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For the Birds – Adaptations to the Cold

Winter arrived with a vengeance over the past three weeks. From the warmth of our houses, many of us marvel at the ability of birds to survive the challenges of winter weather.

The body temperature of birds is normally between 104 and 109 °F; the fire of life (the rate of metabolism) burns hotter in birds than in any other animals. Birds must stoke their internal fires with more food than mammals of similar size whose body temperature may be only 100 °F or so. To say that someone “eats like a bird” really means that person is a ravenous glutton!

The rate at which heat is lost from a bird’s body in the winter depends on the difference in temperature between the bird’s body and the environment; a bird will lose more heat on very cold days than on mild days. Small birds have more of a disadvantage than larger birds. A bird loses heat based on its total surface area, the portion of the body that is in contact with the cold air or water. The heat produced by a bird is proportional to its total volume; every cell in the bird’s body is capable of producing heat. A result of simple geometry is that the ratio of the surface area to volume decreases as an object gets bigger. This geometric rule is cruel for small birds like Golden-crowned Kinglets because they have a relatively large surface area over which heat is lost and only a modest body volume to produce heat. A kinglet is living more on the edge than a jay or crow because of its large surface/volume ratio.

Birds can maintain their body temperatures in the face of severe cold in three basic ways. First, they can try to reduce the loss of heat. The plumage of birds in the winter is often twice as heavy as the weight of the summer feathers. In addition, the feathers of birds can be raised to create improved insulation. The erected feathers trap pockets of air. The insulating quality is improved by lowering the density of a material (light wool is a better insulator than dense metal, for instance). I am sure you have seen Mourning Doves and other birds at your feeder that are puffed up greatly to increase the insulating properties of their feathers.

At night, bird tend to roost in trees, often coniferous ones, close to the trunk. This choice of a bedroom has two benefits. First, the bird is protected from wind chill. Wind blowing across an animal’s body causes heat to be lost far more rapidly than when the air is still.

Second, trees absorb sunlight during the day and heat up. At night, they emit heat in the form of infrared radiation. Humans, houses and any other object emits infrared radiation. We cannot see this radiation but can sense it as heat. By staying close to the trunk, the birds absorb some of the infrared radiation the tree radiates and therefore gain some heat. You have probably seen rings around the bases of trees where the snow has melted, even though the air temperature has remained below freezing. This melting is caused by the snow absorbing the infrared radiation from the trees and heating to the melting point.

A second method of maintaining body temperature is to raise the heat of the internal furnace. When the air temperature falls below a certain critical level, a bird loses heat faster than it can be produced, even though it has puffed up its feathers to the greatest extent. Below this critical temperature, a bird must increase its metabolic rate to counteract the rapid loss of heat to the environment. Just as you do when you get very cold, a bird generates additional heat by shivering. It is not unusual for small birds like chickadees and goldfinches to spend the entire night shivering! The shivering requires additional energy which means that a bird must be even more gluttonous in the winter. No wonder birds flock to our feeders in the winter.

The last method of combating the cold is to simply allow the body temperature to fall. On cold nights, the body temperature of Black-capped Chickadees may allow its body temperature to fall by 10-18 °F. This decrease in body temperature lowers the difference between the bird’s temperature and the temperature of the cold environment, cutting down on heat loss. The bird is able to spend less energy keeping its internal furnace going. When the morning comes, the bird must raise its body temperature either by shivering or by warming in the sunlight.

[Originally published on February 17, 2007]

For the Birds: Maine Christmas Bird Count Highlights III

This column is the last of three on the results of the National Audubon Society Christmas Bird Counts (CBC’s, for short) conducted throughout the state of Maine. Each count could be conducted on any day between December 15 and January 5.

Let’s start with the three counts that experience the coldest winter weather of all the CBC’s in Maine. The Rangeley Count, held on December 17, produced a total of 34 species. Because of the unseasonably warm weather in November and December, ice had not formed over most bodies of water. The open water held six Common Loons and 59 Mallards.

Areas like Rangeley provide great habitat for boreal bird species. Those species did not disappoint this year as nine Boreal Chickadees were found along with 235 Black-capped Chickadees. Twenty-six Gray Jays made for an impressive total. Red-breasted Nuthatches tend to occur in coniferous forest while White-breasted Nuthatches are more often associated with deciduous or mixed forest. The conifers of the Rangeley area yielded 78 Red-breasted Nuthatches but only 3 White-breasteds.

The cone crops this year, particularly for red spruce, are heavy. Winter finches, which wander broadly in the winter abundant cones, put in a modest appearance with 65 White-winged Crossbills, 80 Pine Siskins and 87 Purple Finches.

Eight Northern Cardinals were counted, signifying the expanding range of this species into higher elevations in Maine. Seventeen American Robins were present.

