Abstract
We evaluated the role of habitat fragmentation in promoting song variation and the potential for the generation of dialects within four type I dialect areas of Hermit Warblers (Setophaga occidentalis). The dialect areas differed markedly in the degree of habitat fragmentation due to topographic relief, aspect, and elevation. Geographic variation in song was greatest in the most highly fragmented area, but substantial variation existed in all dialect areas including the area with no obvious fragmentation. Songs in isolated and partially isolated portions of a dialect area differed from songs in the more continuous areas, but geographic variation was also found within the continuous portions of dialect areas. Much of the variation in song structure was clinal, crossing discontinuities in habitat. Within a dialect area, songs varied geographically with differences often apparent over distances ≤10 km in continuous habitat. Despite the great geographic variation in song, evidence that fragmented habitat promotes song variation is insufficient to explain the observed pattern of variation in type I song. Noticeable song variation over relatively small distances suggests males converge on similar type I songs locally while periodic large-scale disturbances, primarily wildfire, are likely important in the partitioning of variable dialects sufficiently in space and time for the generation of new dialects.
Zusammenfassung
Geografische Variation von Typ I-Dialekten bei Einsiedelwaldsängern: Fördert Habitatfragmentierung Gesangsvariation? Wir untersuchten die Rolle der Habitatfragmentierung bezüglich der Förderung von Gesangsvariation und des Potenzials zur Entstehung neuer Dialekte innerhalb von vier Typ I-Dialektgebieten des Einsiedelwaldsängers (Setophaga occidentalis). Aufgrund von topografischer Geländeform, Exposition und Höhenlage unterschieden sich die Dialektgebiete deutlich im Ausmaß der Habitatfragmentierung. Die geografische Variation des Gesanges war in dem am stärksten fragmentierten Gebiet am höchsten, allerdings gab es in allen Dialektgebieten, darunter auch dem ohne nennenswerte Fragmentierung, beträchtliche Variation. Die Gesänge in isolierten und teilweise isolierten Abschnitten eines Dialektgebietes unterschieden sich von den Gesängen in den mehr zusammenhängenden Bereichen, es gab aber auch geografische Variation innerhalb der zusammenhängenden Abschnitte der Dialektgebiete. Ein Großteil der Variation in der Gesangsstruktur verlief klinal und über verschiedene Habitate hinweg. Innerhalb eines Dialektgebietes unterschieden sich die Gesänge geografisch, wobei die Unterschiede oft bereits über Entfernungen ≤ 10 km in gleich bleibendem Habitat auftraten. Trotz der starken geografischen Variation des Gesanges reichen die Belege für eine Förderung der Gesangsvariation durch Habitatfragmentierung nicht aus, um das beobachtete Variationsmuster bei Typ I-Gesängen zu erklären. Deutliche Gesangsvariation über relativ kurze Distanzen deutet darauf hin, dass sich die Männchen lokal zu ähnlichen Typ I-Gesängen annähern, während periodische Umbrüche größeren Ausmaßes, beispielsweise Flächenbrände, sehr wahrscheinlich wichtig für die hinreichende Abgrenzung variabler Dialekte in Zeit und Raum sind und so neue Dialekte entstehen lassen.
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Acknowledgements
We thank David Kramer and Randall Fitzpatrick for assistance in the generation of the dialect maps (ArcGIS) and David Kramer for helpful discussions regarding the statistics.
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This study was both self-funded and funded by Southern Oregon University.
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The authors declare that they have no conflict of interest.
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Communicated by M. Naguib.
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Janes, S.W., Ryker, L. & Ryan, R.M. Geographic variation in type I dialects of Hermit Warblers: does fragmented habitat promote variation in song?. J Ornithol 158, 421–430 (2017). https://doi.org/10.1007/s10336-016-1420-9
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DOI: https://doi.org/10.1007/s10336-016-1420-9