Dramatic climate change affects migratory birds’ bodies in a way that could affect flight

Extreme weather events are affecting birds’ bodies in ways that affect their stability and ability to fly

During regular migrations, birds usually use lighter and faster body movements to make their way up mountains or across ocean waves as they seek to escape the harsh climate. But extreme weather events, such as sea level rise, have disrupted their flight, in ways that may affect their body shape and comfort on the ground.

“Every warm weather destination is just an island in the ocean now, so now all body movements are kind of jarring and they’re sluggish,” Prof Mimoet Toubia, from the Norwegian University of Science and Technology, said. “Most migratory birds only have four to five legs, and a normal flight is controlled by a vibrating system on each of the legs.”

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The result? Researchers found that birds’ bodies lost mass as they flew, and their body mass deficit – the distance to which extra weight was being thrust during flight – is often seven times greater than that during normal flights.

The research team found that on average each stage of flight – when a bird takes off and climbs to altitudes of 250 metres, slows down, and lands or takes off again – carried the weight of the bird, as opposed to the bird taking on all of the weight itself.

Toubia said body weight was in effect not being balanced properly as the birds landed. The team reported the ratio of body mass that carried the weight of the bird to the weight of the body was also reduced by 16%.

“The volume that the body carries during flight seems to have changed quite a lot,” he said. “Other animals that are very similar to us, such as reptiles, have this mode of flight, as well.”

Toubia said that he could not yet explain why the birds showed these effects, but he said that a possible explanation was the fact that mild- and heavy-bodied birds – which are built to conserve energy – were given less fuel.

Low-body-weight birds, such as kestrels and barn owls, are more susceptible to extreme weather events, including sea level rise, and have to compensate for their body weights with extra limbs or elastic ligaments.

Researchers said that the results could have implications for people’s lifestyles, because increasing body mass deficit is likely to cause an increase in your body temperature – in turn resulting in health problems such as weight gain, diabetes and heart disease.

The study, published in the journal Science Advances, was carried out in Norway on bird species that have ocean migration habits and much of their ability to tolerate high temperatures is dependent on diet.

Toubia said he was not aware of any current in-depth studies into how body shape was affected by climate change, adding that the birds would have adapted to a higher body temperature, and their bodies may not be changing due to the consequences of climate change.

“These results suggest that climate change – because of enhanced temperature – will affect our ecosystems, as well as our own bodies,” he said.

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