Hummingbirds Live in a More Colorful World, Study Confirms
Hummingbirds live a more colorful existence than humans do, a new study published in the Proceedings of the National Academy of Sciences Monday confirmed.
While humans only have three color cones, birds have four, meaning they can theoretically see colors on the ultraviolet spectrum, National Geographic explained. Until now, however, no scientist had really tried to discover what a bird's eye view of color would look like.
"Humans are color-blind compared to birds and many other animals," lead study author and Princeton University assistant professor Mary Caswell Stoddard said in a Princeton press release. "Not only does having a fourth color cone type extend the range of bird-visible colors into the UV, it potentially allows birds to perceive combination colors like ultraviolet+green and ultraviolet+red — but this has been hard to test."
To overcome these difficulties, Stoddard and a team of scientists from Princeton, the University of British Columbia (UBC), Harvard University, University of Maryland and the Rocky Mountain Biological Laboratory (RMBL) set up a series of outdoor experiments with broad-tailed hummingbirds in Colorado. They wanted to test the birds' abilities to see nonspectral colors, colors perceived from widely distinct parts of the color spectrum.
The only nonspectral color humans can see is purple, which is not part of the rainbow.
"Instead of being formed by a single light or mixture of similar lights, purple is formed by simultaneously stimulating our non-adjacent red-sensitive and blue-sensitive cones in our eyes," study coauthor and UBC Ph.D. student Harold Eyster explained on Twitter.
Since purple is my favorite color, & birds are my favorite animals, I wondered, "Can birds see purple?" Today, our paper led by Dr. Cassie Stoddard with @dylanhmorris @B_G_Hogan @DavidInouye1 Ed Soucy is in @PNASNews that shows that yes, birds can! https://t.co/lcFuu2yt1l 3/n— Harold Eyster (@HaroldEyster) June 15, 2020
But birds, because of their fourth cone, can in theory see up to five nonspectral colors: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow and ultraviolet+purple.
To test whether the birds really did see these colors, researchers placed feeders containing sugar and plain water in an alpine meadow next to LED tubes designed to emit a variety of colors, including nonspectral ones, the press release explained. The researchers conducted 19 experiments over three years, recording data from more than 6,000 feeder visits. They found that the birds could learn to visit the sugar water feeder even when the two LED tubes marking the feeders were indistinguishable to human eyes.
The details of color vision are usually studied in the lab, but we wanted to know how birds act in the wild. Thus,… https://t.co/3JoxVNIY29— Harold Eyster (@Harold Eyster)1592252910.0
"Seeing them do this right in front of my eyes is one of the most exciting things I've ever witnessed," Stoddard told National Geographic.
The hummingbirds could see purple, ultraviolet+green, ultraviolet+red and ultraviolet+yellow, the researchers confirmed, according to the press release.
University of Chicago evolutionary biologist Trevor Price, who was not involved with the research, told National Geographic that the findings marked a "big step forward" for understanding how birds and other animals see.
"We're really only beginning to scratch the surface in our understanding of color vision in animals," he said.
The scientists think the birds use their enhanced color vision to locate a wide variety of plants for nectar. They found that the birds would be able to distinguish nonspectral colors in 30 percent of birds' plumage and 35 percent of plants from a database.
Birds can see nonspectral colors, and these colors make up a substantial part of the bird visual environment. We ho… https://t.co/160gQITMyo— Harold Eyster (@Harold Eyster)1592252913.0
"The colors that we see in the fields of wildflowers at our study site, the wildflower capital of Colorado, are stunning to us, but just imagine what those flowers look like to birds with that extra sensory dimension," co-author David Inouye of the University of Maryland and RMBL said in the press release.
The findings also have conservation implications.
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By Katherine Kornei
Clear-cutting a forest is relatively easy—just pick a tree and start chopping. But there are benefits to more sophisticated forest management. One technique—which involves repeatedly harvesting smaller trees every 30 or so years but leaving an upper story of larger trees for longer periods (60, 90, or 120 years)—ensures a steady supply of both firewood and construction timber.
A Pattern in the Rings<p>The <a href="https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/coppice-standards-0" target="_blank">coppice-with-standards</a> management practice produces a two-story forest, said <a href="https://www.researchgate.net/profile/Bernhard_Muigg" target="_blank">Bernhard Muigg</a>, a dendrochronologist at the University of Freiburg in Germany. "You have an upper story of single trees that are allowed to grow for several understory generations."</p><p>That arrangement imprints a characteristic tree ring pattern in a forest's upper story trees (the "standards"): thick rings indicative of heavy growth, which show up at regular intervals as the surrounding smaller trees are cut down. "The trees are growing faster," said Muigg. "You can really see it with your naked eye."</p><p>Muigg and his collaborators characterized that <a href="https://ltrr.arizona.edu/about/treerings" target="_blank">dendrochronological pattern</a> in 161 oak trees growing in central Germany, one of the few remaining sites in Europe with actively managed coppice-with-standards forests. They found up to nine cycles of heavy growth in the trees, the oldest of which was planted in 1761. The researchers then turned to a historical data set — more than 2,000 oak <a href="https://eos.org/articles/podcast-discovering-europes-history-through-its-timbers" target="_blank" rel="noopener noreferrer">timbers from buildings and archaeological sites</a> in Germany and France dating from between 300 and 2015 — to look for a similar pattern.</p>
A Gap of 500 Years<p>The team found wood with the characteristic coppice-with-standards tree ring pattern dating to as early as the 6th century. That was a surprise, Muigg and his colleagues concluded, because the first mention of this forest management practice in historical documents occurred only roughly 500 years later, in the 13th century.</p><p>It's probable that forest management practices were not well documented prior to the High Middle Ages (1000–1250), the researchers suggested. "Forests are mainly mentioned in the context of royal hunting interests or donations," said Muigg. Dendrochronological studies are particularly important because they can reveal information not captured by a sparse historical record, he added.</p><p>These results were <a href="https://www.nature.com/articles/s41598-020-78933-8" target="_blank">published in December in <em>Scientific Reports</em></a>.</p><p>"It's nice to see the longevity and the history of coppice-with-standards," said <a href="https://www.teagasc.ie/contact/staff-directory/s/ian-short/" target="_blank">Ian Short</a>, a forestry researcher at Teagasc, the Agriculture and Food Development Authority in Ireland, not involved in the research. This technique is valuable because it promotes conservation and habitat biodiversity, Short said. "In the next 10 or 20 years, I think we'll see more coppice-with-standards coming back into production."</p><p>In the future, Muigg and his collaborators hope to analyze a larger sample of historic timbers to trace how the coppice-with-standards practice spread throughout Europe. It will be interesting to understand where this technique originated and how it propagated, said Muigg, and there are plenty of old pieces of wood waiting to be analyzed. "There [are] tons of dendrochronological data."</p><p><em><a href="mailto:email@example.com" target="_blank" rel="noopener noreferrer">Katherine Kornei</a> is a freelance science journalist covering Earth and space science. Her bylines frequently appear in Eos, Science, and The New York Times. Katherine holds a Ph.D. in astronomy from the University of California, Los Angeles.</em></p><p><em>This story originally appeared in <a href="https://eos.org/articles/tree-rings-reveal-how-ancient-forests-were-managed" target="_blank">Eos</a></em> <em>and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.</em></p>
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