This study was based on spring temperatures, laying dates, and clutch size of the first nesting attempt of the Blue Tit (Parus caeruleus) from 1982 to 2004 in Hrvatsko Zagorje rural area (46° 00′  N, 15° 55′ E), Croatia. The results suggest that timing of breeding of the Blue Tit is influenced by spring air temperatures. There was a significant correlation between spring temperature and years, consistent with a global warming trend. The date of clutch initiation in the Blue Tit population studied did not decrease over a 23-year period. Correlations between spring temperatures and clutch size, and year and clutch size were not significant.