Projected changes in wind assistance under climate change for nocturnally migrating bird populations

Nocturnal migration speed (arrow length), direction, and vertical integration density (VID; birds per km2) estimated at migration altitudes during (a) spring and (b) autumn migration at 143 weather surveillance radar (WSR) stations. Nocturnal wind speed and direction estimated at migration altitudes during (c) spring and (d) autumn migration at 143 WSR stations

Authors: Frank A. La Sorte| Kyle G. Horton| Cecilia Nilsson| Adriaan M. Dokter

Year: 2019

Publication: Global Change Biology

Publication Link:

Access: Open

Affiliations: Cornell Laboratory of Ornithology, Cornell University, Ithaca, New York

Corresponding Author: Frank A. La Sorte, Cornell Laboratory of Ornithology, Cornell University, Ithaca, NY. Email:

Funding: The Wolf Creek Charitable Foundation; National Science Foundation, Division of Biological Infrastructure. Grant Numbers: 1356308, 1661329; AWS Cloud Credits for Research

Keywords: global climate change, migration altitude, nocturnal migration, North America, seasonal bird migration, weather surveillance radar, wind assistance

Abstract: Current climate models and observations indicate that atmospheric circulation is being affected by global climate change. To assess how these changes may affect nocturnally migrating bird populations, we need to determine how current patterns of wind assistance at migration altitudes will be enhanced or reduced under future atmospheric conditions. Here, we use information compiled from 143 weather surveillance radars stations within the contiguous United States to estimate the daily altitude, density, and direction of nocturnal migration during the spring and autumn. We intersected this information with wind projections to estimate how wind assistance is expected to change during this century at current migration altitudes. The prevailing westerlies at midlatitudes are projected to increase in strength during spring migration and decrease in strength to a lesser degree during autumn migration. Southerly winds will increase in strength across the continent during both spring and autumn migration, with the strongest gains occurring in the center of the continent. Wind assistance is projected to increase across the central (0.44 m/s; 10.1%) and eastern portions of the continent (0.32 m/s; 9.6%) during spring migration, and wind assistance is projected to decrease within the central (0.32 m/s; 19.3%) and eastern portions of the continent (0.17 m/s; 6.6%) during autumn migration. Thus, across a broad portion of the continent where migration intensity is greatest, the efficiency of nocturnal migration is projected to increase in the spring and decrease in the autumn, potentially affecting time and energy expenditures for many migratory bird species. These findings highlight the importance of placing climate change projections within a relevant ecological context informed through empirical observations, and the need to consider the possibility that climate change may generate both positive and negative implications for natural systems.

Supplementary Material: At end of document

Intrusive Methodologies: None

Citizen Science: None

Conservation: Not discussed

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