Factors affecting the incidence of dawn calling in red-legged and grey partridges

Seasonal variations in the frequency and the timing of calling in red-legged (Alectoris rufa) and grey (Perdix perdix) partridges, and their relationships with biological and environmental factors, were investigated during 89 morning surveys. In winter, when birds were living in social groups, the vocal activity of both species decreased. Most calling began before sunrise. Yet many variations in the timing of first calls were observed when sunrise was prior to 0530 h, i.e. when the daylength was above 13 hours. On the contrary, when daylength was shorter, calling activity always began approximately 45 minutes before sunrise. Red-legged partridge calls were more particularly stimulated when sunrise was between 0530 h and 0700 h, with no wind, when moonrise was between 0000 h and 0900 h, and when cloud cover was low.