The Misery CBC, centered in the town of Forks, was held on December 29. A total of 25 species was found. As at Rangeley, Northern Cardinals were found on the Misery CBC this year. Boreal species included five Gray Jays, 11 Boreal Chickadees, 48 Purple Finches, 17 Red Crossbills, 55 White-winged Crossbills and 70 Pine Siskins.

The Presque Isle CBC, held on December 30, produced at least 32 species (I don’t have the final totals yet). The highlight was an Eastern Towhee, the first ever recorded for this count. Towhees are quite rare in the northern half of the state at any time of the year. Two Black-backed Woodpeckers were nice finds. No doubt owing to the warm early winter weather, new high counts of Common Goldeneyes and Golden-crowned Kinglets were set.

It’s always interesting to compare the Orono-Old Town (December 16) and the Bangor CBC (December 30) because of their nearly overlapping locations. Counters on the Orono-Old Town CBC found 49 species. Notable birds included a Rough-legged Hawk, a Merlin, an Iceland Gull, two Northern Shrikes, four Bohemian Waxwings (very rare in the state so far this winter), three Red Crossbills, 20 White-winged Crossbills and 34 Pine Siskins. The 48 Tufted Titmice indicate that this species is continuing to expand its range northward in Maine. Lingering birds included a Belted Kingfisher, a Northern Flicker and 13 American Robins. A Carolina Wren was a nice find. The Bangor CBC yielded 50 species, with an interesting mix of birds of northern and southern affinity. Highlights were singleton Bonaparte’s and Iceland gulls, a Red-bellied Woodpecker, a Carolina Wren, a Northern Mockingbird, a new count record 101 Northern Cardinals, 10 Red Crossbills and 11 Common Redpolls. Seventy-one Tufted Titmice were impressive.

We’ll end with some more coastal CBC’s. The Machias Bay CBC, held on January 3, produced a list of 54 species. Thirteen species of waterfowl were found with a single Barrow’s Goldeneye being the most notable. Lingering birds included a Great Blue Heron, a Northern Flicker and 112 American Robins. Gray Jays occur predictably in the coastal spruce-fir forests of Maine from Mt. Desert Island eastward. Two Grays Jays were delightful but not unexpected. One Northern Cardinal was a noteworthy sighting. The only northern finch was a single Red Crossbill.

The North Penobscot Bay CBC held on December 30 had a total of 59 species. This portion of the coast is one of the most reliable in the state for Ruddy Ducks in the winter and the 107 tallied this year did not disappoint. The four Barrow’s Goldeneyes were expected but fewer than expected. A nice list of lingering birds included a Carolina Wren, five American Robins, five Northern Mockingbirds, two Swamp Sparrows and a Brown-headed Cowbird. A Yellow-breasted Chat was an extraordinary find. Six Red Crossbills were notable as well.
The Biddeford-Kennebunkport CBC held on December 30 yielded 93 species. Waterfowl diversity was extraordinary with 18 species found, including a Snow Goose, 13 Brant, two Gadwall and two Ruddy Ducks. Eight species of diurnal raptors included Merlin and Peregrine Falcon. A Dovekie was a highlight. Other noteworthy finds were singletons of the following species: Yellow-breasted Chat, Dickcissel and White-crowned Sparrow.

[Originally published on February 3, 2007]

For the Birds – Christmas Bird Counts II

This column is the second of three on the results of the National Audubon Society Christmas Bird Counts (CBC’s, for short) conducted throughout the state of Maine. Each count could be conducted on any day between December 15 and January 5.

We’ll start with the excellent Portland CBC, conducted on December 16. A new record for total species was set this year: 105 species. One of the highlights of the count was the 26 species of waterfowl. Three species of geese (Snow Goose, Brant and the expected Canada Goose) was noteworthy. Other unusual waterfowl included a lingering Wood Duck, a pair of Gadwall and a single Barrow’s Goldeneye among 282 Common Goldeneyes. Four of the five species of Maine bay ducks (the genus Aythya) were found: Canvasback, Ring-necked Duck, Greater Scaup, Lesser Scaup.

Other highlights of the count were a Pacific Loon, a Greater Shearwater, three Turkey Vultures, and a Virginia Rail. Five Dovekies made a nice addition to the more expected alcids, Razorbills and Black Guillemots. Eight species of diurnal birds of prey included five Northern Harriers , two Merlins and three Peregrine Falcons.

Lingering songbirds included a pair of Hermit Thrushes, 27 Eastern Bluebirds, a Gray Catbird and a Red-winged Blackbird. Orange-crowned Warblers stray to Maine on occasion; one was found on the Portland CBC.

The Bath-Brunswick CBC, also held on December 16, resulted in a total of 83 species. Surprisingly late birds included eight Great Blue Herons, a Turkey Vulture and an American Kestrel. A Black-headed Gull and 169 Black-legged Kittiwakes headed the total of six gull species. A total of 169 Razorbills was notably high.

