As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.

Wednesday 8 July 2020

New study shows iconic golden eagle was once common throughout Wales

JULY 1, 2020

A new study has shown that golden and white-tailed eagles were widespread and common throughout historic Wales.

Scientists looked at their historical distribution as part of their bid to bring the species, which became regionally extinct in the early-1800s, back to the Welsh countryside.

During their research they gained fascinating insights by looking at archeological, fossil and observational records—and even Welsh place names.

The study also includes the earliest evidence of golden eagles existing in Wales in the Devensian period—the final glacial period in Britain—about 20,000 years ago.

Sophie-lee Williams, 28, who manages the Eagle Reintroduction Wales Project as part her Ph.D. at Cardiff University, said: "One of the first challenges for our project was to gather evidence of the past distribution of both eagle species to prove they were once historically native to Wales. In other parts of Britain there's a wealth of data—but in Wales there is a real lack of historical record so we had to be creative. Our research has shown, without doubt, that both species were widespread and common across Wales prior to the 18th Century. We hope this opens up new optimism about restoring these magnificent species to Wales in the near future."

The researchers gathered 151 historic records for eagles across every county in Wales—81 for golden eagles and 70 for white-tailed eagles.

Finn’s weaver faces a risk of extinction

by Deepanwita Gita Niyogi on 23 June 2020

The Finn’s weaver, a lesser-known weaver bird species, currently listed as Vulnerable in the IUCN Red List, is in fact at the risk of extinction, according to the Bombay Natural History Society.

The bird prefers the Terai grasslands, found widely in Uttarakhand and Uttar Pradesh, but the landscape in these states has undergone changes due to conversion for agriculture and development.

The Uttar Pradesh forest department has initiated a Finn’s weaver conservation and breeding programme in the Hastinapur Wildlife Sanctuary.

The Finn’s weaver (Ploceus megarhynchus) is listed as vulnerable in the International Union for Conservation of Nature’s Red List. However, the bird is at the risk of extinction, alerts the Bombay Natural History Society (BNHS) a wildlife research organisation in India that is looking to update the bird’s IUCN listing.

According to BNHS director Deepak Apte, the status of the bird is extremely precarious with real threat of extinction. “We have released a species recovery plan and are trying our best to list the species in the IUCN Red List as a Critically Endangered species. We are also working closely with respective state governments where the species is found, as well as with the government of India,” Apte told Mongabay-India via email.

Mountain meadow restoration can bring birds back

JUNE 25, 2020

by Point Blue Conservation Science

In a new study led by scientists at Point Blue Conservation Science and in collaboration with The Institute for Bird Populations, authors evaluated the successes of mountain meadow restorations by analyzing eight years of bird data collected by field biologists. The authors concluded that, when "pond and plug" and similar techniques were followed, the number of birds of many species increased over time as habitat conditions improved.

The paper, published in Restoration Ecology, may prove of particular value to restoration practitioners, many of whom rely on peer-reviewed scientific journal articles to guide their work.

"This paper is the culmination of many years of work monitoring meadows. And it definitely increases the amount of evidence we have that one of the most commonly used approaches is having the effects we want," says Brent Campos, a lead author of the study.

Cont ..

Sunday 5 July 2020

Survey estimates much higher Alberta bird populations than thought


There may be many, many more songbirds in Alberta forests than previously thought, say University of Alberta scientists who have come up with a new way of counting them.

But researchers say that while the new counts may be good news – some estimates are more than 10 times higher – they don’t change the overall declining trend of the province’s boreal songbirds.

“Our estimates just highlight that our understanding is incomplete,” said Peter Solymos, whose paper was recently published in The Condor, the journal of the American Ornithological Society. “We need to understand the limitations.”

Bird populations across the continent have been in decline for years. A paper last fall estimated populations have dropped by three billion overall since the 1970s.

Numbers have been estimated for years using data from the Breeding Bird Survey, which uses a standard, consistent method across North America.

Solymos said that survey uses assumptions and techniques that may distort Alberta results. It sends counters out along prescribed roads, stopping at regular distances and counting birds heard and seen within a certain time. Those raw numbers are adjusted to account for factors such as birds singing more at some times of day than others.

Solymos said that may work in southern Alberta and the United States, where roads go almost everywhere. But northern Alberta is full of roadless bush. Roadside counts bias results in favour of roadside habitat.

“Roads are usually built in upland environments and go through upland vegetation. (As well), you get the disturbed habitat along the road.

“You get a nonrandom sample. You have to go into the bush.”

