Both the Buzzard and the Goshawk nested mainly in pines. The mean clutch size in the former was 2.8, in the latter 3.6 eggs per breeding pair. There were statistically significant differences in clutch sizes in the Buzzard in particular breeding seasons. The mean number of hatchlings was 2.3 in the Buzzard and 2.6 in the Goshawk. Brood losses were similar in both raptors - 19% in the Goshawk and 24% in the Buzzard. The breeding success (the ratio of the number of fledglings to the clutch size) in the Buzzard was highest in clutches of 3 and 4 eggs, whereas in the Goshawk a similar level of success was achieved with smaller clutches (2 or 3 eggs). Only in the case of the Buzzard there were significant differences in clutch sizes and numbers of fledglings in the various years. In this species the mean number of fledglings was positively correlated with the rodent availability index in a given year. There was no such relationship between the abundance of prey items found in Goshawk nests and the number of fledglings. The correlation between the number of newly-fledged Buzzards and Goshawks in a given year could have been due to diet overlap between the two species.
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Domaniewski, Janusz (1891-1954) Państwowe Muzeum Zoologiczne