Common Loon Adaptations

By in Morphology, Species Accounts

Last weekend, I took my Marine Ecology students on a trip to Cobscook Bay.  One of our activities was a whale watch off Head Harbour on Campobello Island.  Birds were abundant with lots of Northern Gannets, Sooty Shearwaters, a few Manx Shearwaters, Black-legged Kittiwakes, Common Loons, many Bonaparte’s Gulls and even a few Atlantic Puffins.  And yes, we saw marine mammals.  A couple of Minke Whales and groups of Harbor Porpoises tantalized us by breaking the surface of the water briefly.

Perhaps you feel a bit frustrated like me watching these marine vertebrates because a good bit of their lives is lived under the water out of our vision.  Thanks to underwater cameras, small submersibles and SCUBA equipment, we do have some understanding of life under the water surface for marine birds and mammals.

It is not surprising that these animals have particular adaptations that permit them to make a living by diving underwater.  Some of these adaptations are morphological and others are physiological.  Let’s explore some of these adaptations using the Common Loon.

Common Loons are excellent divers, capable or reaching depths of about 200 feet.  A loon can stay under water for as long as 15 minutes.

Loons swim underwater using only their feet.  The wings of loons are relatively short and are held tightly against the body during a dive.

The legs of a loon are set far back on the body.  The legs are splayed out laterally when the bird swims. When a loon is first diving from the surface, it breaks the surface by alternating strokes with the left and right leg.  Once underwater, the legs beat synchronously.

The lateral placement of the legs makes for hydrodynamic efficiency.  If the legs were close together, the turbulent eddies created by one leg would interfere with smooth movement through the water of the other leg.  The lateral arrangement allows a loon to generate maximum thrust while minimizing hydrodynamic drag.

The feet of loons are large and webbed.  The real power in swimming is generated by the rearward movement of those webbed feet against the water.  When the loon moves its feet forward during the recovery stroke, the toes are brought together causing the web to collapse and minimizing the effort needed to get the foot ready for the next power stroke.

Loons have a peculiar yet elegantly adapted leg.  Unlike most birds, the major lower bone (the tibiotarsus or the large drumstick bone on a chicken) of a loon has a prominent extension, called the cnemial crest, that extends well beyond the joint where the upper leg bone (the femur) joins.  This cnemial crest provides a broad attachment for the large muscles of the upper leg.  The massive thigh muscles generate the huge force that allows loons to dive so deeply and so quickly.

The long bones of birds are not hollow as seen in most species of birds.  These heavier bones make it easier for a loon to dive.  Just before a dive, a loon compresses its body, driving out the air trapped within its feathers.  Air trapped in the feathers would increase the buoyancy of the loon and make it harder to dive.

On to a physiological adaptation.  Loons, like other diving birds and marine mammals, have the ability to store large quantities of oxygen in their blood.  Even so, staying underwater for 15 minutes is no easy task.  During diving, a loon undergoes a physiological change called the diving reflex.  Oxygen flow to most body parts is greatly reduced except to the heart and nervous system.

This reflex causes the heart rate to slow, decreasing the amount of oxygen used by the heart.  Muscles and other parts of the body have to perform anaerobic (oxygen-free) metabolism until the bird surfaces.

[First published on October 14, 2012]

Rock Pigeon

By in Species Accounts

I have been reading great reports of interesting fall migrants on Monhegan Island and at other migration hotspots.  Any Maine birder would be thrilled to see a White-eyed Vireo or a Lark Sparrow, both of which have been reported this autumn.  But there is pleasure in seeing the everyday birds as well, even pigeons.

The standardized name for our pigeon is Rock Pigeon.  They are well known to birders and non-birders alike.   How can you avoid seeing pigeons in any city?

Wild Rock Doves were likely found from Scandinavia south through most of Europe, and further south to equatorial West Africa.  Wild populations likely occurred in Russia south to Pakistan and India in Asia.  We will never know the full range of wild Rock Doves because these birds were first domesticated 5,000 years ago.  Captive pigeons were transported around the world.  Domesticated birds readily become feral, hence the pigeon populations in your local park or on farms.

