Pied flycatchers depend almost entirely on tree cavities or nest boxes for breeding. Long-term nest box monitoring programmes provide uniquely detailed welfare and population data for this summer migrant.
Pied flycatcher welfare research from long-term nest box studies has revealed a phenological mismatch: birds are arriving from Africa on roughly the same date as 40 years ago, but oak caterpillar peaks have advanced 10+ days with warmer springs. This timing gap means chicks are born after the caterpillar food peak — a welfare-critical nutritional shortfall. Birds in years with a mismatch show lower chick weight and reduced survival. Nest box programmes that maintain high cavity density allow pied flycatchers to maximise breeding attempts and partially compensate for the climate-driven mismatch by enabling earlier breeding in occupied boxes.