Nocturnal singing by diurnal birds in a temperate region of central Europe

摘要

Most bird species sing by day, with two distinct peaks of vocal activity-around sunrise and sunset. However, even typically diurnal birds also sing during at night what is for them an atypical part of the day. To date, the mechanism and function(s) of such behaviour remain unclear across bird taxa. In our study we focused on night singing by diurnal birds in two different types of environments-forests and open areas in eastern Poland. We examined: (1) which diurnal species sing at night (defined as the period between astronomical dusk and dawn); (2) how intensively different species vocalise at night; and (3) whether the occurrence of nocturnal singing by diurnal birds depends on the type of environment. To do this, we used autonomous sound recorders to record soundscapes in 27 points located in open habitats and 27 points located in forests. At each location the recorder continuously collected data for an entire day during the breeding season, from one hour before dawn to 10 AM the next day. All night songs were classified to their species of origin via manual spectrogram scanning. We recorded 88 bird species in total (12 orders, 32 families), of which 24 species (7 orders, 15 families) sang at night. Night singing was observed significantly more often in open areas than in forests. The frequency and intensity of night singing was species-specific and ranged from occasional singing to regular and intense singing. We hypothesise that elevated light levels have a crucial influence on night singing, but that the effect of light may also be modified by environmental factors (e.g., predator pressure).