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 that feed on them have to breed sooner to avoid missing out on food sources for their hungry chicks.
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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 that 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 Edinburgh and Exeter, as well as Glasgow, Stirling, Cardiff, Durham and Sheffield, found no evidence to support the theory it is worse in southern Britain than the north, where birds might be “buffered” from climate change.
Population declines of birds that feed on insects in southern Britain do not seem to be the result of species facing a greater disconnect between caterpillars emerging and when they nest, the researchers said.
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Dr Malcolm Burgess, of Exeter University and the RSPB, said: “Forests have a short peak in caterpillar abundance, and some forest birds time their breeding so this coincides with when their chicks are hungriest.
“With spring coming earlier due to climate change, leaves and caterpillars emerge earlier and birds need to breed earlier to avoid being mismatched. We found the earlier the spring, the less able birds are to do this.”
Dr Ally Phillimore, from Edinburgh University, added: “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.”
The first leafing dates of oak trees were collected by the public through the Woodland Trust’s Nature’s Calendar scheme and caterpillar abundance was monitored by collecting droppings under oaks.
The timing of egg laying by blue tits, great tits and pied flycatchers were recorded by volunteers in the British Trust for Ornithology’s nest record scheme.
It comes as Scotland’s blue tits, great tits and coal tits suffered a decline this winter.
While the blue tit rose to fourth place in the RSPB’s 39th annual Big Garden Birdwatch, sightings fell by six per cent.
Great tit numbers were down by 7% and coal tits by 11% over the year. More than 29,000 people in Scotland counted 521,428 birds during the January survey.
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For the second year, house sparrows, starlings and chaffinches were the top three birds spotted. The goldfinch soared two places to seventh position as sightings rose by 14 per cent.
RSPB Scotland said while many of the birds will have benefitted from good conditions for their breeding season in 2017, the colder weather in the run-up to the Birdwatch weekend may have influenced which species were seen most during people’s counting hour.
A separate Scottish study found the breeding success of urban blue tits was five times worse than their rural counterparts. It has implications for wildlife, with many animal species, especially birds, suffering reduced reproduction as they trail humans into built-up areas.
The planting of oak trees – caterpillars’ favoured home – is among strategies being suggested along with less use of insecticides. Poor nestling diet was found to be linked to the low breeding success of city blue tits, with them having to rely on indigestible peanut granules instead.
With more than half the human population living in cities they offer certain benefits for birds, but these benefits can be offset by major ecological deficits – as now shown for blue tits.
Martha Boalch, from the Woodland Trust, said: “As seasons and the weather continue to fluctuate, we need to understand our native flora and fauna is coping.”
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She said citizen scientists who collected data for the Nature’s Calendar project, which records the changing seasons, helped provide scientific data on a scale that could not otherwise be achieved.
Man-made CO² rise is 100 times faster than what ended Ice Age
HUMANS have driven a rise in CO² in the atmosphere as large as that which helped end the last Ice Age, according to research.
However, scientists at St Andrews University say the man-made CO² rise has happened 100 times faster than the previous change some 15,000 years ago. They believe we are now seeing only the beginning of “a huge effect on the climate system”.
The claim is made after researchers discovered changes in the circulation of the North Pacific Ocean about 15,000 years ago released large amounts of CO² to the atmosphere, helping warm the planet and end the last Ice Age.
The study, published yesterday in the journal Nature Geoscience, also found the changes in circulation resulted in a reduction of the amount of oxygen in the deep ocean.
The researchers measured the chemical composition of the shells of tiny fossil plankton, called foraminifera, which they used to reconstruct the exchange of CO² between the North Pacific Ocean and atmosphere at the end of the last Ice Age, when carbon dioxide levels in the atmosphere increased.
They found the release of large amounts of CO² from the North Pacific to the atmosphere was caused by a change in its circulation, which could explain a drop in oxygen levels in the Pacific Ocean seen at the same time, first found over 20 years ago.
Scientists are observing a similar loss of oxygen from the ocean as the climate changes today.
Dr James Rae, from the School of Earth and Environmental Sciences at St Andrews University, said: “Although the CO2 rise caused by this process was dramatic in geological terms, it happened very slowly compared to modern man-made CO² rise.
“Humans have driven CO² rise in the atmosphere as large as the CO² rise that helped end the last Ice Age, but the man-made CO² rise has happened 100 times faster.
“This will have a huge effect on the climate system, and one we are only just beginning to see.
“We are going into geologically unprecedented territory. Although CO² has been this high before it has never been this high this quickly.
“The planet is now 1°Celsius warmer than it was 100 years ago and the Arctic is already 4°Celsius warmer, which is like the difference between St Andrews and Paris.
“Looking at rapid climate changes in the geological record can help us try and understand what’s happening at present.”
“It is important to stress we know exactly how to fix this problem and there is still time to do that – that is rapidly reduce the amount of CO² in the atmosphere and there is some really exciting progress in that regard.”
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