Activity rhythm in High Arctic Svalbard ptarmigan (Lagopus mutus hyperboreus)

Abstract

Feeding activity was recorded in captive Svalbard ptarmigan (Lagopus mutus hyperboreus) under natural photoperiodic conditions at 70°N and 79°N. At 79°N, activity was intermittent and non-circadian in summer, when the sun was permanently above the horizon, and in midwinter, when the sun was permanently lower than 6° below the horizon. The intermittent feeding pattern was evident in summer at 70°N, whereas feeding activity in winter appeared to be entrained. In spring and autumn all birds were diurnal, with morning and evening bouts of feeding activity. The phase relationship between the onset or end of activity and the photoperiod showed marked changes, especially at 79°N, but in general, activity onset was more precise relative to twilight than activity end. At 79°N there was a sigmoidal relationship between activity time and photoperiod and activity time was longer in autumn than in spring at equal photoperiods. Based on our results, the activity pattern of Svalbard ptarmigan may be described in terms of a two-oscillator model, although a one-oscillator model cannot be excluded. The possibility is discussed that rhythmic feeding or food availability may act as a zeitgeber in addition to the light-dark cycle.