Take This Moment!

Up to This Moment: Reports on New Research & Information

super moon, super owls - from a photo in the Boston Globe, 7/2014

super moon, super owls – from a photo in the Boston Globe, 7/2014

July 1, 2014 – Owl News

Eagle Owls’ Visual Signaling

Young students often ask me how owls communicate with one another. I answer by first imitating or playing a tape of the hoots, whistles, burbles, and yelps, which are clearly communicating something to someone: an alarm to another owl, a duet with a mate, a signal to a youngster, a youngster crying for food, a scary sound intimidating potential prey or predators. The same students are likely to ask me what the owls’ “ear” tufts are used for, and I have taken to saying that, first, they are not ears nor even used in hearing, and that in addition to being part of the bird’s camouflage, I believe them to also be part of their communication. I hasten to tell them that I have read nothing to back this up, but it makes sense. After all, many of our Strix (Strigidae) owls have these tufts and they can be actively raised, lowered, wiggled, and so on.

Great Horned Owl in Threat Posture
Great Horned Owl in Threat Posture
Great Horned Owl in Hiding Mode

Great Horned Owl in Hiding Mode

Recently a report on an interesting study surfaced: Vincenzo Penteriani, a researcher at the Donana biological station in in Spain, has been working with a team on Eagle Owls, close cousins and similar in looks to our Great Horneds, only quite a bit larger. They were trying to determine the effects the full moon might have on these birds. He discovered first of all that during an eclipse, owls that had been calling fell silent when the moon was covered. Second, and somewhat off his subject (but germane to ours), he observed that in calling owls, a previously hidden patch of white feathers in the throat flashed into view with each vocalization. More studies revealed that this signal was part of the species’ mating ritual. Incidentally, the calls and the ascot-flashing increased on the brightest nights. Almost all our “horned” owls have some white facial feathers (note the GHO in the first photo above) and some have wonderfully bright lace collars. You may recall that in the US, we have two basic types of owls: the Barn Owls are part of the worldwide Barn and Bay Owl group, beautifully feathered and very pale altogether. It seems that the male Barn Owls are paler than the females, but according to researchers, this is not a genetic surety, but a matter of mating choice. The ladies in most of our populations apparently prefer the pale males. The second group includes the Strix (Strigidae) owls, which is to say, all the other owls we have other than the Barnies. Here is a photo that clearly shows a (caged) Great Horned wagging its tufts at me. It must have been signalling something, and I’d love to know what. It was not a friendly gesture, I’m sure.

This Great Horned Owl is waggling its ear tufts at me. And staring.

This Great Horned Owl is waggling its ear tufts at me. And staring.

I cannot find any research on visual signaling in owls in this country. So, for avian students: here may be a nifty topic free for the taking, and one that will lead you out into the world of mysterious moonlight.

Barn Owls Out-compete Traps & Poison

Barn Owl in Flight

Barn Owl in Flight

According to a recent Ag Alert magazine article (May 14, 2014) by Bob Johnson, of Monterey, CA, a test of Barn Owl predation in a Central Valley vineyard showed that these birds beat manmade rodenticides all hollow. A 100-acre vineyard in Lodi Valley put up owl boxes and attracted 18 pairs of Barn Owls. These birds eat from 600 – 1000 mice a year, and they breed several times a year if the small rodent population will sustain them. In this test, a research team put up 18 boxes, filmed the owl activity, and analyzed the pellets. As you probably know, most meat-eating birds vomit out a compact ball of indigestible materials every day or so, their digestive tracts not being set up for voiding hard fecal matter via the cloaca. This efficiency is part of the adaptive package that makes bird flight so efficient.

From: Raptors Are The Solutions

From: Raptors Are The Solution

In the first year, the vineyard teams reported a catch of 10,000 gophers and in Year 2, 15,000. In a subsequent year, the owls began leaving the vineyard because there were now no longer enough prey animals to feed their families. The team logged in some man and woman hours, and filmed the nest boxes to count the number of rodents being brought in, collected pellets, counted bones. They figured the cost of the program at about 24 cents per rodent. Trapping rodents cost the team $11.22 per rodent. Using poison was not priced because the team didn’t use poison, but they figured it averaged a bit less than the $11 and change of the trapping. Strychnine for 100 acres would cost about $1,000 and would have to be renewed frequently to keep up the pressure on the rodent families. It would also kill many animals it was not intended for. If you live below 2500 feet, you might want to hire these critters. Barn Owls, unlike many other predators, will nest near one another if there is ample prey, hence the test team’s 18 boxes for the 100-acre area. One box per ten acres is a good round number. They may be set on a pole at 8 to 15 feet high and they should face East (an owl preference that we probably don’t understand), and have some shade from the heat of the day. After the harvest, a crew needs to clean out the boxes in preparation for the next season. Interested local businesses often give out free owl boxes, built to the proper specs. See the California Raptor Center’s webpage for instructions.

