For the Birds: Arctic Tern Migration; The Life of the Skies Review

The fall bird migration is picking up momentum. Swallows began massing in large flocks and heading southward by the middle of August. Shorebirds that nest on the arctic tundra are building in numbers along Maine mudflats, the first having arrived on their southward passage in July. Black Scoters, Surf Scoters, and Red-necked Grebes have already appeared along coastal waters. Much of the warbler migration will occur in September and sparrow migration in October.

The fall migration is a gloriously protracted spectacle. Without the need to claim a breeding territory or find a mate like spring migrants, fall migrants show less urgency.

The number of birds that participate in the fall migration in North America is staggering. I have seen one estimate of five billion birds moving southward on our continent.

Some migrations are relatively modest undertakings. For instance, the Common Loons that nest on our lakes need only migrate eastward to the ocean to spend the winter. Ruby-crowned Kinglets may only migrate as far south as Pennsylvania or eastern New York for the winter.

With the Olympics still fresh in our minds, considering the most impressive bird migrants seems appropriate. In the past few years, I have written about two of the most amazing species of migrating birds. Both Semipalmated Sandpipers and Blackpoll Warblers fatten along coastal portions of northeastern North America and then embark on a non-stop flight over the ocean of some 2000 miles to get to their South American wintering grounds.

Once these birds get south of the 30th parallel, the northeast trade winds help to propel them to the northeastern shores of South America but their migration is still stunning. These birds cannot stop to rest on the water and cannot feed along the way. They have to pack all the fat they will need to fuel their flight before they depart. These migrations require three to four days of non-stop flight.

But, the North American species that covers the most distance in migration is the Arctic Tern. Members of this species breed in the Western Hemisphere from Greenland at a latitude of 84 degrees south to Cape Cod. Their fall migration takes them to the edge of the pack ice in Antarctica. That requires a flight each fall of 12,000 miles!

Unlike the Semipalmated Sandpipers and Blackpoll Warblers, Arctic Terns can feed along their way since they dive for fish from the air. They can also rest on the surface of the ocean. However, 12,000 miles is an awfully long distance to cover in just a couple of months. The advantages are significant; Arctic Terns experience longer periods of daylight than any other species of bird in the Western Hemisphere.

When the Antarctic summer starts to wane in March, the Arctic Terns retrace their migration back to their northern breeding grounds. The record life span for an Arctic Tern is 34 years. The wings of this bird propelled the bird over 800 million miles in its lifetime. That feat is worthy of a gold medal.

The Life of the Skies

I’ve just finished reading The Life of the Skies: Birding at the End of Nature by Jonathan Rosen and enthusiastically recommend the book.

Describing the book is not easy; perhaps, the best way to describe the book is a meditation on birding at the beginning of the 21st century.

Rosen is a novelist and editor of Nextbooks who took up birding as an adult. Central Park, near his New York City apartment, is one of his favorite haunts although he has traveled broadly to pursue his birding passion.

Rosen interweaves several birding narratives in his book including ones on his efforts to see an Ivory-billed Woodpecker, visiting threatened birding hotspots in Israel along with historical accounts of John James Audubon, Henry David Thoreau and Alfred Russel Wallace, a contemporary of Charles Darwin who independently arrived at the concept of natural selection.

References to poetry appear often throughout the various chapters including poems by Robert Frost, Walt Whitman, Emily Dickinson and Wallace Stevens. He also frequently quotes the writing of Edward O. Wilson, the Harvard professor who is one of the most articulate defenders of the need to conserve the diversity of life on earth.

I found Rosen’s analysis of Robert Frost’s poem, The Ovenbird, to be particularly moving. Written around 1910, this poem is a lament for nature that is lost but still expressing a thread of hope for conservation.

The Life of the Skies explores the relationship between wild birds and humans and the scientific, spiritual and emotional ways that birding is important for humans. I thoroughly enjoyed this provocative book.

[Originally published on September 6, 2008]

For the Birds: Bird Phylogeny Revised

The Swedish naturalist, Carl Linnaeus (1707-1778), developed the system of classification that biologists use today to order the rich diversity of life on earth. Linnaeus gave every species a two-part name, denoting the genus and the species of that organism. A genus contains a number of similar but distinct species. Genera (the plural of genus) are combined into families, families into orders, orders into classes and classes into divisions or phyla.

Linnaeus classified organisms based on their morphological similarity. Species belonging to the same genus are generally more similar to each other than they are to members of their own family that are in different genera.

A classification based on similarity of structure runs into two problems. First, two closely related species may diverge from each other over time and appear to be quite different. Second, distantly related species may converge on similar morphologies over time and thus be mistakenly placed in the same genus or family. As one example, Linnaeus placed the barnacles and the mollusks (snails, clams and their relatives) in the same group because all have a hard shell made of calcium. By looking at the early development of these organisms, biologists came to realize that barnacles are crustaceans and therefore more closely related to shrimp, lobsters and crabs.