Very few Maine CBC’s can boast of two species of wrens. Bath-Brunswick counters found a single Marsh Wren and Carolina Wren. Snow Buntings and Common Redpolls have not appeared in significant numbers this winter in Maine. Single individuals were found for both species.

Yet one more December 16 count, the Mt. Desert CBC, yielded 63 species. Fifteen species of waterfowl were sighted along with two hybrid ducks. One, a Mallard x American Black Duck hybrid, occurs quite commonly and is certainly underreported. In fact, some waterfowl biologist fear that American Black Ducks are being genetically swamped by interbreeding with the far more common Mallards. But the other hybrid on this CBC is quite remarkable, a Common Goldeneye x Hooded Merganser.

Other notable birds included a late Great Blue Heron and a Glaucous Gull. Raptor highlights were two Peregrine Falcons and two Snowy Owls. Songbird highlights included an American Robin, a Pine Warbler to go along with the four Yellow-rumped Warblers, a Fox Sparrow and a fine count of 31 White-winged Crossbills.

The December 18 York CBC produced a total of 74 species. Highlights were a Pacific Loon, a pair of Mute Swans, 16 Dovekies, 71 Razorbills and four Red-bellied Woodpeckers. Notable songbirds included 25 Horned Larks, four Carolina Wrens, a Rub-crowned Kinglet, 26 Eastern Bluebirds and six American Pipits.

The December 26 Eastport CBC count provides a dramatic case of how weather can affect a bird count. The weather on Count Day was hardly conductive to birding: temperatures in the 30’s with gusty winds and driving rain. Only three intrepid counters participated this time. Despite the poor visibility and the difficulty in hearing birds, the Eastport counters tallied 40 species. Three Double-crested Cormorants were found along with the more expected 30 Great Cormorants. Four Northern Gannets were a nice find. Only five Bald Eagles were counted this year; two years ago counters found 111 of these birds of prey.

Only eight Bonaparte’s Gulls and two Black-legged Kittiwakes were found this year. Normally, these birds occur in the thousands in the rapidly moving water between Eastport and Campobello Island. The only alcids found were a pair of Black Guillemots.

Finding songbirds in inclement weather is even tougher than finding waterbirds. Not surprisingly, the Eastport counters found modest numbers of landbirds. For anyone who has birded in this part of Maine, the counts of the following species will be unrepresentative of actual abundance: one Common Raven, 58 Black-capped Chickadees, one Red-breasted Nuthatch and 46 American Goldfinches. Researchers using the CBC data to gauge changes in population numbers clearly must take the weather on count days into consideration.
Three birders flew to Matinicus Island on January 5 to conduct a CBC there. A total of 38 species were tallied. Notable species included two lingering Northern Flickers, 29 Yellow-rumped Warblers, two Swamp Sparrows, eight Red Crossbills and 31 White-winged Crossbills. The counters found 31 European Starlings, a reminder that this introduced species has remarkable colonizing abilities.

[Originally published on January 19, 2007]

For the Birds – Maine Christmas Bird Count Highlights I

This column is the first of three on the results of the National Audubon Society Christmas Bird Counts (CBC’s, for short) conducted throughout the state of Maine. Each count could be conducted on any day between December 15 and January 5.

The greatest value of the Christmas Bird Count database, now spanning 107 consecutive years, is the opportunity to monitor changes in abundance of our regular winter birds. Because counts are strongly influenced by the weather, a dip in numbers in one year of a common species like the Black-capped Chickadee is not a cause for concern. But several years in a row of reduced counts suggest a change in abundance is occurring.

A pattern evident from the Maine counts already completed is that the number of species counted seems to be around normal but the abundance of birds is down for many species. I expect that the lower abundance is not a real decrease in numbers but rather a result of the warm weather we have experienced so far this winter. With virtually no snow cover, land birds can forage effectively on natural foods and therefore are widely scattered across the landscape. Many people have noticed relatively few birders at their feeders so far this winter. So far this winter, irruptive species like Bohemian Waxwings and the northern finches are rare or absent. Most bodies of water in the southern half of the state are still open. Waterfowl are not concentrated in isolated ice-free patches as in most years on Maine CBC’s.

A lot of the anticipation and excitement for a CBC stems from the hope that an unusual species will be sighted or high count of a particular species will be tabulated. Those highlights will be the focus of these columns on this year’s Maine CBC’s.

Today we’ll consider four inland counts, all done within a three-day span. Despite the geographic proximity, these four count circles produced quite different lists of birds.

The Lewiston-Auburn count resulted in a total of 42 species, a bit below the average of 46 species. One of the highlights was a Red-necked Grebe on Lake Auburn, a first for this CBC. An inland Red-necked Grebe in Maine is always a notable sighting. A Peregrine Falcon was the most unusual diurnal raptor to go along with seven Red-tailed Hawks and four Bald Eagles. Only six species of waterfowl were tallied although the 75 Greater Scaup were excellent finds. This diving duck has appeared only four times on the Lewiston-Auburn CBC and the total this year sets a new record number. No Hooded Mergansers were found this year. A single American Coot was a nice find.