Solymos took the bird survey data and combined it with dozens of off-road bird surveys done over the years for forestry companies and agencies such as the Alberta Biodiversity Monitoring Institute.

Out of 81 bird species, Solymos came up with significantly higher estimates for 45 of them. Four species – crows, goldfinches and two types of sparrow – came in lower, and the rest were comparable.

Solymos came up with populations estimates that are, on average, 3.7 times higher.

Some differences are huge. The Breeding Bird Survey puts 70,000 blackpoll warblers in Alberta; Solymos reckons 1.3 million.

Jeff Wells, head of boreal conservation for the Audubon Society, calls Solymos’s work significant.

“It may show that there are more birds in the intact boreal than we thought, which is good news. It means we still have lots of chances to keep them that way.”

France reprimanded over controversial bird hunting practices


Paris has ignored a letter of formal notice sent by the European Commission in July last year, which calls on French authorities to stop illegal bird hunting.

The French government even doubled down in May by publishing a decree, which maintains controversial bird hunting techniques that are prohibited at EU level.

Vivian Loonela, EU Commission spokesperson on the environment, says the infringement case was still open.

“The Commission is aware of the publication of this new decree and will consider this new element in the follow up of the case,” she told EURACTIV in emailed comments.

“The Commission is requesting France to ban non-selective hunting practices, such as glue and nets, which are not in line with the requirements of this Birds Directive,” Loonela said.
While EU countries “may derogate from certain provisions of the directive,” they may only do so “under strict conditions that are not fulfilled in this case,” Loonela explained.

The controversial hunting techniques are decried by the Ligue de protections des oiseaux (LPO), a French conservation NGO affiliated to BirdLife International.

According to conservationists, the French law is illegal because it allows hunting bird species that are in bad conservation state. It also allows the hunting of migratory birds and maintains traditional hunting practices like birdliming, which are “not selective and harms species”.

When it comes to bird hunting, France is an EU outlier, says Yves Verilhac, who represents BirdLife International in France.

“64 species can be hunted in France, contrary to Netherlands which authorises only 2. The average in the EU is 30 species, making France the most lenient country towards hunters,” he claims.

The list of species authorised for hunting in France also includes migratory birds like the greylag goose, whose hunting is “illegal” because it prevent them from flying further North than France, says Verilhac.

In Brussels, the European Commission appeared to back this argument. Loonela said the EU executive “pays particular attention to the compliance of hunting practices in France because 20 of the 64 huntable species are not in favourable conservation status.”

The Commission has opened a new procedure “asking France to step up protection of the Turtle dove as hunting contributes to the decline of this species,” Loonela said.

For bird protection NGOs, the most controversial is undoubtedly traditional hunting techniques like birdliming and nets, which “are not selective” and harm protected species.


Experiment shows it is possible for fish to migrate via ingestion by birds

JUNE 23, 2020 REPORT
by Bob Yirka ,
A team of researchers from the Danube Research Institute and the National Agricultural Research and Innovation Centre, both in Hungary, and Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas in Spain reports that is it possible for fish eggs to survive the trip through the bird digestive tract and subsequently to hatch. In their paper published in Proceedings of the National Academy of Sciences, the group describes their experiments with birds and fish eggs and what they found.
Fish have been found swimming in extremely isolated lakes over the years, raising the question of how they got there. Prior research has shown that most such fish are related to fish in other less isolated areas, which suggests that fish in isolated places must have somehow migrated there. Scientists have suggested that the most obvious explanation for such migration is fish eggs being consumed by birds who carry them in their digestive tracts and then deposit them in a new locale when they defecate. Surprisingly, no one has thought to test this theory until now.

