The first in-depth analysis into the seasonal timing of certain bird and insect behaviours has confirmed that spring is indeed getting earlier each year – but that exactly how much earlier these events now start depends on where in the UK and in which habitat they occur.
The authors of the report have warned these trends could have serious ramifications for ecosystems, as significant variation between groups of animals in the rates of advance means populations are becoming “out of sync” with the life cycles of their prey.
The fifty-year study into natural cycles of egg laying and migration has also dashed environmentalists’ hopes that shaded habitats such as forests are shielding some populations from the destabilising effects of global warming.
Lead author Dr James Bell, who heads up the Rothamsted Insect Survey, said: “There was already good evidence that spring is coming earlier each year, but what we didn’t expect to find was that it was advancing as much in forests as it is in open areas such as grassland.
“Equally, in areas where we’d expect to see much greater acceleration, such as urban parkland, the rates of advance appear to be the same.
“This all points to a complex picture emerging under climate change, which makes ecosystem responses hard to predict, and even harder for conservationists to prepare for.”
An earlier study by the group looking at a 30-year period had shown the average rate of advance varied from about a week earlier for birds and a month earlier for aphids, but this new paper reveals an even more complex picture.
Dr Stephen Thackeray of the Centre for Ecology & Hydrology, leader of the NERC-funded project, said “Our previous research has shown that, in the UK, many signs of spring have been shifting earlier over the last few decades and that this is likely to be driven by climatic change.
“However, we have never before had such a detailed picture of how these changes vary across the UK and its major habitats.”
Published in the journal Global Change Biology, the study charts the seasonal habits of more than 250 UK species of birds and insects, and shows clear evidence that aphids, moths and butterflies are now on the wing, and birds are laying their eggs, much earlier than they were in the mid twentieth century.
The researchers, which also included scientists from the Centre for Ecology & Hydrology (CEH), the British Trust for Ornithology (BTO), Butterfly Conservation, and Science and Advice for Scottish Agriculture (SASA), analysed data collected between 1960 and 2010 from three national monitoring networks – the Rothamsted Insect Survey, the UK Butterfly Monitoring Scheme, and the Nest Record Scheme
The long-term changes they uncovered broadly confirm similar effects being observed the world over – that as global temperatures rise, natural phenomena such as flowering, or emergence from hibernation, are occurring earlier each year.
But by looking in detail at this long-term data, the team have revealed the responses of some species to climate change are not straightforward, nor necessarily predictable.
Moths provide a good example of this; as those species that turn from caterpillars to adults earlier in the year are apparently much more sensitive to global warming than those emerging later in the summer.
Those moths that start flying before June have started doing so much earlier in the year.
Prof Tom Brereton of Butterfly Conservation said it was unclear what was behind these specific patterns, nor why butterflies didn’t show something similar.
“Whatever the reasons, we should be concerned about how dramatically climate change is affecting butterfly and moth life cycles.”
And bucking this trend towards earlier onset are those birds and butterflies that inhabit farmland, as well as birds who live in coastal habitats – providing possible evidence that other factors, such as declining food availability, are applying a different pressure on these populations and delaying the onset of breeding.