Surprisingly low numbers of Herring Gulls (36), Black-capped Chickadees (259) and American Tree Sparrows (19) were found this year. Four lingering American Robins were found as well as four Northern Mockingbirds.

The Augusta CBC was held on the same day (December 16) and produced a list of 57 species. In addition to the expected Herring Gulls, Ring-billed Gulls and Great Black-backed Gulls, two Iceland Gulls, two Glaucous Gulls and a first-winter Lesser Black-backed Gull were found by Augusta birders. Eight species of waterfowl as well as Common Loon were found in the mostly open water in this area. The most surprising species were Bufflehead and Long-tailed Duck.

Other highlights were lingering Eastern Bluebirds, Northern Mockingbirds and Yellow-rumped Warblers as well as Pine Grosbeaks, a Red Crossbill and a Peregrine Falcon.

The Waterville Count (December 17) yielded 50 species. The Kennebec River at the confluence of Sebasticook Stream produced the usual Common Goldeneyes, Barrow’s Goldeneyes, Common Mergansers and Hooded Mergansers. This year, these species were joined by an amazing drake Harlequin Duck that has been present since the middle of November. Winter inland sightings of Harlequins in the northeast are extremely rare. Four Greater Scaup were also noted.

In the zany department, a male Yellow-throated Warbler was found in Waterville; this species normally winters in Florida, the Caribbean or Central America and nests well to our south. At the same time, a female Black-backed Woodpecker was discovered; the closest population of these birds I am aware of are in the Flagstaff Lake region.

Finally, the Unity CBC was held on December 18 and produced a count of 48 species, a record total for this count. Highlights were a mix of southerly and northerly species. A Red-bellied Woodpecker occurred again this year, perhaps indicating this southern species has gained a foothold in the Unity area. A Black-backed Woodpecker was found as well. Lingering birds included Northern Flicker, Swamp Sparrow and Pied-billed Grebe.

[Originally published on January 5, 2006]

For the Birds – Bird Vision

The last column discussed color vision in birds. The ability of birds to see colors and to see the longer ultraviolet radiation we cannot see certainly gives birds a different perception of color than humans. In today’s column, I’ll explore some of the other fascinating characteristics of bird eyes, making comparisons with our own eyes.

Birds rely heavily on their vision. Their excellent eyesight allows them to find food and to detect potential predators from long distances. Females often choose their mates based on the appearance of his plumage.

How keen is a bird’s vision? Their visual acuity is often overstated. For instance, I have read fallacious claims that birds can distinguish the type of a newspaper while soaring from above. In reality, the keenest bird eyes that have been tested are those of the American Kestrel. These small falcons can detect an insect only two millimeters long (less than a tenth of an inch) from a distance of 40 feet. The Hobby, a Eurasian falcon that favors dragonflies for its meals, can detect one of these insects from 200 yards away. Bee-eaters can see a honeybee from a distance of nearly 200 feet. In general, birds can resolve details at a distance of 2.5 to 3 times that of a human.

Relative to our eyes, birds’ eyes are huge. The eyes of a Great Horned Owl are as large as yours. The eyes of an Ostrich are the largest eyes of any land vertebrate, exceeded only by much larger marine mammals. The eyes of a bird contribute up to 15% of the total weight of the head.

Humans and other mammals have round eyes. Thanks to pairs of extrinsic muscles on the back of the eyes, mammals can rotate their eyes to perceive images in different directions without moving the head. The shape of birds eyes is much more variable. Some are round while others are quite flat and some are tubular. Furthermore, birds’ eyes have much more limited movement than seen in mammals. Usually the only movement bird’s eyes can make is toward the bill tip, useful for seeing the food that a bird is manipulating with its beak.

Humans and a number of other mammals have binocular vision. Because our eyes are close set, we can see objects with both eyes. Because the angle of the object from each eye is different, our brains can process the differences in the two images to let us know how far away the object is. In other words, we have keen depth perception.

Birds’ eyes tend to be set on the sides of the head. As a result, a bird has a limited field of vision in which it can see an object with both eyes. Birds therefore have less depth perception than humans. Birds of prey tend to have their eyes set more forward, allowing a broader band of binocular vision. Birds like ducks and songbirds that must watch out for predators usually have their eyes set laterally. It’s very difficult for a predator to advance on such a bird without being seen even if the bird can’t gauge the distance to the predator very well. American Woodcocks are unusual in having their eyes set far back on the sides of the head. Their best binocular vision is behind them! A predator is not likely to sneak up on a woodcock from the rear.

Everyone has seen pigeons bobbing their heads as they walk. A number of birds engage in this behavior. The bird is essentially turning one eye into two to achieve a measure of binocular vision. By moving its head up and down, a single eye can see an object from different angles. The brain does the rest, processing the different images to give improved depth perception.

