Torpor may facilitate opportunistic predation of live-trapped small mammals: a cautionary note

Résumé

Small mammals are often key components in ecological monitoring programs, and live trapping is often used to obtain small mammal density estimates or other metrics. However, an aspect of such trapping that has received little attention is opportunistic predation of captured animals. Here, we report a Common Raven (Corvus corax) preying on a deermouse (Peromyscus spp.) after it was released from a live trap. The mouse was torpid when removed from the trap. The raven preyed on the deermouse right after it was released, likely because the mouse had not yet fully aroused from torpor and was not able to find adequate shelter or evade the raven. Best practices to avoid similar occurrences include passively warming the animal before releasing it or returning it to the trap to arouse from torpor in safety. Our observation further highlights the need for researchers to be vigilant about opportunistic predation of small mammals captured and released from live traps and to take actions to mitigate the risk, especially if the mammals are exhibiting signs of torpor.