Charles Darwin held the view that our classification system of life on earth should be a huge family tree, reflecting the relatedness of organisms. Understanding the relationships of the higher groups (orders, classes and phyla) is difficult based solely on morphology. Spirited arguments among biologists in the scientific literature about the relationships of these higher groups are common.

The analysis of DNA gives us a new way to develop the tree of life in the way Darwin envisioned. DNA is the molecule that ultimately determines the way an organism looks and behaves. The idea behind DNA comparisons is straightforward. More closely related species should have very similar DNA while more distantly related species should have more differences in their DNA.

For birds, the Yale biologist Charles Sibley, working in the 1970’s and 1980’s with his colleague Jon Ahlquist, were the first to use DNA comparisons to examine how the higher groups of birds were related. Their results were groundbreaking.

Sibley and Ahlquist used a technique called DNA hybridization. DNA is a double-stranded molecule with one strand being the mirror image of the other. By heating DNA, the double strands separate. Sibley and Ahlquist recombined single strands of DNA from two species to make hybrid DNA and determined how closely the two strands fit together. Species that made tight DNA hybrids were considered to be closely related.

Their many experiments produced a number of surprising results that are reflected in the current classification scheme used by the American Ornithologists Union and in the organization of field guides. For instance, Sibley and Ahlquist showed that the New World vultures are properly classified with the herons, not with the hawks and falcons. Vireos are not closely related to warblers as formerly thought but rather closer to the crows and ravens.

It is now possible to analyze DNA in much greater detail than Sibley and Ahlquist could do with their hybridization studies. Biologists can determine the sequence of the four molecules (called nucleotides) in DNA. Human DNA has three billion nucleotides; that’s a lot of information to compare!

As an example of the power of this approach, humans and chimpanzees have DNA that differs by less than 1%. Our DNA is slightly less similar to that of gorillas and even less similar to orangutans. So using DNA comparisons, we know that chimpanzees are the closest living relatives of humans and gorillas are the next closest of the great apes to us.

A recently published paper by Shannon Hackett and colleagues in the journal Science presents the results of DNA sequence comparisons for 169 species of birds, representing all of the major groups of birds. Like the work of Sibley and Ahlquist, many surprising relationships were found. We can expect the order of birds in our field guides and checklists to change to reflect his new work.

Here are some of their major findings. The perching birds (the passerines) are most closely related to the parrots! Falcons are closely related to these two groups of birds but not to the hawks and eagles. Thus, the falcon family and the hawk family have converged. The closest relatives of the penguins are the albatrosses. Unlike Sibley and Ahlquist, the new papers shows New World vultures are closest to the hawks and eagles. You can see further results of this important paper at: http://whozoo.org/birds/birdphylogeny.html

[Originally published on August 30, 2008]

For the Birds: Plover and Sandpiper Feeding

Shorebird migration is underway. In the past week, Maine birders have found Greater Yellowlegs, Lesser Yellowlegs, Short-billed Dowitchers, Semipalmated Sandpipers and White-rumped Sandpipers. Most of these species nest in the Arctic. The window of opportunity for nesting in the Arctic is short so it is not surprising that these birds have departed the high latitudes already.

For many Arctic-nesting shorebirds like the Semipalmated Sandpiper, two pulses of migration are seen. The first pulse, the one we are beginning to see now, is almost entirely adult birds. These birds have left their young on the breeding grounds, in many cases before the young have even learned to fly.

Shorebirds do have precocial development; they hatch with feathers and can forage for food shortly after hatching. So, adults departing early is really not a form of child neglect. The young will eventually learn to fly and then depart on their migration. These juvenile birds, arriving in Maine mostly in September, constitute the second pulse of the migration.

Most migratory birds have their migration route hard-wired rather than having to learn a migration route. That becomes obvious with birds like Semipalmated Sandpipers who do not have mom or dad to show them the way. Mistakes do occur, however. The chance of a first-year sandpiper showing up at some unexpected location is greater than the chance of an adult appearing at the same place.

To fuel their migration, shorebirds have to feed gluttonously along the way. I think it is fascinating to watch how different species of shorebirds feed.

Let’s start with the plovers. A careful look at a plover will indicate that its eyes are quite large relative to its head size compared to most sandpipers. These large eyes suggest that vision is of primary importance in finding food. That is indeed true.

The foraging behavior of plovers can be called run-and-peck. A plover on an intertidal flat will look for movements at the sediment surface indicating the presence of a crustacean or polychaete worm. It will then run to the location and attempt to grab the prey item.

Keep an eye out for a behavior of Black-bellied Plovers called foot trembling. A plover will stand on one leg and vibrate the other food right at the sediment surface. This trembling appears to set up vibrations that a bloodworm or other invertebrate predator interprets as a possible prey item. The bloodworm comes to surface looking for dinner and finds that it is on the menu of the plover!

