Long-Distance Range Expansion and Rapid Adjustment of Migration in a Newly Established Population of Barn Swallows Breeding in Argentina

• Published in: Current biology 2017-04, Vol.27 (7), p.1080-1084
• Main Authors: Winkler, David W., Gandoy, Facundo A., Areta, Juan I., Iliff, Marshall J., Rakhimberdiev, Eldar, Kardynal, Kevin J., Hobson, Keith A.
• Format: Article
• Language: English
• Subjects: Animal Distribution; Animal Migration; Animals; Argentina; bird; breeding season; Hirundinidae; human-altered habitats; migration; photoperiod; Population Growth; range extension; Reproduction; Seasons; swallow; Swallows - physiology
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2017.03.006

When bird populations spread, long-distance pioneering populations are often backfilled by a more slowly advancing front [1–3]. The Barn Swallow Hirundo rustica, a globally distributed passerine [4, 5], expanded its breeding range an exceptional 7,000 km when it began breeding 35 years ago in its regular wintering range in Argentina [6], subsequently expanding over 500 km from its starting point [7–11]. Trans-hemispheric breeding attempts have occurred previously in related swallows [12–14], but only this colonization has lasted. Comparative studies of birds show a remarkable diversity in patterns of change in migratory habits [15–21], and these Argentine-breeding swallows might retain ancestral patterns, breeding in Argentina but returning to North America for the austral winter. Feather isotopes from these birds are consistent with the alternative possibility that they migrate no farther than northern South America [22]. Because isotopic patterns cannot definitively distinguish these alternatives, we pursued a solar geolocator study [23, 24] to do so. Data from nine tagged birds show conclusively that Barn Swallows breeding in Argentina have rapidly changed their movements to migrate no farther north in austral winter than northern South America. The phenology of the annual cycles of molt, migration, and breeding for these Argentine-breeding swallows have all shifted by about 6 months, and we suggest that stimulatory day lengths and the proliferation of nesting substrates facilitated their colonization. [Display omitted] •A widespread North American bird has begun breeding and spreading across Argentina•This extends the breeding range 7,000 km into what was formerly the wintering range•Paths quickly shifted to resemble those of other South American migratory birds•The entire annual cycle has shifted by about 6 months North American Barn Swallows began breeding on the southern edge of their wintering range 35 years ago. Winkler et al. show that these birds have quickly changed their migratory route and schedule and the timing of their annual cycle to take advantage of new nesting substrates (road bridges) in areas with temperate photoperiodic cycles.