July 2009

Review of Ghost Bird

By in Movie Reviews

Today’s column is a review of a movie that is premiering now in the United States as part of the Maine International Film Festival in Waterville. The movie is called Ghost Bird and details the controversy over the recent claims that the Ivory-billed Woodpecker still lives. The film was produced and directed by Scott Crocker, a Bowdoin College graduate.

April 28, 2005 was a great day for birders. The Cornell Laboratory of Ornithology held a press conference to announce the finding of an Ivory-billed Woodpecker in eastern Arkansas. Prior to this sighting, this largest of North American woodpeckers was last documented by photograph in 1941.

Over the years, Sightings of Ivory-billed Woodpeckers, some more credible than others, were reported regularly from Louisiana, Florida and more recently Arkansas. None of these observers managed to get a photograph or movie of the birds.

The chance of confusing a Pileated Woodpecker for an Ivory-billed Woodpecker is high, particularly if the sighting is brief. Nevertheless, a spate of sightings from the Cache River in eastern Arkansas was convincing enough for the Cornell Laboratory of Ornithology to mount a large expedition there in the fall of 2004.

Their best evidence for an Ivory-billed Woodpecker was a brief videotape, taken by David Luneau, a professor electronics at the University of Arkansas-Little Rock. Luneau kept his videocamera recording on the gunwale of his canoe and by luck captured a brief flight of a large woodpecker.

The Cornell team also had a series of automated recording devices throughout the Cache River swamp. Recordings were captured of the “kent” calls that Ivory-bills give as well as the double-tap knocks the birds use to communicate.

The elation of a number of ornithologists and birders flagged upon examination of the data. I think the words of Carl Sagan, the eminent astronomer and stalwart of the skeptic movement in the United States, are appropriate in this case: “Extraordinary claims require extraordinary evidence.”

A close examination of the Luneau video convinced some ornithologists that the bird was actually a Pileated Woodpecker rather than an Ivory-bill. The acoustic evidence was questioned because Blue Jays give a “kent” call, even in areas where Ivory-billed Woodpeckers never occurred. Pileated Woodpeckers will give double tap signals.

Ghost Bird explores the impact of the claimed Ivory-billed sightings on the town of Brinkley, Arkansas. According to one citizen, only one person in Brinkley even knew what an Ivory-billed Woodpecker was before the 2005 announcement. At least six businesses have sprung up in Brinkley, all capitalizing on the Ivory-billed Woodpecker. Where else can you get a woodpecker haircut for $25?

Crocker reviews the data used to support the claim of living Ivory-billed Woodpeckers, including multiple showings of the Luneau video. We see lots of footage of the Cache River swamps.

Two skeptical scientists are extensively interviewed. Dr. Jerry Jackson of the Florida Gulf Coast University is the eminent living authority on Ivory-billed Woodpeckers and has conducted searches for these birds. Dr. Rick Prum of Yale University provides his perspective as well.

David Sibley, the author of the best-selling field guide on North American birds, went to Arkansas after the initial announcement. He noted that earlier workers found that Ivory-billed Woodpeckers preferred to forage on Nuttall oaks. In eight days of dawn to dusk field work, Sibley found no evidence of woodpecker excavations or bark stripping on these oaks.

Crocker does a nice job of documenting the history of the decline of the Ivory-billed Woodpecker. Jim Tanner studied Ivory-billed Woodpeckers in the Singer Tract of Louisiana between 1937 and 1941 for his doctoral research at Cornell University. He and his wife Nancy saw and photographed Ivory-bills there for the last time in 1941. Nancy Tanner is still living, and, in the film, offered a fascinating glimpse into history.

The Cornell Laboratory of Ornithology continues to maintain that their evidence is sufficient to demonstrate that the Ivory-billed Woodpecker still survives. Unfortunately, the Lab would not allow any of their employees to be interviewed for this documentary.

