Consumption of lead-contaminated prey by shrews differing in metabolic rate (Sorex araneus and Crocidura gueldenstaedtii).

Shrews are a group of mammals particularly vulnerable to the adverse effects of metals in the soil due to their diet, which primarily consists of soil-dwelling invertebrates. This study experimentally tested whether selected shrew species (the common shrew Sorex araneus and the lesser white-toothed shrew Crocidura gueldenstaedtii) can detect and actively avoid contaminated food (hypothesis H1). The animals were subjected to a cafeteria test, allowing them to forage freely for two hours in an experimental terrarium where they could choose among four types of live prey: lead-free earthworms, lead-free mealworm larvae, lead-contaminated earthworms, and lead-contaminated mealworm larvae. All trials were recorded using a digital camera. The study also compared food preferences between S. araneus and C. gueldenstaedtii, hypothesizing that (H2) S. araneus, with a faster metabolism and higher food requirements, would be less selective in prey type. The results suggest the rejection of H1, as shrews showed no significant differences in their responses to lead-contaminated versus uncontaminated prey. In line with H2, common shrews consumed four prey types, exhibiting less selective foraging compared to lesser white-toothed shrews, which restricted their intake to only two of the available prey types. This study indicates that shrews did not avoid prey containing lead, likely due to sensory detection limitations and their high metabolic demands, which prioritize immediate energy intake over the avoidance of cryptic, sublethal toxins.