Diel Rhythms and Microhabitat Preference of the Newts Triturus vulgaris and T. cristatus at the Northern Border of Their Distribution Area

The diel activity and microhabitat preference of Triturus vulgaris and T. cristatus were studied outdoors in central Norway during summer (adults) and autumn (larvae) using aquaria and photocell equipment. Although aquatic adult newts in high latitudes are generally crepuscular or nocturnal animals, they also exhibit diurnal activity, especially the males. Larvae are normally diurnal, but metamorphosing T. vulgaris larvae showed only slight rhythmic activity. T. cristatus larvae exhibited a phase shift to nocturnal activity in late autumn. The exact time for peak activity during day and night is not only dependent on the 24 h light/dark cycle, but also on the light/temperature conditions throughout the day. Aquatic adults of T. cristatus are mainly bottom living, while adult T. vulgaris spend much of their time in the open water. The larvae show an opposite pattern. This microhabitat specialization probably helps to reduce competition for food, and also reduces cannibalism.