Wild Rock Doves nest in crevices and caves on rocky cliffs near short, shrub vegetation.  Feral pigeons in North America also occur in similar types of habitats, where tall buildings substitute for cliffs.

In North America, the first domesticated pigeons were brought to Atlantic coastal villages in the early 17th century.  These domesticated pigeons gave rise to feral populations, which have spread across the continent.  Rock Doves now occur throughout all of the 49 continental states, the southern portion of all the Canadian provinces and throughout Central America and the West Indies.

Among wild populations, nine subspecies have been described.  The differences among subspecies are based on color and size.  However, these differences in color bear no relationship to the feral pigeons we see.  Through domestication, pigeon fanciers have bred Rock Doves for particular colors and plumage anomalies.  These variants, called sports, were prized by upper crust British gentlemen in Victorian England.  Charles Darwin was a pigeon fancier.

Careful study of pigeons can be a rewarding experience.  A number of interesting behaviors are associated with nesting.  Pigeons mate for life.  Eggs may be laid as early as February and as late as October.  From a thorough study of pigeons in Kansas, we know some birds have over six nests per year.  That’s some serious dedication to family life!

The formation of the life-long pair bond occurs through a series of displays.  This courtship begins with a bout of bowing and cooing, in which the male stands erect, inflates his crop, fans his tail and struts around in a circle.  He bows his head and neck while giving a coo call.

The next stage in courtship is heteropreening (literally preening the other) or nibbling.  The male preens the female first and then the female returns the favor.  Next, the female solicits food from the male.  The male obliges by regurgitating seeds from his crop.

The female then accepts the advances of the male.  She crouches with her wings half-raised and mating takes place, lasting only a second or two.

After mating, the male gives a display in which he stands erect and walks a few steps.  He then launches into a display flight in which the wings are clapped together twice above the back.

Aggressive interactions also take place with characteristic displays.  When a male approaches another male’s mate, particularly if the female is receptive, the female’s mate may crouch and shift the position of its wings.  This behavior conveys aggression.  The intruder may be pecked on the head.  Other intruders may be driven, a behavior involving a type of chasing in which the intruder is literally pushed away.

The male may also give a threat display by standing horizontally, inflating its crop and walking around in circles.  As the male walks, it gives a display call and raises its wings.

[First published on September 30, 2012]

Review of Moonbird

By in Migration

Shorebird migration continues apace through Maine.  I can’t help but marvel at the tremendous migrations many shorebirds undertake.  Semipalmated Sandpipers depart from the Bay of Fundy and fly non-stop over the ocean to the mudflats around the mouth of the Amazon River in Suriname.  The Pacific Golden Plover flies non-stop from Alaska to its wintering grounds in Hawaii (a nice winter vacation!).  The champion is the Bar-tailed Godwit which flies non-stop from Alaska to New Zealand, a distance of over 7,200 miles.

Unlike most land birds, shorebirds tend to congregate at particular food-rich stop-over areas during their migration.  At these stop-overs, the birds can feed gluttonously to put on sufficient fat to fuel their long migratory flights.  Visiting a stop-over area at the right time of year allows a birder to be wowed with large numbers of shorebirds.  But this staging behavior is fraught with peril as well should an environmental disaster like an oil spill despoil the habitat.

The migration of Red Knots involves a series of stop-over areas as the birds move from their wintering areas at Tierre del Fuego (the southern tip of Argentina) to the Canadian arctic.  The most important stop-over area for this species in the New World is Delaware Bay.  The majority of Western Hemisphere knots stop here in late May to feed on the abundant eggs laid by horseshoe crabs in the intertidal regions of the Bay.  These calorie-rich morsels allow the Red Knots to tank up for their next long migratory leg.

