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Multiple paths to saltwater tolerance evolved independently among birds
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L-R: Swamp Sparrow, Kelly Colgan Azar; Song Sparrow, Jennifer Taggart; Savannah Sparrow, Kelly Colgan Azar; Nelson’s Sparrow, Brian Harris.
Salt Regulation Among Saltmarsh Sparrows
Evolved in Four Unique Ways
Study defines four of nature’s solutions to the same problem
For release: July 16, 2019
Ithaca, NY—In nature, as in life, there’s often more than one way to solve a problem. That includes the evolutionary process. A new study in Evolution Letters finds that different bird species in the same challenging environment—the highly saline ecosystem of tidal marshes along ocean shores—were able to evolve unique species-specific ways to address the same problem.
Jennifer Walsh taking sparrow measurements in the field. Photo by Adrienne Kovach. “For tidal saltmarsh species, the challenge is how to maintain the right balance between water and salt concentrations in their cells,” explains lead author Jennifer Walsh, a postdoctoral researcher at the Cornell Lab of Ornithology. “When cells are exposed to salt water, they shrink. If they’re exposed to too much fresh water, they expand. Without the right balance, the cells can die.”
Walsh and colleagues from eight other universities studied the genomes of four sparrow species: Savannah, Nelson’s, Song, and Swamp Sparrow. These were chosen because each of these species has a population living in saltmarsh habitat as well as a separate upland population. This makes it possible to compare the genomes of the two populations and see where they differ. Some of those differences are tied to adaptations evolved in saltmarsh-resident sparrows to control the balance of water and salt concentrations—a process called osmoregulation.
One gene that appears to be important in Savannah Sparrows plays a role in inserting physical channels in the cells. Those channels help the cells resist expansion and contraction from changes in salt levels by allowing exchange of water across the cell wall. Swamp Sparrows show a similar response to salt water, but the genes responsible for forming these channels are completely different. Song Sparrows seem to have adapted through mechanisms that reinforce cell walls so they can expand and contact more quickly in response to salt. The Nelson’s Sparrow takes yet another route—evolving a gene that changes its behavior. Their genetic adaption curbs thirst so they only drink the least amount of salt water necessary and salt levels are kept within bounds. The four sparrow species evolved four different, complex mechanisms to deal with salt, each likely governed by many genes working in tandem.
Upland versus saltmarsh dwellers of the same species with corresponding differences in appearance and salt tolerance. Illustrations by Jillian Ditner, Cornell Lab Science Illustrator.
The researchers also found that the osmoregulatory adaptations evolved at a rapid pace, at least on an evolutionary scale—probably over the past 10,000 to 15,000 years—and that New World sparrows have colonized marshes over and over again.
The saltmarsh sparrows also evolved some shared traits across species that may help them survive the hot, salty, harsh conditions of their environment: a larger bill to better dissipate heat, a modified kidney structure, and darker plumage which may provide some UV protection and help feathers withstand abrasive vegetation. But why live in a saltmarsh at all?
“Sometimes birds move into marshes because, if you can adapt to the environment, it’s actually a pretty good place to be,” Walsh says. “There’s no competition because so few species live there, and there is never, ever a shortage of insects for food.”
This research was funded by the National Science Foundation Postdoctoral Research Fellowship in Biology, as well as a seed grant from the Cornell University Center for Vertebrate Genomics. Co-authors are from the University of Montana, University of British Columbia, the Iolani School in Hawaii, University of Connecticut, University of New Hampshire, University of Maine, University of Delaware, and Benedictine College.
Jennifer Walsh, Phred M. Benham, Petra E. Deane-Coe, Peter Arcese, Bronwyn G. Butcher, Yvonne L. Chan, Zachary A. Cheviron, Chris S. Elphick, Adrienne I. Kovach, Brian J. Olsen, W. Gregory Shriver, Virginia L. Winder, and Irby J. Lovette. (2019) Genomics of rapid ecological divergence and parallel adaptation in four tidal marsh sparrows. Evolution Letters.