June 12, 2014

A Reminder: The Ancestry of Birds

The oldest known fossil of a bird ancestor (so far) is Aurornis xui, discovered in China in 2013, dating back more than 160 million years. The name comes from the Latin word aurora, “dawn,” and the Greek word ornis, “bird.” The species name, xui, honors Xu Xing, a Chinese paleontologist who as it happens did not discover the fossil. The reptile-bird was 20 inches in length from beak to tail, about the size of a pheasant. Like Archaeopteryx, whose fossils date back 150 million years, it had claws on the ends of its wings, a long bony tail, and toothed jaws. Its bone structure shows the first signs of the light, hollow bones of modern birds, though the feather types indicate that it was non-flighted. Archaeopteryx’s wing feathers show a slight off-set to one side of the shaft, which indicates it may have been capable of rudimentary flight.

February 2, 2014

The Sense of Smell in Birds

tuvu head flipped

Have Nose – Will Work by Air!

For many years, we thought birds had little or no sense of smell. But since the late 1960s, avian researchers have learned that all the species (108 total) in which olfaction was tested had some sort of olfactory “bump” or “bulb” in the brain, some larger than others. Until recently, for most, the tests of actual olfactory response were lacking. Still, some birds studied early on showed a keen olfactory sense, accompanied by a relatively large and active olfactory bulb in the brain. Most famously the Turkey Vulture, which a researcher, Kenneth Stager, proved in 1960 was able to sniff out the presence of ethyl mercaptan – the chemical released by decomposing flesh – in extremely small doses. Stager knocked into a cocked hat the flawed test conducted in the 19th century by the artist John J. Audubon that “proved” Turkey Vultures couldn’t smell carrion (his test really suggested that they avoid truly revolting rotten meat). In recent tests TUVUs continue to hidden find day-old (or fresher) carrion from one to three miles away. Their external nares advertise these skills. These birds are even helpful to us – the pipeline gas industry perfumes gas with ethyl mercaptan, and Turkey Vultures collect in the air over a pipe leak. TUVU skull web

Turkey Vulture Skull. Except for the TUVU’s South American cousins, the Yellow-headed Vultures, no other raptor species has this kind of nares or shows sign of finding food by smell.

Some of the best-known studies have suggested that pelagic birds, such as albatrosses and fulmars, possess an equally keen sense of smell, finding fish schools and patches of krill near the ocean’s surface by scent. They have interesting external nares, called tube noses, which are literally external tubes on the upper beak ending in the nares opening. These seem to figure in their nosy skills. The Kiwi, who gets his nightly worms by digging with his beak in soft earth, has his nostrils handily located at the tip of that beak and has been shown to detect prey via scent. Recently, intensive and on-going studies of scent detection in many avian species were reported in Audubon (January/February 2014). The article showcases the work, conducted over the past twenty or so years, of Gabrielle Nevitt (now of the University of California-Davis). She describes successful olfactory tests on many avian species, from Kakapos of New Zealand, to the Oregon Junco. All these species show some response to odors, a few quite surprising. The uses these birds make of odors are also varied, from finding food to attracting mates, to avoiding predators to identifying young in nest burrows and holes. One species, the European Blue Tit, will not enter its nest box if that box has been tagged with the chemical odor associated with weasels. For birdwatchers, this field is another interesting hotspot to watch! Postscript: Here’s a curiosity – like the pelagic birds, the Common Poorwill, a nighthunting insect feeder, has a “tube” nose, that external structure ending in the nares opening. But this bird’s olfactory skills are as yet unreported. And in readily available images, it’s hard to tell if the Poorwill’s cousins, the Whippoorwill and the Nighthawk family have similar structures (the birds are small; their beaks are thin, dark, and hard to see). Still, why advertise what you don’t use? The Poorwill hunts on the wing at night, and surely detecting the pheromones of the insects that are his prey might make his hunts more successful. powiforweb

 Common Poorwill. Partially cleaned skull, with bristles and tube-shaped nares.

