With millions of us loving watching them from our windows, Lockdown ignited a renewed interest in our garden birds.
But by the end of the century, could some species – like the common and popular big tit – vanish from UK gardens? In partnership with Oxford University, researchers at the Norwegian University of Science and Technology have influenced how big boobs respond to the climate crisis.
Are the birds able to respond to the earlier appearance of their chicks’ feeding caterpillars? Birds such as big tits have evolved to coincide with the height of moth caterpillars feeding on oak leaves, which usually occurs in late May and June, in time for their breeding period.
As temperatures increase, however, oaks begin to bloom earlier and caterpillars often hatch earlier, ensuring that by the time great tit chicks can be fed, the height of the caterpillar population is over.
Because parent birds need to raise 1,000 caterpillars per day for their hungry offspring, any mismatch is likely to drastically decrease breeding performance. The researchers noticed that they do not do so quickly enough while the birds can react to climate changes.
Lead author Emily Simmonds reports that when oak leaves and their associated caterpillars emerge 24 days earlier than average, the tipping point is reached. Dr. Humphrey Crick, a scientist working for the British Trust for Ornithology, first made the discovery in the 1990s that birds can and do respond to climate change by breeding earlier than normal. He studied thousands of charts from the long-standing Nest Record Scheme of the BTO, which had been filled out over the past half-century by amateur birdwatchers, documenting egg-laying and chick hatching dates. Crick found a startling trend: the egg-laying date had moved forward by an average of nine days for several birds. Published in the journal Nature in 1997, the resulting seminal paper, ‘UK birds are laying eggs earlier,’ presented some of the first scientific proof that wild animals were already adapting to a changing climate. I recall Bill Oddie presenting Springwatch in 2006, a decade later, with the surprising news that every blue tit nest they encountered had already fled – many weeks earlier than normal.
Since there is only one brood in the blue tits, they have to adapt very quickly to changes such as an earlier spring.
If they don’t do that fast enough, their numbers will decline. In 1997, at the end of his article, Humphrey Crick made this prophetic statement, “For birds, earlier breeding may be beneficial if young birds’ survival is improved by a longer time before winter.”
“In contrast, if they are out of sync with the phenology of their food supply, it may be detrimental to birds. “More than a quarter of a century later, both aspects of this prediction seem to be coming true.
A longer breeding season has advantages in the short term, especially for birds such as robins, blackbirds and song thrushes that raise two or more breeding pairs.
BTO Scientific Director Professor James Pearce-Higgins points out that our smallest birds, such as goldcrests, wrens and long-tailed tits, benefit from another aspect of climate change: the much milder winters of recent years, and he also points to the beneficial results of our habit of feeding garden birds that sustain species such as blue tits, big tits and goldfinches.
Today, he notes, the advantages of higher winter survival rates outweigh the lack of coordination with the availability of food in spring, although that may not always be the case. The way many organisms are now moving northward is another climate-related achievement. The new European Breeding Bird Atlas shows that, since the original survey in the late 1980s, the ranges of European breeding birds have moved north by an average of 28 km – almost 1 km each year. That may not sound like much, but it will allow species once restricted to mainland Europe to cross the Channel and colonize Britain over time.
Since some species adapt much faster than others, some of them have already done so (including cattle egrets and large egrets). Climate change is dramatically changing the bird species of Britain, a study reveals. Continue reading But as our climate becomes less stable, with more extreme weather events such as hurricanes, drought,