Sandpipers, the other major group of the shorebirds, rely on touch to find their food. The bill of a sandpiper is richly endowed with touch receptors, particularly at the tip. A sandpiper probes the sediment until the touch receptors detect the movement of a small invertebrate and the bill clamps down on the prey item.

Particularly for long-billed sandpipers like dowitchers, a significant amount of energy would be required to open the long bill while it was stuck in several inches of mud. To make opening the bill easier, sandpiper bills are rhynchokinetic. That is, the can open the tip of the bill without having to open the portions of the bill closer to the skull. You can see a nice picture of this behavior at: http://birdblog.merseyblogs.co.uk/archives/2006/07/its_called_rhyn.html

Sandpipers on an intertidal flat occur in characteristic spots. Dowitchers and Stilt Sandpipers with their long bills wade in up to their bill and probe rapidly into the sediment. Their probing is often quite rapid and is referred to as stitching (like a sewing machine). Dunlins with somewhat shorter bills tend to forage right at the water’s edge. Short-billed sandpipers like the various peeps feed above the tidemark.

One advantage sandpipers have of using touch rather than sight to find food is that sandpipers can feed at night. Nocturnal feeding is particularly valuable during migration when sandpipers are trying to pack on fat as quickly as possible.

Some years ago, I determined the predation rate of Semipalmated Sandpipers in the Bay of Fundy on their favored prey, the small crustacean Corophium volutator by videotaping foraging birds. Corophium is about 3/8 inch long. I found that each sandpiper was taking about 17,000 Corophium each day. That goes a long weight toward explaining how these sandpipers double their weight in only two weeks.

Recent research has shown that Western Sandpipers acquire a majority of their energy by consuming biofilms. A biofilm is a thin layer of bacteria, detritus and sediment held together by a glue-like material secreted by microalgae and bacteria. Biofilms may be important in the diets of other shorebirds too.

[Originally published on August 23, 2008]

For the Birds: Ontario Conservation Easement

Birds often find humans to be rather undesirable neighbors. In the last three columns, I wrote about the decline of some grassland birds and some efforts to stop the decline. One of the most effective conservation tools that environmental managers have at their disposal is habitat protection. In Maine, remaining grasslands like the Kennebunk Plains and the Wells Barren are now protected, thanks to the work of The Nature Conservancy and other organizations.

But grasslands are not the only habitats we should be worried about. The notion that we have enough forest in Maine and elsewhere at northern latitudes is shortsighted. We know that highly fragmented forests may not be acceptable habitat for a number of breeding birds. Species like Barred Owl, Ovenbird and Scarlet Tanager seek nesting territories within large tracts of unfragmented forest. Highly fragmented forests simply will not do.

The government of the province of Ontario recently announced some great news for conservation, including a great boon for birds that breed in the boreal forest. The Premier, Dalton McGuinty, proudly revealed that the Ontario Government will protect at least half of Ontario’s boreal forest. The protected area will include 86,900 square miles of boreal forest. That area is nearly three times the size of Maine! Corridors between large areas of forest help to minimize the effects of forest fragmentation as unprotected areas are developed and altered.

The decision was primarily impelled by a letter sent to the Canadian government on behalf of over 1500 scientists worldwide, who strongly recommended that 50% of Canada’s boreal forest be protected. These scientists identified the 1.4 billion acre Canadian boreal forest as one of the largest intact forest and wetland ecosystems remaining on earth.

The boreal region is one of the last truly wild spaces on earth. It is home to over 200 sensitive species of animals, such as polar bears, wolverines and caribou. Many of these species are threatened or endangered. The protection of this area will be a huge step in preventing a decline in the biodiversity of the region.

Preserving large tracts of this boreal region is necessary because of increasing pressure from corporate logging and mining concerns. Oil and gas operations represent threats to the habitat as well.

Over 300 species of birds are found in the boreal forests of North America. This forest ecosystem provides breeding habitat for over 40% of the population of 21 warbler species. Nearly 100 species of birds have the majority of their population in the boreal forest during the summer. Ontario’s landmark decision is reason to cheer for all birders.

The protection of this large tract of forest will help combat global warming. The absorption of carbon dioxide by the boreal forest trees is a significant carbon sink.

Altruism

Altruism is the term that biologists use to describe selfless behavior. Although examples of altruism abound for humans, biologists are skeptical of claims of altruistic behavior in other species. After all, much of the behavior of an organism can be understood in trying to reproduce and hence perpetuate one’s genes. Helping other organisms at one’s own expense is hardly the way to get your genes into the next generation.

