It’s no secret that spring is now starting earlier, but exactly how, why and where this is happening is a much more complex question. Using 50 years worth of observations of UK aphids, moths, butterflies and birds (researchers first began to track these species in earnest in the 1960s), a group of researchers led by Dr James Bell of the Rothamsted Insect Survey, has tried to answer some of these questions.

On the one hand, the results confirm current understanding. The study reveals that aphids, moths and butterflies are now flying much earlier than in the mid-20th century and that birds are laying eggs earlier. This early awakening isn’t uniform across species however and the degree of change varies depending on location and habitat. As a result, the researchers have warned that wildlife could get ‘out of sync’ with the life cycles of other species that they rely on for food. Previous research has already demonstrated that secondary consumers (for example some birds) are less sensitive to climate change than the primary producers and consumers they feed on (such as insects and plants), highlighting the potentially desynchronising effect of these changes.

Some of this variation in behaviour is related to differences in the species themselves – moths which turn from caterpillars to flying adults earlier in the year seemed to be more responsive to climate change than those which change later. In other cases, geographical location is key. Spring activity generally occurred later in the north of the country, though the specifics varied from species to species. While butterflies appeared to become active earlier in the warmer, wetter west than in the colder, drier east, the opposite scenario appeared to be true for birds laying eggs.

Other findings were much more surprising. Agricultural habitats saw activity by birds and butterflies occur later than in other areas. The theory is that this is likely to be a product of changes in management practice or another effect unrelated to global warming, such as reduced food sources. In addition, woodland habitats, which are thought to offer animals a more stable climate due their canopy cover, and which researchers hoped might present a ‘buffer’ to climate change, did not appear to do so.

It is this finding in particular that concerns scientists. ‘We should see some sort of buffering by the woodland that would protect them against the advances of temperature, but actually we don’t see that,’ explains Dr Bell. ‘We have to conjecture that even though woodlands are stable micro-climates, they too are advancing at the same rate.’ Though further data collection and research now needs to take place, to establish exactly why this is the case, the outcome seems clear. ‘The implication is that wherever their niche, all species are at greater risk than previously thought,’ says Bell.

 This was published in the June 2019 edition of Geographical magazine

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