In a forest we mostly hear birds rather than see them. An experienced ornithologist recognises dozens of species by voice at dawn. But such people are few, and they cannot stand in every forest every morning all spring. An acoustic recorder can. It is a small box on a tree that records sound on a schedule for weeks and months, day and night.

What passive acoustic monitoring gives

• Voices you would not notice with your eyes. Birds in the canopy, owls at night, corncrakes in tall grass, frogs at dusk, nocturnal bird migration over the forest.
• A whole season instead of one morning. The recorder hears the full dawn chorus every day, not only on the day the surveyor came. So you can see when a species started singing, when it peaked and when it fell silent.
• A recording you can listen to again. Any identification can be checked: open the recording, look at the spectrogram, let a colleague listen.
• The same conditions. A recorder has no "good ear" or "bad day". With the same settings and schedule, locations and years can be compared.

Scale

As of October 2026, biomon.app holds more than 586,000 recordings, almost 49,000 hours of sound from 98 locations. Just to listen to all of it in a row, a person would need more than five and a half years without sleep or days off. Automatic classifiers have made more than 26 million identifications and found 344 species.

Why people are still needed

AI (BirdNET, Perch and other models) identifies species by sound, but very unevenly. It recognises the eastern tree frog, marsh frog, corncrake or great reed warbler almost without errors. The common spadefoot or pool frog almost never. Sometimes a species is among the most frequent by number of detections, while nearly all of them are false.

So on biomon.app people listen to a sample of fragments and answer "correct" or "incorrect". From these answers the platform calculates how reliable the model is for each species and from which confidence level it can be trusted. People are not replaced here but used wisely: instead of thousands of hours of listening, they check a sample and calibrate the machine.

Why it matters right now

Protected areas are losing specialists who know bird voices. A recorder does not replace an ornithologist, but it gives them an archive they can work with from the office, at a convenient time, and return to years later. The same recordings are needed for the European common bird monitoring scheme that Ukrainian parks are already joining.

What a recorder cannot replace

• It will not hear silent species or species outside their singing season.
• It tells you that a species called, but counting individuals by sound is difficult.
• Noise from a stream, a road or the wind shortens the distance at which birds can be heard.
• Mammals are better studied with camera traps.

How to take part

• Deploy recorders by the rules: PAM field methods.
• Help check detections: register on biomon.app and start with Verifying acoustic detections.
• All guides in one place: Monitoring standards.