Phillip Hoose, one of Maine’s own, has recently published a book on Red Knot migration, focusing on one remarkable banded bird.  The book is called Moonbird: A Year on the Wind with the Great Survivor B95.  Phillip is an acclaimed writer, having won a National Book Award and Newbery Honor for his book on the civil-rights activist, Claudette Colvin.  He also authored a book on the conservation of the Ivory-billed Woodpecker.  Moonbird continues his vein of excellent, accessible writing.

Red Knots occur on all continents  except Antarctica as well as many islands.  The subspecies Calidris canutus rufa is the Red Knot we see here in eastern North America.  Hoose points out that conservationists are worried about this subspecies.  In 1995, there were 150,000.  By 2000, the population was plummeting and now fewer than 25,000 remain.  Hoose explores some of the possible explanations of this alarming decline.

The star of the book is a male knot of the rufa subspecies, B95, that was banded in 1995.  B95 is printed on an orange plastic flag attached to one of his legs.             B95 is the only Red Knot with this particular combination of letter and numbers so an ornithologist can identify him by observing the band with binoculars or a spotting scope.

B95 is a survivor, nearly 20 years old.  He has been recaptured four times and observed through spotting scopes on many other occasions.  Hoose rightly describes B95 as the most celebrated shorebird in the world.

We follow B95 over the course of the years, visiting the stop-over areas of the species.  We visit San Antonio Bay along the central Argentinian coast, Lagoa do Peixe National Park in Brazil and of course Delaware Bay.  We learn of the threats to Red Knots along the way (falcons, declining horseshoe crab populations, development).

We also meet conservation heroes: Patricia González in Argentina, Brian Harrington and Amanda Dey in New Jersey, Guy Morrison and Ken Ross in the Canadian Arctic).

Hoose describes the various techniques that shorebird biologists use to capture birds so they may be banded.  You are there!

B95 proves to be a marvelous tour guide and Phillip Hoose chronicles the tour in lucid, fluid prose.  The book is accessible to high schoolers.  The wonderful color photographs and figures enhance the joy of reading this book.

[First published on September 16, 2012]

Bird Vision

By in Physiology

I’ve been looking at a lot of shorebirds recently now that migration has commenced.  Have you ever seen a shorebird bob its head up and down rapidly?  That behavior is the way that a bird with monocular vision can measure distance.

Humans have binocular vision.  That is, we can see most objects with both of our eyes.  The slight angular difference between our left and right eye as we focus on an object allows our brain to do some trigonometry and determine how far away that object is.

But shorebirds and many other birds suffer the risk of predation have their eyes set on the sides of the head.  It is really hard to sneak up on a bird with lateral  displaced eyes.  But except for a narrow field in front of the head (and sometimes behind!), an object can only be soon with one eye.  So one would think that a shorebird would not be able to determine the distance with only a single eye fixed on an object.

That’s where the head bobbing behavior comes in.  The bird is changing the angle at which it beholds an object by moving its eye up and down.  The bird’s brain that then figure out the distance using the same angular measurements that an animal with binocular vision uses.  Birds essentially make one eye do the work of two to allow it to have depth perception.

Birds have the best eyes of any animal.  Bird eyes are huge; the eye of the Ostrich is two inches across, the largest eye of any land animal.  Relative to the weight of the head, bird eyes are large.  Fully 15% of the weight of a European Starling’s head is contributed by eyes.  By contrast, our eyes only contribute about 1% of our head weight.

One would expect that birds have a well-developed sense of color given the striking variety of colors of the feathers and skin of birds.  Like the human eye, the retina of a bird eye is richly endowed with cones, sensory receptors that detect color.  The density of cones in birds is higher than in any other vertebrate.  The density of cones in bird retinas varies from twice to five times the density of cones in the human eye.

At the end of each cone in the retina, one can find a colored oil droplet through which light must pass to reach the retina.  These droplets are red, orange, yellow and green.  The function of these droplets is somewhat controversial but all agree that the droplets must serve to increase visual acuity.

It’s intriguing to note that the oil droplets in the cones on the lower half of the eye tend to be yellow.  Images projected on the lower retina come from above and the yellow pigments filter out the blue of the sky, making objects like Peregrine Falcons easier to pick up.

