Pied flycatchers are declining summer migrants suffering from climate-driven phenological mismatch between their arrival and the peak of caterpillar prey availability in oak woodlands.
Pied flycatcher welfare is directly threatened by climate-driven phenological mismatch. When the spring caterpillar peak advances relative to the birds' arrival and chick hatching dates, parents must work increasingly hard to find sufficient food for growing chicks. In bad mismatch years, chicks experience food shortage during their critical growth period, causing slower development, reduced immune function, and higher mortality. Adults working in food-poor conditions experience elevated physiological stress and reduced survival probability. The adaptive mismatch is a welfare problem that will intensify with continued climate warming unless birds can accelerate their migration timing.