Great tits are nesting earlier due to climate change

A new longitudinal study led by the University of Oxford has found that, as a consequence of climate change, great tits (Parus major) in Britain are nesting and laying their eggs two weeks earlier than they did 60 years ago. Scientists believe that these phenological modifications were connected to changes in the oak trees’ blooming patterns caused by global warming, as well as to the health of the oak trees located nearby the birds’ nesting areas.

In order to examine the impact of global warming on birds, researchers used breeding data gathered over six decades about more than 13,000 great tits living and nesting in a 385-hectare woodland in Oxfordshire.  

“When we consider data for the population as a whole between 1961 and 2020, both female laying date and the annual timing of peak abundance of winter moth larvae have advanced by over two weeks,” explained the study authors.

Great tits belong to a comprehensively studied food-web, feeding on caterpillars, which in turn feed on newly-emerging oak leaves. Due to climate change, early onsets of springs are making the oak trees bloom earlier, and are thus changing both caterpillars’ and great tits’ timing of crucial biological events.

“A significant predictor of the variability in laying date was the health of oak trees located within 75 metres of each nest box,” explained the researchers. “For example, birds breeding in boxes surrounded by healthy oaks advanced their laying by 0.34 days per year, while those nesting in areas with oaks in poor health advanced by only 0.25 days per year. Great tits breeding in oak-rich territories tend to breed earlier and have higher reproductive success.”

This research has important implications for understanding the capacity of organisms to survive and adapt to climate change. Studying the modifications in the timing of biological events of species such as the great tit can shed new light on how animals can adapt to changing environments.

“Further work should test how phenological change varies at different spatial scales in a range of systems and explore both the underlying mechanisms and the ecological and evolutionary consequences of these processes,” the study authors concluded.

The study is published in the journal Nature Climate Change.

—

By Andrei Ionescu, Earth.com Staff Writer