The initial excitement over the re-discovery of the Ivory-billed Woodpecker led to changes in funding for conservation. The U. S. Fish and Wildlife Service provided an initial $10 million dollars to help conserve the Ivory-bill. These funds had to be provided by taking money from other projects designated for the protection of other endangered species. An additional $27 million was provided in 2007. A number of conservation biologists have questioned this re-allocation of limited funds.

[Originally published on July 7, 2009]

By in Uncategorized

For the Birds – Ruby-throated Hummingbird

The Ruby-throated Hummingbird has to be one of most eagerly anticipated birds among our migratory breeding birds. The acrobatic flight of hummingbirds, their iridescent colors and their small size endear hummingbirds to many people.

The hummingbird family is one of the largest of the birds with 328 recognized species. Hummingbirds are birds of the New World with the majority found in the tropics of Central and South America. In North America, only about 20 species occur regularly and only one, the Ruby-throated Hummingbird, breeds in eastern North America.

The Ruby-throated Hummingbird is one of the smaller hummingbirds. A typical one weighs a little more than 3 grams, about the weight of a penny. The smallest hummingbirds are the Bee Hummingbird from Cuba and the Reddish Hermit from Brazil and Guyana, which weigh only 2 grams. On the larger side, the South America sicklebills and the Sword-billed Hummingbird weigh 12-14 grams, a little more than a chickadee. The Sword-billed Hummingbird has the longest bill of any hummingbird at an astonishing five inches! The largest of all hummingbirds is the appropriately named Giant Hummingbird, which tops the scales at 21 g.

Ruby-throated Hummingbirds spend the winter between southern Mexico and western Panama. In migration, some individuals undertake a non-stop migration of 1000 miles across the Gulf of Mexico. The birds have to put on extra fat to fuel this expensive flight. Feeding on nectar and insects, a Ruby-throated Hummingbird will double its weight before it departs across the Gulf of Mexico.

Recent observations indicate that some Ruby-throated Hummingbirds prefer to migrate along the eastern coast of Mexico to reach the United States, a longer but perhaps less demanding migration.

To increase our understanding of Ruby-throated Hummingbird migration, an international volunteer project has begun called Operation RubyThroat. The project is designed primarily for K-12 teachers and their students in the countries of Central America and North America. You can find information on Operation RubyThroat at their web site: http://www.rubythroat.org/

Once in the United States, Ruby-throated Hummingbirds disperse widely. The breeding range extends from eastern Texas along the Gulf Coast to Florida and north in the east to Nova Scotia, New Brunswick and Labrador and west to Minnesota, then spreading westward in the Canadian prairie provinces, stopping just shy of British Columbia. Their breeding range is the largest of any hummingbird breeding in North America.

Hummingbirds are specialized to feed on nectar. A number of plants and hummingbirds have evolved mutualistic relationships. These plants produce sugar-rich nectar, which attracts hummingbirds. As the hummingbirds feed on the flower, pollen attaches to the hummingbird’s head and bill. When the hummingbird visits another flower, some of the pollen it is carried is transferred to the female part of the flower and fertilization is assured. Some plants therefore “pay” hummingbirds in nectar in return for pollination services.

One species that seems particularly adapted for pollination by Ruby-throated Hummingbirds is the trumpet creeper, a woodland vine. Studies have shown that Ruby-throated Hummingbirds deposited ten times as much pollen as other pollinators (bumblebees and honeybees).

Most long, tubular flowers are attractive to hummingbirds. Bee balm is particularly recommended. Of course, a hummingbird feeder is an easy way to attract hummingbirds as well. Choose a feeder with a wide mouth to make cleaning easy. You can buy so-called hummingbird food to dissolve in water. On the other hand, you can save some money and make your own. Just mix four parts of water to one part of table sugar and bring to a boil. When the sugar dissolves, cool and then fill your feeder. You can store the excess in your refrigerator for a couple of weeks.

Keep an eye on your feeder. Particularly in warmer weather, fungi grow in the feeder. You should wash your feeders regularly; easy to clean feeders will make this task a quick one.

