Flight muscle shape reliably predicts flight muscle mass of migratory songbirds: a new tool for field ornithologists

Abstract

The pectoral muscle is the biggest organ within a passerine bird. It provides flight locomotion and is known to act as a protein source during periods with increased protein demands or decreased protein availability. The mass of the flight muscle is dynamic and changes during juvenile growth, reproduction, seasonal acclimatization, fasting and migration. Thus, a tool that accurately and non-invasively quantifies this phenotypic flexibility in flight muscle mass is of interest to ornithologists. We provide a calibration and validation of a "muscle meter" device designed to accurately measure the shape of the flight muscle. For two species of different size, the European starling (Sturnus vulgaris) and the garden warbler (Sylvia borin), we compared the accuracy and precision of different linear regression models for predicting flight muscle mass. The multifactorial linear regression model with the most support for both species included “muscle meter score” (mmscore), tarsus length and body mass (m b), although a simpler model with mmscore and m b had as much support for predicting flight muscle mass of European starlings. A validation exercise revealed that flight muscle mass of these two species could be estimated with a relative error of about 3%. The muscle meter is a simple device, easy and quick to handle, that can reliably and non-invasively estimate flight muscle mass of captive and wild birds when used in conjunction with standard measurements of tarsus length and m b.

Zusammenfassung

Der große Flugmuskel (Musculus pectoralis) ist das größte Organ im Singvogelkörper. Er ermöglicht das Fliegen, stellt aber auch eine körpereigene Proteinquelle dar, die bei erhöhtem Proteinbedarf oder reduzierter Proteinverfügbarkeit genutzt wird. Die Masse des großen Flugmuskels zeigt ein dynamisches Verhalten und ändert sich beispielsweise während des jugendlichen Wachstums, der Reproduktion, der jahreszeitlichen Anpassung, des Fastens und des Zuges. Ein Hilfsmittel, zu einer exakten und nicht-invasiven Erfassung dieser phänotypischen Flexibilität des Flugmuskels ist deshalb von großem Interesse für Ornithologen. Hierzu stellen wir hier das ‘Muskel-Meter’ sowie seine Kalibrierung und Validierung, zur exakten Messung der Form des Flugmuskels vor. Bei zwei unterschiedlich großen Vogelarten, dem Europäischen Star (Sturnus vulgaris) und der Gartengrasmücke (Sylvia borin), haben wir multifaktorielle lineare Regressionsmodelle auf ihre Genauigkeit hinsichtlich einer präzisen Voraussage der Flugmuskelmasse überprüft. Das Regressionsmodell mit der besten Anpassung an die empirischen Daten beider Vogelarten beinhaltet den ‘Muskel-Meter Score’ (mmscore), die Tarsuslänge und die Körpermasse (m b). Das einfachere Modell mit mmscore und m b erzielt eine ähnliche Übereinstimmung, allerdings nur für den Europäischen Star. Eine Validitätsprüfung zeigt, dass die Flugmuskelmasse der beiden Arten mit einem relativen Fehler von 3% abgeschätzt werden kann. In Kombination mit Standardmessungen, wie der Tarsuslänge und der Körpermasse, ist somit das Muskel-Meter bestens für eine rasche und genaue, nicht-invasive Abschätzung der Flugmuskelmasse von Wildvögeln und Vögeln in Tierhaltung geeignet.

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Acknowledgments

The muscle meter development started in 1996 when H.B, H.K and U.B developed the first prototype. We thank Franz Antoni and Klaus Pichler for their excellent support constructing the muscle meter and their help in finding solutions to simplify the measurement envisioning an easy to handle device. Josef Chernichko and other members of the Azov-Black Sea Ornithological Station, Ukraine, made the collection of garden warblers possible. We thank Chris Guglielmo, and other “AFAR” members, for their generous support of the European starling project, and Lillie Langlois, Michelle Boyles and Alexander Gerson for their contributions in running the experiment. David Swanson and an anonymous reviewer provided constructive comments that helped to improve the manuscript. The research project on starlings performed in Canada was approved by the University of Western Ontario Animal Use Sub-Committee (Starlings, protocol no. 2006-011-04). The field trip to Ukraine was funded by an ESF-travel grant to U.B.; the research on European starlings was funded by a NSF-research grant to S.McW.

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Correspondence to Ulf Bauchinger.

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Communicated by C.G. Guglielmo.

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Bauchinger, U., McWilliams, S.R., Kolb, H. et al. Flight muscle shape reliably predicts flight muscle mass of migratory songbirds: a new tool for field ornithologists. J Ornithol 152, 507–514 (2011). https://doi.org/10.1007/s10336-010-0644-3

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Keywords

  • Calibration
  • Validation
  • Pectoral muscle
  • Body condition
  • Passerine