THE BREEDING BIOLOGY OF THE WILLOW TIT IN NORTHEASTERN SIBERIA

We studied the breeding biology of the Willow Tit (Parus montanus) dur ing 1987-1990 in the Magadan region of northeastern Siberia. Clutch si ze and number of fledglings averaged 7.5 and 6.5, respectively, and bo th were correlated negatively with the date of the first egg. Nestling growth rate was correlated positively with the date of the first egg, but was not related to brood size. Body mass at fledging was related negatively to brood size. Males fed nestlings significantly more often than did females, while females spent more time attending nestlings. The number of parental visits per young did not change significantly w ith brood size. During the first 13 days of the nestling period, femal e feeding rate per young was positively related to brood size while fo r males this relationship was negative. The nestling diet consisted mo stly of Lepidoptera larvae, Arachnoidea, and Diptera.