The spring bird migration is coming to an end. The last species to arrive are usually Black-billed Cuckoos, Yellow-bellied Flycatchers, Blackpoll Warblers, Salt Marsh Sparrows and Nelson’s Sparrows.
We all marvel at the ability of birds to fly thousands of miles to nest and then return to their wintering area each year. These herculean feats become even more astounding when we consider the physiology of birds.
Like mammals, birds are endotherms; they maintain a constant body temperature in the face of changing environmental temperature. All endotherms have a minimum idling speed, called the Basal Metabolic Rate (or BMR, for short). You are likely at your BMR as you read this column.
The BMR varies inversely with size. A hummingbird or a mouse has a relatively high BMR while a hippopotamus or ostrich has a lower BMR. But here’s the kicker, a bird has a higher BMR than a mammal of the same size. The fire of life burns brightest in the birds.
Maintaining the BMR requires energy to produce heat. Those costs become more severe at colder temperatures.
Consider what happens when you push your body to its limits, like running a 400-meter dash. You breathe heavily, your heart rate increases and your metabolic rate rises. For humans, maximum performance results in about a doubling of your BMR. Other mammals may be able to triple their BMR.
Birds outdo mammals by a long shot. The demands of powered flight are huge. A migrating bird increases its metabolism to 8 to 10 times its BMR! That is one blazing furnace.
The ideal fuel to keep the metabolism high should pack the most energy per unit weight. Fats are the fuel of choice for birds. Breaking down a gram of fat produces about twice the energy of a gram of carbohydrate or gram or protein. The burning of fats also produces water as a breakdown product, which can be used by a migrating bird. This metabolic water is a necessity for birds migrating over the Gulf of Mexico or other saline bodies of water.
How much fat should a bird carry on a migratory leg? Obviously, a bird needs enough to fuel its flight, particularly if the journey is over water. But, carrying extra weight means that the bird has to work even harder to fly. So, there is an optimal fuel load that ensures completion of the flight but leaves little fuel in the tank.
How well are birds able to find the optimal fat load? Semipalmated Sandpipers provide a nice example. During the fall migration, most Semipalmated Sandpipers depart from the Bay of Fundy, flying over the ocean to reach Suriname in northeastern South America. This flight requires about four days of sustained flight.
Before departing, the Semipalmated Sandpipers gluttonously feed on the abundant crustaceans in the expansive intertidal Fundy mudflats. Over a period of two weeks, a bird doubles its mass from 20 grams to 40 grams or more!
Shorebird biologists in Suriname wait for the arrivals of the sandpipers. Some are captured and their mass is recorded. Most are at or close to their lean weight of 20 grams. The birds are cutting it pretty close.
Ovenbirds provide a nice example of fat dynamics on a shorter time scale. Like most songbirds, Ovenbirds start a migratory leg in the early evening. Some banding stations keep their nets open during the night, capturing migrating songbirds as they land. The data indicate that Ovenbirds captured around midnight, after a short flight, weighed about two grams more than Ovenbirds captured around dawn after a longer flight. With a lean mass of around 18 grams, some Ovenbirds therefore burn 10% of their body weight in a single night’s flight!
We have some good evidence that those lighter birds linger longer than fatter birds before undertaking the next leg of a migration.
Spring migration is in full swing. Excitement among birders is at fever pitch. Each day has the potential to bring in a new species. Try to get out each morning for the next week or so to experience the spectacle of the spring migration. Birds will be in full breeding plumage and song will be in the air.
When weather conditions are right, hordes of migrating birds may descend shortly before dawn. A fall-out occurs and birds seem to be dripping from the trees and bushes.
You can literally see a fall-out occurring through the use of radar. Bird images can be detected on the freely available radar plots. See this video: https://vimeo.com/2020985
Using radar images, you can see a big flight of birds taking off in the early evening and then be on the ground to greet them the next morning.
The spring migration is the time when some competitive birders will undertake a Big Day. A team of birders seek to identify as many species of birds as possible in a 24-hour period in a state, county or other area.
A successful Big Day has to be timed around migration. To understand why, it is convenient to sort our migrants into three categories.
