Common swift (Apus apus)

On Liberation Day, Liesje Mommer – a researcher in underground interactions between plants and fungi – heard them again: swifts! It’s a sound she’s always on the lookout for in spring: the high-pitched screaming calls of the common swift.

Once they arrive, they swirl and scream through the skies, and for many, that marks the start of summer. They fly high above, visible only as crescent shapes or boomerangs. Constantly on the move, they rarely, if ever, land – even sleeping is done on the wing. That’s why swifts sleep with only one hemisphere of the brain at a time. Highly efficient.

And then one day – usually when the academic year begins – it all falls silent. No more screaming, no more swirling in the sky. Until, of course, they return the following year.