New Paper ~ Using citizen science data in SDMs to inform migratory connectivity
Fournier, A.M.V., Drake K.L., Tozer D.C. In Press Using citizen science monitoring data in species distribution models to inform isotopic assignment of migratory connectivity in wetland birds Journal of Avian Biology doi:10.1111/jav.01273
Open Access Preprint: http://biorxiv.org/content/early/2017/06/01/144527
Open Access Data Dryad Digital Repository. http://dx.doi.org/10.5061/dryad.nb115
If you hear me talk about rails for any length of time you’ll soon hear me talk about how difficult they are to detect, and how little we know about them. Low detection, that is the low chance of actually seeing a bird when it is around, causes a lot of issues, one of which is its difficult to study their migration.
Not understanding a bird’s migration limits our ability to understand their population status (how their population is doing) since we don’t know the connections between different parts of their annual cycle. There are many methods of trying to better understand migratory connectivity, but few are appropriate for rails. Satellite transmitters are too heavy. Rails don’t have site fidelity so geolocators don’t work. Rails aren’t recaptured frequently enough or captured across a wide enough area for bird banding to be helpful. So that leaves us, until battery technology improves and makes lighter transmitters, with stable isotopes.
Stable isotopes, in this case hydrogen, are useful for tracking bird migration because the ratio of heavy to light hydrogen varies roughly from southeastern North America to northwest North America. When a bird molts a feather, the hydrogen isotope ratio of the place it is living is preserved in that feather. Since feathers are inert material, we can capture the rail later in the year, pull the feather (causing no harm to the bird) and use that ratio to understand their migration.
One big assumption of using stable isotopes to assign where birds are from is that bird are evenly distributed across the landscape. This simply isn’t true for almost all birds, and is especially bothersome for a bird that has specialized habitat requirements, like a rail. Luckily we can use other information, in addition to the isotopes, to help refine our estimates of where the bird was when it molted its feather.
In this case we have used marshbird monitoring program citizen science data from the US and Canada to create a species distribution model. The species distribution model allows us to show that the birds are not equally spread out over space, and thus improve our estimates.
We used marshbird monitoring program data, because it has been collected in such a way that maximizes the chances of seeing or hearing a bird if one is present, so we get more informative models this way.
The infographic below shows where the citizen science data are from, and where we were able to obtain feathers from. Then at the bottom you can see the three maps showing where the three different species are from. Please note we have very different sample sizes among the three species.
This is certainly not closing the door on migratory connectivity, but it does raise some interesting questions, why are Sora from one area and Yellow Rails from another, even if they are using the same migratory and wintering areas? What is going on with Virginia Rails? Are they really migrating straight east? Isotopes won’t be able to answer those questions for us, but other methods might, and that sounds like a perfect next project.