Some animal behaviorists think that selfless behavior can be worthwhile as long as it is reciprocal. Two organisms might strike a bargain where each agrees to share food if the other is unable to find food. This reciprocal altruism seems like a win-win situation, right? The problem is that cheaters win. I might be more than happy to eat some of your food when I have none but I may selfishly choose not to share when I have food and you do not.

Some recent work on Pied Flycatchers, a species found in Eurasia, has shed some light on how cheaters in system of reciprocal altruism might be punished. Pied Flycatchers will mob a predator, jointly assaulting the predator to drive it away. When a predator is seen, a Pied Flycatcher will give an alarm call to attract other Pied Flycatchers to join the mob. Cooperation usually results in the predator being chased away.

However, some Pied Flycatchers are cheaters. They may not respond to an alarm call and help mob the predator. Experiments done in the field showed that when a Pied Flycatcher that did not help mob a predator sees another predator and gives the alarm call, the birds that mobbed the first predator refuse to help the cheater. It’s a case of “You didn’t help us mob earlier so we are not going to help you now – good luck chasing away that hawk on your own”. So, this study has identified a case of reciprocal altruism where cheaters do not prosper.

[Originally published on August 9, 2008]

For the Birds: Upland Sandpiper and Eastern Meadowlark

This column is the last of three on grassland birds in Maine. In today’s column, we will take a look at Upland Sandpipers and Eastern Meadowlarks, both of which require grasslands for nesting.

Like the American Woodcock, the Upland Sandpiper is a shorebird that has adopted a purely terrestrial lifestyle. Don’t look for Upland Sandpipers foraging on intertidal mudflats with Sanderlings, Semipalmated Sandpipers, Greater Yellowlegs and other members of the sandpiper family. Rather, Upland Sandpipers prefer rather dry habitats with a dearth of trees. Grasslands are their natural breeding areas although lowbush blueberry barrens can serve as nesting sites as well. Grassy areas at airports also provide nesting habitat.

An Upland Sandpiper is a large sandpiper with a long bill. Its neck is markedly thin and its head seems to be too small for its body. The plumage consists of black, brown and tan feathers that make the bird cryptic in the tall-grass habitats it prefers.

The call of the male is a sound that will stick with you. Many people will not recognize the eerie whistle of the male as coming from a bird. Efforts to represent the whistle in human syllables include “whooooleeeeee, wheeelooooo-ooooo”. To some, the call sounds like a “wolf whistle”.

The greatest abundance of nestling Upland Sandpipers is found in the Dakotas, Nebraska and Kansas. Populations can be found westward to the Rocky Mountains and eastward, occurring patchily in New England and some of the Mid-Atlantic States. These birds winter on the pampas and other grassland habitats in South America.

In most nesting areas, Upland Sandpipers have suffered at the hands of humans. First, early European settlers killed them for food as well as collected their eggs. Later, market hunters took even more. But, the most devastating effect caused by humans was the plowing of the tall-grass prairies to plant crops. Breeding Bird Survey data show that numbers of Upland Sandpipers continue to decline over most of its breeding range, North Dakota being the only state where Uppies are holding their own.

The last species we will consider is the Eastern Meadowlark, a species associated with farmlands. Before European settlement, Eastern Meadowlarks were dependent on native grasslands for habitat. Unlike the Upland Sandpiper, meadowlarks have proven to be adaptable, readily nesting in pastures.

Eastern Meadowlarks are found broadly throughout eastern North America. Their northern limit occurs from Minnesota eastward through Ontario and into the Maritime Provinces. Meadowlarks can be found throughout the states south of this line. They even extend discontinuously throughout Central America.

In most of their range, Eastern Meadowlarks are non-migratory. The meadowlarks in New England and other northern states withdraw in late fall to warmer portions of the species’ range. Meadowlarks usually return to Maine in late March to April.

Eastern Meadowlarks are distinctive birds. They have a bright yellow breast with a V-shaped black patch on the upper breast. The description of a yellow V-necked sweater is certainly apt. On the side of the face below the eye, a whitish stripe, the malar stripe, is distinctive. The Western Meadowlark, which overlaps with Eastern Meadowlark in some parts of their ranges, is almost a dead ringer for the Eastern. However, the malar stripe of the Western Meadowlark is mostly yellow.

The upper side of the Eastern Meadowlark is mottled gray, black and brown, allowing the bird to blend in well with its grassland habitat. The outer tail feathers are white, making these feathers a good field mark for a flying meadowlark.

Like other grassland birds, Eastern Meadowlarks will be detected first by their voice. The song of this species is a series of clear, slurred whistles. Some ornithologists have tried to capture the cadence of the song as “song of the earth”.

Despite their use of agricultural fields for nesting, Eastern Meadowlarks are showing alarming declines throughout much of their range. Part of this stems from a reversion of old farms back to forests. Human encroachment to breeding areas also plays a role in the decline of these birds.

