Warmer springs reduce food for forest birds

With climate change expected to drive continued spring warming, chicks such as blue tits will be increasingly mismatched with earlier peaks in caterpillar numbers, scientists say.

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Volunteer data

Researchers from the RSPB and the Universities of Exeter and Edinburgh used data collected across the UK – largely by volunteers – to study the seasonal emergence of oak tree leaves and caterpillars, and the timing of nesting by blue tits, great tits and pied flycatchers.

They examined the impact of warmer springs, when caterpillars emerge earlier and birds need to time their breeding so that the typically short peak in insect availability coincides with when chicks are hungriest.

Nationwide outcome

The study showed no variation in the effect between northern and southern Britain, contrary to what was previously thought.

The first leafing dates of oak trees were collected by citizen scientists coordinated by the Woodland Trust via the organisation Nature’s Calendar.

Caterpillar abundance was recorded by monitoring droppings beneath oak trees, and the timing of egg laying by blue tits, great tits and pied flycatchers was recorded by the British Trust for Ornithology's long-running Nest Record Scheme.

The research team included the Universities of Durham, Sheffield, Glasgow, Oxford, Stirling and Cardiff.

The study was published in the journal Nature Ecology and Evolution.

We found no evidence of north-south variation in caterpillar-bird mismatch for any of the bird species. Therefore, population declines of insectivorous birds in southern Britain do not appear to be caused by greater mismatch in the south than the north. This also means if spring temperatures rise then woodland birds may be mismatched everywhere, and not just in the south.

Dr Ally Phillimore

Related Links 

Tritrophic phenological match–mismatch in space and time, Nature Ecology & Evolution