Light and Bird Poop

by Madeline Choi

When you drive into a heavily populated area, like a city, what do you notice? Do you see all the buildings and people that live there? What about at night, with the bright lights illuminating the city? What you are noticing is a phenomenon called urbanization (process through which cities grow), and urbanization is an anthropogenic (human-caused) consequence. I am a microbiologist, which means that I study things that we cannot see with our naked eye. Specifically, I take a fond interest to bacteria, or what we know as “germs.” However, not all bacteria are bad! There are millions of bacteria that live in your gastrointestinal tract right now that help aid in digestion, help keep “bad” bacteria out (prevent infection), and it has also been recently found that the bacteria within your gut actually communicate with your brain (and your brain also communicates with your gut bacteria). The bacteria within your gastrointestinal tract are formally called the “gut microbiota,” and the complex interactions between your gut bacteria and your brain is called the “gut-brain axis.” My research seeks to understand the impacts of urbanization through the context of light pollution in our model species, the zebra finch. 

Zebra finches are tiny and rather adorable birds native to the dry, arid regions of Australia. They are called “zebra” finches because males have zebra-like stripes on their chest feathers. We use zebra finches as a model because they have been previously used in many studies to study the effects of stress on vertebrates. In my study, I exposed zebra finches to constant light at night, meaning that I kept their lights on for two straight weeks, even at night! They really hated me by the end of the experiment. This constant light at night, or nighttime light exposure, has been found to disrupt circadian rhythms and impact stress levels over time in various species. Obviously, right? Nothing peeves me more than when my husband forgets to turn the hallway light off at night. I wanted to take a different approach -- I wanted to see if there are any effects of this constant light on a molecular level. 

Birds have a cloaca, which is where all excretions occur (poop, pee, and laying eggs). Put simply, I sampled their cloaca (their poop) by using a cotton swab. I put this cotton swab into a tube, and I took it back to the lab. In the lab, I extracted only the bacterial DNA from each sample. Finally, I sent off the DNA to a company so that they could tell me what bacteria is present in my birds’ cloaca at various timepoints in the experiment. The mammalian gut is predominantly composed of two kinds of bacterial families called Bacteroidetes and Firmicutes. It has been found that disruptions in the ratios of these two families can have physiological implications on an organism. Therefore, I predict that the birds that I exposed to constant light at night will have more disrupted ratios of these two bacterial families. In addition to taking cloacal swab samples from my birds, I also took blood samples at various timepoints and mixed that blood into some E. coli, and I measured how well their blood could kill off the E. coli on an agar plate. Blood contains immune components called “complement,” that act in defending against pathogens. So, I predicted that birds exposed to constant light would have decreased immune capabilities, or they would be able to kill off less E. coli cells on an agar plate. 

As if taking blood samples and cloacal swab samples weren’t enough, I also took photos of the birds’ BEAKS! Beak color is a secondary sexual characteristic, which is a trait that is indirectly tied to reproduction. For context, a primary sexual characteristic is a trait that is directly tied to reproduction (e.g., testes in males and ovaries in females). Secondary sexual characteristics arise later in development (e.g., breasts in females and facial hair in males). In birds, secondary sexual characteristics include beak color and elaborate plumage (like the feathers seen in peacocks)! Beak color has been shown to change over time in response to stressors, so I predicted that beak color would be negatively affected in birds that were exposed to constant light at night. Overall, my research attempts to tie the anthropogenic effects of urbanization, specifically light pollution, to physiological effects in avian species. Hopefully, this research will shed “light” on how we as humans can be more aware of our actions on an ecosystem.

Acknowledgement: This research is supported by the National Science Foundation (NSF) and was completed in Dr. Haruka Wada’s stress physiology lab in the Department of Biological Sciences, Auburn University, AL