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Global warming is changing European birds as we know them, a study has found, but it’s not just the increase in temperature that’s to blame.
Researchers discovered that garden warblers are having 25% fewer chicks than their counterparts in the wild. This has major implications for the species. Chiffchaffs lay their eggs 12 days earlier than usual. Redstarts are growing larger, while passerines are becoming smaller.
Researchers analyzed data from Britain and the United States dating back to the mid-90s. NetherlandsOn 60 species, including the house sparrow and the crested Tit, the bullfinch, the reed bunting and the bullfinch. They examine how these birds have changed over the years in terms of their egg-laying patterns, number of offspring, and morphology.
Although research has already linked the way passerines – the swallow family – are getting smaller over timeScientists are predicting higher temperatures weren’t sure whetherThis was either directly due to heat stress or because rising temperatures make it more difficult to forage.
Scientists examined whether changes in temperature over time were related to warming and whether warming affected certain species or traits more than others. They also looked into whether other factors, unrelated to temperature, could have an impact on these effects.
The study, which was published in the Proceedings of the National Academy of Sciences journal last week, found that although more than half of trait changes are linked with rising temperatures – and warming is likely the largest factor driving change over the years – other factors such as urbanisation, pollution, habitat loss and more could also affect shifts in characteristics.
“For example, climate change caused chiffchaffs to lay their eggs six days earlier over the last 50 years, but other unknown environmental factors led to an additional six days, meaning in total they now lay their eggs 12 days earlier than they did half a century ago”, said Martijn van de PolJames Cook University in Australia was the lead author.
This big a change in the schedule can lead to a mismatch between when chicks become adults and when food is available, which can disrupt the ecosystem balance.
According to the study, temperature-related changes can account for as much as 57% of global change in the past decade. The study found that 32% of 60 bird species experienced changes in their bodies due to temperature rises. This average decrease in size was 0.45% for each degree Celsius increase in heat. 86% of birds experienced changes in egg-laying times and 31% saw a decrease in the number or offspring.
“Garden warblers in the UK have experienced a 26% decrease in their average number of offspring over the past half century, which is really concerning for the long-term fate of this species,” said Nina McLean, the lead researcher on the study, from the ANU Research School of Biology. “But only half of this reduction, 13%, can be attributed to climate change.”
Different species are affected differently. Some species, like the redstart are clearly increasing their body condition as well as their offspring number. The researchers speculate the variation of how much different species’ traits are changing is most probably up to non-temperature factors.
“The study gives a well-grounded explanation for why different species change at such different rates. And it is not to do with temperature sensitivity, but with those other, non-temperature factors,” said Shahar Dubiner, an ecologist at Tel Aviv University, who was not involved in the study. Dubiner’s research has, similarly, found dramatic changes in shape and body condition for over half of Israeli bird species – including many who migrate from Europe, such as storks.
Overall, this means warming is likely the largest factor driving trait change, but it’s not the only element at play. Other adjacent factors may play a more prominent role than previously thought – the question is what these other non-temperature factors are, and how they are linked to temperature increase.
