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Winkler, David Ward

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Winkler
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David Ward
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    Data from: Long-distance range expansion and rapid adjustment of migration in a newly established population of Barn Swallows breeding in Argentina
    (2017-03-16) Winkler, David Ward; Gandoy, Facundo A.; Areta, Juan I.; Iliff, Marshall J.; Rakhimberdiev, Eldar; Kardynal, Kevin J.; Hobson, Keith A.
    When bird populations spread, long-distance pioneering populations are often backfilled by a more slowly advancing front. The Barn Swallow Hirundo rustica, a globally distributed passerine, expanded its breeding range an exceptional 7,000 km when it began breeding 35 years ago in its regular wintering range in Argentina, subsequently expanding over 500 km from its starting point. Trans-hemispheric breeding attempts have occurred previously in related swallows, but only this colonization has lasted. Comparative studies of birds show a remarkable diversity in patterns of change in migratory habits, 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. Because isotopic patterns cannot definitively distinguish these alternatives, we pursued a solar geolocator study 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.
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    Data from: Constructing and evaluating a continent-wide migratory songbird network across the annual cycle
    (2018-02-26) Knight, Samantha M.; Bradley, David W.; Clark, Robert G.; Gow, Elizabeth A.; Bélisle, Marc; Berzins, Lisha L.; Blake, Tricia; Bridge, Eli S.; Burke, Lauren; Dawson, Russell D.; Dunn, Peter O.; Garant, Dany; Holroyd, Geoffrey L.; Hussell, David J.T.; Lansdorp, Olga; Laughlin, Andrew J.; Leonard, Marty L.; Pelletier, Fanie; Shutler, Dave; Siefferman, Lynn; Taylor, Caz M.; Trefry, Helen E.; Vleck, Carol M.; Vleck, David; Winkler, David Ward; Whittingham, Linda A.; Norris, D. Ryan
    Determining how migratory animals are spatially connected between breeding and non-breeding periods is essential for predicting the effects of environmental change and for developing optimal conservation strategies. Yet, despite recent advances in tracking technology, we lack comprehensive information on the spatial structure of migratory networks across a species’ range, particularly for small-bodied, long-distance migratory animals. We constructed a migratory network for a songbird and used network-based metrics to characterize the spatial structure and prioritize regions for conservation. The network was constructed using year-round movements derived from 133 archival light-level geolocators attached to Tree Swallows (Tachycineta bicolor) originating from 12 breeding sites across their North American breeding range. From these breeding sites, we identified 10 autumn stopover nodes (regions) in North America, 13 non-breeding nodes located around the Gulf of Mexico, Mexico, Florida, and the Caribbean, and 136 unique edges (migratory routes) connecting nodes. We found strong migratory connectivity between breeding and autumn stopover sites and moderate migratory connectivity between the breeding and non-breeding sites. We identified three distinct ‘communities’ of nodes that corresponded to western, central, and eastern North American flyways. Several regions were important for maintaining network connectivity, with South Florida and Louisiana as the top ranked non-breeding nodes and the Midwest as the top ranked stopover node. We show that migratory songbird networks can have both a high degree of mixing between seasons yet still show regionally distinct migratory flyways. Such information will be crucial for accurately predicting factors that limit and regulate migratory songbirds throughout the annual cycle. Our study highlights how network-based metrics can be valuable for identifying overall network structure and prioritizing specific regions within a network for conserving a wide variety of migratory animals.