Rhodamine-B-marked eggs identify individual predators of artificial nests

Investigations of nest predation are often limited by the researchers’ inability to identify nest predators accurately. I tested a chemical bait marker, Rhodamine B (RB), as an indicator of egg predation at artificial ground nests. In a pen trial, the presence of characteristic fluorescent bands in one or more facial vibrissae from all treatment animals confirmed the suitability of RB as a bait marker in the introduced European hedgehog (Erinaceus europaeus). In a field trial in which artificial ground nests were baited with RB-dosed eggs, five of 21 trapped hedgehogs showed evidence of RB ingestion. One animal showed markings indicating two temporally separate predation events. This ability to identify nest predators to species, demographic class, or individual level could lead to more focused control programmes. Other potential uses of this technique include investigation of individual foraging behaviour, calibration of predation rates in artificial nest studies, estimation of the efficacy of poisoned eggs as a control method, and testing for bait or poison uptake by non-target species.