Improving accuracy of artificial nest predation studies using bird scent: The case of <i>Tetrao urogallus</i> (Western Capercaillie)

Abstract Predation is a key ecological factor influencing prey populations, and for ground-nesting birds, nest predation is a critical determinant of reproductive success. Investigating nest predation in cryptic species poses unique challenges because their nests are difficult to locate, and monitoring efforts can cause disturbances or even increase predation risk. Artificial nests are commonly used to study nest predation. However, this method often fails to accurately replicate real nest predation dynamics, particularly for cryptic species. In this study, we compared the predation rates of real nests of the Tetrao urogallus (Western Capercaillie) with artificial nests monitored using camera traps, both with and without the application of bird scent derived from capercaillie uropygial gland secretions. The results showed that artificial nests treated with bird scent exhibited a predation rate of 52.2%, closely matching the rate observed in real nests (51.4%). In contrast, artificial nests without scent significantly underestimated predation, with a rate of only 6.3%. Martens (Martes martes and M. foina) and red foxes (Vulpes vulpes) were identified as the primary nest predators, with 38–56% of predated nests by these species across treatments, preying similarly toward both real and scented artificial nests. These findings highlight that incorporating bird scent into artificial nest studies significantly improves the accuracy of predation rate estimates. We recommend the widespread adoption of this method in nest predation research to better replicate natural conditions, minimize biases related to scent-dependent predators, and enhance the reliability of nest predation assessments.