Native Plants in Urban Yards Offer Birds "Mini-Refuges"

Landscaping with native vegetation helps local bird species

Yards with plants that mimic native vegetation offer birds "mini-refuges" and help to offset losses of biodiversity in cities, according to results of a study published today in the journal PLOS ONE.

"Native" yards support birds better than those with traditional grass lawns and non-native plantings.

Researchers conducted the study through the National Science Foundation's (NSF) Central Arizona-Phoenix Long-Term Ecological Research (LTER) site, one of 26 such sites around the globe in ecosystems from coral reefs to deserts, from forests to grasslands.

"To a desert bird, what's green is not necessarily good," says Doug Levey, program director in NSF's Division of Environmental Biology. "Arizona birds don't view lush urban landscapes as desert oases. The foraging behavior of birds in greener yards suggests that there's less food for them there than in yards with more natural vegetation."

The research, led by scientists Susannah Lerman and Paige Warren of the University of Massachusetts-Amherst, and Hilary Gan and Eyal Shochat of Arizona State University, looked at residential landscape types and native bird communities in Phoenix, Ariz.

It's among the first to use quantitative measures and a systematic approach--including 24-hour video monitoring--in yards to assess and compare foraging behavior of common backyard birds.

The scientists found that desert-like, or xeric, yards had a more even bird community and superior habitat compared with moist, or mesic, grass lawns.

"We already know that bird communities differ, and that there are more desert birds found in a desert-type yard," says Lerman.

"With this study, we're starting to look at how different yards function--whether birds behave differently by yard type. We're doing that using behavioral indicators, especially foraging, as a way of assessing birds' perceptions of habitat quality between differing yard designs."

Lerman and colleagues conducted the experiment in 20 residential yards at least 1.8 miles apart, making it unlikely that the same birds would visit more than one study yard.

Half the yards were desert-like, while the others had green lawns.

From February through April 2010, homeowners removed bird feeders before and during a 24-hour experimental data collection period.

The researchers set up feeding stations--seed trays--in each yard to simulate resource patches similar to ones where birds feed in the wild. Plastic trays contained 0.70 ounces of millet seed mixed into six pounds of sand. The trays were placed on low stools and left out for 24 hours.

Later, Lerman removed the trays, sifted out and weighed uneaten seed to the nearest 0.01 gram. The amount of seed remaining quantified the giving-up densities (GUD), or the foraging decision and quitting point for the last bird visiting a seed tray.

Trays were videotaped for the entire 24-hour experiment.

The experiment assumed that an animal behaving optimally would stop foraging from a seed tray when its energy gains equal the "costs" of foraging, Lerman says.

Costs include predation risk, digestion and missed opportunities to find food elsewhere.

As time spent foraging at a seed tray increases, so do the costs associated with foraging. When a bird first arrives at the tray, seeds are easy to find, but that gets harder as the tray becomes depleted.

Each bird makes a decision about whether to spend time searching in the tray or to move on to a new patch in the yard.

The "giving up" point will be different for different species and in different environmental conditions. Birds visiting seed trays in yards with more natural food available will quit a tray sooner than birds in resource-poor yards.

Since the method only measures the foraging decisions for the last species visiting the seed tray, the researchers devised a mathematical model for estimating the foraging decisions for all visiting species.

Using the videotapes, they counted every peck by every bird for each tray to calculate the relationship between the number of pecks and grams of seed consumed for each seed tray. This was the GUD-peck ratio for the last species visiting the seed tray.

They then estimated the seed consumption--GUD ratio for all other species visiting the seed tray based on the number of pecks per tray when each species quit.

"We know how many pecks each species had and can put that number into the model and calculate the number of grams at that point," Lerman says. This greatly enhances the GUD method by expanding the ability to assess foraging decisions for all species visiting trays.

In all, 14 species visited the trays, 11 of which visited both yard types. Abert's towhee, curve-billed thrasher (a species unique to the Sonoran desert), house finch and house sparrow were the most widespread tray visitors.

Species that visited trays in both yard designs consumed more seed from trays placed in mesic yards, indicating lower habitat quality compared with xeric yards.

Similarly, foragers in the desert-like yards quit the seed trays earlier due to greater abundance of alternative food resources in those yards, spending more time foraging in the natural yards and less at the seed trays.

Lerman says that by videotaping the trays, counting pecks and measuring giving-up points by species, the research also advanced the GUD method, allowing researchers to disentangle some of the effects of bird community composition and density of competitors, and how these factors affect foraging decisions between two different landscape designs.

