Activity patterns activity patterns in the mole-rats Tachyoryctes Splendens and Heliophobius argenteocinereus

Activity in two unrelated genera of molerats, <i>Tachyoryctes and Heiiophobius</i>, was studied in the field by recording the movements of animals tagged with radioactive wire. <i>Tachyoryctes</i> shows a single marked activity peak and only leaves its nest between 10.00 and 19.00 hour. <i>Heliophobills</i> shows a more dispersed and prolonged activity pattern although peak activity occurs over approximately the same period as in <i>Tachyoryctes. Heilophoblus</i> spends over 50 % of the day out of its nest, <i>Tachyoryctes</i>, under 25%. These differences can be attributed to a different function of the nest in the two genera (Tachyoryctes has a multipurpose nest; Heiiophoblus uses its nest solely for rest), and also to the fact that <i>Tachyoryctes</i> has light-sensitive eyes whereas <i>Heiiophoblus</i> appears unable to appreciate light; Tachyoryctes periodically comes to the surface to forage and this exposure to light may trigger the 24-hour activity cycle