January 17, 2014

New Report on Falcon Vision – Hunting Strategy

A recent study reports on experiments on falcons wearing miniature videocameras mounted on their backs or heads while pursuing flying prey. Researchers Suzanne Amador Kane and Marjon Zamani analyzed videos of hunts by falconry birds – a gyrfalcon, gyrfalcon/Saker falcon hybrids, and peregrine falcons – to determine apparent prey positions on their visual fields during pursuits. These video data were then interpreted using computer simulations of pursuit steering laws observed in insects and mammals.


A comparison of the empirical and modeling data indicates that falcons use cues of the apparent motion of prey on the falcon’s visual field to track and capture flying prey via a form of motion camouflage. With this strategy, the prey remains in a fixed spot in the falcon’s field of view, and the falcon remains stationary from the perspective of its prey until the final seconds before being attacked. The falcons also were found to maintain their prey’s image at visual angles consistent with using their shallow fovea (temporal fovea – falcons have two foveae, temporal and deep, or nasal). These results should prove relevant for understanding the co-evolution of pursuit and evasion, as well as the development of computer models of predation and the integration of sensory and locomotion systems in biomimetic robots.

Having a better idea of how falcons and other predatory birds follow objects that move quickly and unpredictably could help improve the design of robots and unmanned aircraft.

Reported January 15 in the Journal of Experimental Biology.

Note on foveas, or focal points, in raptor eyes: falconhead for web Many animal species have regions within the retina, called foveae or foveas, in which the density of the functional photoreceptors is higher. These also contain a predominance of cones over rods, and are specialized for increased visual acuity. Humans and most mammals have a single fovea. Two foveas are present in various diurnal birds, including raptors: a deep fovea (nasal/central region) and a shallow fovea (temporal region). The central fovea presents a higher density of photoreceptors and generally a steeper and deeper depression compared with the temporal fovea. Findings in studies have suggested a greater visual acuity at the deep central fovea than at the shallower central fovea. Exceptions to the presence of two foveas occur in some raptors, such as owls, which have only one fovea, located in the temporal region. Another unique feature of the fovea of owls is that it presents a relatively higher density of rod photoreceptors, which is a distinctive feature of nocturnal avian species. Unlike the retinas of mammals, the avian retina has no blood vessels in its outer layer; nourishment is mainly supplied from a highly vascularized body known as the pecten oculi, which protrudes into the cavity of the eye. Oxygenation is received from the choriocapillaris, the system of capillaries in the inner vascular layer of the eye. The pecten extends from the optic nerve head into the vitreous body of the eye, and this vascular structure is larger and more elaborate in diurnal birds than in nocturnal ones. The avascular structure of the retina provides a low-scattering passage for light to travel from the retinal surface to the photoreceptors, without forming shadowed areas. For more detail, see the Biology category, Avian Vision Parts I & II.   January 15, 2014   v formation web

Sandhill Cranes flying to a roost or feeding area in loose V formation

Update on Bird Flight  It’s not a new idea that birds flying in formation do so for energy conservation. To get the most out of this, however, would require precision in observation and coordination between individual flock members, and many scientists doubted that birds had that capability. This from the January 2014 issue of Nature:. . . In 2011, as part of a reintroduction program, captive-bred ibises following an ultralight aircraft to their wintering grounds arranged themselves in the shape of a V. Data loggers on their backs captured every position and wing flap, yielding the most compelling experimental evidence yet that birds exploit the aerodynamics of the familiar formation to conserve energy. Theoretical models had previously shown that the familiar V formation could enable birds trailing the leader to save energy. But the models also indicated that the birds’ coordination would have to be exceptionally precise to make a difference, and many scientists had doubted that the animals could achieve such a feat during flight (ecophysiologist Steven Portugal, Royal Veterinary College in Hatfield, UK). To take maximum advantage of the V’s aerodynamics, each bird would have to position its wing in the upward-moving part of the vortex of air swirling off the end of the wingtip of the bird in front. But that vortex moves up and down because the bird in front is flapping. So the bird behind must not only put itself in the right place, but must also flap at just the right time – which changes depending on the distance between the birds – to keep riding the upwash. Faced with this complexity, scientists posited alternative reasons for the formation, suggesting that it might protect the birds against predators or let a flock put better navigators up front. For the new study, Portugal and his colleagues used specialized data loggers they had developed, which record Global Positioning System (GPS) data five times per second in sync with an accelerometer for counting wingflaps. To access a flock of free-flying birds that were tame enough to catch repeatedly, the team turned to biologist Johannes Fritz, who was reintroducing the northern bald ibis (Geronticus eremita) in Europe. The birds were trained to follow human foster parents, who led them from breeding areas in Austria and Germany to wintering grounds in the Italian region of Tuscany, using an ultralight aircraft. At Fritz’s invitation, in August 2011 Portugal fitted 14 young ibises in Salzburg with his data loggers. Portugal collected data for three flight days of the 36-day migration. From that, he selected a problem-free seven-minute segment to analyze. To his surprise, the analysis showed that the birds’ formation fit the theoretical predictions of aerodynamics. “They’re placing themselves in the best place and flapping at the best time,” he says. Portugal and his team also reported that the birds frequently shifted into seemingly less-optimal positions, such as directly behind the bird in front, adjusting their flapping to avoid downwash. It is not clear why they would leave the energy-saving V position. The answer may come with further study and better GPS technology. 

