Prey detection by the predator remains constant across prey densities: evidence from a field experiment in the Arctic tundra

The functional response describes how predator acquisition rates change with prey availability and integrates behavioural processes that occur during predator–prey encounters. Among these processes, prey detection represents a critical yet often overlooked component that can directly influence population dynamics. Variation in detection probability has been proposed as a mechanism driving prey switching and density‐dependent predation pressure, but it has rarely been quantified in natural systems. We conducted a field experiment in the Arctic tundra focusing on the interaction between Arctic foxes Vulpes lagopus and greater snow geese Anser caerulescens atlanticus . We estimated prey detection probability by the predator using artificial nests deployed at various distances (10–120 m) over three years with contrasted prey densities. We then incorporated these distance‐dependent detection probabilities into a mechanistic functional response model to assess how interannual variation in detection probability may influence predator acquisition rates and prey survival. As expected, nest detection probability by foxes decreased as distance increased. More importantly, we found that this relationship remained consistent across years, despite substantial interannual variation in both goose nest and lemming densities, the main prey of Arctic foxes in the study area. Our results suggest that nest detection probability is not modulated by prey density and is unlikely to drive interannual changes in tundra bird nesting success. By combining field experiments with mechanistic modelling, we provide a rare empirical demonstration of how a specific behavioural component can be quantified and integrated into functional response theory. This approach offers a powerful framework to identify the proximate behavioural drivers underlying predator–prey interaction strength in natural systems.