Authors: Amin Dezfuli, Kyle G. Horton, Benjamin Zuckerberg, Siegfried D. Schubert, and Michael G. Bosilovich
Year: 2022
Publication: Bulletin of the American Meteorological Society
Publication Link: https://doi.org/10.1175/BAMS-D-21-0220.1
Keywords: Atmosphere; Ecology; North America; Rossby waves; Interannual variability; Animal studies
Abstract: For ~100 years, the continental patterns of avian migration in North America have
been described in the context of three or four primary flyways. This spatial compartmentalization
often fails to adequately reflect a critical characterization of migration—phenology. This
shortcoming has been partly due to the lack of reliable continental-scale data, a gap filled by our
current study. Here, we leveraged unique radar-based data quantifying migration phenology and
used an objective regionalization approach to introduce a new spatial framework that reflects
interannual variability. Therefore, the resulting spatial classification is intrinsically different from
the “flyway concept.” We identified two regions with distinct interannual variability of spring
migration across the contiguous United States. This data-driven framework enabled us to explore
the climatic cues affecting the interannual variability of migration phenology, “specific to each
region” across North America. For example, our “two-region” approach allowed us to identify
an east–west dipole pattern in migratory behavior linked to atmospheric Rossby waves. Also,
we revealed that migration movements over the western United States were inversely related to
interannual and low-frequency variability of regional temperature. A similar link, but weaker and
only for interannual variability, was evident for the eastern region. However, this region was more
strongly tied to climate teleconnections, particularly to the east Pacific–North Pacific (EP–NP) pattern.
The results suggest that oceanic forcing in the tropical Pacific—through a chain of processes
including Rossby wave trains—controls the climatic conditions, associated with bird migration
over the eastern United States. Our spatial platform would facilitate better understanding of the
mechanisms responsible for broadscale migration phenology and its potential future changes.