Changes in diet and morphology of Finnish goshawks from 1960s to 1990s |
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Authors: | R Tornberg Mikko Mönkkönen Maarit Pahkala |
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Institution: | (1) Department of Biology, University of Oulu, POB 3000, FIN-90401 Oulu, Finland e-mail risto.tornberg@oulu.fi Fax: +358-8-5531227, FI |
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Abstract: | We studied the morphology of the goshawk in northern Finland by measuring skin and skeletal characters of 258 museum specimens
dated between 1961 and 1997. We predicted a decrease in the size of male goshawks from the 1960s because availability of their
main prey, grouse, has decreased since then and grouse have been replaced in the diet by smaller prey during the breeding
season. Based on the assumption that winter is the most critical period for females, we predicted that female size should
have increased because their winter diet consisted of more and more mountain hare, which is a prey generally larger than grouse.
Analyses revealed that male size has indeed decreased since the 1960s, while adult females have increased in size. Our data
suggest that these morphological shifts were the result of selective pressures due to changes in diet. We also found changes
in the (size-independent) shape of the hawks. Relative wing and tail lengths of adult hawks became longer between 1980 and
1990 compared with the 1960–1970 period, while relative juvenile wing and tail lengths tended to decrease. As a result of
these morphological changes size dimorphism between the sexes increased from the 1960s to the 1990s.
Received: 18 January 1999 / Accepted: 14 July 1999 |
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Keywords: | Goshawk Grouse Mountain hare Morphology Reversed sexual size dimorphism |
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