Nest building in Ruby-throated Hummingbirds is done only by the female and takes between 6 and 9 days. The base of the nest is made of thistle and dandelion down. The base is saddled along a branch and is fastened with spider webs. The female stamps down the plant down to make a firm floor. White plant down and bud scales make up the side of the nest. The female uses a figure-8 motion to lace the plant material together. The outside of the nest is adorned with lichens, making a well-camouflaged nest.

Two eggs are laid and hatch 12-14 days later. The female does all the feeding of the young. The young are feed nectar at first with supplements of insects as they grow larger. The young fledge 18-20 days after hatching.

[Originally published on May 1, 2009]

By in Uncategorized

For the Birds – Earth Day

Wednesday is Earth Day. In today’s column, I will review a couple of major studies that have examined the impact of humans on bird populations. Both of these studies are based on citizen-science projects. Many of you will have contributed to the databases.

National Audubon scientists recently released the results of their study of the past 40 years of Audubon’s Christmas Bird Counts. The scientists analyzed the population changes of 305 bird species that occur widely in the winter in North America.

Of this total, 177 species have shifted their range northward. This northward shift is consistent with global warming. The average shift northward over the past 40 years is 35 miles for all 305 species, including those that do not show northward movements.

Of course, averages can mask more dramatic changes for some species. Boreal Chickadee, Purple Finch and Pine Siskin have retreated dramatically into Canada. The center of the ranges of these species has moved 211, 313 and 246 miles northward since 1968.

Species that rely on open water show pronounced shifts in their ranges as well. American Black Duck, Ring-necked Duck and Red-breasted Merganser show a northward shift of their ranges by 150 to 250 miles. These birds are able to winter further north because more open water is available in northern states and Canada.

Consider the increase in average number of the following species in Maine between 1968 and 2008: Mourning Dove (22.4 times increase), Red-bellied Woodpecker (5.5 times), Carolina Wren (5.0 times), Hermit Thrush (9.8 times) and White-throated Sparrow (2.8 times).

What’s the big deal you may ask? Don’t the birds just shift their ranges northward with no overall change in abundance?

Actually, this expansion of ranges toward the poles should give great concern. Consider a typical map of the world using a Mercator projection. On such a map, Greenland looks to be about the same size as Africa. In fact, Africa has 14 times the area of Greenland. A Mercator map distorts the area of land near the poles.

Instead, think about a globe of the earth with lines of longitude on it. Follow two adjacent lines of longitude from the equator to the North Pole, noting how the lines get closer and closer as you move from the equator.

By forcing birds northward, we are funneling them into smaller and smaller areas. Sooner or later, the birds will run out of habitat.

A second major report, The State of the Birds: United States of America, was recently published by a partnership of a dozen government and non-government organizations, including the Cornell Lab of Ornithology, the National Audubon Society and the U.S. Fish and Wildlife Service.

The report used three sources of data on bird population changes: the Christmas Bird Count, the Breeding Bird Survey and the Waterfowl Breeding Population and Habitat Survey.

The report is a balanced report, noting species that are declining and increasing. Environmental threats are thoroughly discussed and reasons for hope are covered as well. The report is mainly organized by general habitat, such as grasslands, arid lands, forests and wetlands.

Let’s consider forests as a representative habitat. The report tells us that North American forests harbor more than 300 species of breeding birds. Although some species are doing well, fully a third of these bird species are declining. The threats are familiar ones: unplanned, urban sprawl; unsustainable logging practices; intense wildfires caused by decades of fire suppression; impact of tree insects and tree diseases driven in part by climate change.

Examining eastern forests, the authors found that 25 species found exclusively in forests have declined in abundance by 25% in the past 40 years. Species of particular concern from eastern forests are Eastern Wood-Pewee, Wood Thrush, Blackpoll Warbler, Cape May Warbler, Pine Siskin, Evening Grosbeak and White-winged Crossbill.

To halt the declines, the authors suggest better planning of human development, green logging practices and doing all we can to slow the rate of carbon dioxide emissions to at least slow down the rate of global warming.

