Climate change creating bird-caterpillar ‘mismatch’

Earlier springs driven by climate change are creating a “mismatch” between when caterpillars hatch and baby birds are feeding, scientists have warned.

Data collected from “citizen scientists” across the UK has helped researchers compare the emergence of oak tree leaves and caterpillars and the timing of nesting by blue tits, great tits and pied flycatchers. With spring coming earlier due to rising temperatures, leaves and caterpillars emerge earlier in the year, and forest birds which feed on them have to breed sooner to avoid missing out on food sources for their hungry chicks.

The earlier the spring, the less able the birds are to do this, and the peak in caterpillars is more out of sync with the peak in chicks demanding food, the study published in the journal Nature Ecology and Evolution found.

With continued spring warming expected due to climate change, the scientists warned the hatching of forest birds will be “increasingly mismatched” with peaks in caterpillar numbers.

The biggest disparity was for pied flycatchers, a migratory species which are not in the UK in winter to react to earlier warm weather, though they feed their chicks more winged insects so may be less dependent on the caterpillar peak.

The research team – led by the RSPB and universities of Exeter and Edinburgh, as well as Durham, Sheffield, Glasgow, Stirling and Cardiff – found no evidence to support the theory that it is worse in southern Britain than the north, where birds might be “buffered” from climate change.

Pied flycatchers are particularly affected