hibernating or sleeping during daylight
• (n.) Continuance during the day. • (n.) The condition of sleeping or becoming dormant by day, as is the case of the bats.
Di`ur·na'tion noun 1. Continuance during the day. [ Obsolete] 2. (Zoology) The condition of sleeping or becoming dormant by day, as is the case of the bats. 
diurnation The habit of some animals, of sleeping, being dormant, or remaining quiescent during the day, as contrasted with their activities at night.