December 24, 2013 – A Heart-felt Wish for the Well-Being of Our Planet


Sandhill Cranes Flying

One of the Sights That Lift the Heart: Sandhill Cranes in Flight

Let Us Take Care:

The Life We Protect May Be All the Life There Is

 December 13, 2013, headline in many national papers: “This week, the Food and Drug Administration announced new policies to curtail the widespread use of antibiotics in cows, pigs and chickens raised for meat.”

Later headlines: The US administration allows the killing of eagles in wind farms in order to further our search for “clean” energy.   People who work closely with wildlife rehabilitation organizations and ecological concerns have known for decades about the dangers of irresponsible use of drugs and chemicals. The story behind the development and final banning of DDT and DDE, the “miracle” pesticides of post-WWII agriculture, is a telling example. They first decimated our smaller, more susceptible cousins, the birds. Years later, their adverse effects began to appear in humans, as well. We are bigger creatures, and the toxic effects of chemical accumulation in our tissues takes longer to show up. Mammary glands are store houses of accumulators. And mother’s milk in the 1970s tested very high in DDT, causing liver problems in some nursing infants. In the same post-war era, powerful antibiotics, such as penicillin, were introduced in the general market, as “miracle drugs.” They too were quickly over-used and misused, to the point that decades later, our water-table is contaminated in many areas, and disease pathogens we had “conquered” are once again surfacing, now immune to the antibiotics that once protected us from them. These are the most widely discussed effects of drug misuse. But others are equally disturbing and deadly. The FDA is finally beginning to acknowledge the terrible consequences of widespread antibiotic use in domestic animals. These, and growth hormones, were long administered to cattle designed for our tables because in order to get the rich, marbled flesh we prize in ever-larger herds, cattle must be fed grains. Cattle are not grain eaters, by design. They are grazers – grass eaters. And grains distress their digestive systems, causing inflammations and infections. When the cattle are given antibiotics to off-set that problem, they are also given growth hormones to speed growth so the animals will live long enough, despite stress, to put on the flesh that makes them so valuable in the meat market. We quickly turn away from problems in our food industry practices until the mass of evidence tips the scale, and then we, the people, panic and make a clamor. Generally not soon enough to prevent problems with wild animals. Monarch Butterflies. Bald Eagles. Peregrine Falcons. Finally, humans. The internet is a powerful spreader of news, so this time the cycle is sending ripples far and wide. For example, in recent decades, a non-steroidal anti-inflammatory drug, diclofenac, was routinely administered to cattle in Asia for the reasons given above. The cattle tolerated the drug well, but it accumulated in carcasses, and did not break down with the animals’ death. Instead, substantial amounts remained in the flesh that was consumed by scavengers. (Incidentally, humans eating these cattle may also be building toward a late effect, as happened with DDT.) But once more other species, this time the scavengers, are our new canaries in the coal mine. Here is the broad picture: India, Pakistan, and other countries in south Asia have for many centuries depended upon the services of large vultures to clean up their waste animal products. Town dumps and open spaces and even city streets have been kept clean and disease-free by millions of vultures who can quickly consume any carrion, and whose digestive systems are able to destroy most common natural pathogens. But diclofenac caused the vultures to die of kidney failure. In the late 1980s, into the 1990s, scientists recorded a swift and alarming drop in vulture species in these areas. Millions perished in a matter of 20 years. Many scientific groups sought the cause, and in 2006, the Peregrine Fund identified the culprit, diclofenac, and convinced several areas in Pakistan, in particular, to limit or ban the use of the drug in animals. Some of the vulture species began to recover quickly, but the largest and once most numerous and useful have not made much of a comeback. The surviving populations are too small, and breed too infrequently by nature, to rally. Most recently, India, which had instituted a partial ban, is once more killing its vultures. Veterinarians have found a loophole in the ban and are again treating cattle destined for the meat market with the toxic drug. And once more, vultures are paying the price. That’s not all: other problems are growing. Rabies, a disease carried by mammals but not by birds, has begun to spread in south Asia among humans. The feral dogs, who have taken over the garbage areas of India and Pakistan in the absence of vultures, are spreading this fatal disease by biting humans who come near them or try to drive them away. And that is only one disease. Vultures are thorough and swift. Other scavengers, even microbes, are not. And the garbage areas once quickly cleaned by the birds are today stinking, disease-ridden sumps. The death of the vultures is having a cultural effect, as well. In Asia several ancient societies have for thousands of years counted on vultures to consume their human dead. It is not only part of their death and burial rituals, but often it is key to their beliefs in not contaminating the planet. Burial and cremation, they say, make the air and water impure and are not acceptable forms of disposing of the dead.

