DNA in the air betrays animals

It is a 16-kilo, crocodile-green gadget on a tripod with something on it that looks like a ship’s rudder. The Bukard Spore Trap was originally designed to filter pollen out of the air. Wageningen scientists studied whether the gadget can also be used to find out which vertebrates inhabit an area. The animals continuously shed flakes of skin, hairs, feathers and saliva – all of which contain DNA. With that DNA, the researchers hope to be able to identify animals in the vicinity without needing to spot them or capture them on camera: timeconsuming methods which can also miss a lot of small species.

The study was led by Marcel Polling, animal ecologist at Wageningen Environmental Research. ‘We weren’t the first. In 2022, Danish researchers proved that an air sampler can capture the DNA of nearly all the animals in a zoo.’ Nor is it a new idea to analyse DNA traces from an environment: scientists have long collected information about the life present in water and soil in this way. The Wageningen study set out to establish whether an air sampler placed out in nature could also filter suffcient, reliable DNA out of the air to provide a picture of the mammals and birds present.

Tape with vaseline

The Bukard works along the lines designed by the British biologist John Malcolm Hirst in the 1950s for capturing fungal spores and pollen out of the air. In this system, the particles stick to a microscope lens covered in Vaseline. Inside the Burkard is a long roll of tape covered in a thin layer of Vaseline. ‘A mechanism rolls the tape slowly across the opening on the front of the machine, so that a new section is continuously being exposed to the air,’ explains Polling. ‘This enables the Burkard to go on collecting material for longer. You can see from the location on the tape on which day the DNA was captured.’ The weather vane above the machine ensures that the opening of the sampler is always facing the wind. In order to capture as many particles as possible, the Burkard also draws air in at the rate of about 10 litres per minute. The engine that drives the suction is powered by a solar panel on the ground next to the machine.

For their research, Polling and his colleagues positioned the Burkards for a week at each of three different locations: a forest, an orchard and a solar farm. Camera traps recorded the animals that passed by. ‘That enabled us to check whether the Burkard really captured DNA from animals that had been in the vicinity.’

As well as pollen, the researchers found miniscule particles of animal matter containing DNA in the Vaseline. ‘We’re not really sure whether they are bits of hair or of skin. The particles are too small for that,’ says Polling. ‘But they do contain enough DNA to analyse.’

100 bird species

‘We found the DNA of more than 100 bird species, dozens of mammals and a few amphibians. Surprisingly enough, there was also some fish DNA. All were sea fish, so that DNA probably came from human garbage.’ The nine mammal and seven bird species that the cameras had recorded were also found on the tape. The results were published in the scientific journal Environmental DNA in August 2024.

Polling’s fellow ecologists are enthusiastic about this technology, he says. Its potential for measuring biodiversity is obvious: without having to spot or capture animals, researchers can get a comprehensive impression of the diversity in an area. ‘What we don’t yet know is how wide an area the air sampler covers. How far does the DNA come from? How much DNA does there have to be in the air before it shows up in the sample? How old can the DNA be? What is the impact of the wind, exactly?’ Ongoing follow-up research aims to answer these questions.

Magellanic penguin

Not all the DNA in the samples could be accounted for. The DNA of an exotic parrot and a Japanese quail could be traced to a local pet owner, but that of the South American Magellanic penguin remains a mystery.

‘You could say that the air sampler works too well in some cases,’ says Polling. During the follow-up study too, the Burkard captured DNA from all sorts of exotic species. ‘Pets in the area, we think.’ One solution might be to measure over a shorter time. ‘So we gave people doing bird inventories a kind of handheld model of the device. Then you take a sample over an hour instead of a day. With any luck, this way we will mainly capture DNA from the immediate vicinity.’