Friday 3 July 2020

Dawn song of the male great tit attracts other males rather than females

JUNE 23, 2020

Female great tits (Parus major) stay clear of territories with better singing males while competing males are attracted to the territories with better singers. This unexpected conclusion was reached by researchers of Wageningen University & Research in collaboration with the Netherlands Instituut for Ecology (NIOO-KNAW). This conclusion is diametrically opposed to the current assumption that male birds use their song to impress females and repel males to stay away from their territory.
Previous research showed that songbirds often cheat on their partners. One would thus expect male birds to use their song to lure any close-by females. But nature tells a different story, the research team discovered.
"Our knowledge to date on the daily behavior between males and females is largely based on knowledge under lab condition because it is so difficult to follow a songbird for a long time," professor Marc Naguib explains. "We know what colors are prefered by the females, and what songs they prefer if they exhibit an immediate reaction. But how they show territorial behavior and respond to males in the open field was hitherto almost unknown."
Dawn song attracts male competition
Ph.D. researcher Nina Bircher and her co-authors expected that the most enthusiastic singers would attract the most female interest. This appeared completely false. The male great tits with the most extensive repertoire that started singing the earliest and showed the most persistence attracted fewer females. Male great tits, however, entered their singing competitor's territory, captivated by the performance, the researchers write in the scientific journal Behavioral Ecology.
The reason for this behavior remains a mystery. Naguib: "Males may enter the competitor's territory to check out why the competitor is better than they are, or why he may be more suited to produce offspring." Whatever the reasons, the discovery sheds new light on the complexity of songbirds social and communication network.
The prevailing assumption that the female great tit would more frequently enter a different territory when she is fertile is thus not supported. The premise is she would visit other territories specifically for extra-pair mating. In reality, however, this research shows that she enters territories other than her own once she has laid eggs in an effort to find food for her young.

Long-tailed tits avoid incest by recognising the calls of relatives

JUNE 23, 2020
Long-tailed tits actively avoid harmful inbreeding by discriminating between the calls of close family members and non-family members, according to new research from the University of Sheffield.
Inbred animals typically suffer from reduced survival and reproductive success, so incest is usually avoided. But, in species where young stay close to where they were born, relatives are often encountered as potential mates, increasing the risk of harmful inbreeding.
Long-tailed tits often breed close to home, allowing kin to help raise each other's chicks, but also incurring a risk of incest that reduces the reproductive success of offspring. The research, led by Dr. Amy Leedale from the University of Sheffield's Department of Animal and Plant Science, found that despite this risk, close relatives are actively avoided when pairs form each spring.
Long-tailed tits use distinctive calls to recognize close relatives so that they can help raise their offspring. The authors suggest that these calls also explain how the birds avoid inbreeding.
Dr. Amy Leedale, who led the research as a Ph.D. student at the University of Sheffield, said: "We recorded the calls of males and females in many pairs of long-tailed tits and found that the calls of breeding pairs were less similar than the calls of close relatives that they could have bred with. Call similarity within breeding pairs was, instead, similar to that observed among distant relatives or unrelated birds."
Long-tailed tit calls are learned in the nest, when parents, offspring and siblings are closely associated. Call similarity can therefore act as a reliable indicator of close relatedness in adulthood. This study reveals a potential mechanism by which long-tailed tits can avoid harmful inbreeding as well as gaining benefits from cooperating with kin.

Research suggests a better way to keep birds from hitting power lines

JUNE 24, 2020

by Steve Lundeberg, Oregon State University
Suspended, rotating devices known as "flappers" may be the key to fewer birds flying into power lines, a study by Oregon State University suggests.
The findings by researchers in OSU's College of Agricultural Sciences are important because around the globe both the number of power lines and concern over bird fatalities are on the rise.
Research has documented more than 300 species of birds dying from hitting power lines, with one study estimating that more than 170 million perish annually in the United States and another estimating the global death toll to be 1 billion per year. There's also the problem of power outages that bird strikes can cause.
Conservation managers and utilities many years ago developed flight diverters, basically regularly spaced devices that make the lines more visible, as a step toward reducing the number of birds flying into the lines.
The most common type are the PVC spirals, which are durable and easy to install, but how well they actually work isn't well understood. Though they've been in use for nearly four decades, strike rates remain high for a number of species.
OSU researchers Virginia Morandini and Ryan Baumbusch were part of an international collaboration that compared the effectiveness of three types of flight diverters: yellow PVC spiral; orange PVC spiral; and a flapper model with three orange and red polypropylene blades with reflective stickers.
The flapper hangs from a power line and its blades, 21 centimeters by 6.2 centimeters, rotate around a vertical axis.

