Sex ratio, survival and territorial behaviour of polygynous Hen Harriers Circus c. cyaneus in Orkney

• Published in: Ibis
• Main Author: Picozzi, N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1984
• Subjects: Circus cyaneus
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1984.tb00256.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1984.tb00256.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1984.tb00256.x

Polygyny is widespread among Orkney's Hen Harriers Circus cyaneus . From 1975–81, it was associated with a sex ratio estimated from resightings of colour‐marked birds up to six years of age to be 29 females:ten males. The sex ratio of fledglings changed significantly from a greater proportion of females in the 1950s and early 1960s to a greater proportion of males subsequently. The mean estimated ‘survival’ rates (birds colour‐marked in Orkney which were seen there in later years) of males and of females 0–2 years old were 14 and 29%. The mean estimated annual survival rates of males and females from 2–6 years old were 72 and 90%. It is suggested that the uneven sex ratio resulted in more frequent intra‐sexual encounters and displays by females. The results of temporary removals of two females (immediately replaced) and of two males (not replaced) in spring indicates that there was a shortage of males in the population.