Asymmetric iris heterochromia in birds: the dark crescent of buttonquails

Abstract

I describe for the first time the unique coloured pattern of the iris of buttonquails (Turnicidae). This unique pattern is due to the presence of a dark-brown crescent in the iris below the pupil, whose form and extent varies in response to light conditions. This dark crescent is present in the eyes of all individuals of Turnix species at every life stage, a consistency that has not been previously observed for the iridal marks found in other avian groups. This consistency suggests that the crescent-shaped spot in buttonquails’ eyes is a character subjected to natural selection, probably related to light regulation. This possibility deserves further study.

Zusammenfassung

Asymmetrische Iris-Heterochromie bei Vögeln: der dunkle Halbmond der Laufhühnchen

Dies ist die Erstbeschreibung eines einzigartigen Musters der Irisfärbung bei Laufhühnchen (Turnicidae). Dieses beruht auf dem Vorhandensein eines dunkelbraunen Halbmondes in der Iris unterhalb der Pupille, dessen Form und Ausmaß sich in Abhängigkeit von den Lichtbedingungen ändern. Diesen dunklen Halbmond findet man in den Augen aller Individuen sämtlicher Turnix-Arten in allen Lebensphasen, eine Durchgängigkeit, welche bisher noch für keine der Irisflecken anderer Vogelgruppen beobachtet wurde. Diese Kontinuität spricht zudem dafür, dass dieser halbmondförmige Fleck in den Augen der Laufhühnchen ein Merkmal ist, welches der natürlichen Selektion unterliegt, vielleicht im Zusammenhang mit der Lichtregulation, eine Möglichkeit, welche eine nähere Untersuchung verdient.

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Acknowledgements

The Haut Commissariat aux Eaux et Forêts et à la Lutte contre la Desertification authorised the surveys done in Morocco, and Abdeljebbar Qninba helped with all the logistics. The ZooBotánico de Jerez gave me the opportunity to study the captive birds. Daniel López Velasco and Marcel Holyoak shared their high-quality photographs of the Quail-plover; Jacinto Román helped with preparation of the figures, and Eloy Revilla, Miguel Clavero, Pedro Jordano, Miguel Delibes and two anonymous reviewers made very valuable comments on the manuscript. The author was funded by a grant (BES-2015-074938) from the Severo Ochoa Program to the Centres of Excellence in R + D + I (SEV-2012-0262-01) of the Spanish Ministry of Economy and Competitiveness.

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Correspondence to Carlos Gutiérrez-Expósito.

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Communicated by F. Bairlein.

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Gutiérrez-Expósito, C. Asymmetric iris heterochromia in birds: the dark crescent of buttonquails. J Ornithol 160, 281–285 (2019). https://doi.org/10.1007/s10336-018-1606-4

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Keywords

  • Turnix
  • Vision
  • Light regulation
  • Natural selection
  • Pupil