When time is of the essence: Choosing a currency for prey-handling costs

Abstract

1. Heartbeat rate was measured in shore crabs Carcinus maenas (L.) feeding on mussels Mytilus edulis L. in order to estimate the energetic cost of handling prey and to assess the relative importance of energy and time as costing currencies. 2. Energetic handling costs represented approximately 2% of corresponding gains. 3. The tendency of profitability (gain per unit handling time) to increase with prey size was weakened by including energetic handling costs. 4. Time was judged to be a more appropriate currency than energy for costing prey-handling behaviour. 5. The importance of time as a costing currency, either through the principle of lost opportunity or through exposure to mortality risk, may extend to other behavioural systems, including aggression.