How do you solve a problem like migration?

This post was initially published on the Science Borealis blog on April 27th, 2020. Check out their blog for more great science stories, published every Monday!

An ornithological pedicure: taking a claw clipping from a western bluebird for stable isotope analysis. Photo credit: Catherine Dale.

I can feel the rapid thrumming of the bluebird’s heart against my palm as I carefully manoeuvre its foot into position over a tiny Ziploc bag. I pick up my nail scissors and take a deep breath to steady my hand. I will only get one chance to make sure the miniscule claw clipping lands in the bag. If it doesn’t, I will have no chance of finding it…and no way to discover where this bird spent the winter.

Field biology often requires unusual skills. I have spent the last decade becoming an experienced bird pedicurist, because analyzing the chemical composition of tissues like claws and feathers is one method scientists use to determine the movements of migratory animals.

Unfortunately, this method suffers from the same drawback as many others: a lack of precision. As a result, many aspects of bird migration remain a mystery. But this spring, researchers at the Max Planck Institute of Animal Behaviour in Germany are entering the final testing phase of a new space-based tracking system, which they hope will revolutionize our understanding of animal movement.

The puzzle of migration

For Canadians across the country, the return of our migratory birds marks the beginning of spring. Each year, 2.6 billion birds cross the Canada-U.S. border, heading north to their breeding grounds.

Two thousand years ago, Aristotle believed the spring reappearance of barn swallows meant they were emerging from their winter hibernation at the bottom of ponds. Although we now understand more about animal migration, many questions remain – largely because it’s very difficult to track individual animals as they travel vast distances around the globe.

For many years, the only approach was to mark animals with bands or tags in the hopes of re-sighting them somewhere else. But the sheer number of animals that migrate makes seeing a marked individual again extremely unlikely.

A flock of shorebirds takes to the air at Oak/Plum Lake Important Bird Area, a migration stopover site in Manitoba. The mixed-species flock includes Wilson’s phalaropes, red-necked phalaropes, stilt sandpipers, pectoral sandpipers, dunlin, white-rumped sandpipers, and semipalmated sandpipers. Photo credit: Christian Artuso.

Putting the pieces together

In the 1990s, migration research took a leap forward when scientists realized the chemical composition of animal tissue reflected the place where it was grown. By analyzing the ratio of various isotopes in tissue (termed stable isotope analysis), researchers can roughly reconstruct an animal’s geographic history…which is why I found myself giving bluebird pedicures.

Scientists can also now track moving animals directly by fitting them with tags that record location. These tags can be divided into two broad categories. Archival tags, such as geolocators, record and store movement information. In order to find out where a tagged animal has been, researchers must recapture it and retrieve the tag.

Recapturing migratory animals often proves difficult, especially as many fail to return from migration. So when possible, researchers prefer to use tags that remotely transmit data to a receiver, eliminating the need to recover them.

But transmitting tags face a fundamental constraint: transmitting takes power, and the more power a tag requires, the larger it needs to be. Tags must weigh less than 5% of an animal’s body weight to avoid affecting its behaviour or survival. Considering that many migratory birds weigh less than 10 grams, making tags small enough for them to carry is a huge challenge.

A sanderling carrying a Motus nanotag. The tag’s long antenna is easily visible. Photo credit: Jessica Howell.

The amount of power required to transmit data depends largely on where the receivers are. Tags for ground-based tracking systems – with receivers located on the Earth’s surface – can be very small. For example, the nanotags used by the Motus Wildlife Tracking System range from 0.2 to 2.6 grams, and can even be carried by some large insects. However, the range over which ground-based systems can track individuals is limited. Animals carrying Motus tags can only be detected within approximately 15 km of a receiver.

In contrast, satellite tags send data to receivers on orbiting satellites. They can track movement at a much larger scale than ground-based systems, and have been used for years on big animals, such as seabirds and caribou. But most satellite tags are too heavy for small migratory birds.

The Icarus Initiative

In 2007, Martin Wikelski, the Director of the Max Planck Institute of Animal Behaviour in Germany, proposed a novel space-based system for tracking animals across the globe.

It took more than 10 years, and the cooperation of the Russian Space Agency (Roskosmos) and the German Aerospace Centre (DLR), for the system to become a reality. In March 2020, the International Cooperation for Animal Research Using Space (Icarus) entered its final testing phase. The first Icarus tags are waiting to be shipped to researchers, and the system will be available to the scientific community this fall.

“We wanted to build [a tracking system] specifically for wildlife,” Wikelski says of Icarus. “It’s built by the community, for the community.”

The International Space Station, pictured here in 2009 after a visit by the space shuttle Discovery to add additional solar panels. Photo credit: STS-119 Shuttle Crew and NASA.

Icarus tackles the trade-off between tag size and transmission distance in part by the simple expedient of moving the receiver closer. Conventional satellite tags transmit their data to Argos satellites, which orbit the poles at an altitude of 850 km. Icarus tags will transmit their data to a receiver on the International Space Station (ISS), orbiting at an average altitude of 400 km.

