Studying invasive species by non-invasive methods: Real-time qPCR successfully detects protected vertebrate species in raccoon scats

Abstract Invasive alien species pose a major threat to biodiversity, particularly through predation on rare and endangered species. In Europe, studies on the impacts of invasive mammalian predators such as raccoons remain scarce, and existing diet analysis methods often fail to detect such predation events. This study therefore evaluates the suitability of real-time quantitative PCR (qPCR) as a sensitive method for detecting predation on rare species. Faecal samples from a feeding trial with two captive raccoons, as well as from free-ranging individuals in central Germany (2021–2023), were analyzed. In the feeding trial, a reference bird species ( Gallus gallus domesticus ) and an amphibian ( Pelophylax ridibundus ) were provided. Additionally, marker systems for seven bird and amphibian species were applied to field samples. DNA of both reference species was detected, although P. ridibundus showed delayed and less consistent detection compared to G. gallus domesticus . In field samples, DNA of three target species ( Anas strepera , Triturus cristatus , Bufo bufo ) was detected in five out of 52 samples. These results demonstrate that qPCR can detect predation events on rare species, although actual predation rates are likely underestimated. The method represents a valuable targeted tool but requires further validation for improved interpretation.