Thursday 2 July 2020

Cowbirds change their eggs' sex ratio based on breeding time

JUNE 24, 2020

Brown-headed cowbirds show a bias in the sex ratio of their offspring depending on the time of the breeding season, researchers report in a new study. More female than male offspring hatch early in the breeding season in May, and more male hatchlings emerge in July.
Cowbirds are brood parasites: They lay their eggs in the nests of other birds and let those birds raise their young. Prothonotary warblers are a common host of cowbirds.
"Warblers can't tell the difference between their own offspring and cowbirds," said Wendy Schelsky, a principal scientist at the Illinois Natural History Survey and co-author of the study. "They do a really good job of raising cowbirds, even though cowbird chicks are larger and need more food."
The researchers studied the interactions between cowbirds and warblers for seven years to determine whether there was a difference in the relative number of males and females among cowbird offspring. They collected DNA samples from cowbird eggs or newly hatched chicks.
"Other scientists have not seen any difference in the sex ratios of brood-parasitic birds," said study co-author Mark Hauber, a professor of evolution, ecology, and behavior at the University of Illinois at Urbana-Champaign. "This is the first time anyone has detected a seasonal bias and we believe that it is due to our large sample sizes."
More female than male cowbirds are hatched early in the nesting season, and the pattern is reversed in July, new research finds. An adult female cowbird, upper right, perches on tree stems above an adult male cowbird. Credit: Photo (c) by Michael Jeffords and Sue Post
The researchers think their results may reflect the different developmental trajectories of male and female cowbirds.

Resident parasites influence appearance, evolution of barn swallows

JUNE 24, 2020
by Kelsey Simpkins, University of Colorado at Boulder
Barn swallows live almost everywhere on the planet, recognizable by their forked tail and agility in the air. Yet while they share these characteristics, these little birds often look slightly different in each place they live—with some so distinct they're splitting off to become new species.
Researchers at CU Boulder think that local parasites are influencing why barn swallows in Europe, the Middle East and Colorado are choosing their mates differently. Their new research, published in Evolution, finds that these parasites could be playing an important role in changing the traits displayed to attract mates early in the process of the creation of new species.
"It's possible we haven't appreciated just how important parasites might be in shaping the evolution of their hosts," said lead author Amanda Hund, who conducted the research as a doctoral candidate in the Ecology and Evolutionary Biology Department.
Every organism, including humans, has co-evolved with a unique community of parasites, that by definition live at the expense of their host. While they are not beneficial to us like many other microbes are, parasites have shaped our own immune system, pheromones and even our mate selection, previous research has shown.
Hund set out to characterize as many parasite communities as she could in barn swallows, to find out if they could be influencing their mate selection, and therefore the male birds' physical traits and the creation of new species.

Antarctic penguins happier with less sea ice

JUNE 24, 2020

by Research Organization of Information and Systems
Researchers have been surprised to find that Adélie penguins in Antarctica prefer reduced sea ice conditions, not just a little bit, but a lot. As climate models project rapid reduction of the continent's sea ice over the rest of the century, this iconic polar predator could be a rare global warming winner. Their research findings are published on June 24, 2020 in Science Advances.
In recent decades, Antarctica has experienced a steady increase in the extent of its sea ice—frozen seawater—even as its polar twin, the Arctic, has suffered through a marked decrease. But this is not expected to last for much longer as the climate changes, with Antarctica also projected to see a decline in its sea ice, with all the consequences of such changes to the maritime habitat for the organisms that live there.
But such consequences aren't always negative.
Polar biologists have known for some time that Adélie penguins, the most common species of penguin in Antarctica, tend to see population increases during years of sparse sea ice and suffer massive breeding failures during those years with the greatest growth of sea ice.
But until now, researchers didn't really know why this happened. The handful of studies that made mention of the relationship between population growth and sea ice have only ever established a correlation, not a cause.

Wednesday 1 July 2020

Warming climate is changing where birds breed

Migratory behavior and winter geography drive differential range shifts of eastern birds in response to recent climate change
Date: May 26, 2020
Source: S.J. & Jessie E. Quinney College of Natural Resources, Utah State University
Spring is in full swing. Trees are leafing out, flowers are blooming, bees are buzzing, and birds are singing. But a recent study published in Proceedings of the National Academy of Sciences found that those birds in your backyard may be changing right along with the climate.
Clark Rushing, Assistant Professor in the Department of Wildland Resources and Ecology Center, Quinney College of Natural Resources at Utah State University, and colleagues at the U.S. Geological Survey wanted to know how climate change has already affected where birds breed. They used data from the Breeding Bird Survey -- one of the oldest and longest citizen-science programs in the world -- to conduct their research. "Thousands of devoted volunteers, cooperators, and a joint U.S.-Canadian wildlife management team have contributed to the success of the surveys for the last 54 years," said Andy Royle, a USGS senior scientists and co-author of the study. "The Breeding Bird Survey is fundamental to our understanding and management of wild bird populations in North America."
The research team combined Breeding Bird Survey data with powerful computer models to discover changes in breeding range for 32 species of birds found in eastern North America. What they found is surprising:
Some birds' ranges are expanding. Birds that both breed and winter in North America are extending their ranges north to take advantage of new, warm places to breed. These birds are also maintaining their southern ranges. These results bring hope that some bird populations, such as Carolina wrens and red-bellied woodpeckers, may be resilient to future climate change.