Wintering migrants are birds that winter here but depart in the spring for more northerly breeding grounds. American Tree Sparrows, Snow Buntings and Lapland Longspurs are good examples.
Then we have the breeding migrants. These are the species that winter to our south but return to Maine to breed.
Some of these breeders are short-distance migrants like American Woodcocks, Red-winged Blackbirds and Yellow-rumped Warblers that may overwinter as far north as the mid-Atlantic states. None leave North America for the winter.
Other breeding species leave North America to winter in the West Indies, Central America and South America. We refer to these birds as Neotropical migrants or long-distance migrants. Familiar examples are Broad-winged Hawks, Ruby-throated Hummingbirds, Cliff Swallows, Red-eyed Vireos and most of our warblers.
The third category of migrants are the passage migrants. These birds winter to our south and breed to the north of us. We see them only fleetingly as they migrate through Maine en route to nesting or wintering territories. The White-crowned Sparrow is one such passage migrant from the Maine perspective. These handsome sparrows winter broadly throughout the southern two-thirds of the United States. They pass through Maine on their way to northern Canada where they breed. We get to see them again in the fall as they head for points south to winter. A number of shorebirds are passage migrants as well.
The passage migrants are the species that make or break a successful Big Day. The day has to be chosen to try to maximize the number of passage migrants that can be found to augment the expected resident species, migratory breeding species and lingering winter residents. For Maine, that sweet spot seems to be the third week of May.
The northerly and southerly paths of passage migrants may vary. The Semipalmated Sandpiper is a case in point, breeding on the North American arctic tundra and wintering in the region of the Amazon delta in South America.
Most Semipalmated Sandpipers migrate north through the center of North America with a major stop-over site in Cheyenne Bottoms, Kansas. Relatively few migrate along the Atlantic Seaboard.
After breeding, most Semipalmated Sandpipers work their way to the Bay of Fundy. We see many more of these sandpipers in the fall in Maine.
Why the difference? As is often the case with birds, food drives behaviors. The small crustaceans that sandpipers feed on in the fall in the Bay of Fundy are at low abundance in the spring but rebound over the course of the summer. Semipalmated Sandpipers have to find a more reliable source of food in the spring migration and the marsh insects of middle America fit the bill.
The recent discovery of two rare birds in Maine and the March for Science on April 22 provide a way to think about the power of science as a way of knowing.
On Earth Day, tens of thousands of people gathered in Washington, D.C. to promote the strength of science in improving our world and in advancing our knowledge. Many satellite Marches for Science, including several in Maine, were held for supporters who could not make the trek to our nation’s capital.
Scientific thinking unfortunately has little traction in our government. Of the 541 members of the U.S. Congress, only six have a degree in science or math. We have never elected a scientist as President although Grant, Hoover, Eisenhower and Carter did have engineering degrees.
Yet, the scientific approach has much to offer. First, science is evidence-based. As scientists, we must always be open to alternative explanations as we continue to learn. In other words, science is provisional. We must go where the evidence takes us.
Second, the scientific method embodies the notion of skepticism. We always need to question our interpretations. Although the distinction may seem subtle, scientists seek to disprove hypotheses, not confirm or “prove” them.
To explain a pattern, a scientist will come up with one or more hypotheses that can explain the pattern. Then, she will design an experiment to try to knock that explanation down. If her experiment is consistent with her hypotheses, she can design a different experiment to further test it. Colleagues may repeat her experiment. If the hypothesis stands up to these tests, we treat it as provisionally true. If the experiments fail to support the hypothesis, we reject it and move on to test other possible explanations. Scientists try to disprove.
The beauty of this approach is that it removes one’s ego from the process. We all have great ideas. If we try to prove them, we run the risk of cherry-picking information to find information that is supportive and ignore, perhaps subconsciously, information that would disprove one’s great idea.
Psychologists call this effect confirmation bias. We selectively accept observations that conform to our expectation and blithely ignore observations that don’t fit.
