A warming planet is doing more than raising temperatures. It is also disrupting nature's calendar, and scientists say one of Europe's most recognizable birds could eventually pay the price.

The great tit (Parus major), a common woodland songbird found across Europe, parts of Asia and North Africa, depends on a remarkably precise schedule each spring. As trees leaf out, winter moth caterpillars emerge in abundance, providing the protein-rich diet needed to raise newly hatched chicks. The problem is that climate change is shifting that timetable.

Long-term research from the University of Oxford's Wytham Woods, analyzed by ecologist Dr. Emily Simmonds and colleagues, suggests that while the birds are breeding earlier in response to warmer springs, they are not adapting quickly enough to match the increasingly earlier emergence of caterpillars.

The findings, published in Ecology Letters, point to a growing mismatch between predator and prey. For every 1°C increase in temperature, great tits advance their nesting by about 4.35 days, while caterpillars appear roughly 6.38 days earlier. That widening gap could leave nestlings without enough food during the most critical stage of development.

Researchers modeled several future climate scenarios and found the greatest risk under continued high greenhouse gas emissions. In the worst-case projection, breeding could lag nearly 24 days behind peak caterpillar abundance—a level of seasonal mismatch that could trigger rapid population collapse despite birds appearing healthy today.

Perhaps the study's most striking takeaway is that stable wildlife populations are not always secure.

"What I find most interesting is the idea that populations that seem stable could suddenly go extinct," Simmonds said, describing the food mismatch as a potential ecological tipping point rather than a gradual decline.

The outlook is not entirely bleak. Under low- and medium-emissions scenarios, simulated great tit populations remained relatively stable. The birds may also possess other adaptive strategies not included in the model, including shifting to alternative prey such as spiders or other caterpillar species, though scientists caution these dietary changes may not provide equivalent nutrition for growing chicks.