Better way to keep birds from hitting power lines

Date: June 24, 2020
Source: Oregon State University    
Suspended, rotating devices known as "flappers" may be the key to fewer birds flying into power lines, a study by Oregon State University suggests.
The findings by researchers in OSU's College of Agricultural Sciences are important because around the globe both the number of power lines and concern over bird fatalities are on the rise.
Research has documented more than 300 species of birds dying from hitting power lines, with one study estimating that more than 170 million perish annually in the United States and another estimating the global death toll to be 1 billion per year. There's also the problem of power outages that bird strikes can cause.
Conservation managers and utilities many years ago developed flight diverters, basically regularly spaced devices that make the lines more visible, as a step toward reducing the number of birds flying into the lines.
The most common type are the PVC spirals, which are durable and easy to install, but how well they actually work isn't well understood. Though they've been in use for nearly four decades, strike rates remain high for a number of species.
OSU researchers Virginia Morandini and Ryan Baumbusch were part of an international collaboration that compared the effectiveness of three types of flight diverters: yellow PVC spiral; orange PVC spiral; and a flapper model with three orange and red polypropylene blades with reflective stickers.

Genetic outcomes of great gray owl population in four states

Date: June 3, 2020
Source: University of Wyoming
A University of Wyoming researcher led a study of great gray owls in a four-state region, showing that range discontinuity could lead to genetic drift and subsequent loss of genetic diversity in these birds.
Lower genetic diversity in these owls means they are more susceptible to changes in their environment and, thus, less able to adapt quickly.
"With lower genetic diversity, such owls have less ability to adapt to changes that include extreme fire effects on their habitats; human developments; stresses caused by diseases such as West Nile virus and trichomonas, a nasty parasite that damages their oral cavity and can lead to starvation; and other diseases," says Holly Ernest, a UW professor of wildlife genomics and disease ecology, and the Wyoming Excellence Chair in Disease Ecology in UW's Department of Veterinary Sciences and the Program in Ecology. "Another stress can be overzealous photographers who get too near nesting sites and scare great gray owl moms and dads off their nests and endanger the nestlings."
Ernest was the senior and corresponding author of a paper, titled "Population Genomic Diversity and Structure at the Discontinuous Southern Range of the Great Gray Owl in North America," that was published online May 31 in Conservation Genetics, a journal that promotes the conservation of biodiversity. The journal publishes original research papers, short communications, review papers and perspectives. Contributions include work from the disciplines of population genetics, molecular ecology, molecular biology, evolutionary biology, systematics, forensics and others.
Beth Mendelsohn, a 2018 UW Master of Science graduate in veterinary sciences and the Haub School of Environment and Natural Resources, from Missoula, Mont., is the paper's lead author. Mendelsohn is now a raptor biologist conducting research to improve owl and hawk conservation in Rocky Mountain ecosystems.

Monday 29 June 2020

Pinker flamingos more aggressive

Date: June 7, 2020
Source: University of Exeter
Bright pink flamingos are more aggressive than paler rivals when fighting over food, new research shows.
Pink plumage is a sign of good health in lesser flamingos, and a flush of colour often means they are ready to breed.
So when the birds squabble over food, the pinkest flamingos -- both male and female -- tend to push the others around.
The study, by the University of Exeter and WWT Slimbridge Wetland Centre, also found the birds fight more when food is available in a small area such as a bowl -- so the findings suggest captive birds should be fed over a wide space where possible.
"Flamingos live in large groups with complex social structures," said Dr Paul Rose, of the University of Exeter.
"Colour plays an important role in this. The colour comes from carotenoids in their food, which for lesser flamingos is mostly algae that they filter from the water.
"A healthy flamingo that is an efficient feeder -- demonstrated by its colourful feathers -- will have more time and energy to be aggressive and dominant when feeding."
Dr Rose studied the behaviour of Slimbridge's lesser flamingos in different feeding situations: at an indoor feeding bowl, a larger indoor feeding pool, and outdoors with food available in a large pool.

