A spatio-temporal comparison of avian migration phenology using Citizen Science data

The effects of climate change have wide-ranging impacts on wildlife species and recent studies indicate that birds' spring arrival dates are advancing in response to changes in global climates. In this paper, we propose a spatio-temporal approach for comparing avian first arrival data for multiple species. As an example, we analyze spring arrival data for two long-distance migrants (Ruby-throated Hummingbird Archilochus colubris; and Purple Martin Progne subis) in eastern North America from 2001-2010 using Citizen Science data. The proposed approach provides researchers with a tool to compare mean arrival dates while accounting for spatial and temporal variability. Our results show that on average, Purple Martins arrive 29.95 to 31.84 days earlier than Ruby-throated Hummingbirds, but after accounting for this overall difference, spatial nuances exist whereby martins arrive earlier in the southern United States and migrate northward at a slower rate than hummingbirds. Differences were also noted in how climate and weather variables such as the North Atlantic Oscillation index, winter temperature, winter-spring precipitation, sampling effort, and altitude impacted migration dates. Our method may easily be generalized to analyze a broad range of temporal and spatial Citizen Scientists data to help better understand the ecological impacts of climate change.