The cones in the upper retina tend to have red droplets.  Images hitting the upper retina come from below the bird.  The red droplets filter out the green of vegetation, making objects of other colors easier to see.

Recent research has shown that some birds are capable of seeing ultraviolet light, wavelengths that are too short for humans to see.  The world must look quite different through birds’ eyes.

How good is bird vision compared to humans?  It’s hard to be quantitative but it is certain that birds have much more acute vision than we do.  We have some remarkable anecdotes for Old World birds.  The European Bee-eater can see a bee at a distance of 100 yards!  The Eurasian Hobby, a falcon that specializes on dragonflies, can see a dragonfly at 200 yards.  From North America, Golden Eagles can detect the movement of a rabbit from a distance of a mile.

[First published on September 2, 2012]

eBird Reporting; Giant Swallowtail

By in Butterflies, Software

Maine Birders Rock!

I have written several times in this column about the value and utility of eBird (www.ebird.org).  This online resource is a powerful way to share bird sightings with the world at large.  eBird can be valuable if you are planning a trip to an unfamiliar location.  The data in eBird are used by ornithologists and environmental managers in research.  Finally, eBird makes it easy to maintain your various life lists.  You can see your World life list, life list for any country, state or county.  The lists can be produced for a single year or for all of your birding lifetime.  Want to see how many species you saw in York County in 2009.  No problem – eBird will search your records and provide your list.

The eBird personnel commonly report the number of eBird records submitted from various states.  It is no surprise that California and Texas usually lead these lists.  These states have very large populations.

Jeff Hutchinson, a birder from Texas, takes issue with these lists.  He points out that the number of eBird records standardized by state population size or area would be much more informative.  He did that analysis and shared his results on the Texas Birds listserv.

He first calculated the number of eBird records per one million people in each state.  The most intensively birded state: Alaska with 3,376 records per million residents.  And taking the silver medal is Maine with 1,448 records per million residents.  California and Texas are relatively poorly birded with 184 and 332 eBird records per million residents.

Hutchinson suggests that Alaskans and Mainers are probably more nature-conscious than populations from states with large urban centers.

Jeff extended his analysis by standardizing eBird reporting for the size of the state.  Maryland has the most eBird records per 1000 square kilometers (152), New Jersey is second (105) and Massachusetts is third (99.  Maine finishes a respectable tenth with 51 records per 1000 square kilometers – not bad considering the low population density of our state.  Alaska plummets to the bottom with only 1.4 records per 1000 square kilometers in that huge state.

Finally, Hutchinson combined the two ways of standardizing the data into a single measure that takes into account both human population size and state or province size.  It’s a bit like comparing apples and oranges but the idea has merit.  By his combined approach, Alaska is the most intensely birded state as measured by eBird records.  The next four are Maryland, Massachusetts, New Jersey and Maine.

This interesting analysis indicates that Maine birders have embraced the eBird technology to a greater degree than birders in most other states.  Furthermore, we are out in the field a lot.  And why not?  We have a marvelous bird fauna to observe and enjoy.

Giant Swallowtails

I am one of the coordinators of the Maine Butterfly Survey, a seven-year project to map the distribution of butterflies in Maine.  This year, we have reason to expect an influx of an usual butterfly into the state.  The Giant Swallowtail has been seen widely in Massachusetts and Vermont this summer and we now have a few records for Maine.  There is only one previous record of the species in Maine.  If you see one of these large, spectacular butterflies, please send me an email.

The Maine Butterfly Survey requires documentation of any sighting before we accept the record.  Photographs are perfectly fine means of documentation.

Giant Swallowtails are distinctive butterflies.  Black Swallowtails are the most likey species with which they might be confused.  The crossing of the yellow bands on the forewings of a Giant Swallowtail (making an X) does not occur with the two separate yellow bands of a Black Swallowtail.  The underwings of the Giant are mostly pale yellow while the Black Swallowtail underwings are mostly black with a row of orange spots.

