It was found that severe frosts in the first week after hatching, as well as heavy rains, can reduce the mass of chicks at the time of leaving the nest by up to 3%. In cases where hot weather coincides with heavy rains, mass loss can reach 27%, especially among late broods. Featherless chicks are unable to effectively regulate their temperature and are forced to expend energy to maintain warmth, which affects their growth. Additionally, rains wash caterpillars off vegetation, depriving the birds of a primary food source.
An interesting aspect of the study was the finding that moderate temperatures typical of Oxfordshire contribute to an increase in chick mass. This occurs due to increased insect activity, making them easier to find. However, in hotter regions, such as the Mediterranean, similar temperatures already have a negative impact.
According to the researchers, early nesting helps mitigate most of the adverse effects of weather conditions, as it coincides with the peak abundance of caterpillars and helps avoid summer heat. Nevertheless, with the increasing number of extreme weather events caused by climate change, the adaptation of birds will become an increasingly challenging task.
