Between 1970 and 1995, nestbox data about clutch size, hatching date a
nd fledging success were collected for a total of around 1500 first br
oods of Nuthatches in two north German study areas (near Brunswick 52.
16 N 10.32 E and near Essen 51.24 N 6.59 E). The average clutch size w
as 6.8 eggs (Brunswick), the average hatching date 9 May (Brunswick) a
nd 6 May (Essen), and the mean number of fledglings per successful bro
od 5.6 (Brunswick) and 5.2 (Essen). Over time hatching dates significa
ntly advanced in both areas. Data of further years are needed to clari
fy if the recent unusual sequence of early breeding years in the Nutha
tch is already a consequence of the anthropogenic ''greenhouse effect'
' or just due to normal variation of weather conditions.