Bacteria on eggs reveal bird nesting habits in wetlands

The study compared bacterial levels and types on eggs from birds that build wet nests versus those that build dry nests in wetland areas. They used two main methods: traditional bacterial culture, which involves growing bacteria in a lab, and a more advanced genetic technique called automated ribosomal intergenic spacer analysis (ARISA). ARISA identifies bacteria based on their unique genetic fingerprints, allowing for a broader assessment of the bacterial community than culture methods alone.

The results showed a striking difference in bacterial abundance. Eggs from wet-nesting birds had significantly more bacteria – several orders of magnitude more – than those from dry-nesting birds. This makes sense, as moist environments naturally encourage bacterial proliferation. More importantly, the types of bacteria found tended to group based on the nesting strategy. This suggests that the way a bird builds its nest plays a significant role in shaping the bacterial community on its eggs.

This study builds upon previous work demonstrating the dynamic nature of bacterial communities in birds throughout their lives^[2]. That earlier research on black-legged kittiwakes showed that chicks have a wider variety of bacterial types than adults, with the bacterial community becoming more stable as the bird ages. This suggests that young birds are actively acquiring bacteria from their environment, and that the adult bacterial community represents a more refined and established state. The current study extends this understanding to the earliest stages of life, showing that nesting strategy may be a key factor influencing initial bacterial colonization.

Furthermore, the importance of bacterial infections in wild bird mortality is well-documented^[3][4]. Research has identified various pathogens, including Campylobacter species, that can be carried by wild birds and cause disease. While the current study didn’t specifically focus on pathogens, the high bacterial loads found on wet-nesting eggs raise the possibility of increased infection risk. The research on Greater white-fronted geese, which identified Neisseria and other bacteria as causes of embryo mortality, highlights the potential for eggshell-associated bacteria to directly impact embryonic development.

The findings of suggest a link between nesting strategy and eggshell-associated bacteria, but the researchers acknowledge that more work is needed to confirm this. Future studies should include more comprehensive sampling and advanced genetic approaches to fully understand the source and function of these bacteria. Investigating whether wet-nesting birds have developed specific adaptations to manage the higher bacterial loads, such as antimicrobial properties in their eggshells, could also be a promising area of research.