March 2007

For the Birds – Red-winged Blackbirds

Con-ka-ree! The Red-winged Blackbirds have returned; spring must be on the way. The March arrival of these beautiful birds is a welcome sight as a Maine winter starts to give way to spring. The males are all black except for a brilliant red patch, edged in yellow on each wing. The smaller females are drab and inconspicuous, in their mottled brown and white plumage.

Red-winged Blackbird is one of the most abundant birds in North America. On some Kansas Christmas Birds Counts, over 6 million red-wings in massive flocks have been counted in a 175 square mile area! Abundant breeders throughout Maine, red-wings depart for more southerly climates during the winter. Their breeding range extends northward to southern Alaska and southward to Costa Rica. In North America, Red-winged Blackbirds nest in every one of the lower 48 states and all of the Canadian provinces.

Red-winged Blackbirds breed in marshes and other areas with dense, grassy vegetation. The males perch on shrubs and the tops of cat-tails. Red-wings are therefore easier to see than woodland birds. The abundance and high visibility of Red-winged Blackbirds make them good subjects for ornithological study. Not surprisingly, they are one of the most studied North American birds.

These birds are unusual among North American songbirds in that the males are polygamous, that is a male may have many mates. It is not uncommon for a male red-wing to have seven or more females in its territory and at least one male had 15 females in his harem. DNA analysis indicates that not all of the offspring produced by females on a male’s territory are sired by him. That means that females sometimes engage in “extra-marital affairs” with other males when their mate is not looking. In fact, these dalliances, referred to as extra-pair copulations by ornithologists, are the rule rather than the exception in most species of birds in which paternity has been tested by DNA analysis.

Red-winged Blackbird males arrive on the breeding grounds ahead of the females. The dominant males stake out territories that they proclaim as their own with songs and displays. One of the most common territorial displays is called the Song Spread. The male exposes the red patches on its wings and sings is metallic con-ka-ree song. Younger and weaker males are usually not able to establish a territory and breed.

The females arrive a week to several weeks later than the males. They then choose a mate based not on the characteristics of the male but rather on the quality of the territory. Usually, the healthiest and strongest males lay claim to the best territories. Only seven percent of second-year males are successful in establishing a territory and siring young. The percentage rises to 57% for males in their third year of life.

When you see a male Red-winged Blackbird at your feeder or in a marsh, you may not be able to see the red on the wings. Sometimes, even the yellow margin of the red patch is not visible. The red patches are called “coverable badges” by ornithologists. Coverable because they can be hidden and badges because they signify authority. When a dominant male is approached by another male attempting to drive the first male off of its territory, the territory owner will expose its badge. This aggressive display tells the intruder to back off. Subordinate males make sure they don’t uncover their badges in the presence of dominant males to avoid being attacked.

Similar behavior can be seen in schoolyard bullies. A 10-year bully adopts a swagger to try to intimidate smaller children, uncovering his behavior or “badge”. However, in the presence of a 13-year old bully, the 10-year old bully alters his behavior, covering his “badge”, so as not to offend the bigger bully.

Interestingly, the color red seems to signal a willingness to fight in other species of Maine birds. Male Ruby-crowned Kinglets expose the red on their crowns only as an aggressive behavior. Similarly, Eastern Kingbirds flash their red crown feathers as warnings to other kingbirds during the nesting season.

Outside of the nesting season, Red-winged Blackbirds are well known for forming large flocks that roost together. Sometimes, other species like Brown-headed Cowbirds, Common Grackles and European Starlings may roost with them. These flocks pose significant threats to agriculture. A large flock of red-wings can devastate crops of corn, sunflowers or rice. Farmers have invested large amounts of time and effort in ways to keep red-wings away from their crops. The result of these efforts is that humans now pose one of the most significant sources of mortality for Red-winged Blackbirds.

[Originally published on March 17, 2007]

For the Birds – Cold and Unfeathered Legs

In the last column, I described some of the ways that birds are able to survive the challenges of cold weather. I did not have enough space to describe how birds keep their unfeathered lower legs from freezing. Several readers inquired about this problem for birds in cold environments. I’ll tackle that problem this week, including a foray into some chemistry.

For most birds only a portion of the legs is unfeathered. The long bone you see without feathers is called the tarsometatarsus. This compound bone corresponds to the bones of your foot. The tibia (shin bones) and the femur are usually well feathered. So, it’s the elongated foot bones and toes of birds that have no insulation.

The unfeathered lower parts of birds’ legs have a very high surface area, just the ticket for losing heat to the cold winter air. To keep the legs as warm as the rest of the body, birds would have to pump a huge amount of heat-carrying blood to those exposed areas. Instead, birds allow the legs to cool, pumping a modest amount of blood into the extremities. In Herring Gulls, the upper part of the exposed leg may have a temperature of only 40 °F and the bottom of the foot is just barely above freezing!

Allowing the tissues of the lower leg to get so cold requires some fascinating modifications of the cells of those body tissues. Every living is covered with a membrane. This membrane is mostly made of molecules called phospholipids. Each phospholipid has two strings of carbon atoms, called fatty acids, pointing toward the center of the membrane. To function properly, the phospholipids of the membrane need to be able to move past each other. The membrane needs to be fluid enough to allow small molecules like oxygen to diffuse in and carbon dioxide to diffuse out. When a membrane is exposed to colder temperatures, the phospholipids pack in tightly. Oxygen cannot get into the cell; frostbite and often cell death occur.

Each carbon atom in the fatty acids of a phospholipid has four binding sites. Usually, two of the binding sites are used to bond to the two adjacent carbon atoms. The other two binding sites usually bind to a hydrogen atom. However, it is possible for two adjacent carbon atoms to each lose one of their hydrogen atoms and establish two bonds with each other. When these double bonds occur, they introduce a kink in the fatty acid.

You can see the effect of these types of bonds in your kitchen. Butter is made of fatty acids with no double bonds; it is a saturated fat. At room temperature, butter is a solid. Not the condition you would want for your membranes! Olive oil, liquid but viscous at room temperature, has one double bond in its fatty acids. In other words, it is a monounsaturated fat. Safflower oil is even thinner than olive oil because it has polyunsaturated fatty acids (two or more double bonds).

By adding double bonds to the fatty acids of the cell membranes in the leg, birds ensure that their membranes remain fluid in cold temperatures. The kinkiness caused by the double bonds keeps the fatty acids from packing too close. The membranes remain fluid.

Birds have a trick to keep their legs from losing too much heat. They arrange the arteries that bring blood to the leg and the veins that return blood to the heart as a counter-current system. You can see counter-current systems in many heating plants in large buildings. The furnace is situated at the center of the building. Cold air from outside is pumped into the furnace through a long pipe. The warmed exhaust air in the building is pumped out through a pipe parallel to the intake pipe. As the exhaust air moves toward the outside of the building, much of its heat is transferred to the colder intake air moving in the opposite direction. By the time the intake air reaches the furnace, the air has been warmed significantly by the exhaust air. Much of the heat of the exhaust air is recovered before the air is pumped outside. The counter-current arrangement of bird arteries and veins accomplishes the same energy savings.

Why do most birds not have feathered legs? The answer lies in the fact that a bird’s metabolism must be raised to provide the energy for flight. Excess heat is produced by this rise in metabolism and must be eliminated, even in the coldest weather, so a bird doesn‘t overheat. The unfeathered legs are the sites where that heat is lost.

[Originally published on March 3, 2007]

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]