Utilizing stable hydrogen isotopes to understand range changes using the Magnolia warbler (Setophaga magnolia)
Stable hydrogen isotopes may be useful in indicating range changes as climate change affects neotropical avian migrants. In North America, avian feathers contain a hydrogen isotope signature that indicates the latitude where the feather was grown. By analyzing the hydrogen isotopes in feather samples, the average breeding latitude can be determined. If these breeding latitudes are determined for distinct time periods and compared, changes in population distribution and breeding latitude should be distinguishable. This technique might be especially useful for neotropical migrants, like the Magnolia warbler (Setophaga magnolia), which shows significant local variation. Hydrogen isotope analysis will generate a representation of the breeding latitude on larger scale that negates local variations. During spring and fall migration of 2014, prebasic tail feathers were pulled from Magnolia warblers as they went through a banding station, which provide a representation of current breeding latitudes. Prebasic body feathers were also collected from study skins at the Carnegie Museum of Natural History to provide data on the historic breeding latitudes. Feather samples were sent to the Stable Isotope Laboratory at Cornell University for analysis. The resulting hydrogen isotope data was manipulated using a spatial analyst operation in GIS to model the probability that the isotope signatures originated from a particular region in North America based on a stable hydrogen interpolation of precipitation data collected at 178 stations throughout North America.
Seven models were created for both the current dataset and the historic dataset, creating fourteen models total. These models included the entire current and historic dataset as well as breakdowns using males, females, immatures, adults, early migrants, and late migrants. The models for the current dataset were then overlaid with the models for the historic dataset and analyzed for change detection. The analysis indicated the entire population of Magnolia warblers are experiencing slight shift to more northerly breeding latitudes. A small separation in average breeding latitudes of immature and adult individuals was also distinguishable. However, these minor changes are probably insignificant to the Magnolia warbler population at this time. The use of stable hydrogen to analyze range change has demonstrated successful use on the Magnolia warbler and provided beneficial information though. Overall, stable hydrogen isotopes should continue to be utilized as a method for detecting range change on neotropical avian migrants. This type of analysis could be extremely valuable if a species is shifting over time as natural resource managers could adapt management plans accordingly.