Editors: Download graphic and images for use with stories about this research
Pat Leonard, Cornell Lab of Ornithology, (607) 254-2137, email@example.com
In May 2019, five scientists accomplished a long-held goal: to catch at sea and track one of the rarest seabirds of the Atlantic, the Black-capped Petrel. Now, after placing GPS transmitters on 10 birds they caught off Cape Hatteras, North Carolina, they’re hoping the birds will lead them back to an undiscovered nest site.
“That’s sort of what the dream is, that they’re going to take you to a whole new island that no one knew about,” is how Patrick Jodice, of Clemson University’s South Carolina Cooperative Fish and Wildlife Research Unit, describes the tracking project. Finding new nest sites could be a major step forward in conservation of this endangered bird. As the story unfolds, we can all follow along via a real-time map of where the birds are going.
Once an abundant nesting bird on several Caribbean islands, the Black-capped Petrel was almost made extinct by introduced predators and hunting. Today, Hispaniola (home to Haiti and the Dominican Republic) is the only known nesting island left—though research led by Adam Brown of Environmental Protection in the Caribbean suggests they may also nest on the island of Dominica.
Here’s the mysterious part: these endangered seabirds are fairly commonly seen in the Gulf Stream, supporting a global population estimate of about 1,500 breeding pairs. But scientists know of only about 50 nest sites—so where are the remainder? Some are probably elsewhere on Hispaniola—the birds nest in hard-to-reach burrows, and they visit their nest sites only in complete darkness, so they’re hard to find. But scientists believe there must also be nesting areas on other islands that we don’t know about.
“Once you see where they nest and how secretive they are,” Brown says, “It wouldn’t be surprising to find them in an entirely new place.” Tagging the birds at sea may finally give researchers an answer.
That’s how Jodice found himself 30 miles off Cape Hatteras, bobbing among 6-foot swells in an inflatable motorboat along with collaborators Brad Keitt of the American Bird Conservancy, Clemson research associate Yvan Satgé, Chris Gaskin of the Northern New Zealand Seabird Trust, and pelagic birding guide Brian Patteson.
The team used a net gun designed by Gaskin to snare the birds as they flew close to the boat. The satellite tags are solar powered and weigh only 6 grams (less than 3% of a petrel’s weight). Once a tag is placed on a petrel, it sends the bird’s location back to Jodice’s team for 6 hours at a stretch, after which it goes offline to recharge for 28 hours (during which time the bird can travel up to 360 miles) before turning back on.
Once the team started catching petrels, they were relieved to find some with dark faces and others with white faces. This color variation may reflect the existence of two groups of Black-capped Petrels that nest in different locations (a pattern that’s known in other seabird species). All the currently known nest sites are of the dark-faced morph, so the team will be watching especially closely the movements of the four white-faced individuals they tagged.
The banding expedition took place toward the end of the petrels’ nesting season, which runs from November to June. So far, all 10 birds have stayed in the Gulf Stream about 1,000 miles (at least 2 days’ flight) north of the Caribbean islands, indicating they are probably not currently breeding. According to Jodice, they may have already fledged chicks, their nests might have failed early, or some of the birds may not have bred at all this year. Black-capped Petrels spend at least 4 years as subadults before beginning to breed, so it’s possible some were still too young to nest.
The "dark-faced" form of the Black-capped Petrel has sooty black completely surrounding the eye. All known Black-capped Petrel nest sites are for this dark-faced form. Photo by Brian Sullivan/Macaulay Library.
The "white-faced" form of the Black-capped Petrel has more white in front of and above the eye. There are currently no known nesting sites of the white-faced form. Photo by Steve Kelling/Macaulay Library.
“We’re still very much in the pilot phase of understanding this species,” Jodice said. By following these 10 petrels, his team will learn how the species uses the western North Atlantic, and could identify critical foraging areas, he said. As an example, in 2014 researchers put satellite tags on nesting Black-capped Petrels and learned for the first time that some individuals forage in parts of the Caribbean, the Gulf of Mexico, and an area off Venezuela. And the GPS tags have a potential life of 6 months, so it’s possible that some of these little devils (to use a colloquial name) will lead Jodice and his team back to their nest sites this November.
