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The effect of meteorology on the singing rate of 13 common bird species

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Birdsong is mainly used by birds to reproduce and defend their territory. Although the intensity of singing activity follows circadian rhythms, various factors can modify it, including weather conditions. The present study investigates the effect of 12 basic meteorological variables on the singing activity of 13 common bird species in Mediterranean areas during the reproductive period and evaluates the temporal suitability of bird census to detect the maximum of species. 8 recording devices and the data from a nearby weather station were used in the study. The registers were grouped into 5-minute periods during daytime over 36 days. The determination of significant variables at the community level was performed with a Random Forest analysis. The variability in the intensity of birdsong for each species was studied using GLMM models. Air temperature, relative humidity, solar irradiance, wind speed, and atmospheric pressure, together with the time of the day, were selected as the variables that significantly regulate avian singing activity. They explain 76% of the variability in the singing activity of the community. The effects of each variable are species-specific, but common patterns can be identified. Singing activity is low in extreme temperatures, but the optimal temperature varies among species. The response to humidity and solar irradiance are linked to the time of the day, during mornings most species sing the most when humidity is ~80% and solar irradiance has little effect. Wind speed negatively affects singing activity while atmospheric pressure affects it positively. Generally, the time of the day with maximum singing activity is the early morning hours, following circadian rhythms. We concluded that the optimal time to conduct bird census is early in the morning, on days when wind speed is minimum, atmospheric pressure is high, and temperature is above 11ºC. The high interspecific variability makes it impossible to determine a more specific condition for temperature, irradiance, and humidity. Therefore, we suggest conducting replicas of the census, in order to include different atmospheric conditions, this practice would maximize the detection of the majority of species

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