Variable allocation of activity to daylight and night in the mallard

The solar day-night rhythm imposes a strict diel activity pattern on many organisms. Among birds, most species are generally either active during the day and rest during the night, or vice versa. However, many waterbird species can be active during both daylight and darkness. Hence, these species are much less limited by an external clock to allocate their activities over time than species showing a strict day or night pattern. Before miniaturized data-logging systems became available, it was difficult to follow animals day and night. Therefore, few details about short-term activity budgets are available for free-living animals. To study the activity budget of mallards, Anas platyrhynchos, in relation to time of the day, season and external factors, we used tags containing an accelerometer providing detailed activity information. We observed a relatively constant diel pattern with more activity during daylight than at night and peak activities during twilight. Activity over the season (September-April) was remarkably constant. Compared to the average activity per half-day, excess activity alternated every 12 h, suggesting an increased need for rest during daylight after a night with excess activity, and vice versa. Between days, activity was allocated to half-days in a very flexible manner: Either day or night activity was increased for a number of days, before increased activity gradually switched to the other half-day. We observed no synchrony in this pattern among individuals, highlighting the behavioural flexibility of this generalist species.