 “Vulture panel” from the ancient city, Catal Huyuk. This artwork, showing vultures feeding on human corpses, dates from about 8,000 years ago.

So in India and Pakistan today, a number of living societies are facing a difficult problem: to somehow provide protection for the vultures they count on in their burial rituals, or else give up their age-old rites of passage.

Vulture in Flight

Vulture in Flight

There is no easy cure for our mistakes, after we have made them. But we can prevent them. Or at least reduce them. It means another cultural jolt, however: we, in the West, must put quick profits aside and spend time counting the consequences before we make changes. Today, that means not only drugs, but energy production and genetically modified foods as well. Built in pesticides in plant seeds are killing the pollinators. On this beautiful planet, we are all connected. And if we want to, we can surely act on the knowledge that when we seek changes for our human purposes, we would do well to consider before acting the consequences not only for ourselves, but for our neighbors and for the whole. It means first of all acknowledging the universal web of life, and second, putting that general life above our smaller desires.

Monarch Butterfly

Monarch Butterfly

How do we get to this point? It’s been said many times that we don’t protect what we don’t love, and we love what we know and need. So clearly education is the first step. The second, more radical, to my mind, is that we somehow must encourage the deep belief that the life of the planet and its denizens is a religion more powerful than any other. Powerful and full of miracles, and toned with the voice of the whirlwind. Many creatures, over the eons Earth has existed, have arisen and passed into extinction, most long before we walked upright and began to turn the world to suit our restless brains. It was usually, but not always, a long, slow process. Today we are increasing the spread and speed of changes, however, and if we don’t take care, we run the danger of presenting Earth with more than she, in her beautiful fashion, can absorb and contain. We need to learn to respect and care for this cradle of life. Treat Earth like the universal shrine she is. Take time. Pay attention. Be patient. This means, for example, not allowing wind “farms” to kill birds because it would cost to much not to kill them, but agreeing on styles of wind turbos that will allow birds to see and avoid them. And so with every one of our schemes. Some day the Sun, in its natural evolution, will kill Earth, burn her up and blow her away. But it would be a sad irony if before then, one of her most successful species, instead of working to preserve and perhaps move life elsewhere in the Universe, destroys the very base of that life. And Earth’s life, if it began in the singular accidental moment some biochemists now suggest, may well be the only life there is.   December 6, 2013

Bird Brains, Revisited

Courtesy of the University of Tübingen & World Science New information on bird brains: A portion of the avian brain with no direct counterpart in humans may be responsible for some of birds’ strategic, intelligent behavior. Recently, researchers have studied crows, which belong to a family of birds known as corvids, which we have long known to be capable of intelligent decision-making and behavior. It also includes ravens, jays, and magpies. In the current study, a region of the brain known as the nidopallium caudolaterale comes into play during a simple computer game that the study crows were taught (treats were the reward).

