Space weather disrupts nocturnal bird migration

Abstract

Space weather, including solar storms, can impact Earth by disturbing the geomagnetic field. Despite the known dependence of birds and other animals on geomagnetic cues for successful seasonal migrations, the potential effects of space weather on organisms that use Earth's magnetic field for navigation have received little study. We tested whether space weather geomagnetic disturbances are associated with disruptions to bird migration at a macroecological scale. We leveraged long-term radar data to characterize the nightly migration dynamics of the nocturnally migrating North American avifauna over 22 y. We then used concurrent magnetometer data to develop a local magnetic disturbance index associated with each radar station (ΔBmax), facilitating spatiotemporally explicit analyses of the relationship between migration and geomagnetic disturbance. After controlling for effects of atmospheric weather and spatiotemporal patterns, we found a 9 to 17% decrease in migration intensity in both spring and fall during severe space weather events. During fall migration, we also found evidence for decreases in effort flying against the wind, which may represent a depression of active navigation such that birds drift more with the wind during geomagnetic disturbances. Effort flying against the wind in the fall was most reduced under both overcast conditions and high geomagnetic disturbance, suggesting that a combination of obscured celestial cues and magnetic disturbance may disrupt navigation. Collectively, our results provide evidence for community-wide avifaunal responses to geomagnetic disturbances driven by space weather during nocturnal migration.

Keywords: bird migration; geomagnetic disturbances; radar; space weather.

Fig. 1.

Conceptual and geographic layout of our study system. (A) Space weather from the Sun, such as coronal mass ejections, disturbs Earth’s magnetic field, causing the auroras and potentially decreasing the magnetic field’s reliability for migrating birds. Artwork by John Megahan. (B) Distribution of NEXRAD radar stations (dark blue circles) and SuperMAG inventory magnetometer stations (purple crosses) used in this study in relation to topography (grayscale) (4). We used the three closest and active magnetometer stations surrounding each radar station (SI Appendix, Fig. S1) to interpolate ΔBmax, or maximum change in the magnetic field from quiet conditions, every hour. Some magnetometer stations had periods of missing data (SI Appendix, Fig. S2 and Table S1), so we sampled magnetometers from a larger geographical area than the radar stations to achieve a robust time series.

Fig. 2.

Migration intensity predictions with geomagnetic disturbances. (A) Our MLT residual model and (B) NLME model predict decreases of 11% and 17%, respectively, in migration intensity at high geomagnetic disturbance (ΔBmax) in the spring. (C) Our MLT residual model predicts migration intensity decreases of 9% at high ΔBmax in the fall, but the corresponding NLME model (D) does not recover a similarly strong relationship. The spring models and the fall MLT residual model begin predicting decreased migration intensity with geomagnetic disturbances of around 500 nT.

Fig. 3.

Crosswind component of airspeed predictions with geomagnetic disturbances at different cloud cover levels. (A) Our spring NLME model does not predict changes in the crosswind component with magnetic disturbance or different cloud cover levels. (B) Our fall NLME model predicts a 25% decrease in effort flying against the wind at high ΔBmax and 100% cloud cover. The model otherwise predicts no changes in the crosswind component during geomagnetic disturbances at lower cloud covers.