Severe storm stress leaves its mark in tail feathers of grassland sparrows

The stress of severe thunderstorms on nestling birds has been linked to feather malformation in an American grassland sparrow species.

grasshopper sparrow

Scientists found a high incidence of a phenomenon called “pallid bands” – or reduced melanin – in the tail feathers of juvenile grasshopper sparrows (Ammondrammus savannarum) captured in a mist-net survey in August 2013 near El Reno, in central Oklahoma.

The area experienced a massive tornado on 31 May 2013, with violent storms, hail and winds of up to 475 km/hour.

A research team from the University of Oklahoma, led by biologist Jeremy Ross , discovered the feather “fault bars” while studying ground-nesting birds in the El Reno region.

The findings are published online in the open access journal PeerJ .

In a short news report published by the university, Ross says the study “may be the first example of severe thunderstorms being scientifically implicated in sub-lethal stress impacts on wildlife.”

Data collected on the nesting behaviour of grassland sparrows indicated that nestlings would have been growing tail feathers when the storm occurred.

“During extremely heavy storms adult birds may flee and abandon their nests to the weather,” the research paper says.

“Young that survive ‘riding the storm out’ may be traumatized by the event itself or because of reduced provisioning by adults. The developing feathers of young birds can provide indicators of such environmental stressors, including structural and pigmentation deficiencies.”

The study suggests that the impacts of the El Reno storm – including “impact trauma, abrupt ground-level cooling, and/or reduction in insect prey” – would have caused widespread stress within populations of grasshopper sparrows. And, this stress would be reflected in feather tissue.

Feather malformations, known as fault bars, can coincide with spikes of stress hormones in the blood, “particularly corticosterone, and are thought to form because the deposition of keratin and melanin into the growing feather is disrupted,”  the study says.

The University of Oklahoma researchers have used the term “pallid band” because they say it reflects not only the reduced pigmentation, but the weakened structure of the feathers.

And that’s why this discovery is about much more than some pale bits on a bird’s tail feathers.

As the study explains, the pallid bands contain structural weaknesses that could affect flight performance.

So, if extreme weather events become more frequent and intense as a result of climate change, this could have worrying ecological consequences for grasshopper sparrows and possibly, many other birds.


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