Overview
- Published March 11 in Global Change Biology, the University of Oxford study draws on six decades of Wytham Woods data covering over 80,000 individual great tits.
- Cold snaps in the first week after hatching and heavy rain later in development each reduce mass at fledging by up to about 3%, a key predictor of survival.
- When intense heat coincides with heavy rain, fledging mass can drop by as much as 27%, with the steepest losses seen in broods hatching later in the season.
- Breeding earlier within a season buffers many weather-related effects but increases exposure to late cold spells, and the study reports strengthening selection against smaller fledglings.
- Moderate warm spells in temperate Oxfordshire are linked to heavier fledglings and small survival gains, contrasting with hotter regions, and researchers call for fine-scale monitoring and targeted habitat management.