Data collected by Icarus will be stored in Movebank, a free online database accessible by the public.  The system will also incorporate a citizen science initiative: Animal Tracker. While Icarus tags tell scientists where an animal is, citizen scientists can provide information about what it’s doing there. Using the Animal Tracker app, people can follow tagged animals online, and anyone who spots those animals in the wild can submit their observations to the database.

Of course, like any tracking system, Icarus will have some limitations, at least initially. The first tags will weigh five grams, which – while smaller than many satellite tags – is still too heavy for most migratory birds. However, the design of a new generation of tags weighing only one gram is already underway.

Satellite coverage will also be an issue. The receiver on the ISS will be able to pick up signals from most of the Earth’s surface; however, high latitude regions in the north and south will not be covered. Eventually, Wikelski’s goal is to deploy dedicated Icarus satellites strategically to cover the entire globe.

But even with these limitations, scientists are eager to begin harnessing the power of Icarus to tackle some of the unsolved mysteries of migration. Dr. Kevin Fraser, an Assistant Professor in the Department of Biological Sciences at the University of Manitoba, is keenly awaiting his first shipment of tags. He and his graduate students plan to put them on saw-whet owls – and they are most interested in the birds that don’t come back in the spring.

Banding a saw-whet owl. Kevin Fraser’s lab hopes to use Icarus tags to track these small owls during migration. Photo credit: Kevin Fraser.

Fraser’s previous research has largely depended on archival tags, meaning tagged birds must be recaptured to determine where they went. Individuals that don’t return to the study sites to breed – those that die along the way, or the young birds that disperse to breed elsewhere – are lost data.

“Most of what we know about migration, we know from birds that have successfully migrated,” Fraser says. “We know much less about where survival might be limited, or what the juveniles are doing. But [with Icarus], for the first time, we will be able to track 100 gram birds (the smallest yet) in near real-time, without the bias of only focusing on survivors and adults.”

Solving the puzzle

With the sliver of claw safely stowed in a bag for later analysis, I’m ready to liberate my captive bluebird. I position its feet over my empty hand and release my hold. For a moment, it perches on my palm, apparently unaware of its freedom…then, in a flutter of wings, it’s gone.

Of the 450 bird species found in Canada, 78% spend at least part of the year outside our borders. This fall, four billion birds will cross our southern border to spend the winter in warmer climes. More than a billion of them will not return, succumbing to the dangers of the journey or the hazards of their wintering grounds.

Icarus offers us a unique window into the world of migratory birds, and a chance to improve their odds. If we know where they go and how they get there, we can begin to understand the perils they face – and perhaps develop solutions.

The incredible journey

Even though it’s still August, and the air is hot and humid, I’m sure I’m not the only one who has noticed that the days are getting shorter, the nights are getting longer, and some of the leaves have a distinct reddish tinge to them.  We may prefer to pretend it’s not happening, but we all know it: fall is on the way.  For millions of birds across North America, it’s time to start thinking about packing their bags and turning their sights to the south.  As summer draws to a close and our forests and fields begin to empty out, I’d like to share a post about migration that I originally wrote for Land Lines, the Nature Conservancy of Canada’s blog, back in the spring – when all the birds were just returning.

“We’ve got rocks and trees, and trees and rocks, and rocks and trees, and trees and rocks, and…rocks and  trees, and trees and rocks, and water…in Canada.”

-Arrogant Worms, “Rocks and Trees”

Canada: land of rocks, tress, water...and endless highways.

Canada: land of rocks, trees, water…and endless highways.

Ever since getting my driver’s licence, I’d dreamed of driving across Canada.  As a concept, it seemed romantic and adventurous – the perfect way to really get to know my own country.  But the reality, it turned out, was a bit different.  As I set off from Sudbury on my second day of cross-country driving, I wanted to be excited.  The first day had been easy: only six hours in the car, and a friend waiting for me at the other end.  But today was the real start of the adventure.  Today, I’d be leaving the relative safety of roads I knew well and passing into territory that was unknown, at least to me.

As I pointed my car west and hit the gas, I was more terrified than excited. Six thousand kilometers is a lot of road – especially when you’re driving alone.  In an effort to kickstart my enthusiasm, I reached over to slide the “Canadiana” mix CD a friend had made for me into the car’s CD player.  As the first strains of the Arrogant Worms’ “Rocks and Trees” came over the speakers, I glanced out the window and couldn’t help but laugh.  A vast, lonely landscape met my gaze, composed of…well, rocks, trees, and water.  Somehow, the song wasn’t actually making me feel any better.

The purpose of this epic journey was to get myself out to BC, and begin my PhD research on the population of western bluebirds that breeds in BC’s Okanagan Valley.  Although there are bluebirds (of one species or another) across the country, I was particularly interested in this population because of their migratory behaviour: the western bluebirds in the Okanagan are partial migrants.  This means that while some birds migrate south in the fall, others hang around the Okanagan, gather into flocks, and brave the snow and cold of a Canadian winter.

Western bluebird flock (and one lone goldfinch) check out a heated bird bath on a cold winter day. Photo credit: Eva Durance.

Western bluebirds (and one lone goldfinch) check out a heated bird bath on a cold winter day. Photo credit: Eva Durance.

