Sexing and ageing of the Canary Island Stonechat Saxicola dacotiae by moult

Authors: Juan Carlos ILLERA and Juan Carlos ATIENZA

Published: Volume 49(2), December 2002. Pages 273-281.

Language: Spanish

Original Title: Determinación del sexo y edad en la Tarabilla Canaria Saxicola dacotiae mediante el estudio de la muda

Keywords: age, Canary Islands Stonechat, Fuerteventura, moult, Saxicola dacotiae, sex, wing formula and wing length

Summary:

The aim of this study is to offer data for sexing juveniles and ageing Canary Islands Stonechats Saxicola dacotiae, an endemic and endangered bird, using data on wing measurements, moult, wing-formula and the inside colour of the upper mandible of wild-caught birds which were examined alive and then released. From January 2001 to July 2002, 92 individuals, both juveniles (EURING 3 or 5) and adults (EURING 4 or 6), were captured in several localities of the Fuerteventura Island (Canary Islands, Spain). From 24 June to 2 July 2002 the moult pattern of 26 individuals were studied in detail. The postjuvenile moult was partial, whereas the postbreeding moult was complete. The moult period lasted from April-May to July in adults and from March to July in juveniles. The postjuvenile moult included all lesser coverts (CPe) and median coverts (CMe) and a variable proportion of the larger coverts (CMa), although males changed significantly more feathers than females. After moult is finished, ageing of spring-summer birds can be safely based on the presence of moult limits: birds with moult limits within CMa feathers are always juveniles. The CMa 8-10 and the inner web of CMa 7 are full white in adult males, whereas unmoulted CMa feathers are similar to CMa 6 in juveniles. Moreover, the inner web of the third primary covert (PC3) and PC4 are also white in the adult males whereas the outer webs are black, but grey in juveniles with a lighter tip. Wing-lengths of juvenile males were significantly larger than wing-lengths of juvenile females. The inside of the upper mandible was dark grey in adults and yellowish in juveniles. The tip of the ninth primary falls between the third and fourth primaries or, exceptionally, it is as long as the third primary. This pattern was not influenced by either age or sex. The wing tip was made by P6 and P7 (70%, n=9), by P6 (15%, n=2) or by P7 (15%, n=2). Sexing juveniles can be possible if the moult of CPe feathers had started, since CPes of adult males are black and those of adult females are grey. Besides, juvenile males showed a conspicuous light spot at the tip of CP3 and CP4 but juvenile female did not. These results showed that moult, colour of feathers changed or kept, wing length and the colour of the inside of the upper mandible can be reliably used, when considered together, for ageing and sexing any juvenile individual of the Canary Islands Stonechat.

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