Prenatal exposure to stress hormone could impact bluebird immune function
ATHENS — Many studies have shown that prenatal stress in mothers can be linked to adverse outcomes in the physical, emotional, cognitive and behavioral wellbeing of children. Now a study at the University of Georgia is examining how pre-hatch exposure to the stress-associated hormone corticosterone influences immune function in baby bluebirds.
Taylor Miller, a doctoral student in the Department of Poultry Science at the College of Agricultural and Environmental Sciences, has been monitoring more than 50 bluebird boxes at the UGA Golf Course and more than 40 boxes in other locations on and around UGA’s Athens campus to test the immune response of newly hatched birds to corticosterone.
Corticosterone is the major adrenal stress hormone produced by bluebirds and is an important stress-induced modulator of several physiological functions in birds, similar to the function of cortisol, the main stress hormone in humans, Miller said.
As in other egg-laying species, bluebird mothers are exposed to stress from factors ranging from the availability of food to the influence of humans on their ecosystems. An increase of corticosterone in the mother correlates to an increase of the hormone in the eggs she lays.
This is similar to the phenomenon of bluebirds producing more testosterone when there is greater competition for nesting sites and resources, Miller explained. If a mother bird is in an environment where other birds often intrude into her territory, that mother bird will produce more testosterone. This testosterone is then deposited in the eggs she lays, making the offspring larger and more aggressive, helping them to grow up to defend their own territory more effectively.
Miller is seeking to determine how prenatal corticosterone exposure due to stress in the mother impacts the offspring.
“It is important to emphasize the volatile nature of the environment around the world today as environmental change happens,” she said. “It is important to know how stressed these birds are, what they are having to overcome, how they are being affected and how their offspring are being affected.”
Baby birds are naturally exposed to pathogens and parasites as nestlings, and anthropogenic factors — the encroachment of humans on
wild habitats — are also contributing to disease in animals.
“All nestlings have innate immunity, that is the first line of defense,” Miller said. “We want to know how prenatal corticosterone exposure impacts the immune response.”
To test how increased corticosterone may affect the birds’ offspring, Miller monitors the bluebird boxes daily, searching for newly laid eggs. She injects some of the eggs in each nest with
corticosterone, while other eggs are injected with a control solution that does not include corticosterone.
Bluebirds are an ideal species for the study because they are cavity-nesting species — they will nest in boxes researchers place in the territories where they live and can have several nestings, laying two to three clutches of eggs between early spring and the end of the breeding period in mid to late summer, Miller said.