To focus on an object, the eyes of humans and other mammals change the curvature of the lens in each eye. In birds, both the cornea (the clear outermost layer of the eye) and the lens can change their curvature to allow the image of an object to be focused on the retina. The change in corneal shape is caused by muscles not present in mammal eyes.

Changes in the curvature of the cornea are effective for objects seen on land. However, the refractive index of the cornea is virtually the same as the refractive index of water. A change in corneal curvature does little to help a diving bird focus. Diving birds have well developed muscles around the lens and rely on changes in lens shape to focus underwater.

[Originally published on December 16, 2007]

For the Birds – Color Vision and Beyond

Among the mammals, humans and the great apes have the best color vision. In the retinas of our eyes, cells called cones are sensitive to different wavelengths of light. Humans and apes have cones with three different light-sensitive pigments called photopsins. One type of photopsin is most sensitive to yellowish-green light, another is most sensitive to blue-green light and yet one more is most sensitive to bluish-violet light. However, all three pigments are sensitive to all colors of the rainbow to varying degrees. The combination of the response of the three pigments to a colored object allows our brains to determine color. For instance, red is perceived when the yellow-green photopsins are stimulated much more than the blue-green photopsins in our cones.

Some humans, including yours truly, only have two types of photopsins in our cones. Such people are colorblind. Color blindness is a misnomer in that most colorblind people can discern some colors; color blindness in which the world is seen in shades of gray is very rare. A colorblind (or better, color deficient) person usually has difficulties in distinguishing red from green and distinguishing pastel colors.

Most mammals have vision similar to a colorblind human because they only have two types of color pigments in their cones. But even humans with normal color vision see the colors of the world much less vividly than birds. Birds have four different photopsins in their eyes. Birds are able to distinguish shades of color in ways that humans really can’t experience. The colors of the world must be really vibrant to a bird.

The cones of birds are more numerous than those of humans. The cone density of human in the center of the retina is about 200,000 cones per square millimeter. For a bird the density ranges from 400,000 to a million cones per square millimeter.

In humans, the cone density falls off rapidly away from the center portion of the retina. In birds, the density of the cones is relatively high in the outer portions of the retina.

Albatrosses and other seabirds have dense ribbons of cones around the retina. These strips are thought to play a role in allowing these oceanic birds to see the horizon to maintain proper orientation.

In recent years, ornithologists have discovered that birds can see into the ultraviolet (UV, for short) part of the spectrum. Human eyes are not capable of seeing these short wavelengths. Birds have an extra set of cones that have peak sensitivity in near-UV wavelengths. How different a bird’s vision must be from our own. For instance, we perceive the color of a Scarlet Ibis as a rich red color. However, the plumage of a Scarlet Ibis also reflects UV radiation invisible to us. Birds however detect both the red color and the UV reflectance, causing the birds to see a Scarlet Ibis as a purple bird!

Recent research had identified a number of ways that birds use ultraviolet reflectance. European Starlings preferentially feed nestlings with UV-reflecting skin. The Redwing, a Eurasian relative of the American Robin, prefers to feed on Viburnum berries that reflect UV compared to berries that do not reflect UV. European Kestrels use their UV-sensitive eyes to find voles, their favored prey. Voles use their urine to mark their trails across meadows. These urine markings reflect UV radiation, giving the kestrels a huge advantage in finding prey.

UV reflectance seems to play an important role in mate selection in birds. Blue and violet feathers are particularly rich in UV reflectance. Male Eastern Bluebirds with bright UV patches tend to make better fathers; males with UV-rich plumage pair earlier, feed young more often, and have greater success in fledging young. Human eyes cannot see these differences that bluebirds clearly can. Thanks to technology we can measure UV reflectance even if we can’t see it ourselves.

[Originally published on December 2, 2006]

For the Birds – Edibility of Birds and Gaudiness of Their Plumage

Most Thanksgiving meals center around a roasted turkey. On Thursday, you will be likely asked by the person carving the turkey if you would like dark or white meat. Apart from a difference in taste and texture, these two types of muscles differ in their physiology as well.

Domesticated turkeys and chickens have white muscles for the breast muscles, the largest muscles in the body. These muscles move the wings to provide the power stroke and the recovery stroke during flight. The drumstick and thighs have dark meat; these muscles are used for walking.

The difference between the two types of muscles lies in the basic function of muscle contraction. Dark muscle is mostly aerobic muscle; the muscles depend on oxygen to function. The dark color comes from a pigment called myoglobin that has a very high attraction to oxygen molecules. When blood flows through the capillaries of the muscles, the oxygen in the blood (carried by hemoglobin) is transferred to the myoglobin in the muscles. When oxygen becomes low in the muscles, oxygen is released from the myoglobin.

Aerobic muscles are efficient, making these muscles great for activities requiring endurance. On the other hand, they contract relatively slowly so are not effective in causing lightning-fast movements that might be used to avoid a sudden attack from a predator.

