Stressed out? Every year migratory birds battle stress, and win
Laura Nielsen for Frontier Scientists –
On the tundra a wire walk-in trap has been placed over seed scattered atop icy Alaskan ground. A Longspur alights nearby. It twists its head to eye the seed, hops inside then briefly flaps – unsettled by the trap door closing behind it. The Longspur settles and eyes the ground again, beginning to peck. PhD student Jesse Krause, a researcher from the University of California Davis' Birds and Seasonality project, dashes forward to start a carefully-timed testing process.
"The lab I’m in is very interested in hormonal regulation of physiology, so we do a lot of stress physiology, capturing birds and doing a standardized restraint handling procedure to understand their stress response and how they are able to cope with unpredictable events such as early spring storms." ~Krause
Captured birds are measured for size and weight, and their more distinctive markings are photographed. The scientists will sample some of each bird’s blood – they take no more than 1% of the bird’s body mass, roughly 250 microliters.
By puffing air at each bird’s underbelly, the researchers can glimpse skin beyond the feathers. Birds’ skin is transparent. Through the skin you can see stores of fat that provide important energy for long flights. You can also spot pools of lipid resting against muscle, waiting to help provide energy for muscle contraction.
Birds like the Smith’s Longspurs, Lapland Longspurs or White Crowned Sparrows which migrate to the Arctic to breed must get a lot done during summer's short reign. They enter on the heels of icy spring storms, and have only about 4-5 weeks' time to breed, nest, lay eggs and raise chicks on the summer insect population before they molt and depart again for the migration back to more southerly wintering grounds.
How do the tiny songbirds manage? 'Team Bird' Birds and Seasonality project scientists are looking into a fascinating phenomenon. These migratory birds change their stress response in order to cope with Arctic challenges.
The songbirds migrate to an environment that is very unpredictable. Unfortunately, being stressed out uses energy. As Dr. John Wingfield, professor of Neurobiology, Physiology and Behavior at the University of California Davis explains, stress responses in birds are like those that occur in humans.
"The interesting thing is: the hormonal responses to general stress are the same throughout the vertebrates. The same hormones are involved in fish, in frogs, in reptiles, in birds, and mammals included ourselves. And as far as we know, these birds are one of the few vertebrates so far [observed to], in some cases, turn off their stress responses completely." ~John Wingfield
The scientists are looking at a class of chemicals known as corticosteroids. Examples of corticosteroids include corticosterone, cortisone, and cortisol – each of which impact stress responses. Members of Team Bird comment on stress hormones:
Jesse Krause, University of California Davis PhD student, explains corticosterone.
Corticosterone is the “Stress” hormone in birds which is basically the same as cortisol in humans. So it is a slightly different structure: they are both derived from cholesterol but they both perform the exact same function in that they help regulate glucose levels and modulate the immune system." "The cort. can affect 25% of the metabolic processes in the body so it is something that has a very broad impact on the body when it is elevated." "It’s part of flight or fight response that when you're scared the first thing that is released is efrenefren from your adrenal gland and that makes your eyes dilate and your heart start beating faster. Then you also release cort. later on, it starts at 3 minutes, so you can start controlling some of the metabolic processes, prepare the body for possible injury, so: modifying the immune response." "You could [then] look at peak cort. levels that occur at 30 and 60 minutes." ~Krause
Adjunct professor Marilyn Romanovsky, from the department of Neural Biology, Physiology and Behavior at the University of California, Davis, talks about energy demand.
"Corticosterone gives us a ... measure of energy demand because these levels tend to go up when the birds are under duress or increased demand for energy to mobilize: fuel or mobilize in terms of activity." ~Marilyn Romanovsky
Birds with high stress levels use more resources ... and are more likely to abandon a nest if an icy spring storm threatens their own safety. Birds with too strong of a flight response wouldn't thrive throughout unpredictable Arctic breeding seasons. So it appears that something had to change.
Arctic breeders alter stress levels
"We were interested in how the stress response was being modulated. And so in these birds when they arrive in the Arctic they have this really high stress response. You can say it is very active, it is almost hyperactive in a way, compared to other times of year. So they have this high stress response and the thought is: it allows them to respond to, you know, these spring snow storms, possible predation, and all sorts of things."
"Once they have those nestlings you see this reduction in the stress response. So for instance during their arrival you may see them peak out at 80 Nano grams a mil. And once they have young they will peak out at 40 Nano grams per mil. So basically the stress response is cut in half. And one reason for that is cort. does promote survival so if you get into a really bad storm, let’s say, and you have nestlings, cort. levels are elevated for too long and that will promote nest abandonment. So the question is what is controlling that reduction in the response that you see during the parental phase." ~Jesse Krause
So the birds somehow dampen their own response to stress. It works against frigid Arctic storms... and against stressors caused by humans.
