This dataset contains first egg dates for great tits (Parus major) and blue tits (Cyanistes caeruleus) from Monks Wood, Brampton Wood and Wennington Wood in Cambridgeshire, England, over a 23 year period. The dataset runs from the breeding season in 1993 to the end of the breeding season in 2015. The first egg dates are presented as the number of days from the start date which was set as the 1st April each year. Because the timing of breeding of great tits and blue tits is influenced in large part by ambient temperature and the phenology of their main prey, the data were collected as a measure of spring phenology. These data comprise part of a larger long-term study of the influence of habitat (extent, structure and composition) and landscape factors on abundance, distribution and breeding success of woodland birds in English lowland deciduous woodland. Full details about this dataset can be found at https://doi.org/10.5285/2efa9bf4-e5c0-42f9-8fcb-90dca2bb9c66
