The Effect of Elevation on Bird Migration

1. Findings Introduction The overall study of how birds migrate and whether elevation patterns affected their flight was studied. Data records for the bird species such as Setophaga ruticilla, Dendroica petechia, Dendroica fusca, and Wilsonia citrina, and were observed in Maryland, Pennsylvania and Virginia, Delaware and New Jersey. The birds that were studied are long distance, neo-tropical migrants and migrate thousands of miles over a short period of time ranging from several weeks to four months with a consistency in their arrival dates each year. Over time bird populations have seemed to decrease in number when viewed before and after migration. No specific study has previously been able to target why this is happening and data, dating back to the 1880’s, was used from the North American Bird Phenology Program (BPP). It has provided clues as to the past arrival dates for specific species and whether elevation directly affects those dates. A study like this has not been tried yet at BPP and with the study hopefully some answers to dwindling bird populations will be addressed. Birds are very receptive to the earth and any changes and fluctuations experienced by our environment; in trying to figure out what has been affecting later arrival dates, the study also shed light on how the earth has or has not been affected over time. It is predicted that the higher in elevation a certain area is, the longer it takes the bird to travel and thus causes a later arrival date. If the Julian Date1 increases then the elevation has also increased. Null: If the Julian date decreases then the elevation has decreased and there is no correlation between the two variables. 1. Julian Date: Calendar notation in which each date is represented by a number. In this case the arrival date was replaced with a number. i.e. Date: May 20th will be a Julian date of 120. A total of 2,172 migration cards were analyzed in this study. The results of this study showed that there was a weak negative correlation between the Julian date and altitude for three of the four species tested: Setophaga ruticilla, Dendroica petechia, and Dendroica fusca. Overall the study supported the null hypothesis. Wilsonia citrina was the only species to support the hypothesis of a positive correlation between elevation and Julian date. The slopes for Setophaga ruticilla, Dendroica petechia,Dendroica fusca and Wilsonia Citrina were -18.48, -15.59, -19.97, and 15.49 respectively. In studying this linear correlation, when the P-value yielded less than 0.05 data was assumed to be statistically significant and the Setophaga ruticilla, Dendroica petechia, and Dendroica fusca had low P-values of 0.01, 0.00, and 0.00, whereas the Wilsonia citrina had a higher P-value of 0.91 and was not statistically significant. Results became increasingly significant as more independent variables were added. A multiple regression test was used to analyze first how altitude and latitude both affected Julian date, and then how altitude, latitude and the year of arrival affected the Julian date All four of the P-values for the tests ran for the four species were shown to be significant. More of the statistical figure and results can be seen in the chart below. Right: Holding bird caught during direct observations Left: In BPP office The Effect of Elevation on Bird Migration Some of the filing cabinets at BPP Bird Migration Cards Photos above courtesy of Jessica Zelt Photos below Courtesy of http://www.pbase.com/dadas115/warblers http://sdakotabirds.com/species_photos/american_redstart.htm Bird Location using Quantum GIS 1.6.0 Setophaga ruticilla Dendroica petechia Dendroica fusca Wilsonia citrina = Bird Setophagaruticilla Birds were plotted using Latitude versus Longitude on a map to provide a visual of where birds were observed Conclusion Methodology Dendroica petechia For all the tests, r2 values were very small. This was a result of the abundance of data values, at various altitudes, and latitudes which can be seen on the graphs, and the trend line representing a small amount of them. The r2 values increased as more variables were introduced into the statistics, showing that the more variables factored into the statistics, the more the data was thoroughly represented. This shows that although the variables studied played a role, they are not the only thing affecting the arrival dates. Overall, the study provided a better insight and understanding of how the variables, mainly altitude, but also latitude and year, played a role in later arrival dates. Due to the study conducted, many more studies will be conducted at the Bird Phenology Program using all the bird migration cards available. Future studies can look at different samples such as, more neo-tropical migrants, only one sex, compare past migrations cards to current migration or instead at fall migration dates. Dendroica fusca Acknowledgments I would like to thank my Mentor Ms. Jessica Zelt and also Mr. Sam Droege, whom was like an additional mentor to me for being such a large help and providing all the needed resources as well as much more. I would also like to thank my parents for always being supportive in my ventures. Wilsonia citrina Michaeline Fraser