Birds reveal a link between gut microbiome and fitness

Just like humans, birds also host a blend of microorganisms – both friendly and harmful – that make up their microbiome. This “little world” within living organisms plays a vital role in overall health, and it seems that the diversity of microbes is a key factor in the way the microbiome affects each individual.

If you want to fuel your immune system and absorb nutrients more efficiently, you need a rainbow of different microbes in your gut. Conversely, low diversity could leave you susceptible to illnesses.

This relationship between microbiome diversity and health has intrigued researchers for years.

To understand this link better, scientists from Florida Atlantic University’s Charles E. Schmidt College of Science embarked on a five-year study.

The researchers examined how songbird gut microbiomes relate to traits that indicate health and breeding success. While laboratory studies have explored gut microbiome connections in captive animals, knowledge about these relationships in wild animals – particularly birds – remains limited.

Bird health is tied to microbiome

The researchers focused on the Northern cardinal (Cardinalis cardinalis), a common backyard bird known for its vivid red plumage, red beak, and black mask. This study provides the first-ever description of how a wild bird’s microbiome relates to its ornamentation and body condition.

The results revealed that a cardinal’s gut microbiome diversity can be predicted by its body condition and the quality of its red plumage and beak.

“Our findings confirm the hypothesis that a wild bird’s health is tied to its microbiome, and that the ‘sexiness’ of a male’s ornaments can signal his health,” said Rindy Anderson, Ph.D., senior author and an associate professor in FAU’s Department of Biological Sciences.

Microbiomes and carotenoid pigments

The Northern cardinal’s sexually selected carotenoid pigments provided a unique opportunity for this study.

Carotenoid-based coloration reflects individual quality, making the cardinal’s vibrant red coloration a perfect subject for exploring connections between traits and gut microbiota.

“This study has important applications for conservation biology and contributes to a better understanding of ways to improve animal health in settings such as wildlife hospitals, zoos and aquaria, and captive breeding programs for endangered species,” said Morgan Slevin, first author and a Ph.D. candidate in FAU’s Department of Biological Sciences.

Observing Northern cardinals

To investigate these relationships, the researchers sampled the cloacal microbiomes of wild cardinals.

The team measured the birds’ body condition index, assessed the coloration of their sexual ornaments (beak and plumage), and collected blood to estimate their glucocorticoid response to stress.

This approach helped the researchers to describe the baseline relationships between various aspects of the microbiota-gut-brain axis in free-living songbirds.

“Overall, cardinal ornament redness and saturation positively correlate with individual quality,” said Slevin. “Thus, deeper red coloration indicates greater carotenoid pigmentation. We were able to show that a cardinal’s coloration related to its microbiome diversity.”

Microbiome structures of birds

The study revealed several important connections: Both alpha and beta bacterial diversity were related to individual variation in body condition and sexual ornaments.

Beak saturation related to beta diversity, suggesting birds with similar beak coloration profiles had more similar microbiome structures.

Furthermore, the team found that glucocorticoid concentrations did not correlate with microbiome diversity or ornamentation quality.

“While we anticipated that birds with the most saturated beaks would be the highest quality individuals, and that the highest quality individuals would have the most diverse microbiomes, our results suggest that maintaining a diverse microbiome might instead come at a cost to beak saturation,” said Slevin.

Implications and future research

These findings highlight the intricate relationships between gut microbiomes, physical traits, and overall health in wild songbirds. They add to a growing body of research linking avian host fitness to internal bacterial community characteristics.

“Ultimately, our study and those that follow should move us closer to answering the overall question of whether a bird’s gut microbiome can predict individual quality,” said Anderson.

The research not only deepens our understanding of microbiome diversity in wild birds but also provides insights that could inform conservation efforts and animal health management.

By continuing to explore these connections, scientists aim to unlock more secrets about how microbiomes influence the health and survival of living organisms.

In the end, understanding these microbial relationships may hold the key to promoting healthier ecosystems and wildlife populations.

The study is published in the journal Oikos.

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