[First published on August 19, 2012]

Shorebird Migration

By in Migration

We are all accustomed to misleading or even paradoxical phrases in our conversations that we often use without thinking.  Shouldn’t a “near miss” be a glancing collision?  Have you ever gotten a “free gift”?  Biology is not immune from such phrases and “fall bird migration” is at the top of my list.

Even though none of use wants to admit that the days are growing shorter, we are still in summer.  Nonetheless, migration of birds is well underway.  The southward movement will continue through autumn and into early winter.  “Fall migration” is misleading; I prefer “post-breeding migration”.  The majority of our swallows depart by the end of August and therefore never spend an autumn day in Maine.

Shorebirds (particularly sandpipers and plovers) are now migrating through Maine from their more northerly breeding grounds en route to more southerly wintering grounds.  Shorebirds are some of our earliest and most remarkable migrants.

The majority of shorebirds that pass through Maine during migration breed at high latitudes on the Arctic tundra.  For about six weeks (June to the middle of July), the arctic tundra is great habitat for sandpipers and plovers.  Insect life is abundant and the sun never sets.

We describe the reproduction of shorebirds as precocial.  The chicks hatch fully feathered, a striking contrast to the altricial development of most songbirds whose young hatch as naked, blind chicks.  Within hours of hatching, young shorebirds are walking around, catching their first insect meals.  The shorebird parents (sometimes only the mother in some species like the Buff-breasted Sandpiper and sometimes only the father in Red-necked Phalaropes and Red Phalaropes) guard the young but do not typically feed the young.  The young do have cryptic coloration, blending into the tundra to avoid the eyes of predators like Arctic foxes and Snowy Owls.

The short breeding season in the arctic means that parents only have time for one brood per season.  To increase the chances of surviving another year and reproducing again, sandpipers are under pressure to begin their southbound migration as soon as possible.

Because the nestlings can fend for themselves, the parents usually migrate from the breeding grounds before their young have even learned to fly!  As a result, southbound shorebird migration occurs in two pulses.  Along the Maine coast, the first adult shorebird migrants begin showing up by the middle of July.  The first juveniles show up later; juvenile sandpipers and plovers will arrive mostly in August and September.  In some species like the Semipalmated Sandpiper, the adult females leave the breeding grounds before the adult males producing a three-step migratory wave along the migration route: adult females, adult males and then juveniles.

After the parents have departed, the juvenile shorebirds learn to fly on their own and depart for wintering grounds they have never seen.  With no adults to guide them, the juveniles must have the migratory route somehow encoded in their brains.  We know that juvenile navigation is not as accurate as that of adults.  During the southbound migration, shorebirds that occur as rarities are usually juveniles.

By ageing shorebirds, birders can increase their enjoyment and appreciation of the southbound migration.  How does one go about determining if a shorebird is a juvenile or adult?  Some adult migrants still have some of their breeding plumage.  So a Black-bellied Plover or Dunlin with a black belly during southbound migration has to be an adult.  However, adults often molt into their winter plumage along the migratory route and may resemble juveniles.  A look at the wear of the feathers can usually allow one to distinguish such adults from juveniles.  As a general rule, juveniles have brighter and crisper plumages.  The feathers of the juvenile are only a few weeks old and the adult feathers are a couple of months older and hence more worn.

[First published on August 5, 2012]

Albinism Continued

By in Morphology, Physiology

In my last column, I discussed some instances of birds with aberrant plumages, including albinos.  In today’s column, I will continue the discussion of albinism in birds.

An albino bird is incapable of producing the pigment melanin.  Melanin is responsible for most of the black and brown feathers in birds as well as the coloring of the iris of each eye and the color of naked parts of a bird like the legs.  A true albino lacks melanin in the feathers, eyes and legs.  It therefore has a pure white plumage, pink eyes (reflecting the blood vessels in the retina of each eye) and pink legs.

Albinism is relatively common in some groups of birds and rare or unknown in others.  Of course, birds with red, yellow or orange feathers get their feather coloring from the pigments called carotenoids.  The carotenoids are acquired from their diet rather than synthesized by the bird like melanin is.  Albinos are only expected for birds whose primary pigment is melanin.

