SEXUAL AND SEASONAL, VARIATION IN CONDITION AND SURVIVAL OF SWEDISH GOSHAWKS ACCIPITER GENTILIS

• Published in: Ibis
• Main Authors: Marcström, Vidar, Kenward, Robert
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1981
• Subjects: Accipiter gentilis
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1981.tb04033.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1981.tb04033.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1981.tb04033.x

Summary Winglength was the most powerful intersex discriminator, giving 99.5% separation by itself and 100% combined with bodyweight or keel length. Females but not males, had longer wings and were heavier as adults than as juveniles. Pectoral fat and muscle indices explained 81–91% of variation in total fat and 93–96% of variation in total lean dry weight for male and female hawks but bodyweight change explained only 56–60% of variation in the fat index compared with 75–76% for pectoral lean dry weight. The best size index, keel length, explained only 6.4% of bodyweight variation in males and 11.2% in females. Winglength was very weakly correlated with keel length. Taking size difference into account, females were heavier with higher wingloading than males but had relatively lighter flight muscles and therefore a lower power availability relative to their flight requirements than in males. On the other hand, females had greater maximum fat stores (17% of bodyweight) than males (14%) and could have survived longer than males without food. These differences would be adaptive for the different role of each sex during breeding. The weight of first capture of live‐trapped adults and juveniles increased between September and December, possibly because moulting (in adults) or hunting inexperience (in juveniles) kept weights low in autumn but also perhaps because the benefit of having large reserves for surviving, relative to the cost of decreased agility in flight because of increased wingloading, was greatest in mid‐winter. Shot hawks weighed more than the live‐trapped birds but showed the same trends, as did retrapped individuals. Females but not males, tended to lose weight in January before a further increase in the spring. Records of hawks retaken more than two months after first capture showed that between October and January survival in females but not males, was enhanced by high bodyweight. Since female weights were also significantly lower in southern Sweden than in central and northern areas, it is suggested ...