Common Raven - Bird Genius

Common Raven – Bird Genius

Corvids have long been known to make and use tools, remember large numbers of feeding sites, and plan their social behavior according to what other members of their group do. Scientists have wanted to understand this particularly because birds’ brains are physiologically quite from those of mammals. Neurobiologists Lena Veit and Andreas Nieder at the University of Tübingen in Germany trained crows to do memory tests on a computer. The birds were shown an image and were rewarded with treats for remembering it. Shortly afterwards, the subjects had to choose, using their beaks, one of two images on a touch screen, a task based on switching behavioral rules. One of the test images was identical to the first image, the other different. Sometimes the rule was to choose the same image, and sometimes it was to pick the different one. The crows were able to do both tasks and to switch between them as appropriate. This demonstrates a level of concentration and mental flexibility that few animal species can muster – it is an effort even for humans. The crows were quickly able to do these tasks even with new sets of images. The scientists could observe brain cell activity in the nidopallium caudolaterale, a brain region researchers have associated with the highest levels of cognition in birds. One group of nerve cells in the brain became active exclusively when the crows had to choose the same image; another group of cells always responded when the crows were operating on the different-image rule. By watching this activity, the researchers were often able to predict which rule the crow was following even before it made the choice. The nidopallium has no direct counterpart in humans, although it is believed to have similarities to a part of the human brain region known as the auditory cortex. The study, published in the latest issue of the journal Nature Communications, provides valuable insights into the “parallel evolution” of intelligent behavior. “Many functions are realized differently in birds because a long evolutionary history separates us from these direct descendants of the dinosaurs,” Veit said. “This means that bird brains can show us an alternative [way to achieve intelligent behavior with a significantly] different anatomy.” Crows and primates have different brains, but the cells regulating decision-making are very similar. Just as we can draw valid conclusions on aerodynamics from a comparison of the very differently constructed wings of birds and bats, here we are able to draw conclusions about how the brain works by investigating the functional similarities and differences of the relevant brain areas in avian and mammalian brains,” said Nieder.

October 28, 2013

New Research in Bird Perception

McGill and Quebec University researchers have recently shown that some populations of certain corvid species make unusual calculations to avoid getting killed by cars when they are feeding by the roadside. They seem not to judge the speed of individual cars, in order to avoid getting hit, but to calculate an average, presumably by observation. Their reactions can be predicted by the speed limit on the road!


May 28, 2013

New Research in Bird Vision (from 2010)

eagle eye 2

Golden Eagle Eye

Researchers at Washington University School of Medicine in St. Louis have recently studied the eye of the chicken and mapped five types of light receptors. They discovered that the receptors were laid out in interwoven mosaics that maximized the chicken’s ability to see many colors in any given part of the retina. . . . (Study published in Plos One, quoted in Science News, date not available).

“Based on this analysis, [these] birds have clearly one-upped us in several ways in terms of color vision,” says Joseph C. Corbo, M.D., Ph.D., senior author and assistant professor of pathology and immunology and of genetics. “Color receptor organization in the chicken retina greatly exceeds that seen in most other retinas and certainly that in most mammalian retinas.”

Corbo plans follow-up studies of how this organization is established. He says such insights could eventually help scientists seeking to use stem cells and other new techniques to treat the nearly 200 genetic disorders that can cause various forms of blindness [in humans].

Earlier studies in Britain found that [Common] Kestrel vision was complex and included color receptors not found in mammals. Ongoing studies continue to map the vision capabilities of many bird species.

Diurnal birds probably owe their superior color vision to not having spent a period of evolutionary history in the dark, according to some researchers. Birds, reptiles and mammals are all descended from a common ancestor, but during the age of the dinosaurs, most mammals became nocturnal for millions of years.

Most birds, now widely believed to be descendants of dinosaurs, never spent a similar period living mostly in darkness. As a result, diurnal birds have more types of cones than mammals.

“The human retina has cones sensitive to red, blue, and green wavelengths,” Corbo explains. “Avian retinas also have a cone that can detect violet wavelengths, including some ultraviolet, and a specialized receptor called a double cone that we believe helps them detect motion.”

In addition, most avian cones have a specialized structure that can be compared to “cellular sunglasses”: a lens-like drop of oil within the cone that is pigmented to filter out all but a particular range of light. Researchers used these drops to map the location of the different types of cones on the chicken retina. They found that the different types of cones were evenly distributed throughout the retina, but two cones of the same type were never located next to each other.