In Great Britain, a survey by B. L. Sage of over 3,000 records of albinism indicated that only 19 families of birds were represented.  In decreasing order of incidence, albinism was most common in these families: thrushes, crows and relatives, swallows, weaver finches, starlings, and finches.

Albert Gross conducted a similar survey of albinism for North American birds and found albinism to be more widespread.  The 1,847 records were distributed among 20 orders and 54 families.

American Robins were the most commonly reported (8.2% of all records) and House Sparrows were next (5.5% of records).  Waterfowl were also well represented.  As Gross points out, these patterns may be misleading.  Robins and House Sparrows are common around our homes so albinos of these species are more likely to be noticed than more secretive or human-averse birds.  Hunters may preferentially shoot ducks with odd plumages.

Perhaps you have seen birds that show white feathering on only a portion of the body.  Gross provided a classification to separate these variants from true albinos.  He defined an incomplete albino as a bird that lacks melanin from the plumage, eyes or naked parts but not all three regions as seen in a true albino.  An incomplete albino might have pink legs, white feathers but dark eyes.

An imperfect albino has the melanin reduced or diluted but never absent in any or all of the three areas.  My most memorable sighting of an imperfect albino occurred in March, 2000 at Colby College.  A flock of around 100 Bohemian Waxwings descended to the ground beneath some ornamental fruit trees.  Among them was one washed-out bird with tan body feathers rather than the rich gray-brown of a typical Bohemian.  The black mask on the face was diluted as well to a dark brown.  This imperfect albino was a striking bird with a beauty all its own.

The final category Gross described is partial albinism.  A partial albino has the lack of melanin confined to a localized area.  A Black-capped Chickadee is my most memorable partial albino.

In the winter of 1995-1996, I was monitoring the use of sunflower seed feeders near Flagstaff Lake by a population of chickadees that I had color-banded so I could recognize individuals.  I was not able to band all the chickadees that came to the feeders so I had no way to distinguish chickadee A from chickadee B if they were unbanded.  However, an unbanded chickadee arrived one day missing all of its tail feathers.  The bird had likely dropped its tail feathers (a phenomenon called fright molt) in a close encounter with a predator.  The bird slowly regrew is tail feathers over the winter but they all came back pure white. The chickadee I called “White Tail” in my field notes was a partial albino.

[Originally published on July 22, 2012]

Albinism and Other Feather Oddities

By in Morphology, Physiology

We have been having an odd visitor at our feeder.  It’s a male Hairy Woodpecker with a difference.  Instead of black and white feathers and red on the nape, many of the typically white feathers are buffy in color.

Such variants occur regularly in Hairy Woodpecker populations in western North America and in the southern United States but this morph is a first for me in New England.

Woodpecker specialists have found some Hairy Woodpeckers stained with tannins from trees on their feathers, imparting a brown to cinnamon coloration.  But the fairly even distribution of the buff on our woodpecker suggests the coloration comes from pigments laid down in the feathers.

The aberrant plumage of this Hairy Woodpecker got me to reminesce about other birds I have seen with unusual appearances.

Albino birds lack any pigment whatsoever in their feathers.  Such birds lack the enzyme tyrosinase, an essential enzyme needed to make the pigment melanin.  The feathers are therefore pure white.  Albinos also lack coloration in their legs, feet and bill.   The eyes of true albinos appear pink because no melanin is present in the iris of a bird’s eye, allowing the pinkish color of the blood vessels of the eye to be seen through the iris.  The lack of melanin in the iris diminishes the vision of an albino.  Albinos have it rough: their white plumage makes them conspicuous and their reduced visual acuity makes it harder to detect approaching predators.

A bird with white feathers is not necessarily an albino.  For example, a Snowy Egret has all white feathers.  The bird does not deposit melanin in the feathers when they are being formed. However, the black color of the legs and the dark color of the eyes indicate that these long-legged beauties are not albinos.

