Effect of extreme weather on the breeding parameters of great tits Parus major: comparison of two very different seasons

Abstract Climate change and extreme weather events may be seen as an opportunity to help understand the mechanisms by which birds adjust their breeding parameters to environmental variability. In the breeding season of 2020, several factors, such as a prolonged drought period, a relatively warm winter with no snow cover, and a cold spring (the coldest May in Poland since 1991) affected many bird populations in Poland. The great tit Parus major tended to produce much smaller clutches, much fewer fledglings, and had very low breeding success, increasing with the progress of the breeding season in 2020, in contrast to the more typical breeding season characterised by average weather parameters in 2018. In light of the results obtained, we agree with the view that the phenotypic plasticity of the breeding parameters of the studied birds, such as phenology, may be insufficient to adjust to the upcoming extreme weather events. Additionally, further examining of the impact of extreme weather events on the breeding biology of animals is an important goal for future studies.