Buda, J. | Search bioRxiv

bioRxiv2026

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.

ecology↗

bioRxiv2026

Species-specific responses of diurnal birds to nocturnal conspecific song playback

The vast majority of birds are diurnal and concentrate their vocal activity during daylight hours. However, some diurnal birds can also be vocally active at night, although the functions of this phenomenon remain poorly understood. We conducted playback experiments in the Warta Landscape Park (central Poland) to determine whether nocturnal singing by diurnal birds serves breeding-related functions by analysing responses to playback of songs from unfamiliar conspecific males. The sedge warbler (Acrocephalus schoenobaenus) was selected as the focal species because it exhibits relatively high levels of nocturnal song activity, while nine additional diurnal species detected near focal sedge warbler territories were included to explore whether responsiveness to nocturnal conspecific song extended across a broader taxonomic range. Playback experiments were conducted during the early and late stages of the breeding season and during the early and late parts of the nautical night. Out of 10 species tested, three responded vocally: sedge warbler, Savi s warbler (Locustella luscinioides), and common snipe (Gallinago gallinago). Sedge warblers did not modify song rate and song duration but increased flight activity after nocturnal playback. Savi s warblers and common snipes produced more vocalisations after playback than before in May, a pattern consistent with territorial defence function. General nocturnal vocal activity was higher at the beginning of the season, suggesting that birds motivation to establish territories and form pairs can extend into the night, providing additional benefits. Moreover, the probability of singing by the sedge warbler was higher in the latter part of the night. Our study demonstrates that nocturnal stimulation of foreign male playback of diurnal birds can elicit vocal responses from conspecifics, suggesting that nocturnal singing can occur in the absence of obvious artificial light pollution, but in the case of some species and environmental conditions, it may contribute to nocturnal social communication, especially in the early breeding season.

animal behavior and cognition↗