If a new nesting island is discovered, it will open up a new chapter in conservation of the species. Human encroachment into the forests where petrels nest poses the number one threat, according to Jennifer Wheeler of Birds Caribbean. “Petrel conservation can’t happen outside the human context,” she says. But new efforts will be able to take cues from a decade of work in Boukan Chat, Haiti, home to many known Black-capped Petrel nests. There, strategic local outreach has resulted in successful coexistence between petrels and the community. And if it can happen in Haiti, one of the poorest countries in the Americas, it can happen elsewhere, Wheeler says.
Elizabeth Serrano ’20 is an Animal Science major at Cornell University. Her work on this story was made possible by the Cornell Lab of Ornithology Science Communication Fund, with support from Jay Branegan (Cornell ’72) and Stefania Pittaluga.
Edie reports that both parents had normal coloration, as did all four of its siblings. The finding was especially surprising because this particular nest was one in which the female preferred to stay on the nest during nest checks, even after the young had hatched. Edie wasn’t sure what she would find when she checked the nest on June 12th, but she certainly wasn’t expecting to find a snow-white nestling. At first, she was confused, thinking another bird might have laid an egg in this nest…except she knew that there aren’t any pure white cavity-nesting species in her area. She snapped a photo so she could leave the birds in peace and examine the evidence later. It wasn’t until later that she realized how rare her sighting was.
A Vision In White
A Vision In White
Notice how the bill has darkened to yellow in this photo, a sign that not all pigments are absent.
OTHER TYPES OF COLOR
Not all color is derived from pigment. As adults, Tree Swallows get their iridescent blue-green plumage from the structure of their feathers, which scatter light. The feathers have a base of melanin, so if you were to destroy the structure of the feather, you would see only gray. This albino nestling will not obtain the iridescent teal plumage as an adult because there is no base of melanin, which plays a role in the scattering of light.
By comparing these two photos, we can see that the bill changes from pink to yellow; however, this is no trick of the light! Albinism is a lack of melanin, which is made by the body; however, other pigments may still be present in the body. Carotenoids are the class of pigments responsible for oranges and yellows, and albinistic birds can have them in spades (check out this yellow albino American Goldfinch). Unlike melanin, carotenoids are obtained from the diet. From the change in bill color, we can deduce that by the time the second photo was taken, the little nestling had obtained enough carotenoids through its diet to change the bill color to yellow. Therefore, the bills of typical Tree Swallow nestlings must contain both melanin and carotenoids, with the black hues masking the underlying yellow. In the albinistic nestling, there is nothing to mask the yellow color.
Female Tree Swallow On The Nest
Female Tree Swallow On The Nest
The blue-green color in adult plumage is a result of feather structure, rather than pigment.
THE EYES HAVE IT
Although difficult to see in the photos, Edie reports that the eye was red rather than the typical dark brown. The eye, containing no other pigments, appears as red due to the underlying blood vessels. Pink or red eyes are a good indicator that a bird is truly an albino, rather than a species that just happens to be all white (like the White Tern).
ONCE IN A LIFETIME
Albinism is rare, with estimates ranging from 0.05% to 0.1% frequency in birds. A sighting this unique might come only once in a NestWatcher’s lifetime, so keep your eyes out for unusual birds. Thanks to Edie’s observations, we can all share in the joy of discovering something unexpected.
It seems that Lee Pauser had the same question about some Northern Flickers in his California nest box. Lee wrote to NestWatch observing that the nestlings sounded like a swarm of bees, but he hadn’t seen any documentation confirming this experience. However, there is one reference in the literature to the “nestling buzzing” vocalizations of this species. According to a dissertation written in 1990 by S. Duncan, the nestlings make this buzzing sound when their nest hole is darkened, as when a parent returns to feed them, or if a predator happens to appear in the nest entrance. The buzzing chorus has a frequency and energy spectrum that is said to be similar to a swarm of agitated honey bees (Duncan 1990). Now I haven’t been particularly inspired to get close to a swarm of agitated honey bees, so I will have to take Duncan’s word on this. To my ear, the nestlings do sound like insects, but perhaps more like cicadas than bees.
Listen in on this video captured by Lee Pauser on May 27, 2019.