“This is the ideal way to uniformly sample the color space of your field of vision,” Corbo says. “It appears to be a global pattern created from a simple localized rule: you can be next to other cones, but not next to the same kind of cone.”

Corbo speculates that extra sensitivity to color may help birds in finding mates, which often involves colorful plumage, or when feeding on berries or other colorful fruit. It has further implications in birds of prey: the Kestrel, for example, can see the ultraviolet component in mouse and vole urine trails in the grass, which helps them locate their prey.

“Many of the inherited conditions that cause blindness in humans affect cones and rods, and it will be interesting to see if what we learn of the organization of the chicken’s retina will help us better understand and repair such problems in the human eye,” Corbo says.

Much further work is needed to understand the vision of different species of birds. We’d like to know, for instance, if hawks have the same color reception as falcons, two types of predatory birds that we recently learned developed along somewhat different evolutionary paths.

 Update on Research Methods

To gain insights into the evolution and ecology of visually acute animals such as birds, biologists often need to understand how these animals perceive colors. This poses a problem, since the human eye is of a different design than that of most other animals. The standard solution is to examine the spectral sensitivity properties of animal retinas through microspectrophotometry — a procedure that is rather complicated and therefore only has allowed examinations of a limited number of species to date. We have developed a faster and simpler molecular method, which can be used to estimate the color sensitivities of a bird by sequencing a part of the gene coding for the ultraviolet- or violet-absorbing opsin in the avian retina. With our method, there is no need to sacrifice the animal, and it thereby facilitates large screenings, including rare and endangered species beyond the reach of microspectrophotometry. Color vision in birds may be categorized into two classes: one with a short-wavelength sensitivity biased toward violet (VS) and the other biased toward ultraviolet (UVS). Using our method on 45 species from 35 families, we demonstrate that the distribution of avian color vision is more complex than has previously been shown. Our data support VS as the ancestral state in birds and show that UVS has evolved independently at least four times. We found species with the UVS type of color vision in the orders Psittaciformes and Passeriformes, in agreement with previous findings. However, species within the families Corvidae and Tyrannidae did not share this character with other passeriforms. We also found UVS type species within the Laridae and Struthionidae families. Raptors (Accipitridae and Falconidae) are of the violet type, giving them a vision system different from their passeriform prey. Intriguing effects on the evolution of color signals can be expected from interactions between predators and prey. Such interactions may explain the presence of UVS in Laridae and Passeriformes.” (Odeen & Halstad, “Complex Distribution of Avian Color Vision,” Molecular Biology & Evolution, Journal, Vol 20, 2003)

Reading on Bird Senses:

Farner & King, eds. Avian Biology (Vol. III, Arnold J. Sillman, “Avian Vision”), 1973

Proctor & Lynch. Manual of Ornithology, Yale University, 1993

Cornell University. Home Study of Bird Biology, 1999

Fox, Nick. Understanding the Bird of Prey, 1995

Sinclair, Sandra. How Animals See: Other Visions of Our World, 1985

Ziegler & Bischof, (eds). Vision, Brain, and Behavior in Birds, 1993

McDonald, Helen. Falcon. Reaktion, 2006

Goldsmith, Timothy. “What Birds See,” Scientific American, July 2007

Johnsgard, Paul. Owls of North America, 1988; Hawks & Falcons of North America

Lynch, Wayne. Owls of North America and Canada, 2007

Birkhead, Tim. Bird Sense, 2012

Hanson, Thor. Feathers, 2012

Witton, Mark. Pterosaurs, 2013

van Grouw, Katrina. The Unfeathered Bird, 2013 * A remarkable book.

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    it please help out.

  2. 7Sadmin3 says:

    Hi, Aundrea – I can send you an email whenever I post something new. Simple! I usually have something new every month, but not always. You can check in from time to time. How did you find my blog? Sallie Reynolds

  3. JC Finch says:

    Hi Sallie,

    I’m really enjoying your raptor blog! Please add my e-mail to your list.

    I recently wrote an article about Chuck-will’s-widows that have nested on our property. They’re not raptors but apparently closely related to owls, and I’ve found that they do seem to time their nesting so that the young will hatch near the time of the full moon. I wonder if you’ve ever observed such a thing with owls. If it’s really true and consistent, what a cool evolutionary adaptation!

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