Diurnal activity patterns of Goosanders Mergus merganser on a Scottish river system

Abstract

Goosanders were counted as they arrived and departed from overnight communal roosts. All birds left the roost before sunrise and returned from 50 minutes prior to, until 10 minutes after sunset. Relative to sunset, they arrived later on short midwinter days, and earlier on the longer days of February and March. Goosanders did not roost communally from April to August, except in May, in an area where males gathered prior to their leaving to moult. The diurnal behaviour of Goosanders, quantified using three methods, showed that most of the daytime was spent foraging and loafing. Foraging peaked in the first two hours of the day, decreasing thereafter for adults, less so for bird in their first winter, and least for ducklings. Calculations of total daily foraging times suggested adults fed for 3-4 hours, young birds for 5-6 hours and ducklings for about 10 hours. Total time spent flying could not be estimated accurately, though there was significant seasonal variation in the frequency with which it was recorded. Other behavioural activities included social interaction which was overt as birds gathered to roost, suggesting communal roosting provided an important venue for pair-formation.