Torpor During Reproduction in Mammals and Birds: Balancing Energy Expenditure for Survival

Torpor and reproduction in mammals and birds are widely viewed as mutually exclusive processes because of opposing energetic and hormonal demands. However, the number of species that express torpor during reproduction is ever increasing, to some extent because of increased recent work on free-ranging animals. We summarise current knowledge about those birds and mammals that do use torpor during reproduction. We conclude that use of torpor during times when animals are reproducing are related to energetic constraints placed upon them from less predictable environmental conditions.