Do you hear bees? Or just hungry birds? Keep in mind that Lee’s box only has two nestlings in it, whereas the more typical 6-7 young would likely be more convincing. If Duncan’s hypothesis is correct, this could be a form of mimicry that may be intended to convince would-be predators that the nest hole is actually full of noxious honey bees. Similarly, some species of harmless snakes will rattle their tails vigorously to convince predators that they are, in fact, rattlesnakes (check out this milk snake doing its best rattlesnake impression). The key is that the mimicry must be convincing in order to work, but it need not be perfect.
Have a listen to this colony of honey bees, recorded in Ontario in 1958.
And here are the flickers again on June 3, 2019, still buzzing away.
This mimetic behavior is poorly studied, and I am unaware of any other species which might produce a similar sound. It’s possible that Gilded Flickers also have this vocalization. Until 1995, they were considered to be the same species as Northern Flicker. However, I was unable to find any media or literature that referred exclusively to this Sonoran Desert species after it was split from Northern Flicker. If you have media of this species, we would love to accept it!
What do you think? Would these nestlings stop you in your tracks? Or do you know your birds from your bees?
Duncan, S. 1990. Auditory communication in breeding Northern Flickers (Colaptes auratus). Ph.D. diss., University of Wisconsin, Milwaukee.
defensehoney beemimicryNorthern Flicker
Amanda Rodewald, senior director of conservation science at the Cornell Lab of Ornithology, was at the nation’s Capitol last week to defend two core conservation policies at risk of reinterpretation and weakening by the current presidential administration.
On Thursday June 13, Rodewald testified before the House Subcommittee on Water, Oceans, and Wildlife to speak against the Trump administration’s proposed reinterpretation of the Migratory Bird Treaty Act (MBTA). The treaty between the U.S. and Canada was ratified by Congress in 1918, and another version of the MBTA was signed between the U.S. and Mexico 20 years later. The act forbids both the purposeful and the incidental killing of a wide range of migratory birds. In December 2017, the Interior Department, under the Trump administration, issued a memorandum that sought to reinterpret the MBTA’s applicability in cases of incidental take.
“The exclusion of incidental take renders the [MBTA] impotent on most sources of mortality for migratory birds and eliminates a powerful incentive for industry,” Rodewald said at the House hearing.
Under the reinterpretation, companies that unintentionally kill birds (“incidental take”) would no longer be liable for the deaths they caused. In 2010, the Deepwater Horizon oil spill killed more than a million birds, for which the British oil company BP paid more than $100 million—funds that were used to restore damaged Gulf coastlines and bird habitat. But under this reinterpretation, companies like BP that kill birds due to negligence would no longer be subject to penalties.
Rodewald stated that incidental take from industry accounts for upwards of 1.1 billion bird mortalities each year. She cited examples from the Nixon, George W. Bush, and Obama administrations of the U.S. Fish and Wildlife Service working with power companies to avoid bird electrocutions and collisions and reduce the more than 30 million birds killed by power lines annually.
“I am not arguing that we should try to eliminate all human-caused mortality of birds,” Rodewald said. “But we can and should take active steps to reduce harm where possible, and the MBTA helps us to do that.”
Earlier in the week, Rodewald coauthored an opinion article with scientists from Ohio State University and the University of South Florida that argued against another Trump administration reinterpretation—the proposed rollback of the Waters of the US (WOTUS) rule.
“The proposed rule does not reflect the best-available science and, if enacted, will damage our nation’s water resources,” the authors wrote in Proceedings of the National Academy of Sciences of the U.S.A.
The proposed rule will weaken the Clean Water Act protections for one-fifth of streams in the U.S. and over half of wetlands, leaving millions of miles of streams and over 16 million acres of wetlands more vulnerable to pollution.
According to Rodewald and coauthors, the proposed rule eliminates “protection for all ephemeral streams and non-floodplain wetlands, irrespective of connectivity and the consequences for downstream waters.
“The current administration’s proposed rule at once contradicts both the rich body of evidence about water connectivity and the clearly articulated mandate of the Clean Water Act.”
