Dynamics of Microbial Communities on Eggshells and on Nest Materials During Incubation in the Oriental Tit (Parus Minor)

Eggshell microbial communities may affect hatching success and nestling’s condition. Nest materials are in direct contact with the eggshells, but the relationships with the eggshell microbiome during incubation have not been fully elucidated. Here, we characterize eggshell and nest-material microbial communities and their changes during incubation in the Oriental Tit (Parus minor). Microbial communities on the nest material were relatively stable and remained distinct from the eggshell communities, and had higher diversity and greater phylogenetic clustering compared to the eggshell communities from the same nest, resulting in lower phylogenetic turnover rate of nest material microbiome during incubation than expected by chance. While the species diversity of both communities did not change during incubation, we found significantly greater changes in the structure of microbial communities on the eggshell than on the nest material. However, eggshell microbiome remained distinct from nest material microbiome, suggesting independent dynamics between the two microbiomes during incubation. We detected an increase in the relative abundance of several bacterial taxa on the eggshell that likely come from the bird’s skin, feathers or cloaca/intestine, which suggests some exchange of bacteria between the incubating bird and the eggshell. Furthermore, incubation appeared to promote the abundance of antibiotic producing taxa on the eggshell, which may hypothetically inhibit growth of many bacteria including pathogenic ones. Our results suggest that the future studies should focus on simultaneous monitoring of absolute abundance as well as relative abundance in communities on eggshells, nest materials and the incubating bird’s body.

Alarm calls evoke a visual search image of a predator in birds

One of the core features of human speech is that words cause listeners to retrieve corresponding visual mental images. However, whether vocalizations similarly evoke mental images in animal communication systems is surprisingly unknown. Japanese tits (Parus minor) produce specific alarm calls when and only when encountering a predatory snake. Here, I show that simply hearing these calls causes tits to become more visually perceptive to objects resembling snakes. During playback of snake-specific alarm calls, tits approach a wooden stick being moved in a snake-like fashion. However, tits do not respond to the same stick when hearing other call types or if the stick’s movement is dissimilar to that of a snake. Thus, before detecting a real snake, tits retrieve its visual image from snake-specific alarm calls and use this to search out snakes. This study provides evidence for a call-evoked visual search image in a nonhuman animal, offering a paradigm to explore the cognitive basis for animal vocal communication in the wild.

Effect of nestlings’ age on parental responses to a predatory snake in Parus minor

Predator-specific alarm calls may have a variety of context-specific functions. Parents of the oriental tit, Parus minor, use the ‘jar’ call in response to the presence of a snake near the nests, and the nestlings respond by escaping the nest cavity. This specific function can be observed only when nestlings are able to fledge. Do tits use the ‘jar’ call only in a situation when nestlings are physically able to jump out of the nest? We measured parental responses to live snake in 8 nests. The use of ‘jar’ call by parents was not modified by the ability of their nestlings to escape out of the nest. This suggests that fledging in response to ‘jar’ call by old nestlings evolved later than the evolutionary emergence of referential snake alarm calls, and that the ancestral function of ‘jar’ call was probably not related to triggering of fledging in old nestlings.