The results build upon evidence that native landscaping can help mitigate the effects of urbanization on common songbirds, she says.

 -NSF-

Iridescent, Feathered Dinosaur: New Evidence That Feathers Evolved to Attract Mates

The detailed feather pattern and color of Microraptor--a pigeon-sized, four-winged dinosaur that lived about 120 million years ago--had a glossy iridescent sheen.

Its tail was narrow and adorned with a pair of streamer feathers, suggesting the importance of display in the early evolution of feathers, say scientists reporting the findings in this week's issue of the journal Science.

By comparing the patterns of pigment-containing organelles from a Microraptor fossil to those in modern birds, the scientists determined that the dinosaur's plumage was iridescent with a glossy sheen like the feathers of a modern crow.

The new fossil is the earliest record of iridescent color in feathers.

A reconstruction of Microraptor will help scientists approach the controversy of how dinosaurs began the transition to flight.

"Specifying the color and iridescence of feathers in avian dinosaurs was not possible 20 years ago," says H. Richard Lane, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research.

"This development, in combination with the arrangement of tail feathers, is leading to a deeper understanding of the early development of avian plumage signalling. "

Since it was discovered as the first four-winged dinosaur in 2003, Microraptor has been at the center of questions about the evolution of feathers and flight.

Scientists have proposed aerodynamic functions for various feathery features such as its tail, forewing shape and hind limbs.

Once thought to be a broad, teardrop-shaped surface, or with a shape more like that of a paper airplane meant to help generate lift, Microraptor's tail fan is actually much narrower with two elongate feathers off its tip.

The researchers believe the tail feathering may have been ornamental, and likely evolved for courtship and other social interactions and not as an adaptation for flight.

"Most aspects of early dinosaur feathering continue to be interpreted as fundamentally aerodynamic, optimized for some aspect of aerial locomotion," says Julia Clarke, a paper co-author and paleontologist at The University of Texas at Austin (UT-Austin).

"Some of these structures were clearly ancestral characteristics that arose for other functions and stuck around, while others may be linked to display behaviors or signaling of mate quality," she says.

Feather features were shaped by early locomotor styles, Clarke believes. "But, as any birder will tell you, feather colors and shapes may also be tied with complex behavioral repertoires and, if anything, may be costly in terms of aerodynamics."

Modern birds use feathers for many different things, ranging from flight to thermoregulation to mate-attracting displays, says Matt Shawkey, a paper co-author and biologist at the University of Akron.

"Iridescence is widespread in modern birds, and is frequently used in displays," says Shawkey. "The evidence that Microraptor was largely iridescent suggests that feathers were important for display even relatively early in their evolution."

The feather color displayed by many modern birds is partially produced by arrays of pigment-bearing organelles called melanosomes, about a hundred of which can fit across a human hair.

Generally found in a round or cigar-like shape, a melanosome's structure is constant for a given color. Iridescence arises when narrow melanosomes are organized in stacked layers.

After a breakthrough by Jakob Vinther of UT-Austin in 2009, paleontologists started analyzing the shape of melanosomes in well-preserved fossilized feather imprints.

By comparing these patterns to those in living birds, scientists can infer the color of dinosaurs that lived many millions of years ago.

Paleontologists deduced that Microraptor was iridescent when Shawkey discovered that melanosomes in the most common iridescent feathers were uniquely narrow.

Information on the feather color of a variety of dinosaurs has recently come to light.

The first color map of an extinct dinosaur showed black-and-white spangles, red coloration and grey body color in a species called Anchiornis.

Based on the new data from Microraptor and other findings, a complex color repertoire that includes iridescence is likely ancestral to a group of dinosaurs called Paraves that originated at least 140 million years ago.

It includes dinosaurs like Velociraptor as well as Archaeopteryx, Anchiornis and living birds.

"This study gives us an unprecedented glimpse of what this animal [Microraptor] looked like when it was alive," says Mark Norell, paper co-author and paleontologist at the American Museum of Natural History (AMNH).

Clarke, Norell and an AMNH team, including AMNH researchers Mick Ellison and Rui Pei, worked closely to analyze the bony anatomy and digital overlays of the feathering in the new specimen and in eight previously described Microraptor specimens.

The scientists studied feathering, and melanosome shape and density, from a Microraptor fossil.