The white meat of a turkey or chicken has mostly anaerobic muscles. They work in the absence of oxygen. Such muscles have no need for myoglobin to store oxygen and the absence of myoglobin causes the muscles to appear white. These muscles are called fast-twitch muscles because they can contract very quickly. The disadvantage of these muscles is that they tire quickly as well.

If you have ever seen the meat of a game bird, you know that the breast is made of dark muscle. In fact, most birds have a predominance of dark muscle in their breasts. That dark muscle allows them to fly for long distances. They also have some fast-twitch muscle fibers to allow a rapid take-off or burst of speed. Our domesticated turkeys and chickens have mostly fast-twitch fibers in their breast muscles because of selective breeding.

Many species of birds are eaten by humans around the world. Some species have strong, disagreeable flavors while others are quite pleasing to the human palate.

In 1941, Hugh Cott, a biologist at Cambridge University, made an insightful observation while he was in Egypt preparing specimens of birds to take back to England. He noted that swarms of hornets were feeding readily on the skinned remains of a Palm Dove but avoided the flesh of a Pied Kingfisher (a bird with black and white plumage). Cott wondered if the striking plumage of the Pied Kingfisher was warning coloration, telling would-be predators that it would be a particularly distasteful meal. In a similar vein, the black and white fur of a skunk is considered to be warning coloration.

Cott set out to test his hypothesis that drab colored birds are tastier to a predator than birds with bold coloration. He gave the flesh of 38 species of local Egyptian birds to humans and asked for their opinion of the quality of the meat. The three species with black and white feathers were universally considered the least edible. The same flesh was presented to cats and hornets. Both species avoided the black and white birds as well. Cott continued his studies and suggested that the more vulnerable a bird is to a predator, the nastier its flesh tastes. Cott regarded brightly colored birds and slow moving birds as the most vulnerable. These distasteful birds seem to be relying on chemical defense, storing noxious chemicals in their flesh.

A fascinating variation on this chemical defense in birds comes from Papua New Guinea. In 1989, a graduate student named Jack Dumbacher, was conducting research on some birds of paradise. His research involved capturing birds of paradise in mist-nets so they could be banded for later identification. Other birds were captured as well in the mist-nets. One of the most common was a bright orange and black colored bird called the Hooded Pitohui. This species is known only from Papua New Guinea.

Dumbacher found the pitohuis give off a strong odor. Further, he discovered by accident that the pitohuis have a toxin in their feathers that causes a numbing sensation in a person’s mouth. Chemical analysis showed the chemical is a highly lethal compound called batrachotoxin, the same poison found in poison-dart frogs. Dumbacher suspects that the pitohuis are acquiring the toxin from their diet rather than making it themselves.

[Originally published on November 18, 2006]

For the Birds – Starling Roosting Behavior

If you have driven or been walking in urban areas or near farms lately, you have likely seen large flocks of birds, wheeling in all directions. Those birds are European Starlings and they are preparing to go to roost. Here are some fantastic photographs of starling flocks in flight: http://epod.usra.edu/archive/images/sortsolsum-05042006-hw.jpg

Many species of birds have communal night–time roosts. Because of their preferences for urban habitats, starlings’ roosting behavior is one of the most frequently observed. I’ve seen flocks of more than 1,000 birds in Maine but that pales in comparison to a roosting flock of starlings, Common Grackles and Brown-headed Cowbirds in Kentucky that had over a million birds in an area of only five acres. Not a good place to park your car!

Why roost in such large numbers? One advantage is that there is safety in numbers. It’s awfully hard for a predator to sneak up on a large number of sleeping birds without being detected. In cold weather, huddling together helps to conserve heat. A third and more controversial explanation hinges on information sharing. This explanation presumes that birds forage for food in different areas during the day and then let other birds in the roost know about profitable feeding areas. Some of the best evidence for information sharing has been obtained for Turkey Vultures. For many other species that have communal roosts, ornithologists have found no evidence that roosting birds share such information.

A century ago, flocks of starlings could not be seen in Maine, or scarcely anywhere in North America for that matter. The species was introduced in North America by the release of 60 birds in 1890 by Eugene Sheflin. Sheflin was a wealthy drug manufacturer who was attempting to introduce all of the birds mentioned in Shakespeare’s plays into Central Park as a hobby. Aided by a second introduction of 40 birds in 1891, a starling population in North America took hold and began to spread rapidly.

In Maine, a flock of 25-30 starlings was first seen in 1913 in Rumford. The first ones reported in Waterville were seen in 1921. To the east, starlings appeared in Nova Scotia in 1915. A glance at a map in your bird field guide shows that starlings are now present in all of the lower 48 states, all of the Canadian provinces, Mexico and Alaska. The population in North America now exceeds 200 million birds. This astounding increase is one of the most successful introductions of exotic species.

