**9. Bacterial community composition in migratory and nonmigratory birds**

In order to clarify the intestinal bacterial communities among different avian species, those of seagulls, Eurasian wigeon, and barn swallow were compared at their class levels (**Figure 8**). For this research, feces of the European herring gull and Slaty-backed gull were collected in Hokkaido (northern Japan). Slaty-backed gull (*Larus schistisagus*) is a large gull, measuring about 60 cm in length, breeding around northern Japan in the summer season and traveling to the south of mainland Japan and South Korea in the winter season. The global population was estimated to be 25,000–1,000,000 individuals, while the national population was estimated to include >1000 wintering individuals in Japan [43]. The European herring gull (*Larus argentatus*) is a large seagull with a total body length of approximately 60 cm, breeding in eastern Siberia in the summer season and traveling to Japan or to more southern areas in the winter season. These seagulls mainly eat fish, but they also eat crustaceans, insects, and other bird eggs. The global population was estimated to be 2,060,000–2,430,000 individuals, but the population was estimated to be decreasing at a rate of approximately 30% in 39 years [44].

Although the intestinal bacterial community of the Eurasian wigeon was dominated by Clostridia and Bacteroidia, those of the seagulls were dominated by Gammaproteobacteria. **Figure 8** shows the results of PCA, comparing the similarities between the intestinal bacterial communities of the migratory birds with other birds

*Dissemination of Intestinal Microbiota by Migratory Birds across Geographical Borders DOI: http://dx.doi.org/10.5772/intechopen.82707*

### **Figure 8.**

*Principal component analysis of class abundance data from migratory birds and nonmigratory birds.*

registered on the public database. It is highly likely that migratory birds may eat different foods; therefore, differences across individuals were large as compared to those in poultry. However, as compared with other birds, individual intestinal microbiota from the barn swallow was relatively similar. In particular, intestinal bacterial composition from the Eurasian wigeon (□) collected from different seasons (December and April) was found to be highly diversified. The extent of the difference in them surpassed the extent of the difference among other birds. It may be reasonable that each of the intestinal bacterial communities was formed by the food consumed, be it an insect meal, an herbivorous meal, an omnivorous meal, or a carnivorous meal.

### **10. Conclusion**

The use of culture-independent methods for studying wild bird-associated microbial communities could have been shown to be beneficial in the expansion of our current knowledge. The NGS targeting the 16S rRNA gene allows a comprehensive clarification of the bacterial communities, their succession while spending a winter or breeding, and their associated movement with migratory birds. The application of NGS is expected to improve our understanding of the overview of not only bacterial communities but also organisms ingested as part of the diet in wild birds. Narrowing down the target organisms using NGS will enable us to identify unknown pathogens or reveal the potential migration status of known pathogens that have escaped noticed so far due to methodological constraints. In addition, the relationship between intestinal microbial communities and diet of living organisms needs to be studied in greater detail.

Investigation of community composition in parallel with functional investigations (e.g., drug resistance) is expected to improve our understanding of the mechanisms by which multidrug-resistant bacteria spread around the world. Addressing the current implications of birds as potential vectors of antibiotic-resistant bacteria is of great interest. Analysis of the indigenous bacterial flora of migratory birds may highlight the importance of human hygiene and the environmental significance of the transfer of antibiotic-resistant bacteria associated with natural bird migratory patterns. When wild birds act as vectors of diseases, it is important to identify the true source of infectious organisms. NGS, as a culture-independent method,

facilitates further understanding of the complexities and interactions of the genera inherently associated with birds, such as sputum, feces, and feather, as well as of those acquired from the wintering or breeding environment.
