiversity of forests is crucial for its conservation or restoration. Collecting “external DNA” left by animals is a good way to find out what’s living there without having to see them or even be there at the same time – and this drone from Swiss researchers makes sampling from tree branches safer and easier.

External DNA can come in many forms — dead skin or feathers, detritus, liquids — and can be found in soil, water, or on surfaces such as rocks and tree branches. Basically anywhere an animal hangs out, it leaves a trace of itself and we can detect that. Until recently, this type of DNA amplification and analysis may have been too complicated or expensive, but the tools to do it have become much cheaper and easier to use.

However, there remains the question of collecting the DNA, and while biologists can certainly take soil and water samples or scrape the sides of trees, high branches where birds, small mammals and insects live their entire lives are inaccessible without special equipment. Try telling your department head that you need an extra $20,000 to get a tree climbing team because there wasn’t enough guano on the forest floor.

The adventurous roboticists at ETH Zurich have come up with a clever method to sample external DNA from tree branches, which can be easily done from the ground. In a paper published in Science Roboticsthey propose a drone-based solution: an aerial robot that can fly to high branches and extract samples from them without harming the branch or itself.

The drone looks a bit like a modernist lighting fixture, with a beautifully crafted wood frame and plastic shield, and strips of masking tape or “moistened cotton” on the bottom surfaces. After being guided to a generally favorable position, it hovers above a branch to be sampled and tracks any movement such as swaying or bouncing, synchronizing its approach. When it makes contact, it pushes with enough pressure to ensure that loose eDNA materials are transferred to the strips, but not so much that it pushes the branch out of the way. Essentially, it leans on the tree.

Diagram of the paper showing how the drone works.

During the first drone trips in the arboretum surrounding the institute (we know a lot about forests at universities, just as we know a lot about the psychology of students), the team was able to identify dozens of species of plants and animals (as well as microorganisms). That they collected much more before it rained than after suggests that the method is recent, which can be helpful or limiting depending on what a project needs.

The team plans to continue working on the drone, allowing it to go farther into trees or higher, or adapting its collection technique to work in other conditions.

“Our results pave the way for a generation of robotic biodiversity explorers capable of exploring eDNA at different spatial and temporal scales,” the researchers write. “By allowing these robots to reside in the environment, this biomonitoring paradigm would provide information about global biodiversity and potentially automate our ability to measure, understand and predict how the biosphere responds to human activity and environmental change.”

Below you can see the drone in action:

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