Starlings are most frequently seen in cities and towns but are also common around farms and in suburban areas. They typically do not occur in heavily forested areas. Like many introduced species, starlings have had a negative impact on many native birds. Starlings nest in cavities and aggressively fight for such nest sites. As a result of this competition with starlings, native cavity-nesting species like Northern Flickers, Great Crested Flycatchers, Tree Swallows, Purple Martins, House Wrens and Eastern Bluebirds have been displaced from favored breeding sites. Bluebirds and flickers have been most profoundly affected. Fortunately, bluebird populations have been rebounding as many people have erected nest boxes whose openings are small enough to exclude starlings.

Starlings have quite a broad diet; about half of their food is insects that are taken from the ground. Starlings’ preference for weevils, cutworms and Japanese beetles makes these birds valuable from an agricultural perspective.

Starlings change in an interesting way from a spotted plumage in the winter to a glossy-black plumage in the summer. After an early fall molt, the tips of the new black body feathers are tipped with white and buff, giving the bird a speckled appearance. Over the winter, the tips of these feathers wear away, removing the speckling. The breeding plumage is said to be acquired by wear, rather than by molt.

The vocalizations of starlings are impressively varied, ranging from a clear “wolf” whistle to high-pitched trills to harsh chattering. Starlings are also accomplished mimics, accurately reproducing the sounds of other starlings and other birds, other animals besides birds and even inanimate noises. Male and female starlings are both capable of mimicking human speech.
Wolfgang Amadeus Mozart had a pet starling. It died three years after he purchased it from a pet shop. Devoted to his starling, Mozart gave the starling a first-class funeral (far grander than his own funeral). Eight days after his starling’s death, Mozart wrote a sextet called A Musical Joke. The odd structure of the piece baffled early critics but now it seems that the intertwined themes and the off-key whistles represented the singing of his dear pet.

[Originally published on November 6, 2006]

For the Birds – Ig Nobel Awards and Woodpeckers

You can’t say scientists don’t have senses of humor. On October 5, the 16th Annual Ig Nobel prizes were awarded at Harvard. The Ig Nobel awards are given out around the time that the Nobel prizes are awarded.

The Ig Noble Prizes are awarded to scientists whose work first makes you laugh and then makes you think. Scientific work that is awarded an Ig Nobel Prize is usually serious, carefully done research, published in reputable scientific journals, but may cause you to ask “Huh?” when you first hear about it.

Here are some of the projects that have received Ig Nobel Prizes. Antonio Mulet from the University of Valencia received an Ig Nobel Chemistry Prize for their work on ultrasonic velocity of cheddar cheese as affected by temperature. Basile Audoly and Sebastien Neukirch of the Université Pierre et Marie Curie in France received an Ig Nobel Physics Prize for their insights into why, when you bend dry spaghetti, it often breaks into more than two pieces. How about the Ig Nobel Biology Prize won by Bart Nols of the University of Wageningen in the Netherlands for demonstrating that female malaria mosquitos are equally attracted to the smell of limburger cheese and human feet?

The Ig Nobel Prize ceremony is a festive occasion, with many attendees dressed in costume. The Ig Nobel Prizes are awarded by Nobel Prize laureates. Each winner is given one minute to give her or his acceptance speech and the time limit is enforced by an eight-year girl who acts as the mistress of ceremonies.

An Ig Nobel Ornithology Prize was awarded this year. I think this research provides a great example of how good science can have a humorous side. That prize was awarded to Ivan Schwab and the late Philip May for their work exploring and explaining why woodpeckers don’t get headaches.

Schwab is an opthalmologist and hence a medical doctor, not an ornithologist. May came from a similar medical background. Their work was not published in ornithological journals but rather in medical journals. Two articles were published in the highly regarded British medical journal, the Lancet, and a more recent article in the British Journal of Ophthalmology.

As we all know, woodpeckers use their bills to forage for food, to excavate roosting and nesting sites in trees and to communicate with other members of their species by drumming on a resonant tree or perhaps a gutter on your house. Schwab and May studied the hammering behavior of Pileated Woodpeckers.

Consider the stress the heads of these birds must endure. A Pileated Woodpecker may hammer 20 times in a one second and 12,000 times per day. Each hammer ends with a strong deceleration, equal to 1,200 times the force of gravity. That’s a sudden stop! Schwab points out that that force would be like you running into a solid wall at 16 miles per hour – face first.

So what sort of adaptations do Pileated Woodpeckers have that allow them to avoid massive headaches? First, the skull is strong, and thick with spongier bone found where the skull joins the neck vertebrae. Flexible cartilage is found at the base of the bill to act as a shock absorber, cushioning some of the force of the hammering.

The brain of a woodpecker fits very tightly within the skull with very little cerebrospinal fluid present. That arrangement contrasts with a human brain where our brain is more loosely situated within our skulls, bathed in cerebrospinal fluid. Humans sometimes suffer contre-coup (brain bruising) injuries following a blow to the head. The head stops moving but the brain doesn’t. Woodpeckers do not have to worry about such brain bruising.

