Visual cues modulate nest defense behavior in Japanese Tits: Insights from the appearance, posture and size of snake dummies

Predator dummies are usually used to explore the impact of predator features on the anti-predator behavior of birds. Previous studies have shown that the morphology and behavior of aerial predators can signal different threat levels to birds. However, whether subtle changes in ground predator dummies cause changes in the nest defense behavior of parent birds is unclear. In this study, we aimed to investigate whether Japanese Tits (Parus minor) exhibit different nest defense behaviors in response to experimentally manipulated variations in the appearance, posture, and size of virtual snake proxies (common nest predators). During the incubation period, we observed the nest defense behaviors of the parent tits against taxidermized Siberian Ratsnakes (Elaphe schrenckii) with varied characteristics and rubber-made model snakes. The tits exhibited more intense responses to taxidermized large (body length about 120 cm) coiled ratsnakes than to large coiled model snakes. They exhibited weaker responses to taxidermized small (body length about 20 cm) coiled ratsnakes than to taxidermized small sinusoidal ratsnakes. In addition, they exhibited more intense responses to taxidermized large coiled ratsnakes than to taxidermized small coiled ratsnakes, and more intense responses to taxidermized small sinusoidal ratsnakes than to large model snakes. However, there was no difference in the response of tits to taxidermized small sinusoidal ratsnakes and taxidermized large coiled ratsnakes, or to taxidermized small coiled ratsnakes and model snakes. Thus, the presence of scales, a sinusoidal posture, and a large body size of snake dummies can induce more intense behavioral responses in Japanese Tits. We suggested that Japanese Tits can discriminate subtle differences in ground predator dummies of nests and exhibit different nest defense behaviors.