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Scanning behaviour of foraging Ruffs Philomachus pugnax during spring migration: is flock size all that matters?

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Abstract

This study tested for effects of flock size and other potentially important variables (location, vegetation cover, wind force, cloud cover, date, time of day, feeding habitat, number of other waders and peck rate) on the vigilance level of foraging Ruffs Philomachus pugnax during spring migration at Seewinkel, an important stopover site for waders in Eastern Austria. Therefore, foraging Ruffs were filmed at four different salt ponds, with a final total of 681 film sequences being available for analysis. To test for effects of predictor variables on scan rate (number of scans per 30 s) of foraging Ruffs, generalised linear models (GLMs) were calculated including all variables and all possible subsets. Three variables remained in all 30 best GLMs (selected according to Akaike’s information criterion) testing for effects on scan rate of foraging Ruffs: feeding location, feeding habitat and flock size. These variables also significantly affected Ruffs’ scan rates according to Wald statistics. Besides differences of scan rates between feeding locations, the vigilance level was significantly higher in terrestrially foraging Ruffs than in birds feeding at semi-aquatic habitat patches. Furthermore, scan rate decreased with increasing flock size. Our study emphasized that, even when controlled for other variables affecting scan rates, flock size still remains important for explaining variance in vigilance levels of foraging Ruffs.

Zusammenfassung

Die vorliegende Studie testete Effekte von Truppgröße und anderen potentiell wichtigen Variablen (Standort, Vegetationsbedeckung, Windstärke, Bewölkung, Datum, Tageszeit, Nahrungshabitat, Anzahl anderer Limikolen und Pickrate) auf das Sicherungsverhalten von Kampfläufern Philomachus pugnax während des Frühjahrszuges im Seewinkel, einem wichtigen Rastplatz für Limikolen in Ostösterreich. Hierfür wurden Kampfläufer während der Nahrungssuche an vier Salzlacken gefilmt. Insgesamt standen 681 Filmsequenzen für Analysen zur Verfügung. Um Effekte der Prädiktorvariablen auf die Sicherungsrate (Häufigkeit des Sicherungsverhalten pro 30 s) furagierender Kampfläufer zu testen, wurden Verallgemeinerte Lineare Modelle (VLMs) berechnet, wobei alle Variablen und alle möglichen Kombinationen von Teilmengen der berücksichtigten Variablen inkludiert wurden. Drei Variablen verblieben in allen 30 besten VLMs (ausgewählt nach dem Akaike-Informationskriterium) zum Testen von Effekten auf die Sicherungsrate von Kampfläufern: Standort, Nahrungshabitat und Truppgröße. Für diese Variablen zeigte auch die Wald-Statistik einen signifikanten Effekt auf die Sicherungsrate auf. Neben Unterschieden der Sicherungsrate zwischen den Standorten, wiesen an Land furagierende Kampfläufer eine signifikant höhere Sicherungsrate auf als semi-aquatisch Nahrung suchende Vögel. Zudem nahm die Sicherungsrate mit zunehmender Truppgröße ab. Unsere Arbeit hebt – bei gleichzeitiger Berücksichtigung anderer, die Sicherungsrate beeinflussender Variablen – die Bedeutung der Truppgröße hervor, um die Varianz der Sicherungsrate von furagierenden Kampfläufern zu erklären.

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Acknowledgments

In particular, we are grateful to Alfred Grüll, Alois Herzig (Biologische Station Illmitz) and Bernhard Kohler (WWF Austria) who provided invaluable support throughout the field work. Will Cresswell and a second anonymous reviewer provided helpful comments on an earlier manuscript version.

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Authors and Affiliations

  1. Department of Animal Biodiversity, Faculty Centre of Biodiversity, University Vienna, Rennweg 14, 1030, Vienna, Austria

    Claudia Schütz & Christian H. Schulze

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  1. Claudia Schütz
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  2. Christian H. Schulze
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Correspondence to Claudia Schütz.

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Communicated by F. Bairlein.

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Schütz, C., Schulze, C.H. Scanning behaviour of foraging Ruffs Philomachus pugnax during spring migration: is flock size all that matters?. J Ornithol 152, 609–616 (2011). https://doi.org/10.1007/s10336-010-0631-8

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  • DOI: https://doi.org/10.1007/s10336-010-0631-8

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