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.

Social animals often form dynamic relationships with group members, which have been associated with increased social learning, survival and reproductive success. Social relationships can be shaped by both group and individual factors; however, few studies have addressed their combined impact. In this study, we aimed to examine whether group factors and individual factors jointly affect social relations. We selected Budgerigars (Melopsittacus undulatus) as the focal species to investigate the influence of sex, personality, and body length as well as sex ratio and group size on social relationships. The results showed that the birds in 3-individual groups had higher aggression network weighted degree values than those in 5-individual groups. Individuals within opposite-sex groups showed higher levels of aggressive and affiliative interactions than those in same-sex groups. Additionally, females attained higher social ranks despite exhibiting significantly lower aggression behaviors than males. Individuals with longer body lengths exhibited higher aggression network weighted degree values. Our results suggest that group factors primarily influence the social networks, while individual factors play important roles in shaping the social relationships.

Individuals may gather information about environmental conditions when deciding where to breed in order to maximize their lifetime fitness. They can obtain social information by observing conspecifics and heterospecifics with similar ecological needs. Many studies have shown that birds can rely on social information to select their nest sites. The location of active nests and the reproductive success of conspecifics and heterospecifics can provide accurate predictions about the quality of the breeding habitat. Some short-lived species can facultatively reproduce two and/or more times within a breeding season. However, few studies have focused on how multiple-brooding individuals select nest sites for their second breeding attempts. In this study, we use long-term data to test whether the Japanese Tit (Parus minor) can use social information from conspecifics and/or heterospecifics (the Eurasian Nuthatch Sitta europaea, the Daurian Redstart Phoenicurus auroreus and the Yellow-rumped Flycatcher Ficedula zanthopygia) to select a nest site for the second breeding attempt. Our results showed that the nest boxes occupied by tits on their second breeding attempt tended to be surrounded by more breeding conspecific nests, successful first nests of conspecifics, and fewer failed first nests of conspecifics than the nest boxes that remained unoccupied (the control group). However, the numbers of breeding heterospecific nests, successful heterospecific nests, and failed heterospecific nests did not differ between the nest boxes occupied by tits on their second breeding attempt and the unoccupied nest boxes. Furthermore, the tits with local successful breeding experience tended to choose areas with more successful first nests of conspecifics than those without successful breeding experience. Thus, we suggest that conspecifics' but not heterospecifics’ social information within the same breeding season is the major factor influencing the nest site selection of Japanese Tits during second breeding attempts.

The reproductive behaviors of birds are mainly controlled by the hypothalamus-pituitary-gonad axis. Many studies have shown that reproductive hormones are tightly linked to the breeding sub-stages. However, only a few studies have examined the temporal trend of hormone levels among different reproductive stages in multiple brooded species. We investigated the changes in plasma luteinizing hormone (LH) and prolactin (PRL) concentrations during different reproductive stages of the facultative double-brooded Great Tit (Parus major). We found that the concentrations of LH and PRL in females were significantly higher than those in males. Females had significantly higher LH and lower PRL concentrations in the pre-breeding period than in the first/second brooding periods, and there were no significant changes between the first and second brooding periods. The concentrations of LH and PRL in males had no significant difference between the pre-breeding period and the first brooding periods, while LH and PRL concentrations in the second brooding period were significantly higher than those in the first brooding period. We conclude that there are sex-based differences between LH and PRL at different stages of reproduction. The changes in LH and PRL in both males and females should be related to their physiological functions. Especially for males, individuals with higher levels of LH and PRL are more likely to maintain second clutches.