I’ve had the pleasure of seeing an albino House Sparrow, conspicuous among a flock of 20 others in normal plumage.  I’ve also had a fleeting glimpse of a pure-white European Starling.

But two other albinos are even more memorable, both seen during my college days.  One was an albino Northern Mockingbird, a strikingly beautiful wraith.  You have likely seen Northern Mockingbirds exposing their white wing patches with a distinctive two-step motion.  The flashing white can be seen for quite a distance.  Ornithologists are still not sure of the purpose of the behavior.  I think it is used mostly to either court females or deter other males.  Other ornithologists think otherwise, suggesting the display is used to scare insects, making them fly up and become easy prey for the mockingbird.

Whatever the function of the display, I felt some empathy toward this albino mockingbird.  It had the motion of displaying its wing patches down perfectly but of course the white patches were no different from the rest of the plumage.  The bird did not have an inkling that it was colored differently from normal Northern Mockingbirds.

The other albino was a bird seen in Salisbury, Massachusetts over a Presidents Day holiday.  A group of us from Baltimore drove into New England in search of various northern owls.  Snowy Owl was high on our list, most of us never having seen one before.

Birders had reported several Snowy Owls in Salisbury and we were keen to find one.  En route, we saw an all-white bird perched about half-way up a large oak tree.  Remarking to ourselves that the perch seemed to be an odd place for a Snowy Owl (they are usually perched on or near the ground), we jumped out of our cars in the cold air and set up our scopes.  It was not a Snowy Owl but rather a Red-tailed Hawk.  It was a magnificent bird.  We later found Snowy Owls but that albino red-tail remains a much more memorable bird.

[First published on July 8, 2012]

Bird Song Complexity

By in Behavior

In the last column, I wrote about the morning chorus, the marvelous dawn symphony performed by singing birds during the breeding season.  The chorus is still going strong (much to the dismay of some would-be sleepers).   I’ll expand on the topic in today’s column, exploring the complexity of bird songs.

The males of some species give a very simple song like the harsh “fee bee” of the Eastern Phoebe or the “hey sweetie” or “fee bee-ee” song of the Black-capped Chickadee.  Although some individual variation occurs among males of these species, the repertoire of different songs is low.

On the other hand, some of our breeding birds have long, complex songs with great variation. Some of this variation occurs between males and some of the variation occurs in a single male.

Red-eyed Vireos give their familiar singsong vocalization, “here I am – where are you – over here”.  By recording Red-eyed Vireos and analyzing the songs with sound analysis software, my students and I have found that one male may give over 40 songs.  Males are tireless; a single bird may sing over 20,000 songs in a day.

You may be surprised to know that the Brown Thrasher has the most varied repertoire of any bird studied.  A single male can sing over 2000 songs!

Species with complex songs include virtuosos like Bobolinks, Ruby-crowned Kinglets and Song Sparrows.  Each male gives a long song with many phrases.  A bird may omit, replace or add particular phrases to produce different renditions of its song.  The speed of note production can be dazzling.  The ethereal song of a Winter Wren includes over 100 notes given in less than 10 seconds.

Ornithologists have been intrigued by the variety of repertoire sizes of male songbirds and have noted some interesting patterns.  Species with large repertoires tend to have high parental care by the male of a pair.  Migratory songbirds tend to have greater repertoire sizes than related non-migratory species.  Finally species that are polygynous (males have multiple female mates) have larger repertoire sizes.

In a fascinating paper, Susan Peters of Duke University and three colleagues described the results of a study of song complexity in the Song Sparrow.Song Sparrows are widely distributed in North America.  They have a complex song that usually begins with three clear notes and then a complicated and variable series of single notes, phrases of several notes, and trills.  Song Sparrows have a large repertoire of songs.   The phrase “maids maids maids put on your tea kettle-ettle-ettle-ettle” captures some of the cadence and complexity of the songs.

Some populations of Song Sparrows are migratory while others, typically in more moderate climates, are year-round residents.  All Song Sparrows are monogamous and males of sedentary and migratory populations contribute equally to brood rearing.

