Global warming is not only threatening the existence of our winged friends but also leaving them smaller in size!
Look at the impact of climate change on birds: Their legs are growing shorter, wings slightly longers, and they weigh less. All due to climate change, said a study published in the recent edition of journal Ecology Letters.
Researchers from the University of Michigan and the Field Museum in Chicago came to these conclusions after measuring 70,716 birds, representing 52 species in the period spanning last 40 years.
David Willard, a Field Museum ornithologist from University of Michigan, had started measuring the dead birds since 1978 after a migratory bird died after colliding into buildings in Chicago. He collected the specimen for the Field Museum of Natural History. These include sparrows, thrushes and warblers that were collected between 1978 and 2016.
The scientists think that warmer temperatures reduced the birds’ size, and wingspans increased to compensate, since smaller bodies mean less energy to power the birds through their long seasonal migrations.
“Warming temperatures seem to be having a pretty consistent and almost universal effect on a large number of different species, regardless of other aspects of their biology,” said study author Benjamin Winger from the University of Michigan.
Fifteen species of common birds, including swamp sparrows and dark-eyed juncos, made up the majority of the specimens. The study “Shared morphological consequences of global warming in North American migratory birds” notes that from 1978 to 2016, birds on average lost 2.6 per cent of their mass and their legs shortened by 2.4 per cent. Their wings, meanwhile, lengthened by 1.3 per cent.
What generated interest among the scientists was that wing length — an index of body shape that impacts numerous aspects of bird’s ecology and behaviour — has consistently increased across species.
“The changes that are being documented are not something you could see with your eye,” Willard said in the study. But that they appear in such a large sample, and one involving diverse bird species, indicates the trends are real and widespread, he adds.
The study examined precipitation, vegetation and other factors that could contribute to bird size. They determined an increase in summer temperatures is the strongest predictor for smaller birds.
“In years when temperatures were a bit warmer, the bodies got smaller. In years when temperatures were a bit cooler, we saw an increase in body size, even though the long-term trend was to decline,” Winger said. “So that leads us to believe that temperature is pretty important here.”
Smaller animals have larger surface-area-to-volume ratios, and this allows them to lose body heat more quickly. Winger proposes that hotter temperatures could apply pressure on birds to become smaller to stay cooler.
The lengthening wings were unexpected, the scientists said. Flight requires the most energy of all the ways back-boned creatures move. The authors hypothesise the wingspan changes could help the birds eke out an energetic edge. “Birds with longer and more pointed wings,” Winger said, “might be more efficient fliers.”
In the long run, this change in size, might have adverse ecological implications, said the researchers. “The observed concomitant increase in wing length may have expansive ecological implications, particularly as the divergent trends in body size and wing length combine to drive a change in shape that may face opposing selective pressures,” said the study.
According to bird experts, climate-change induced warming temperatures, shifting seasons, changing precipitation, and rising sea levels are disrupting the behavior of birds and the ecosystems that support them.
Migratory birds are one of the crucial components for understanding the morphological responses of organisms to increasing temperatures. The extreme energetic demands of long-distance migration have shaped the morphology of migratory birds for efficient flight, as per Mass Audubon, an organisation engaged in wildlife protection.
More than 30 per cent of our breeding birds are already declining and are in need of conservation action. The effect of climate change on birds will become more severe in the future unless we reduce our greenhouse gas emissions and protect the natural resources birds need to adapt to change.
According to the State of the Birds 3 report released in 2017, of 143 breeding bird species evaluated in the, 43 per cent (61 species) are Highly Vulnerable to the effects of climate change predicted to occur by 2050. Of the other species, 15 per cent (22 species) are Likely Vulnerable and 42 per cent (60 species) are Least Vulnerable.
The report also found that warmer temperatures are forcing birds to winter and breed farther north than in the past. Many species once found farther south, including popular birds like northern cardinals and tufted titmice, are expanding their ranges into New England.
An assessment of 305 common North American bird species found the average latitude of bird wintering range is now about 40 miles farther north than it was in the 1960s.
(This article has been published with support from the India Science Media Fellowship 2019 by the Wellcome Trust/DBT India Alliance and Nature India.)