Seasonal variation in wing length and body mass in the Northern Wheatear Oenanthe oenanthe at the Gran Sasso area

Strinella E., Pirrello S., Artese C., De Faveri A.

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In this study, we use the ringing data on Northern Wheatears captured during the period 2004-2013 in the Gran Sasso area. We considered 3222 ringed individuals to analyze seasonal variation in wing length and body mass of adults (males and females) and juveniles. During the breeding season (7 May-4 August) the wing length of adults was 2.8 mm longer in males, whereas the body mass did not differ between the sexes. The wing length increase in August can be caused by the passage of adults and juveniles from other territories that likely replaced individuals that were present during the breeding season in this area. In addition, the inter-annual fluctuations of captures probably reflected variations in weather condition between years, which is one of the major factors influencing the timing of migration (e.g. bad weather solicits early departures from breeding grounds) and reproduction (e.g. bad weather delays depositions and increases the parental effort) of high altitude bird species.