Peters and her colleagues compared the repertoire sizes of two sedentary populations of Song Sparrows (in North Carolina and Washington state, both of which have relatively mild winters) to migratory populations of Song Sparrows from Maine and Pennsylvania.  Most of the Song Sparrows in the latter two states migrate south in the winter.

The researchers recorded Song Sparrows in all of these states and then analyzed them to compare the number of different songs from each population.  Their analysis revealed that the Washington and North Carolina sedentary populations were more similar to each other than to either the Pennsylvania or Maine populations.

Surprisingly, these ornithologists found that the sedentary populations had more complex repertoires than the migratory populations.  These results conflict with the conventional wisdom that migratory species generally have larger and more complex repertoires than non-migratory species.  It is clear from the work of Peters and her colleagues that we have much to learn about reasons for differences in the complexity of bird song.

[Originally published on June 24, 2012]

Morning Chorus

By in Behavior

The overworn expression that there is no accounting for taste certainly applies to music.  At this time of year, I thrill to the music of the birds whose concerts start well before the crack of dawn.  As a reader of this column, I’m sure you share my joy of the morning chorus.  On the other hand non-birding friends and family may complain vigorously about the infernal early morning ruckus disturbing their sleep.

Locally, American Robins are the first to welcome the new day with their caroled song around four AM, nearly an hour before dawn.  Others join the choir and by dawn it is possible at a stationary poit to hear ten or more species singing.  For the next hour, the male songbirds sing energetically and often.  The frequency of singing starts to decline and by 10 AM, the chorus is essentially over.  That is why Breeding Bird Surveys and other ornithological counts relying heavily on identification by sound must be done in the early morning.

Why do birds sing with such vigor early in the morning?  We don’t really have a compelling explanation.  Some ornithologists believe that the early morning is the best time for males to attract females that might have arrived on migration during the night.  Or, perhaps singing allows a male to reassert possession of his territory to any males that might have arrived during the night.  In the early dawn hours, light is too weak to permit birds to forage efficiently so singing may be a profitable use of the time.  Often, weather conditions are calm in the early morning and songs can be broadcast then for maximal distance.

The singing behavior of some songbirds is quite different during the early morning hours compared to the remainder of the day.  The long, dry trill of a Chipping Sparrow is a familiar and easily recognized song that can be heard off and on throughout the day.  A male typically sings the song from a perch at least twenty feet high.

But an early riser has the chance to witness singing behavior that has only recently been studied.  For the first half hour after dawn, male Chipping Sparrows sing from the ground!  Males in adjacent territories gather in a central arena and sing very short songs in machine-gun like fashion to each other.  Presumably, males are establishing a dominance hierarchy by these social singing events.

The change in behavior is really quite striking.  At 4:30 AM, the Chipping Sparrows are singing from the ground at a rate of about 40 songs/minute.  Then 45 minutes later, the males sing their longer, more familiar trills from perches in trees at a rate of three or four songs minute.

Many warblers are known to sing two types of song.  Accented songs usually end emphatically like the “pleased-pleased-pleased-to-meetcha!” of the Chestnut-sided Warbler and are seem to function primarily in mate attraction.  Unaccented songs are used to proclaim territorial ownership to other males.

Chestnut-sided Warblers in the dawn chorus sing almost entirely unaccented songs.  Interestingly, every male has a distinctive song so individual recognition is possible.  Later in the day, the males switch to the more easily recognized accented song.  These accented songs are nearly identical among the males in a given area.

Confirming the functions of these two song types, unaccented songs are typically given from the periphery of a bird’s territory while the accented songs are given in the middle of a territory.

The crescendo-like “tea-CHER, tea-CHER, tea_CHER tea_CHER tea_CHER” song of the Ovenbird is an easy song to recognize.  However, during the early morning, Ovenbird males fly above the canopy and sing a warbled flight song with a couple of “tea-CHER” phrases in the middle of the jumble of notes.  At least 11 other warbler species sing early morning flight songs.

[Originally published on June 10, 2012]

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