Streby, H.M., G.R. Kramer, S.M. Peterson, J.A. Lehman, D.A. Buehler, and D.E. Andersen. In press. Tornadic storm avoidance behavior in breeding songbirds. Current Biology.
- •Migrant songbirds evacuated their territories to circumvent a severe tornado outbreak
- •Obligate migrants can make facultative migrations outside of normal migration periods
- •Infrasound from tornadic storms could be a long-distance cue for evacuation migration
Migration is a common behavior used by animals of many taxa to occupy different habitats during different periods [ 1 ]. Migrant birds are categorized as either facultative (i.e., those that are forced to migrate by some proximal cue, often weather) or obligate (i.e., those that migrate on a regular cycle) [ 2, 3 ]. During migration, obligate migrants can curtail or delay flights in response to inclement weather or until favorable winds prevail [ 4, 5 ], and they can temporarily reorient or reverse direction when ecological or meteorological obstacles are encountered [ 6 ]. However, it is not known whether obligate migrants undertake facultative migrations and make large-scale movements in response to proximal cues outside of their regular migration periods [ 3 ]. Here, we present the first documentation of obligate long-distance migrant birds undertaking a facultative migration, wherein breeding golden-winged warblers (Vermivora chrysoptera) carrying light-level geolocators [ 7, 8 ] performed a >1,500 km 5-day circumvention of a severe tornadic storm. The birds evacuated their breeding territories >24 hr before the arrival of the storm and atmospheric variation associated with it. The probable cue, radiating >1,000 km from tornadic storms [ 9–11 ], perceived by birds and influencing bird behavior and movements [ 12–14 ], is infrasound (i.e., sound below the range of human hearing). With the predicted increase in severity and frequency of similar storms as anthropogenic climate change progresses [ 15 ], understanding large-scale behavioral responses of animals to such events will be an important objective of future research.