As an overview, we have seen that grassland birds are declining through much of their range. While we should be concerned, there is some reason for hope. In recent years, the science of landscape ecology has matured. Landscape ecologists study how variation in habitat at large scales affects the distribution of organisms. Landscape ecologists understand the importance of interconnected reserves, of conserving habitat near already protected habitat and of evaluating the conservation potential of available tracts of land. Active management of grasslands will need to be continued to prevent forests from taking over.

[Published on July 26, 2008]

For the Birds: Grassland Sparrows

This column is the second of three on grassland birds in Maine. In today’s column, we will take a look at three sparrows (Savannah, Vesper and Grasshopper) that require grasslands for nesting. In the next column, I’ll discuss the Upland Sandpiper and Eastern Meadowlark and end with some of the conservation challenges of these habitats.

The three sparrows in today’s column are more often heard then seen so learning to recognize them by song is the best way to find these somewhat shy birds.

The Savannah Sparrow is the most common of the three. Its breeding range covers most of the northern two-thirds of North America, extending into the arctic tundra. It is a migratory breeder in most parts of its range. During the winter, Savannah Sparrows withdraw to the southern tier of the United States and into much of Central America.

The species was named the Savannah Sparrow by Alexander Wilson, a contemporary of Audubon. Wilson collected a specimen in Savannah, Georgia and honored this charming southern city by naming a sparrow after it.

The song of the Savannah Sparrow has a distinctive buzzy quality. The song typically begins with a few short notes, then a buzzy trill and a final note or two of lower pitch. The song carries well, particularly the trill and final notes. A singing male can usually be seen singing from a grass stem or short shrub.

Visual identification of this species is straightforward. A Savannah Sparrow has a streaked breast like a Song Sparrow. The Savannah Sparrow’s streaks are less bold than those of a Song Sparrow and typically do not coalesce into a dot as in most Song Sparrows. The best field mark is the yellow line above the eye that is especially conspicuous in front of the eye.

During the breeding season, Savannah Sparrows mostly feed on insects. Outside of the breeding season, they switch to a diet of seeds they are able to find on the ground.

Like the Bobolinks discussed in the last column, a male Savannah Sparrow may have more than one female partner. The insect abundance in a grassland or meadow is abundant enough to allow a male to help feed two clutches of nestlings.

Vesper Sparrows have a broad distribution in North America, not quite rivaling the broad range of the Savannah Sparrow. Vesper Sparrows nest across the middle third of our continent and winter in the southern tier of states south into Mexico.

The song of the Vesper Sparrow has a distinctive beginning of two to four long clear notes followed by a downslur and then a series of flute-like trills, first rising in pitch and then falling. Vesper Sparrows sing throughout the day but continue to sing in the evening after most birds have ceased to sing. Those evening songs are the reason the bird is called the Vesper Sparrow.

The dependence of Vesper Sparrows on grassland habitats is doubly reflected in its scientific name, Pooecetes gramineus. Pooecetes means “grass dweller” and gramineus means “fond of grass”. In Maine, grasslands and blueberry barrens are the best places to find this sparrow.

The Vesper Sparrow is a rather large sparrow. These sparrows have a streaked breast and distinctive white outer tail feathers. Some of the wing coverts are rufous in color, giving rise to the older common name of Bay-winged Bunting.

We believe that Vesper Sparrows were rare in the east before European settlement. The clearing of forest for pastures allowed Vesper Sparrows to increase in eastern North America. The species is declining in the east now because of the reversion of so many farms to forest.

Grasshopper Sparrows are the least common of the three grassland sparrows. They breed broadly throughout the eastern two-thirds of the United States but are usually found in low numbers. Their populations have declined in many portions of their range because of the destruction of grasslands and prairies these birds require for nesting.

The common name of this species stems from its insect-like songs. Male Grasshopper Sparrows are unusual among sparrows in that they sing two distinctly different songs. Their Primary Song consists of one to three high-pitched notes followed by an insect-like trill. It can be described as tsick, tsick, tsurrrrrrr. This song is used to repel other males from its territory. A second song, the Sustained Song, consists of a more musical series of short buzzy notes given either from a perch or in flight to attract a female.

The pronounced flattened head, the large bill and upper orange breast make the Grasshopper Sparrow easy to identify once sighted.

[First published on June 28, 2008]

For the Birds: Bobolinks

A suite of birds collectively called the grassland birds nest in New England. This group of birds includes the Upland Sandpiper, Savannah Sparrow, Vesper Sparrow, Grasshopper Sparrow, Eastern Meadowlark and Bobolink. Wildlife biologists are concerned about this group of birds because their populations are declining in New England, including our Maine populations.

Grassland habitats are rather limited in New England and have invited development into farms or towns because tree cutting is not required adapt the line for human uses. Fortunately, grassland birds are adaptable and often nest in hayfields or blueberry barrens. However, many hayfields in Maine are no longer maintained and are reverting to forest. We have much more forested land now in Maine than we did in 1900. Thus, the decline of their required habitat helps explain the decline of these grassland birds.