"We also see this reflected in capturing and handling them. When we capture and handle the birds ... put bands on their legs and take other measurements and so forth, we find actually [that] they are resistant to being handled in terms of the stress response."
"We think this is an adaptation for the birds to arrive in early spring in the Arctic when conditions are very very severe. This allows them to get on with the early stages of nesting, form a pair bond, and actually begin nest building so that the young will actually hatch at a time when there is plenty of food to feed them. Unless they are able to do that, the young would hatch too late in the season to survive.
"And one of the things that we are very interested in is: how they are able to turn off this stress response?" ~Wingfield
Flipping the switch
In order to discover how the migratory birds flip their stress response switch, the scientists have to look deeper.
Dr. Simone Meddle, associate professor at the University of Edinburgh, is a behavior endocrinologist who studies brains.
"Looking at their behavior and understanding how the birds' physiology regulates the behavior, we need to look at the brain." "What we are beginning to understand is not only do these birds not show a response to stress, they are able to change the chemistry, the neurochemistry of the brain. And they do this very quickly when they arrive in the Alaskan tundra."
"We capture birds on their territory, we take measurements from these birds, we take blood samples. And from a very small number of birds, we anethitize them and once they are anethitized with an overdose of anesthetics, then we can remove the brain and then we freeze that very quickly on dry ice." "Then we take it back to the laboratory. We are able to cut ... very thin sections (they are about 20 micro. thick sections) and then using a variety of molecular, cellular molecular techniques, looking at the messenger RNA. Looking for gene expression in the brain. And we are able to use insitu hybridization to find out exactly ... what part of the brain is controlling the stress access. And understand critically how there is an adaptation to breeding in the Arctic." ~Meddle
By looking at super-thin slices of brain, scientists are able to better understand how messages about the stressful habitat are being transmitted and being read. So far their work suggests that when the song birds arrive at their breeding grounds, the receptors in the brain that normally respond strongly to stress hormones become less sensitive. The lessened sensitivity allows the birds to better cope with the tumultuous Arctic spring weather. However, that's still a hypothesis; the scientists have more testing to do before they can say for certain how the birds manage the feat. They'll keep at it.
"If we are able to understand how these birds switch off access at the level of the brain, maybe this has implications for us humans. Because it would be great if we could understand how these birds are able to do it." "For humans living in stressful environments if we could switch off our stress access, that would be quite useful." ~Meddle
In the end, the diverse organisms of our astounding planet have a lot to teach us. And science opens the door.
"You’ll find out that trying to understand stress is an incredibly complicated thing." "I think in any field the more you know, the more you realize you don’t know. So yeah. That’s science for you." ~Krause
After undergoing testing, some of the captured songbirds are fit with radio transmitters. The transmitter, a tiny 3 centimeter backpack that weighs no more than 3% of the bird’s body weight, is placed carefully so it will not interfere with wing motion. After roughly 40 days the backpacks will fall off, but before then the researchers will use the data they transmit to track the birds and discover when they depart for the long migration back to wintering grounds. A more permanent way of keeping track of birds is to fit them with bands, minuscule colored anklets that help researchers recognize the birds which return to the same breeding grounds year after year.
With the samples they’ve obtained, the team gains information that can be inferred to the larger population of similar Arctic-breeding songbirds that wing their long flights North and South and North again on the winds of a rapidly changing planet.
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
- FrontierScientists interviews with the quoted scientists during their 2013 research season at Toolik Field Station
- 'Arctic & Alpine, 2010 Report on Climate Change' The State of the Birds (2010)
- 'Birds' Gates Of The Arctic National Park & Preserve, Alaska (April 6, 2014)
- 'Climate Change and its Impacts' U.S. Fish & Wildlife Service, Arctic National wildlife Refuge, Alaska (December 29, 2009)
- 'Measuring and Forecasting the Response of Alaska’s Terrestrial Ecosystem to a Warming Climate' U.S. Geological Survey Fact Sheet, by John Pearce, Tony DeGange, Paul Flint, Tom Fondell, David Gustine, Leslie Holland-Bartels, Andrew Hope, Jerry Hupp, Josh Koch, Joel Schmutz, Sandra Talbot, David Ward, and Mary Whalen (December 26, 2012)
- 'Shifting Skies: Migratory Birds in a Warming World' Doug Inkley, National Wildlife Federation (June 18, 2013)
- 'Understanding the Science of Climate Change: Talking Points – Impacts to Alaska Boreal and Arctic' Natural Resource Report, National Park Service, U.S. Department of the Interior (July 2010)