Picture a morning at the end of March, exams are looming, stubborn snow is still lingering, but suddenly birdsong, the signal that summer is on its way. Migratory birds bring not only messages of spring, but also pathogens. The transfer of zoonotic diseases (diseases that can be transmitted from animals to humans) is something that we have all become increasingly aware of since the beginning of the COVID-19 pandemic. Since the pandemic, there has been increased public interest in pathogen transmission research, and understanding how pathogen infection affects host behavior and ecology is the first step.
Dr. Tosha Kelly, a researcher that studies host-pathogen interactions in bird species, says “Our understanding of how the physiological systems of wildlife and pathogens interact, and how these interactions scale up to affect host ecology is complex and poorly understood.” A research study that she conducted, investigating how avian malaria infection alters the migration behavior of the white-throated sparrow, explored a new facet of these complex interactions.
Migration behavior is fascinating to study under the lens of pathogen transmission because of the diverse and complicated ways they interact. The obvious interaction being that travelling individuals are exposed to a large geographical range, increasing pathogen spread. However migratory behaviors also present the opportunity to reduce the spread of pathogen infection. Individuals that cannot make the migration journey are quarantined from those that can.
But how do we study the birds that have been exposed to a pathogen but do not develop infections, the resistant birds? Dr. Kelly and their colleague’s experiment set out to understand this phenomenon in the lab by experimentally inoculating the white-throated sparrows. This allowed her and her team to know not only when the birds became infected, but also how many parasites they were exposed to. Meaning that she could directly identify the resistant birds, as well as understand what parts of their migration journey were impacted.
To study migratory behavior in captivity, Dr. Kelly and her team measured a phenomenon called zugunruhe, a German word meaning ‘migratory restlessness.’ This is a form of anxious behavior demonstrated by birds aware that it is time to migrate. What they found was that zugunruhe decreased earlier in the resistant birds than it did in the infected birds. Meaning that the costs associated with fighting off a pathogen infection affect a bird’s ability to complete its migration journey.
Dr. Kelly investigated how the cost of fighting pathogen infection affects migration, but as she said in her article, “how migrations affects disease spread depends fundamentally on how disease affects migration.” The effect of host behavior and environment on pathogen transmission is a two-way street and one cannot be fully understood without considering the other. The exciting thing about studying how host ecology is interrelated to pathogen transmission is that there are so many different environmental and behavioral factors that can be considered.
Sackville, NB is a popular stopover point for migratory birds, and there are lots of different factors about its environment that could impact pathogen transmission. Beth Macdonald, a researcher and lab instructor at Mt. A who has conducted research on semipalmated sandpipers in the area, said, “the life of a bird is an energetically expensive one, and any extra stressor is a big deal.” The stress of migration is something that is interrelated with pathogen infection, but there are many other stressors within even the Sackville environment whose impact on pathogen susceptibility could be studied.
Researchers at Mt. A are often investigating stressors within the environment. One of these researchers is Erin MacMillan, a MSc student studying microplastics in shorebird environments. Microplastics are another potential stressor like the stress of migration that could be viewed under the lens of pathogen transmission. “It is in the best interest of all scientists to work together and push knowledge forward,” said MacMillan. It is this attitude that will bring scientists studying different environmental factors together to advance the understanding of the interactions of host ecology and pathogen transmission.