Today’s column is the first of three on the grassland birds of Maine. We’ll start with one of the most beloved birds of Maine, the Bobolink.

With their beautiful plumage (mostly black with white on the back and wings, and a yellow patch on the back of the head and nape), male Bobolinks are strikingly handsome birds. Some waggish authors have described them as having tuxedos on backwards.

The female is nondescript, brown on the uppersides with streaking and yellowish underneath. This plumage makes them nearly impossible to see in a grassy field.

The male’s song is equally distinctive: a long, bubbly series of metallic notes. A student of mine, an obvious Star Wars fan, said the song sounds like the robot R2D2! The Bobolink song has inspired poetry. The American poet, William Cullen Bryant, based his poem “Robert of Lincoln” on the song of the Bobolink.

The breeding range of Bobolinks extends across the northern tier of the United States from Maine to Washington as well as the southern portion of the Canadian provinces.

Bobolinks winter south of the equator in South America, The wintering habitat is the grasslands known as the pampas in southwestern Brazil and Argentina. Each year, a Bobolink makes a round-trip of 12,000 miles. We know of one banded female that lived to be nine years old. Presuming she made the trip every year, she traveled the equivalent of circling the globe at the equator four times.

Orientation and navigation have been fairly well studied for Bobolinks. Researchers have found that the primary cue for navigation in Bobolinks is the earth’s magnetic field.

Bobolinks arrive in central Maine by the second week of May. Males are conspicuous as they stake out territories and await the arrival of the females. When a female passes overhead, a male will perform an aerial song display to attract the female’s attention. If the female lands, the male will go through a series of courtship behaviors to court the female. These behaviors include a low circle flight on stiffly held wings and an abrupt drop to a low perch or the ground. When the male drops, he holds his wings in a shallow V (like the gliding silhouette of a Turkey Vulture) and gives a few buzzy notes, dangling his legs on the descent. When he touches the ground, he may hold his wings in the shallow V for several seconds.

A female is slow to choose a mate. A male may have to perform this elaborate courtship sequence five times a minute for a half-hour or more. A pair bond is formed when the female leads the male on a long chase, flying for up to six minutes.

Bobolinks are examples of polygynous birds; a male may have more than one female on his territory. The frequency of polygyny seems to be related to habitat quality. In high quality habitats where food is easier to find, a male frequently has two or more mates. In lower quality habitats, single females are typically found with the males. In Wisconsin, over half a population of males had at least two mates and one male had four mates. On the other hand in New York, fewer than 15% of the males had more than one mate.

Nests are always made on the ground in dense vegetation. The nest is usually located at the base of herbaceous, non-grassy vegetation like goldenrods or clover. The female chooses the nest location and builds the nest in one or two days.

A female typically lays five eggs although as many as seven can be laid by some females. Both the female and the male feed the young. Even a male with multiple mates participates in feeding although most assistance may be given to his primary mate.

[First published on June 14, 2008]

For the Birds: Red-eyed and Philadelphia Vireos

Red-eyed Vireos have returned from their South American wintering grounds. One of the most common songbirds in North America, the Red-eyed Vireo’s song is a distinctive but somewhat plain series of two- and three-note phrases. Some authors render the song in human terms as “here-I-am, where-are-you, over-here, in-the-tree” that will resonate with anyone who has heard a Red-eyed Vireo singing. Red-eyed Vireos are energetic songsters, singing throughout most of day with rates as high as 85 phrases/minute.

The Philadelphia Vireo occurs in northern New England and much of southern Canada. This vireo closely resembles the Red-eyed Vireo but has a less distinct line above the eye and has a yellow wash on the underparts. The Philadelphia Vireo is also smaller, averaging 12 grams in weight to the 17-gram weight of a typical Red-eyed Vireo. Both species can be found in the same deciduous woodlands.

Most nesting male songbirds defend their territories against other males of its species. If you play a recording of a Yellow Warbler in the territory of a Yellow Warbler, the male will quickly come toward the source of the sound and look to chase off the unwelcome intruder. However, playing a tape of the song of a Black-throated Blue Warbler or a Chestnut-sided Warbler will produce no reaction by the Yellow Warbler. In general, male songbirds defend their territories against members of their own species but not against members of other species.

The two vireo species above provide an exception to this rule. Red-eyed Vireos and Philadelphia Vireos defend their territories against their own species and against the other species. In other words, both vireos show interspecific (between-species) and intraspecific (within-species) territoriality.

The song of the Philadelphia Vireo is very similar to the singsong phrases of the Red-eyed Vireo song. Even highly experienced birders pass off singing Philadelphia Vireos as the more common Red-eyed Vireos. The reason for the similarity will soon be apparent.