To come to their conclusions, the researchers worked closely with Quanguo Li, Ke-Qin Gao and Meng Qingjin at the Beijing Museum of Natural History.

The samples and preservation of melanosomes were assessed by Vinther and compared to a database of melanosomes from a variety of modern birds assembled by Shawkey and Liliana D'Alba at the University of Akron.

Along with NSF, the U.S. Air Force Office of Scientific Research, the Natural Science Foundation of China, the Beijing Municipal Bureau of Human Resources, and the Beijing Academy of Science and Technology also funded the research.

-NSF-

Hummingbird Courtship Displays and Acoustics (Image 3)

A composite of an Anna's hummingbird (Calypte anna) diving to a female. The tail is spread to make a loud sound at the bottom of the dive. Chris Clark, a postdoc at the Peabody Museum of Natural History at Yale University, is studying how hummingbird feathers produce various sounds during their courtship displays.

When Clark attended graduate school, his Ph.D. work focused on the roles of sexual selection and flight performance in shaping hummingbird tail morphology. In 2008, he published a paper titled "The Anna's Hummingbird Chirps With It's Tail," which received wide publicity and helped launch his current research focus. Clark's paper described how Anna's hummingbirds (Calypte anna) make a loud sound with their tail feathers during courtship displays rather than vocally.

After completing his doctorate, Clark and his advisor, Richard Prum, were awarded a grant from the National Science Foundation to study the physics of the sounds feathers make. Clark traveled to Latin America, where he recorded the courtship displays of a number of hummingbird species that produce distinctive sounds with their tail feathers including sheartails and woodstars. He then took his research into the lab, where he used a wind tunnel to reproduce the sounds feathers make when the birds are in flight in the wild, and studied how feathers produce sounds over a range of air speeds. [Research supported by National Science Foundation grant IOS 09-20353.] (Date of Image: unknown)

Credit: Christopher Clark, Yale University

Hummingbird Courtship Displays and Acoustics (Image 2)

Chris Clark, a postdoc at the Peabody Museum of Natural History at Yale University, searches for Lucifer hummingbirds in Big Bend National Park in west Texas. Clark is studying how hummingbird feathers produce various sounds during their courtship displays.

When Clark attended graduate school, his Ph.D. work focused on the roles of sexual selection and flight performance in shaping hummingbird tail morphology. In 2008, he published a paper titled "The Anna's Hummingbird Chirps With It's Tail," which received wide publicity and helped launch his current research focus. Clark's paper described how Anna's hummingbirds (Calypte anna) make a loud sound with their tail feathers during courtship displays rather than vocally.

After completing his doctorate, Clark and his advisor, Richard Prum, were awarded a grant from the National Science Foundation to study the physics of the sounds feathers make. Clark traveled to Latin America, where he recorded the courtship displays of a number of hummingbird species that produce distinctive sounds with their tail feathers including sheartails and woodstars. He then took his research into the lab, where he used a wind tunnel to reproduce the sounds feathers make when the birds are in flight in the wild, and studied how feathers produce sounds over a range of air speeds. [Research supported by National Science Foundation grant IOS 09-20353.] (Date of Image: unknown)

Credit: Anand Varma

Hummingbird Courtship Displays and Acoustics (Image 1)

A male Anna's hummingbird (Calypte anna). Chris Clark, a postdoc at the Peabody Museum of Natural History at Yale University, is studying how hummingbird feathers produce various sounds during their courtship displays.

When Clark attended graduate school, his Ph.D. work focused on the roles of sexual selection and flight performance in shaping hummingbird tail morphology. In 2008, he published a paper titled "The Anna's Hummingbird Chirps With It's Tail," which received wide publicity and helped launch his current research focus. Clark's paper described how Anna's hummingbirds (Calypte anna) make a loud sound with their tail feathers during courtship displays rather than vocally.

After completing his doctorate, Clark and his advisor, Richard Prum, were awarded a grant from the National Science Foundation to study the physics of the sounds feathers make. Clark traveled to Latin America, where he recorded the courtship displays of a number of hummingbird species that produce distinctive sounds with their tail feathers including sheartails and woodstars. He then took his research into the lab, where he used a wind tunnel to reproduce the sounds feathers make when the birds are in flight in the wild, and studied how feathers produce sounds over a range of air speeds.

[Research supported by National Science Foundation grant IOS 09-20353.] (Date of Image: unknown) [Image 1 of 3 related images.]

Credit: Christopher Clark, Yale University