Space does not permit consideration of all the habitats covered in this thoughtful report. Copies are available for download at http://www.stateofthebirds.org/ I encourage you to read the document ; it will be well worth your time.

Finally, here are some suggestions for ways we can combat climate change. Visit http://www.birdsandclimate.org to sign the petition urging lawmakers to take steps to slow global warming. Determine your energy profile and carbon footprint. A number of carbon footprint calculators are available on-line. Become a locavore; buy locally grown produce and other food as often as you can. Plant more trees. Happy Earth Day!

[Originally published on April 18, 2009]

Bird Nests

By in Reproduction

A characteristic feature of all bird species is a nest in which eggs are laid. Nests range from small depressions in the forest floor to massive structures weighing more than a ton. In today’s column, I will provide an overview of the diversity of bird nests.

The simplest nests are scrapes on the forest floor, fields or beaches. The nest of aKilldeer is a good local example. The female lays four eggs in a nest scrape just big enough to contain the eggs. As you would expect, the eggs are well camouflaged. In the woods, American Woodcocks and Whip-poor-wills create nest scrapes for their eggs. For most species that create nest scrapes, little effort is made to line the nests with soft material. Birds that make nest scrapes spend very little energy in making a place to lay eggs and raise their young.

Most birds construct a bowl-shaped nest just large enough to fit an adult’s body. Let’s use an American Robin nest as a typical example of a bowl-shaped nest. Robins are not great architects but still have a remarkably complex nest. The outer part of the nest is formed of twigs, coarse grass and sometimes pieces of cloth, string or other human-made products. This outer layer gives the nest strength. Within this outer layer, robins place a smooth layer of mud. Finally, a layer of fine grasses is laid down to surround the eggs and aid in insulation. Once the outer part of the nest is built, the female sits in the middle of the nest for the rest of the construction. A snug fit is therefore guaranteed for the incubating mother. The nest is usually in a tree between three and 25 feet high.

Other species use specific materials for the inner lining of their nests. Palm Warblers, a ground-nesting species in bogs, often place Ruffed Grouse feathers in their nests. Tree Swallows line their nests with feathers, particularly white ones. Ruby-throated Hummingbirds create tiny nests to hold their two eggs. The nest is made of down and small pieces of plant material bound together with spider webs. The outer part of the bowl is covered with bits of lichens to aid camouflage. Black-capped Chickadees make their nests in a tree cavity. The outer part of the nest is made of moss and the inner part of spider webs, soft grasses and plant down.

Waterbirds typically create bowl-shaped nests on the margins of lakes or ponds or even on floating vegetation. In most cases, the outer layer of the nest is made primarily of vegetation. If water levels rise, waterbirds will quickly add additional vegetation to keep the inner part of the nest dry. The inner lining is made in part of down feathers that the female pulls from her breast. These down feathers create a wonderfully warm place for the eggs. You take advantage of the excellent insulating qualities of duck down if you own a down coat or sleeping bag.

The largest nests in Maine are made by birds of prey. An Osprey nest may be five feet across. The outer portion is made of sticks and miscellaneous debris. The inner lining is made of smaller twigs, grasses and other soft material. Both the male and female participate in nest building. The male tends to bring material to the nest site and the female incorporates the material into the nest.

The largest nests in Maine are made by Bald Eagles. Some nests may be eight feet in diameter and 12 feet high. The weight may exceed one ton! Like Ospreys, Bald Eagles use the same nests year after year, adding material to the nest each spring. Great Horned Owls will readily adopt an abandoned Osprey or eagle nest.

Some of our birds place domes over the tops of their nests. Such nests are characteristic of many of our wrens. The family name for the wrens, the Troglodytidae, comes from the Greek for cave dweller, reflecting the shape of the nest. One of our most common warblers, the Ovenbird, builds a domed nest on the forest floor. The shape of the nest suggests a Dutch oven. By the way, there is an unrelated group of tropical birds called ovenbirds that create clay-shaped, domed nests which look just like a brick oven.

