Wilson’s Warbler http://www.utahbirds.org/birdsofutah/BirdsS-Z/WilsonsWarbler.htm
There are approximately 450 native migrating bird species that for at least part of the year reside in Canada, but where do they go when they aren’t in the True North Strong and Free? If you ask just about anyone, they’ll tell you that birds fly south for the winter, but where exactly is south? South could be as close as the next city, the USA or as far as Tierra Del Fuego. Also do they make stops on their way to this “south” and do they mix with other populations? The truth is there isn’t much information on where many migrating species go or the route they take to get there.
But why should we care where they go when they leave Canada, they seem to always come back in the spring. The truth is not all birds are coming back, there has been a marked decline in the population size of many migrating neotropical bird species. As the leading cause of species loss, humans need to figure out whether these bird populations are facing stressors in their breeding, wintering, stopover range or some combination of the three so we can help manage them. The first step in doing this is learning the birds’ migration route.
The effort to understand the movement patterns of birds began in North America during the 1800s when the famous ornithologist John James Audubon started tying silver string to the legs of eastern phoebes, Sayornis phoebe, to see if individuals that left in the fall returned in the spring. Of all the birds Audubon marked, 2 returned in the spring. This little experiment transformed into the bird banding/ringing program we know today with different coloured metal bands replacing the pieces of silver string.
Though the bird banding program has been essential to the understanding of bird ecology, life history and migration it is has one major flaw. This flaw is that banded birds must be spotted again and it’s estimated that only 1 in 10,000 banded birds are recaptured, leaving a large data gap. So why use bands, why not use GPS tracking devices? Well, they do for larger birds but for many bird species the size and weight of a tracker is too much of stress so a better solution is needed. This solution is up and coming from Dr. Kristen Ruegg’s lab at UCLA and it has been dubbed The Bird Genoscape Project.
Ruegg and company have taken on the task of creating a protocol that will allow them to identify where a migrating bird has come from by using just a feather. To get a full comprehensive understanding of this protocol please refer to Ruegg et al. 2014 but I’ll briefly explain their methods here: Variation in DNA is what makes individuals unique but a huge portion of an organism is actually shared with the individuals of the same species. As groups or populations of a species become more isolated and breed with other individuals in their populations more, the populations start to diverge, this is population differentiation. Individuals in a breeding population will be more similar to each other than to other populations.
The UCLA team used the concept of population differentiation to find the small bits of DNA, called single nucleotide polymorphisms (SNPs), that are unique to each breeding population, a genetic fingerprint some might say. For their study they looked at the Wilson’s warbler, Cardellina pusilla, taking small blood samples from individuals in each breeding population and each population’s genetic fingerprint was made.
With a genetic fingerprint for each breeding population Dr. Ruegg and her collaborators were able to collect feathers from Wilson’s warblers across North America and identify where it came from with an 80-100% success rate. So a feather collected in Colorado in the late fall could be traced back to the British Columbia breeding population, meaning Colorado is a stop off point. This solves the major problem that banding had; you don’t need to come in contact with the same bird to get information, any bird in the species will work.
From Ruegg et al. 2014. Each colour depicts a breeding population, arrows are stopovers and circles are wintering grounds
An interesting finding from UCLA’s study was that there are 6 breeding populations of Wilson’s warblers opposed to the 2-3 that biologist previously thought and that 3 of the breeding populations actually share a wintering ground and flight path. Two of these three breeding populations are stable but one population is declining, suggesting the cause of decline stems from the declining population’s breeding ground. If the issue stemmed from the wintering ground of the flight path, the other populations should be affected too.
So what’s next? Ecological managers now know where the issue is likely originating from for the Wilson’s warbler but still need to identify the root cause. As for The Bird Genoscape Project, Dr. Ruegg has moved on to repeating this study with the American Kestrel. There is also work being done with museum samples to see if ranges and flight paths have shifted with time. It’s looking like The Bird Genoscape Project can only get bigger, spreading to more migrating bird species and become an essential tool for bird conservation just as bird banding did in the past.
For more information see:
Ruegg K.C., Anderson E.C., Paxton K.L., Apkenas V., Lao S., Siegel R.B., Desante D.F., Moore F., and Smith T.B. 2014. Mapping migration in a songbird using high-resolution genetic markers. Molecular Ecology 23:5726-5739.
Kristen’s interview with Podcast Eye’s on Conservation is available on iTunes