BREEDING BIOLOGY OF THE EURASIAN NUTHATCH IN NORTHEASTERN SIBERIA

The breeding biology of Eurasian NuthatChes (Sitta europaea asiatica) was studied in 1986-1990 in two habitats, riparian and upland forests, in the Magadan region, northeastern Siberia. Clutch sizes and breedin g success averaged 6.49 eggs and 57.5%, respectively, and varied among years. Habitat influenced clutch size but not numbers of young fledge d from successful nests. Within seasons, date of first egg was correla ted negatively with clutch size, while in years in which breeding star ted later, nuthatches laid significantly larger clutches. Female age h ad a significant effect on the timing of the start of breeding, wherea s neither female nor male age influenced clutch size or number of fled glings. Mass of young at the time of fledging was independent of brood size. The yearly mean brood size correlated positively and significan tly with mean yearly nestling growth rate and mean body mass of nestli ngs at 18 days of age.