Researchers dedicated five years to investigating the gut microbiomes of Northern cardinals, a familiar backyard songbird recognized for its striking red feathers. This research delves into how the diversity of microbiomes affects the birds’ health, physical condition, and even their decorative features, like color. It marks the first comprehensive investigation into how gut microbiomes impact fitness-related traits in wild birds, filling a notable gap in previous research that largely focused on captive species.
Every living organism is home to microbiomes made up of both helpful and harmful microbes that can affect overall health. The diversity within a microbiome plays a crucial role in host fitness: lower diversity may result in immune problems and decreased nutrient absorption, while higher diversity can enhance resilience against stress and diseases.
To shed light on this topic, a team of researchers from Florida Atlantic University’s Charles E. Schmidt College of Science has been investigating how the gut microbiomes of songbirds relate to traits tied to health and reproductive success. Although previous studies in laboratories with captive animals have identified links between gut microbiomes and various traits, there is limited knowledge about these connections in wild animals and specifically in birds.
Focusing on the widely recognized Northern cardinal (Cardinalis cardinalis), this new study offers the first insights into how a wild bird’s microbiome correlates with its physical features and health status. This beautiful songbird, famous for its bright red feathers, also has distinctive characteristics like a red beak and a black facial mask.
Findings from the study, published in the journal Oikos, indicate that the diversity of a cardinal’s gut microbiome is linked to its physical condition and the quality of its ornamental features—red feathers and beak.
“Our results support the idea that a wild bird’s health is connected to its microbiome, and that a male bird’s attractive traits can indicate its overall health,” stated Rindy Anderson, Ph.D., the senior author and an associate professor at FAU’s Department of Biological Sciences.
This species, which boasts carotenoid pigments chosen through sexual selection, provides a unique opportunity to investigate how these traits are associated with gut microbiota. The vivid coloration of the cardinals serves as a well-recognized example of how carotenoid pigments can signal an individual’s quality.
“The insights gained from this study are valuable for conservation biology and offer a greater understanding of strategies to enhance animal health in contexts like wildlife rehabilitation, zoos, aquaria, and captive breeding for endangered species,” remarked Morgan Slevin, the lead author and a Ph.D. candidate within FAU’s Department of Biological Sciences.
To study the interplay between microbiota and host fitness, researchers collected samples of the cloacal microbiomes from wild cardinals and assessed their body condition index, examined the coloration of their ornamental features (beak and plumage), and took blood samples to evaluate the glucocorticoid response to stress. They aimed to comprehend the microbiota-gut-brain connection in free-living songbirds and documented the foundational relationships, or lack thereof, among various aspects of this system in wild cardinals.
“In general, the redness and saturation of cardinal ornaments positively correlate with individual quality,” commented Slevin. “Therefore, a deeper red hue suggests a higher level of carotenoid pigmentation. We demonstrated that a cardinal’s color is related to its microbiome diversity.”
Both alpha and beta bacterial diversity were linked to individual variations in body condition and several sexual ornaments, but not to glucocorticoid levels. Notably, the saturation of the beak was also associated with beta diversity, suggesting that birds with similar beak coloring profiles possessed similar microbiome structures.
“While we expected that the birds with the most saturated beaks would be the highest quality individuals and that these individuals would have the most diverse microbiomes, our findings indicate that maintaining a diverse microbiome might come at the expense of beak saturation,” Slevin added.
Research from a free-living songbird population contributes to a growing body of evidence linking the fitness of avian hosts to their internal bacterial communities.
“In the end, our study and future research should help clarify whether a bird’s gut microbiome can indeed predict its individual quality,” concluded Anderson.
