ABSTRACT
Abstract. Modern climate change has resulted in an advancement of spring phenology throughout the Northern Hemisphere, and studies suggest that many birds are arriving earlier to their breeding grounds in response to these changing spring conditions. Past studies on spring arrival of migrating birds often rely on long-term records from a single banding station and focus on identifying climatic cues at species’ breeding grounds to explain variation in arrival times. As a result, the role of climate variability on wintering grounds and its associated impacts on spring migration in birds remain unresolved. Using data from Project FeederWatch, a continentalwide citizen science program focused on wintering birds, we studied the variation in spring arrival for five shortdistance, temperate migrants from 1990 to 2011. We hypothesize that short-distance migrants respond strongly to climate conditions on their wintering grounds, which then play a critical role in driving spring arrival to breeding regions. To test this hypothesis, we quantified spring arrival to the upper midwestern United States by calculating
first the median arrival dates and explored how interannual variation in winter climate conditions altered these arrival times. For American Robins (Turdus migratorius), we found annual variation in temperature on wintering grounds was strongly related to first-arrival date, but not a strong predictor of median arrival dates. For other species, such as Red-winged Blackbirds (Agelaius phoeniceus), first-arrival dates were most influenced by precipitation during winter and spring months. These findings suggest that climate on wintering grounds plays an important role in the migration phenology of temperate migrants, but that these effects will likely be variable across species and different subpopulations. Our findings highlight the impact winter climate variability can have on migration phenology and demonstrate the importance of considering the heterogeneous nature of climate change.
