Flying without wings: Losing feathers has a detrimental effect on migrating birds

July 2, 2015
The researchers used a trained jackdaw in a wind tunnel to study flight. Credit: Aron Hejdström

Birds that moult at the wrong time of the year could be disadvantaged, according to a study by scientists at Lund University, Sweden. Birds depend on a full set of feathers for maximum efficiency when flying long distances, but the study shows that moulting has a detrimental effect on their flight performance.

The researchers trained a jackdaw to fly in a and measured different types of drag experienced by the bird. "We expected the bird not to be able to glide at the lowest speeds that it could glide at before moult and our results confirmed this", says Marco Klein Heerenbrink, who is involved in the research.

The results imply the bird could not fully compensate for the missing feathers during moult. This suggests that if a migratory bird departs prematurely before it has fully moulted, it is likely it will need more energy to make the journey and may need more stopovers too.

The annual loss of flight feathers poses a potential challenge to due to the resulting reduced wing area and altered wing shape. However, birds have extraordinary flexibility in , which is thought to help maximise the efficiency of their wings and may compensate for missing flight feathers. "Understanding how moult affects the flight of a bird, can tell us something about the different moulting strategies birds use," says Klein Heerenbrink.

"In the wind tunnel, we can set a flight speed for the bird to fly at", he says. "The bird will try to stay in place relative to the walls of the wind tunnel. This means we can vary the speed, and the bird will attempt to adjust to this. For gliding flight we tilt the wind tunnel. This gives a vertical component to the airflow, simulating descending flight. If the bird can hold its position, this means that its weight is balanced by the aerodynamic forces (lift and drag)."

To compensate for the missing feathers, the bird needs to either move the wings forward or unload weight from the tail. There is a limit to how far the bird can move the wings forward and unloading from the tail requires increasing the loading on the main wings, which are already struggling due to the moult gaps. "So the bird has a difficult time finding the right balance," says Klein Heerenbrink.

Long distance migrants benefit from having a complete set of high quality flight feathers on their departure and this study implies it would be particularly bad to start migrating while certain feathers (called the outer primaries) are missing.

Explore further: A small vortex on the wing makes the elegance of birds' flight

More information: This work will be presented by Marco Klein Heerenbrink (Lund University, Sweden) at the annual meeting of the Society for Experimental Biology (SEB) in Prague on Thursday 2nd July 2015.

Related Stories

Small bird fills big fossil gap

June 2, 2015

The 115-million-year-old remains of a tiny toothed bird with a two-pronged tail resembling a pair of darts have filled knowledge gaps about feather evolution, scientists reported Tuesday.

Early birds had an old-school version of wings

November 21, 2012

In comparison to modern birds, the prehistoric Archaeopteryx and bird-like dinosaurs before them had a more primitive version of a wing. The findings, reported on November 21 in Current Biology, lend support to the notion ...

Falcon feathers pop-up during dive

February 6, 2014

Similar to wings and fins with self-adaptive flaps, the feathers on a diving peregrine falcon's feathers may pop-up during high speed dives, according to a study published in PLOS ONE on January 29, 2014 by Benjamin Ponitz ...

Recommended for you

Finding a lethal parasite's vulnerabilities

December 15, 2017

An estimated 100 million people around the world are infected with Strongyloides stercoralis, a parasitic nematode, yet it's likely that many don't know it. The infection can persist for years, usually only causing mild symptoms. ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

AKron
not rated yet Aug 04, 2015
Never in my wildest imagination did I ever think that losing feathers would have a detrimental effect on birds. That's just astounding!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.