The reproductive success of birds depends on many factors, including nest construction and placement. In the mountainous regions of southwestern Iran, broods of Eastern Rock Nuthatch Sitta tephronota were surveyed in 2016 and 2017. During the study, 11 broods in rocky cavities and 16 in abandoned Syrian woodpeckers' Dendrocopos syriacus tree cavities were compared in terms of breeding performance (phenology, clutch size, hatching success, number of fledglings, breeding success). The Eastern

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... Nuthatch began egg-laying on March 24 and continued until April 15. The number of eggs in the clutch ranged from 3 and 7 (mean 5.6±1.19, median 6, N = 27). The two types of clutches compared usually contained 6 eggs, and the number of nestlings was statistically lower in tree cavities than in rocky nests. Hatching success was almost 30% higher in rocky nests than in tree cavities. In broods located in trees, 4 nestlings hatched most often (42%, N = 12), and in rock nests, 5 nestlings hatched (50%, N = 10). Rocky nests were also statistically greater (by over 40%) for breeding success. For all analysed broods and broods with success, roughly two extra fledglings left the rocky nests compared with tree cavities. 5 fledglings (50%, N = 10) most often left rocky nests, whereas, in general, 4 fledglings (50%, N = 10) left tree nests. Research results did not confirm that woodpecker cavities are safe nest sites for cavity dwellers.