In northern New England forests, insect prey may become quite hard to find during the breeding season. Because both vireos eat largely the same species of insects, there is an advantage for a territorial vireo to keep a member of its own species and members of the other vireo species away from its food sources.

In most cases, the vireos avoid direct confrontations over the boundaries of a territory. Instead, a territorial bird proclaims his ownership of a territory by singing from perches throughout his territory. Similarly adjacent territory owners sing throughout their territory. The neighboring birds recognize unseen but real boundaries, avoiding physical interactions.

In the case of actual fighting between the two vireo species, the smaller Philadelphia Vireo usually comes out on the short end. One observed fight involved three minutes of violent contact, wing beating and pecking, with the larger Red-eyed Vireo winning the battle.

The problem the Philadelphia Vireo has is how to maintain exclusive ownership of a territory, defending against a larger and stronger Red-eyed Vireos that may be trying to expand his territory to find scarce food. Philadelphia Vireos have solved the problem by becoming a social mimic. These birds mimic the song of the Red-eyed Vireo.

Play-back experiments have shown that Red-eyed Vireos cannot tell the difference between a Red-eyed Vireo song and a Philadelphia song. No wonder birders have trouble telling the two species apart by song! On the other hand, Philadelphia Vireos can distinguish between a Philadelphia Vireo song and a Red-eyed Vireo song.

Red-eyed Vireos assume that a neighboring Philadelphia Vireo is a Red-eyed Vireo and accept it grudgingly as a neighbor. If the Red-eyed Vireo only knew its neighbor was the meek Philadelphia Vireo, the latter could be evicted. Philadelphia Vireos mimic the song of the Red-eyed Vireo to level the playing field; it’s a case of brains over brawn.

Computer analysis of the songs of these two species reveals that Red-eyed Vireos never sing the same phrase twice in succession. Philadelphia Vireos, occurring in the absence of Red-eyed Vireos, may sing the same phrase twice before a new song is sung. However, in the presence of a Red-eyed Vireo, the Philadelphia Vireo never gives identical consecutive phrases, indicating that the species actively mimics the Red-eyed Vireos. Pretty clever birds!

[First published on May 31, 2008]

For the Birds: Spring Migration; Hog Island Camps; Maine Butterfly Survey

Migration

The marvelous spectacle of spring migration is here. Soon, the Black-billed Cuckoos, Blackpoll Warblers and Yellow-bellied Flycatchers will arrive in good numbers. The appearance of these late-arriving species signals the end of the spring migration.

Today, I want to consider why birds migrate. Each spring, several billion birds stream into North America from Caribbean islands, Central America and South America where they have spent the winter. Why do so many birds undertake these arduous migrations? The benefits must exceed the costs. What are the benefits migrating breeders receive?

To answer these questions, we have to understand both why birds migrate north to breed and why they leave their northern breeding grounds to return to tropical or subtropical areas. The explanations stem from the fact that the earth is tilted on its axis.

Let’s start with equatorial regions. Despite the tilt of the earth, equatorial regions have twelve hours of daylight each day. As one proceeds north, the length of day and night becomes unequal. When the northern hemisphere is tilted toward the sun, we have summer and temperate regions have day lengths that increase as one moves toward the North Pole.

The long summer days mean that plants can photosynthesize for sixteen hours or more each day, longer than plants at the equator. So during the northern summer, plant production spikes, providing food for insects that in turn provide food for birds. During the northern summer, food availability in temperate regions may exceed that of tropical regions. Birds migrate to the north to take advantage of the summer flush of food. The further north one goes, the longer the day length and bigger the spike in plant growth.

All good things must come to an end and the movement of the earth around the sun ultimately leads us to autumn with ever-shortening day lengths. Plant production decreases as light becomes less available and temperatures fall. Insect abundance declines. Many migratory breeding birds depend on insects so must leave for southerly areas to avoid starvation.

The cost of migration is more than paid for by the abundance of food in the summer at higher northern latitudes. But not all tropical birds migrate. What are the costs and benefits of staying put? The benefit is the energy saved by not migrating. The cost is that competition for food is very high in the tropics and destruction of nests by predators is very high. Tropical birds typically have multiple nests each season with a modest number of eggs, most of which are doomed to failure.

Hog Island Audubon Center

A landmark of environmental education since 1936, Hog Island Audubon Center’s residential programs educate, adults, children and families about coastal wildlife in Maine. The sessions are based on a 330-acre island in midcoast Maine’s Muscongus Bay. The sessions are led by some of the world’s most respected naturalists and environmental educators. You can find more information about their offerings at: http://www.maineaudubon.org/explore/camp/hi_overview.shtml

I want to call your attention to a new session called Family Birding Adventures geared for families with kids between the ages of six and thirteen. One of the highlights of the week will be a trip to Eastern Egg Rock to see nesting Atlantic Puffins. The session will be led by Jason and Laura Guerard, naturalists from the Cape May Bird Observatory. Jason and Laura met on Hog Island and Jason later proposed to her there. For more information, visit the website above or call (888) 325-5261 ext. 215.

