Spatial Responses to Climate Change in a Long-Distance Migratory Songbird: the Scarlet Tanager (Piranga olivacea)

Abstract

In the 21st century, climate change is threatening the populations of many species with extinction (Parmesan & Yohe, 2003). Migratory species, some of whose breeding ranges are located in areas of fast-paced change, are at risk (Møller et al., 2008; Sander et al., 2020). We propose an assessment of the spatial response to climate change of such a species, the Scarlet Tanager (Piranga olivacea). P. olivacea migrate to the northern regions of North America (Mowbray, 2020), where rapid climate change may threaten the species’ suitability to their historical breeding areas. To test whether P. olivacea are responding spatially to climate change, we will use a two pronged approach looking at occurrence and morphological change from across their breeding range over time. First, we will assess spatial responses to climate change by comparing historical breeding occurrence and climate data (March-August, ca. 70-50 years ago; 1950-1970), to current occurrence data (years 2000-2020), to build a forecast of potential future breeding distribution for this species using Maxent software (Phillips et al., 2018). Breeding season occurrence data for historical and current time periods will be sourced from museum records from www.gbif.org, and will be matched with environmental data (i.e., temperature, precipitation,land cover). Recent research has supported that migratory birds are growing longer wings in response to climate change, presumably under selection pressure to support improved flight efficiency for migrating longer distances to access appropriate environmental conditions for breeding (Weeks et al., 2020). We will assess morphological changes over time in breeding P. olivacea in response to predictions under climate change hypotheses by measuring museum specimens from the American Museum of Natural History and the Louisiana State University Museum of Natural Science. We intend to infer whether P. olivacea possesses adequate adaptive potential to keep pace with relevant climate change metrics, and more broadly whether climate change is driving selection on morphology to reach a more northern breeding distribution for this species. If the historical distribution is explained by climate variables but P. olivacea has not shifted its breeding range or exhibited morphological shifts, this may be evidence of low adaptive capacity. Climate, morphological and occurrence data will be analyzed to determine the suitability of P. olivacea in its current breeding range, as well as alternative responses including shifts in the species’ reproductive windows. Our data will include bill length, mass, and hand-wing index variables for morphological analyses, while precipitation, temperature, and land cover will be included in the environmental datasets. Statistical analysis will be run by the American Museum of Natural History’s Maxent software, v. 3.4.4. Results will provide support for conservation efforts for forest-dwelling long distance migrant birds threatened by climate change, and can aid in the understanding of climate change’s effects on migratory species as a whole.