Study on shorebirds suggests that when conserving species, not all land is equal

Date: June 9, 2020
Source: Princeton University
Princeton University researchers may have solved a long-standing mystery in conservation that could influence how natural lands are designated for the preservation of endangered species.
Around the world, the migratory shorebirds that are a conspicuous feature of coastal habitats are losing access to the tidal flats -- the areas between dry land and the sea -- they rely on for food as they travel and prepare to breed. But a major puzzle has been that species' populations are plummeting several times faster than the rate at which coastal ecosystems are lost to development.
Nowhere is the loss of tidal flats and shorebird species more acute than along the East Asia-Australasian Flyway (EAAF). An estimated 5 million migratory birds from 55 species use the flyway to travel from southern Australia to northern Siberia along the rapidly developing coast of China -- where tidal flats can be more than 6 miles wide -- at which birds stop to rest and refuel.
Since the 1980s, the loss of tidal flats around the Yellow Sea has averaged 1.2% per year. Yet, the annual loss of the most endangered bird species has averaged between 5.1 and 7.5%, with populations of species such as the critically endangered spoon-billed sandpipers (Calidris pygmaea) climbing as high as 26% each year.

Antioxidant-rich diet reduces stress response during bird migration

Date: June 18, 2020
Source: University of Rhode Island
A research team led by a University of Rhode Island ornithologist had birds fly in a wind tunnel to simulate migration and found that birds that consume dietary antioxidants before and during fall migration can reduce the endocrine stress response triggered by long-duration flights.
The results, published this week in the Proceedings of the Royal Society B, emphasize the importance of protecting habitat with an abundance of available berries containing antioxidants at migratory stopover sites.
"This reduction in the endocrine stress response may be a major benefit birds gain in fall by eating fruits at stopover sites during migration," said Scott McWilliams, URI professor of natural resources science, noting that many species of birds select berries containing anthocyanins, a type of dietary antioxidant present in purple-colored berries. "We know birds prefer certain berries that have lots of antioxidants."

Sunday 28 June 2020

Mysterious Australian Night Parrots may not see in the dead of night

Australia's most elusive bird, the Night Parrot, may not be much better at seeing in the dark than other parrots active during the day
Date: June 9, 2020
Source: Flinders University
Australia's most elusive bird, the Night Parrot, may not be much better at seeing in the dark than other parrots active during the day.
An international study, co-led by Flinders University's Dr Vera Weisbecker, has revealed the critically endangered parrot's visual system is not as well-adapted to life in the dark as would be expected for a nocturnal bird, raising concerns it might be adversely impacted by fencing in the Australian outback.
"Night Parrots must be able to find their way at night -- to find food, avoid obstacles while flying, and escape predators," says Dr Weisbecker.
"We therefore expect their visual system to show adaptations for seeing in the dark, similar to other nocturnal birds -- New Zealand's Kakapo parrot and owls with enlarged eyes for example. However, we found that this wasn't the case."

Spectacular bird's-eye view? Hummingbirds see diverse colors humans can only imagine

Team trains wild hummingbirds to discriminate UV color combinations
Date: June 15, 2020
Source: Princeton University
To find food, dazzle mates, escape predators and navigate diverse terrain, birds rely on their excellent color vision.
"Humans are color-blind compared to birds and many other animals," said Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology. Humans have three types of color-sensitive cones in their eyes -- attuned to red, green and blue light -- but birds have a fourth type, sensitive to ultraviolet light. "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," said Stoddard.
To investigate how birds perceive their colorful world, Stoddard and her research team established a new field system for exploring bird color vision in a natural setting. Working at the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado, the researchers trained wild broad-tailed hummingbirds (Selasphorus platycercus) to participate in color vision experiments.
"Most detailed perceptual experiments on birds are performed in the lab, but we risk missing the bigger picture of how birds really use color vision in their daily lives," Stoddard said. "Hummingbirds are perfect for studying color vision in the wild. These sugar fiends have evolved to respond to flower colors that advertise a nectar reward, so they can learn color associations rapidly and with little training."
Stoddard's team was particularly interested in "nonspectral" color combinations, which involve hues from widely separated parts of the color spectrum, as opposed to blends of neighboring colors like teal (blue-green) or yellow (green-red). For humans, purple is the clearest example of a nonspectral color. Technically, purple is not in the rainbow: it arises when our blue (short-wave) and red (long-wave) cones are stimulated, but not green (medium-wave) cones.
While humans have just one nonspectral color -- purple, birds can theoretically see up to five: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow and ultraviolet+purple.
Stoddard and her colleagues designed a series of experiments to test whether hummingbirds can see these nonspectral colors. Their results appear June 15 in the Proceedings of the National Academy of Sciences.