Short-term effects of experimental artificial light at night on nocturnal vocal activity in a temperate bird community

Artificial light at night (ALAN) can alter the daily timing of birds activity, but the immediate effects of brief nocturnal illumination on vocal behaviour remain poorly understood. We experimentally examined whether short-term exposure to a local artificial light source affected nocturnal vocalisation rates and whether responses differed among species and between stages of the breeding season. Experiments were conducted at ten sampling points in western Poland, during nautical night in the early and late stages of the breeding season. Bird vocalisations were recorded continuously for 30 min before illumination, for 38 min during gradual and full illumination, and for 30 min after the lights were switched off. We recorded 28,839 vocalisations from 13 species. Of the five species analysed formally, only the Eurasian coot showed a significant illumination effect, with a higher vocalisation rate after illumination than before or during illumination. The sedge warbler showed higher estimated rates during and after illumination than before illumination, but the overall phase effect was not significant after false-discovery-rate correction. No phase effects were detected in the common nightingale, common quail, or Savis warbler. Descriptive patterns show increased vocal activity during or after illumination in the Eurasian skylark, common cuckoo, and corn crake, but limited spatial replication prevented formal testing. Overall, brief illumination did not produce a clear and consistent response across the recorded species. Short-term ALAN exposure may affect nocturnal vocal activity with some delay, but responses appear to be strongly species-specific. The observed patterns identify candidate species for further controlled experimental study.