Blue-winged Teals Migrate by Suppressing the Response of Stress Hormones
Bird migration is an extraordinary feat. It often means summer in the north and winter in the south, but for the majority, when and how this journey takes place does not seem to depend on environmental conditions. If seasonal changes alone cannot account for migratory patterns, what does?
Professor of Biology and Environmental Studies Morgan Wilson looked at the blood levels of corticosterone, a stress hormone, in the Blue-winged Teal waterfowl species. These birds travel even when local weather conditions are favorable.
Not surprisingly, migration is a difficult process. In order to do it, most songbirds seem to have figured out a way to suppress a full stress response. In other words, while these birds cannot control when corticosterone levels will rise, they can quickly maintain the effect. Ornithologists reasoned this out by comparing corticosterone levels in migrating birds to that of non-migrating birds.
Wilson predicts something similar is happening for the Blue-winged Teal. Coming up with an explanation requires only a good idea; testing the idea requires cooperation from jumpy birds. The birds have to be caught before making the measurement, which is done by taking several blood samples from the same bird over a period of 60 minutes. Wilson and his colleagues spent more than 500 hours waiting, trapping, and measuring the waterfowls.
It’s a stressful experience. Immediate afterward, each bird’s corticosterone levels will rise. In migrating birds, Wilson and his colleagues found that this is quickly maintained within 15 minutes of the initial spike. On the other hand, non-migrating birds experience a complete stress response.
One explanation for the ability to dampen the effects of corticosterone during migration is energy conservation. Rising corticosterone taps into fat and other valuable reservoirs. While migrating, birds need to quickly counter these natural responses in order to save their resources, and therefore themselves, for the long haul.
While the ability to suppress a full stress response is correlated to the migration patterns of some bird species, what causes them to leave wintering grounds is another question. Eventually, Wilson hopes to make the migration himself to Venezuela.