Seasonal rhythms of locomotor activity and thyroid function in male badgers(Meles melesL.)

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Abstract
Adult male badgers were housed in outdoor pens equipped with an infra‐red actographic system, in the Chizé forest (Western France: 46°19'N; 00°24'W). Various parameters characterizing the diurnal general locomotor activity rhythm were measured: duration of the total activity phase and the actual activity outside the burrow in relation to sunset, sunrise or night duration, activity of passage and profile of seasonal variations. Simultaneously the thyroid activity was controlled by bi‐monthly or monthly measurements of plasma thyroxine concentration. 1. In the nycthemeral rhythm of general locomotor activity, there is a close synchronization between the beginning of the activity phase and sunset; nevertheless, from November to March, the beginning of activity occurs 2 h or more after sunset. The end of activity always takes place before the sunrise ("anticipation mechanism") and the delay exhibits a seasonal variation (minimum in summer, maximum in late autumn‐early winter). 2. General locomotor activity is minimal in January; the phase duration is maximal in summer, then decreases at the end of the season reaching a reduced level from November onwards. During spring and early autumn, we measured an intense passage activity. This was considerably reduced in early winter. These seasonal variations of the nycthemeral rhythm of the general locomotor activity were considered in relation to the annual cycle of the plasma thyroxine concentration. Two periods of high hormonal level were observed: in spring and late summer‐early autumn. The lowest thyroxine concentrations were measured at the end of autumn and winter. Hence, late autumn‐early winter is a period during which in the badger, both thyroid activity and general activity are considerably reduced. This state may be called “wintering” during “wintering”, badgers may stay many days in the nest, without food.