Distinctive nests are made by Baltimore Orioles. Their nests are made of grasses, vines, and hair. The nest is a deep pouch, bound to the forks of a branch at the rim. Two sprites of the Maine woods, the Ruby-crowned Kinglet and Golden-crowned Kinglet also create hanging nests that are much smaller and more difficult to see than oriole nests.

[Originally published on June 27, 2009]

Clutch Size Variation

By in Reproduction

Most of the birds in Maine are in the process of nesting now. Among the different bird species, there is great variation in many facets of reproduction. For instance, whether one or both parents brood, the type and location of the nest, the size of the eggs.

One striking feature that varies widely among different species is clutch size, the number of eggs laid in a single nesting attempt. Some birds (albatrosses, petrels, some penguins and some terns) have a clutch size of only one. Hummingbirds and doves always have clutch sizes of two. At the other extreme, some ducks and geese, pheasants and rails may have clutch sizes as high as 20 eggs. Our songbirds have clutch sizes varying between two and 12, depending on species.

Why is there such striking variation in clutch size among different species? This question has been the basis of a great deal of research. In this column, I will briefly introduce some of the findings of this body of research.

To begin, we must realize that reproduction is a taxing experience for birds. Birds that undertake a particularly heavy reproductive effort in one year may reduce their chances of surviving to reproduce the next year. Birds have to make a trade-off between producing very large clutches in a short life and moderate-sized clutches over a longer life.

David Lack, a British ornithologist, was one of the first scientists to rigorously study clutch size variation in birds. He came to the conclusion that a female bird should lay the number of eggs that will produce the most fledged, independent offspring.

Let’s consider Lack’s conclusion for three females which lay three, five and seven eggs, respectively. The female and her mate with only three eggs will probably succeed in fledging three young. The pair with five eggs will have to work harder but still might lose only one chick, fledging four young. The pair with seven eggs have bitten off more than they can chew. The demands of the seven hungry chicks are too much for the parents and perhaps four of the seven chicks will die from starvation. So, what is the best clutch size to have for this species? A clutch size of five – a trade-off between ambition and caution. The pair with only three eggs is not ambitious enough; the pair with seven eggs is too ambitious.

Ornithologists have tested Lack’s prediction by altering the clutch sizes of birds. One species that has been studied intensively is the Tree Swallow. These birds frequently nest in nestboxes at high densities, making it easy for an ornithologist to monitor large numbers of nests. Tree Swallows usually lay five eggs. Experiments are done by removing one or two eggs from some nests and placing them in other nests. After the egg-switching, some nests have three, four, five, six and seven eggs. The results largely confirm Lack’s prediction. A clutch size of five is the most productive clutch.

In other species, that have been examined, birds lay one less than the most productive clutch. Scientists believe that these birds are cutting back on their reproductive effort in a single year to increase their chances of having a long life.

Clutch size within a species often shows striking variation with latitude. The typical pattern is that tropical members of a species have lower clutch sizes than members of the same species that live in the temperate zone. For instance, female Northern Flickers that live in the tropics only lay clutches of three or four eggs while flickers in the northern U. S. A. and Canada may have ten or more eggs.

One possible explanation for this variation is the number of predators. The tropics have many more predators that are threats to eggs and nestlings, including snakes, other birds and various mammals. The chances of a nest being found and destroyed by a predator in the tropics is very high. In the temperate zone, the number of predators is much reduced. Many temperate nests are never discovered by predators.

Ornithologists therefore argue that tropical birds should not invest heavily in a single clutch because it is likely to be lost. It’s not prudent to make a large investment in a risky environment. It is much better to have a low clutch size, allowing the parents to live a longer life. With luck, one of the many clutches a female will lay over her lifetime will escape the predators. On the other hand, a temperate bird does not have the same high risk from predators so can lay a bigger clutch. It’s OK to make a large investment if there is little chance of losing it all.

[First published June 27, 2009]