Maine Butterfly Survey

The Maine Butterfly Survey, a five-year project to map the distribution and abundance of the butterflies and skippers of Maine, has begun its second year. This project relies heavily on volunteers. The first year yielded over 1500 records (specimens or photographs). Volunteers established four new state records and a large number of county records in the first year of the project. Two volunteers photographed Pipevine Swallowtails in late September 2007. These two records represent the first records of the species since 1907. You can see all of the 2007 records at the MBS website: http://mbs.umf.maine.edu/

As the Volunteer Coordinator for the project, I would like to encourage you to participate in the project. All participants are asked to attend a training workshop. Each workshop participant will be given equipment, a handbook and voucher forms. The last 2008 workshop will be held on Saturday, June 21 at Colby College in Waterville. The workshop will begin at 9:30 and conclude around 2:30. Lunch will be provided. If you are interesting in attending the workshop, please email me to reserve a spot. Enrollment is limited.

[originally published on May 17, 2008]

For the Birds: New Bird Books for Beginning Birders

The spring migration is perhaps the most exciting time of year for North American birders. After a long Maine winter, the sounds of the first Eastern Phoebes and Red-winged Blackbirds and the sights of colorful warblers hold the promise of a glorious Maine summer. There is nothing like a spring birding excursion to hook a novice on birding.

Two books geared for beginner birders have recently appeared. One is meant for adults and one for kids. I’ll review the two books in today’s column. Perhaps, you have a friend or family member who might appreciate a copy of one of these books.

Finding Your Wings, written by Burton Guttman, is a different kind of book in the Peterson Field Guide series. This book is really a workbook designed to help a person new to birding to learn how to really look at birds how to identify them. Along the way, a diligent user of Finding Your Wings will learn much about bird behavior, classification and the etiquette of birding.

This workbook is designed to be used in conjunction with a field guide of North American birds. The workbook is specifically written to accompany either Roger Tory Peterson’s A Field Guide to Birds of Eastern and Central North America or A Field Guide to Western Birds. However, any North America field guide can be used in conjunction with Finding Your Wings.

The workbook begins with basic principles and skills of birding, continuing with an overview of the major bird orders and then more detailed descriptions of the topography of birds. Other chapters deal with molting, identifying birds in flight and learning to identify birds by their songs or calls. The book concludes with six chapters on groups of birds that pose particularly challenging identification problems. Bird groups covered include hawks, shorebirds, gulls and sparrows.

The content of the book sounds like standard fare for a birding book. The unusual, and I think innovative, aspect of Finding Your Wings is the activities and quizzes that fill the book. Doing the activities and taking the quizzes is key to getting the most out of the workbook.

Four kinds of activities are used in the workbook. Indoor Exercises require the reader to refer to a picture provided or pictures in a field guide to answer questions. A reader might be asked to look at the account for a Clay-colored Sparrow and then write down a description of the head of the bird. In so doing, the reader would learn the names of distinctive markings like the supercilium, auricular stripe and malar stripe. Answers are provided at the end of the book.

Field Exercises require the beginning birder to make observations in the field, such as determining the wing beat rate of different birds. Quizzes allow readers to test their knowledge gained from the Indoor and Field Exercises. Finally, several Games are described that are great for social learning.

The second book, also in the Peterson Field Guide series, is called The Young Birder’s Guide to Birds of Eastern North America by Bill Thompson III. This field guide was developed with the advice of Thompson’s 11-year old daughter and other members of her fifth-grade class. The field guide is designed to be used by kids on their own.

The field guide begins with the usual generic information on birding: binoculars, bird morphology, field guides, birding clothing. One section seeks to convince youngsters that birding is cool and that they should not be self-conscious about going birding.

The bulk of the book is the description of 200 species of common birds found in eastern North America. A page is devoted to each species. Of course, the amount of text one expects in a typical field guide is reduced in this “for kids” guide. Each page has one or two color photographs and a range map, covering all of North America. A line drawing is provided for each species, showing some interesting behavior. For instance, the drawing of the Hermit Thrush shows the distinctive behavior of these birds in raising the tail rapidly and then slowly letting it fall to a normal position. Each species account has five text sections. Look For provides brief information on the characteristics used to identify the species and Listen For gives a description of the vocalizations. The Remember section is used to emphasize distinctive identification features or behaviors. Find It describes the habitat of each species. Finally, a WOW! section describes a neat feature of a species such as the courtship flight of the Scissor-tailed Flycatcher or 1800-mile non-stop migratory flight of Brant.

[Originally published on May 3, 2008]