UV vision reveals chicks' healthy glow

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12 Years
Sep 18, 2007
Seattle, Cascadia
An article my mom sent to me:

UV vision reveals chicks' healthy glow

They are not telepathic, and they don't have X-ray vision, but mother birds do have a "superpower" that lets them detect the nutritional status of their chicks merely by looking at them. Researchers have discovered that the ability to see ultraviolet light means the birds can constantly monitor their chicks' healthy glow.

Growing feathers that reflect UV light is metabolically expensive. Birds that are healthy can grow these feathers easily, but malnourished or ill individuals cannot. In species that can see in the ultraviolet part of the spectrum, this is used to select food and help choose potential mates from the crowd .

Marion Tanner and Heinz Richner at the University of Bern in Switzerland found that in some species even nestlings had UV reflective feathers.

"We really wondered why juveniles would build these energetically expensive feathers when they were incapable of breeding," says Tanner.

They suspected that UV reflection from baby bird feathers could be sending a health signal to the parents to guide their feeding decisions.
Survival tactic

To test this, they observed 155 wild nestling great tits in 25 different nest boxes near Bern. They weighed the chicks and covered half of them in an ointment that blocked UV reflectance, and the rest in a similar ointment that had no blocking properties.

Fledglings were then kept separately in cages on a tree near their nest-box for one day. Cameras filmed the parents' visits and feeding. In the evening, the fledglings were collected and weighed.

While males were unaffected by the presence or absence of UV reflection, females were found to feed reflective offspring preferentially, indicating that they were favouring high-quality offspring over weaker offspring.

This might be to ensure that at least one chick survives should resources become scarce.
'New world'

"It’s an amazing discovery that UV vision is being used in parental/chick relationships," says avian biologist Megan Ross at Lincoln Park Zoo in Chicago, US.

"Nestlings call and posture all the time, but if you think about it, UV reflectance is really the most honest signal of health that they can send," adds Marty Leonard at Dalhousie University in Halifax, Nova Scotia.

But parental response to UV may change. When food supplies are limited or parasites are common, parents may use UV reflectance differently, suggests Tanner.

"The next step is to look at how UV reflectance affects parent food allocation in different environments. It’s all very exciting, but I really have no idea what we will find," adds Tanner.

"This is a whole new world of interactions that we didn’t even know existed," says Leonard.

Journal reference: Behavioral Ecology (DOI: 10.1093/beheco/arm142)
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* Megan Ross, Lincoln Park Zoo
* http://www.lpzoo.org/conservation/who_we_are/m_ross.php
* Heinz Richner Homepage
* http://evolution.unibe.ch/short_cv.htm
* Ultraviolet Vision at University of Bristol
* http://www.bio.bris.ac.uk/research/vision/4d.htm
Very interesting! Thank you for sharing!
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