Using high-speed videocameras, Schwab and May showed that Pileated Woodpeckers contract powerful muscles that connect the bill to the skull only a microsecond before impact. These contracted muscles spread the force of the impact to the posterior and base of the skull, bypassing the brain.

The woodpeckers also strike with their bill exactly perpendicular to the tree, preventing concussions or tearing of the membranes that surround the brain.

In addition to an upper and lower eyelid like we have, birds have a third eyelid called the nictitating membrane that offers additional protection to the eye. It closes horizontally. In woodpeckers, the nictitating membrane closes just before bill impact. The membrane certainly protects the eyes from flying debris but also literally keeps the eyes from popping out of the head as the woodpecker hammers.

Visit the Ig Nobel Prize website at: http://www.improb.com/ig/ to find more details about Schwab and May’s research.

[Originally published on October 30, 2006)

For the Birds – Long-billed Bird Syndrome

A bird’s beak is a remarkable structure. The shape of the beak tells us much about the type of food a bird eats. It’s obvious that a hawk’s bill is adapted for tearing, that a heron’s bill is adapted for spearing and that a finch’s bill is adapted for crushing seeds.

The lower jaw or mandible of a bird is composed of a pair of dentary bones that fuse at the tip. The upper jaw or maxilla is made up of nasal bones near the base and premaxillary bones at the tip.

Unlike the upper jaws of mammals (including us) that are fused to the skull, the upper jaw of a bird attaches to the skull at a flexible hinge. When a bird opens its mouth, the lower jaw moves downward and the upper jaw moves upward relative to the skull. Birds can therefore open their mouths wider than a mammal.

The beak of a bird is covered by a sheath called the rhamphotheca. The sheath is made of keratin, the same material that makes your fingernails. In most birds, this sheath is hard but in waterfowl and shorebirds the sheath is soft and leathery.

As a bird feeds, abrasion causes the sheath to wear away at the tip. The skin overlying the bones of the maxilla and mandible continuously lays down new keratin to replace the lost material.

It’s interesting to note that the beak length of some birds changes from winter to summer. As an example, House Sparrow beaks are longer in the summer. During the summer, House Sparrows eat softer foods compared to the winter when hard seeds are the staple of the diet. Feeding on the hard seeds breaks down the sheath more quickly and the winter bill length therefore is slightly reduced.

Birds kept as pets often are not given hard enough foods to allow the birds to wear down the tips of their bill. That is why parakeet owners provide their birds with cuttlebone.

In the past ten years, a serious and even grotesque condition called long-billed bird syndrome has been documented. Bud Anderson, a hawk biologist at the Falcon Research Group in Bellingham, Washington noted a Red-tailed Hawk in 1996 with an overgrown beak. Since then, Anderson has recorded 86 hawks with deformed bills; all but nine were Red-tailed Hawks.

The condition is caused by hypergrowth of the sheath. The hypergrowth can take a number of forms but the end result is that the function of the bill is severely compromised. Examples can be seen at: http://www.frg.org/frg/lb_syndrome.html

The condition is lethal without intervention. Hawks with the condition are underweight because they cannot process prey with their bill. They are usually plagued with feather lice, presumably because their deformed bill does not allow them to preen.

Long-billed hawks are easily captured. They quickly come to a prey lure because they are desperately hungry. A rehabilitator can remove the excess sheath and release the bird after it recovers its weight.

The long-billed hawk syndrome has mostly been documented along the west coast of North America, from San Jose north to Richmond, British Columbia.

However, the long-billed syndrome is not restricted to hawks. Recently, a biologist near Anchorage, Alaska documented over a thousand Black-capped Chickadees with overgrown bills. Biologists in Montana have found the syndrome in Red-winged Blackbirds.

Julie Craves, a Michigan bird bander, and Colleen Handel, a biologist with the U. S. Geological Survey, have compiled records of the long-billed syndrome in North America. They found records of overgrown bills in over 110 species of birds, mostly songbirds. Records of this condition have been reported from places as far-flung as Florida, Baja California, Maine and several Canadian provinces.

At this point, the cause of the syndrome is not known. We do not know if the condition results from the same cause in all the species that have been reported to have these deformed bills.

For hawks, the condition is found in both young and adult birds. Blood tests of afflicted hawks show that white blood cell counts are normal; one would expect elevated counts if the birds harbored some of disease organism. Veterinarians tested affected birds for thyroid disorders and beak and feather disease, two diseases that cause deformed growth in parrot beaks. The tests for both diseases were negative.

Currently, veterinarians are looking for pathology of the cells that produce the keratin sheath in long-billed birds. Perhaps some clues to the cause of the syndrome will be forthcoming.

You can help by reporting any birds you see that have long bills to Bud Anderson at: [email protected]

[Originally published on September 17, 2006]