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Globally, many avian (bird) species are undergoing changes in their geographic range. One example of such change is range expansion, which could result in a variety of consequences on avian life and ecology, such as their song. As birds are expanding in new ranges and into habitats of varying natural conditions, they may experience differences in natural selection pressures. Differences in selection pressures, including environmental and sexual, have been found to contribute to song trait divergences. Previous studies have discovered such geographic variation in avian song, but not in the context of range expansion. In my study, I explore how the recent northward expansion of Northern Cardinals in the U.S and Canada may be related to song trait divergences between populations in historically established Southern regions and those in newly expanded Northern regions. To do this, I compared 79 Northern Cardinal adult male songs recorded during the year 2022 in each the Northern and Southern region, obtained from the Macaulay Library of Ornithology, across various behavioral song traits. I found that song traits differed between populations in the two regions. As Northern Cardinals expanded their range northward, their songs appeared to have smaller frequency ranges, lower complexity, higher syllable rate and longer durations. These differences could be attributed to a facet of varying natural and sexual selective pressures that are differentially faced in the new and old ranges.
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Jiang, Annie, "A Changing Red Song: How Northern Cardinal Songs Are Evolving Through Their Northward Expansion" (2023). Senior Projects Spring 2023. 20.
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