Diurnal, nocturnal, and seasonal patterns of singing activity in marsh warblers

Based on over 1,300 h of sampling, we studied diel and seasonal budgets of song activity of marsh warblers in three different ways. Two study areas in the Czech and Slovak Republics (300 km apart) and seasons in several conse cutive years were covered. Song activity varied over the 24-h period and wi th season. Marsh warblers sang both during the entire day and night. Most s inging males (64.3%) were recorded in the first half of the 24-h period. Th e number of individuals singing in daylight was 1.8 times higher than in th e dark. Increased nocturnal singing activity was recorded in May and especi ally from early through mid-June. In general, the singing activity was mark edly connected with the twilight** periods. It increased at dawn with a pea k after twilight (the highest level within the entire 24-h period). In the evening, it reached its highest level at dusk. After twilight it rapidly de creased and reached the lowest level within the 24-h period. However, the d ifference between the number of individuals singing in the two twilight per iods is not significant. Marsh warblers sang for a relatively short period from early May through around mid-July, showing a distinct peak at the end of May and the high level of singing activity at the beginning of June. The y exhibited both similar diel and seasonal activity patterns in the course of the individual years of study. Between the two study areas, there was a small difference in rate of singing activity in June.