“The apparent opposition to enacting science-based policies undermines decades of efforts—and investments by tax-paying Americans— to clean and protect our nation’s waters,” Rodewald and her coauthors wrote. “Every nation’s citizens need clean water to be healthy and productive—today and into the future.”
Winny Sun’s work on this story was made possible by the Cornell Lab of Ornithology Science Communication Fund, with support from Jay Branegan (Cornell ’72) and Stefania Pittaluga.
Arthur Allen examines a Belted Kingfisher as Cornell graduate student
Brina Kessel (far right) looks on. In 1961, Allen gave Kessel a copy of his
Book of Bird Life with the inscription “to the best student we ever had.”
Brina Kessel was born in Ithaca, New York, to graduate student parents who both took ornithology classes from Arthur A. Allen, the founder of the Cornell Lab of Ornithology. In college Kessel enrolled as an undergraduate at Cornell, where she became acquainted with Allen and Paul Kellogg, occasionally helping them with their frog and birdsong recordings. Many of the undergraduate men in the 1940s were away from school contributing to the war effort, so Kessel was not held back by the sort of misogyny that might have limited her opportunities for research as an undergrad.
Kessel enrolled at the University of Wisconsin in 1947 to seek an advanced degree and learn from Aldo Leopold. Unfortunately, Leopold passed away from a heart attack soon after she enrolled, and then she learned the University of Wisconsin would not allow women to pursue a PhD in wildlife management. So she returned to Cornell for doctoral studies on starling ecology under Allen’s supervision.
Kessel landed her first job as a lecturer at the University of Alaska Fairbanks and before long was head of the department. Soon after her faculty appointment, she put in a proposal to travel by boat down the Colville River studying the birds of that region with her grad school friend (and future Cornell ornithology professor) Tom Cade. That river, however, flowed into the U.S. Naval Petroleum Reserve on Alaska’s North Slope, and she was told: “You can not come up on to the Reserve because the Navy will not allow any woman on the Petfore Reserve unless they are married, and with their husband.” Kessel was sorely disappointed but sent a male University of Alaska freshman in her stead to gather her field data.
Kessel would later lead many field expeditions herself and was elected to serve as the 45th president of the American Ornithologists’ Union in 1992. Kessel passed away in 2016, and her estate created the Kessel Ornithology Endowment Fund at the University of Alaska Fairbanks.
Bob Montgomerie is a professor of evolutionary biology at Queen’s University, Canada. This story is condensed from Contemplating the Tundra, part of the American Ornithological Society’s “Celebrating the History of Women in Ornithology” series.
Scientists who study the brain activity of humans during REM sleep often ask their human subjects what they dreamed about in order to decipher what the brain activity patterns mean. Birds also exhibit signs of REM sleep. Are they dreaming?
It’s a fascinating question, but unfortunately there’s no answer right now. In birds, the patterns of neuronal activity in different brain regions during REM sleep can be measured, but (obviously) scientists cannot ask birds about their dream content.
However, in male Zebra Finches the neurons in the song system of the brain show spontaneous bursting patterns during sleep. It is thought that this kind of dreamlike replay during sleep might aid song learning and memory.
“Most people have heard of natural selection,” says lead author Kang-Wook Kim at the University of Sheffield. “But ‘survival of the fittest’ cannot explain the color diversity we see in the Gouldian Finch. We demonstrate that there is another evolutionary process, balancing selection that has maintained the black or red head color over thousands of generations.”
The researchers independently zeroed in on the gene found on the Gouldian Finch sex chromosome that regulates melanin to produce either red- or black-headed finches. Rather than competing, the two teams decided to join forces and share their data. For the yellow morph, a different gene not located on the sex chromosome is controlling the head pigmentation, but that gene hasn’t yet been found.
Gouldian Finches—Australian songbirds that have become popular for captive breeding as pets—occur in three morphs for head color. A team of scientists isolated what was happening at the genomic level to cause the different head colors. Graphic by Megan Bishop.
“The probability that we’d locate the exact gene region that governs plumage differences in both the Gouldian Finch and the two warblers was almost zero,” says Toews, who is now a professor at Penn State University. “But now that we’ve done it, it opens up the possibility that the same region in other species may also be controlling plumage color.”