I’ve been fascinated by avian migration ever since taking my first Animal Behaviour course as an undergraduate.  This fascination has shaped the last eight years of my life, informing my research interests as a graduate student.  Migration is a common phenomenon:  every year, billions of individuals from more than 350 bird species across North America embark on migratory journeys.  Migration is ubiquitous, and each spring and fall, as I hear the honks of Canada geese passing overhead, I’m tempted to call it ordinary.  But this common phenomenon is composed of extraordinary feats.  As summer winds down in the northern hemisphere, birds like the 25g northern wheatear set off into the unknown, often travelling thousands of kilometers south to spend the winter in more hospitable climates.  In the case of the wheatear, individuals breeding in the Canadian Arctic and Alaska brave the perils of crossing the Atlantic, ultimately covering 14,000 km to reach their wintering grounds in sub-Saharan Africa.  Then, come spring, they do it all over again in reverse.

Migration captures the imagination of scientists and the public alike.  But what is it about these journeys that inspires and enchants us?  That’s a question I’d never been able to answer satisfactorily, but as I faced the vast, lonely distances of my own incredible journey, the answer became clearer: migration may be common, but it is also an extraordinary story of adventure and challenge.

It's just possible that I should have left earlier...

It’s just possible that I should have left earlier…

To begin with, you must decide when to leave.  For birds, timing of migration is affected by many things – from predator abundance to food availability and individual condition – but it’s crucial that they get it right.  This is especially true in the spring, when arriving too late on the breeding grounds can undermine the success of an individual’s breeding season.  However, timing is also important in the fall, when staying too late can mean encounters with the kind of weather you’d rather avoid – as I found out the hard way.

Of course, once you’ve decided to leave, it’s also very important to know where you’re going.  Unfortunately for me, I’m one of the most directionally challenged people imaginable.  (Despite the fact that driving from Ontario to BC essentially involves following the Trans-Canada highway west, a number of people were actually placing bets on whether I’d end up in BC or Nova Scotia.)  Luckily, I had help: before I embarked on my journey, my mother dragged me to the CAA to purchase a staggering number of maps.  I ended up with a separate map for every Canadian province west of Quebec, a very long set of driving directions, and a North American road atlas for good measure.  Despite this plethora of directional aids, I can’t deny making the occasional U-turn on quiet parts of the Trans-Canada.

Just in case you’ve misplaced your country: thank goodness for maps, directions, and road signs.

Just in case you’ve misplaced your country: thank goodness for maps, directions, and road signs.

Birds, of course, have to manage without the help of the CAA.  Instead, they get their directional cues from a variety of sources: the sun, the stars, and the Earth’s magnetic field.  Recent research also suggests that scent cues may play a role in guiding migrants to their destination.  In fact, despite decades of study, we’re still learning new things about how birds manage to navigate the vast distances involved in migration.

You can meet almost any need along the way, as long as you pick your stopping places carefully. If you find yourself suddenly in need of custom embroidery halfway across the continent, the World’s Largest Truckstop in Iowa is the place for you.

You can meet almost any need along the way, as long as you pick your stopping places carefully. If you find yourself suddenly in need of custom embroidery halfway across the country, consider taking a detour to the south: the World’s Largest Truckstop in Iowa is the place for you.

Now on your way, you face another problem: finding places to stop.  As I made my way across the country, I realized that Canada’s seemingly endless rocks, trees, and water didn’t make that challenge easy to overcome.  I quickly learned to appreciate the value of a good refueling point, preferably one with gas, clean washrooms, good coffee, and food packaged within the last decade.  As every migrant knows, finding ideal stops as you navigate an unfamiliar world is not easy.  You need to be able to quickly size up potential sites for their value.  If you decide to stop, you need to quickly figure out what to eat and how to avoid being eaten yourself.  For me, the most important part of finding stops was learning to compromise.  Under less than ideal circumstances, I decided, fresh food was optional.  Even clean washrooms could be optional – after all, all those trees have to be good for something.  Gas and good coffee, however, were non-negotiable.

Even when you finally reach your general destination, the challenges aren’t over.  It’s important to know exactly where and when to stop.  When I crossed the border from Alberta into BC, I cheered, pulled over, and took a victory photo.  Little did I know that finding my new home in the Okanagan would involve more U turns than the rest of my trip put together.  My directions said, “Follow the highway around a curve and the driveway will be on your left”.  Unfortunately, the highway in the Okanagan is nothing but curves.  I drove past my new accommodations three times before finally focusing on the right curve, noticing the driveway, and making the turn.  I don’t think I’ve ever been so happy to stop driving in my life.

During the course of my PhD, I made the drive to the Okanagan and back three times.  Each time, I took a different route, and each journey brought its own adventures, trials, and excitement.  Of course, I had it easy during my ‘migrations’: unlike me, birds travel under their own power, at the mercy of the unpredictable (and often nasty) elements.  But I still feel that my cross country travels gave me a unique opportunity to gain a more personal understanding of the ordinary, extraordinary phenomenon of migration.

Well worth the trip: the Okanagan Valley from above.

Well worth the trip: the Okanagan Valley from above.