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Effect of habitat, date of laying and density on clutch size of the Great Tit Parus major in northern Finland |
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| Authors: | Markku Orell Mikko Ojanen |
| Institution: | M. Orell, Dept of Zoology, Univ. of Oulu, Kasarmintie 8, SF-90100 Oulu 10, Finland. M. Ojanen, Div. of Biology, Dept of Anatomy, Univ. of Oulu, Kajaanintie 52A, SF-90220 Oulu 22, Finland. |
| Abstract: | The sizes of 1034 Great Tit clutches were studied at the Oulu area (c. 65°N, 25°30'E) in northern Finland. The average size was 9.86 eggs in the first clutch and 7.51 in the second in 13 study areas. The decrease in clutch size from the first to the second laying was most pronounced in those females laying the largest first clutches. Irrespective of habitat, the clutch size was larger in the sparsely populated areas than in the densest area (Taskila). The clutch size decreased according to the season in all the areas, but this was not as pronounced in Taskila as in the other areas. The annual average size of the first clutches was inversely related to the breeding density and pronouncedly so to the mean dale of laying. The latter was suggested to be an adaptation to the short season in the northern areas. An analysis of data from 27 study areas in Europe, north of the Mediterranean region, suggests that the clutch size does not vary with latitude or longitude. |
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