Professor Richard Dawkins relates an anecdote of attending a seminar by a distinguished, older scientist. At the conclusion of the talk, a young student asked a perceptive question that essentially caused the speaker’s lifetime of research to crumble. Rather than becoming angry, the scientist went over and shook the student’s hand for his role in moving science further by disproving his hypothesis.
If you ever hear someone say that I proved my hypothesis, you know they do not understand the scientific method.
Let’s go back 2400 years to Greece. Aristotle wrote about many Greek birds. He noted that the five swallows there (including the familiar Barn Swallow) disappeared in the winter. He knew of no reports of occurrences of these birds elsewhere during the winter. He proposed that these birds hibernate. That is a perfectly good hypothesis; it can be tested.
As it turns out, this hibernation hypothesis became part of natural history lore and was not disproven for 2300 years. Even the great ornithologist Elliot Coues in 1882 was agnostic on the issue. Of course, now we have the evidence that swallows migrate to tropical areas to pass the winter.
Extraordinary claims require extraordinary evidence. The recent finding of a Fieldfare (a robin relative) in Newcastle and a Vermilion Flycatcher in Bremen on Hog Island should rightly invite skepticism. Fieldfare had never been reported in Maine and we have an earlier sight record of Vermilion Flycatcher but no photos. Fortunately, observers provided photographs of both of these recent rarities. They are confirmed records.
As birders, we should question other observers’ sighting and prepare to have our own sightings questioned. These doubts should not be taken as insults on our abilities but rather the proper performance of scientific, skeptical inquiry.
Spring is a wonderful season for naturalists. The earth is awakening after a winter’s slumber. Our eyes and ears are tuned to the sound of the first spring peepers, the first Ruby-throated Hummingbird, the first blooming Trillium in the forest, the first leaves on red maples, and even the first black fly.
The documenting of these firsts in spring has a formal name, phenology. But being aware of phenological events is not just an academic exercise. Even in the 1700s, British farmers judiciously waited to plant their crops until particular species of migratory birds arrived. The farmers sowed their seeds according to an ornithological calendar.
For the past 23 years, I have been coordinating a volunteer-based phenology study to document the first arrival of over 100 species of Maine migratory breeding birds. Observers are asked to report their first sighting of as many of those species as they see along with their geographic location. We know have over 65,000 arrival dates. The project has taught us much about the timing and variability of the arrivals of the various migratory species that nest in our state.
To make this information available to any birder, I have developed a web application to allow a user to explore the data. I invite you to visit: https://hobbes.colby.edu/arrival/
A drop-down menu allows you to choose a species and slider bars permit you to select a year and display features. Clicking on the Data Summary tab will give the average, median and other summary dates for a species/year combination.
Tracking changes in phenological events is important in the face of global climate change. Although some people deny the role of human activities in leading to global temperature increases in the face of overwhelming evidence, the fact that the earth is warming is undeniable. The polar ice caps are melting, sea level is rising, and average temperatures are rising around the globe.
Many phenological events are driven by temperature. We have good evidence that the arrivals of migratory birds are earlier now than in past years. One such study compared arrivals of migratory birds in Worcester, Massachusetts and Ithaca, New York. Both of these areas have long-standing bird clubs with records of arrival dates extending back into the 19th century. Virtually all of their migratory species are now arriving earlier than they did 50 years and more ago.
Numerous such studies have corroborated the pattern of earlier arrivals. Several bird banding stations that have been operative for 60 years or more reveal the same patterns.
You can explore the Maine data for trends of earlier arrivals over the past 23 years. Just choose Year with the Radio Button at the bottom left and click on Scatterplot.
Although the graphs for most species show a downward trend, indicating earlier arrivals, most of those relationships are not statistically different. For perhaps multiple reasons, Maine migratory birds are not responding as strongly to climate change as birds nesting in states to the south of us.
Some of our migratory breeding birds winter within the continental U.S. (short-distance migrants) while others winter in tropical areas of the Caribbean, Central America and South America (long-distance migrants). Short-distance migrants seem to be more responsive to spring-time temperatures. When a northeastern spring is mild, the birds continue their migrations and arrive in Maine relatively early. In cold springs, the birds rightly delay their migrations until conditions improve, resulting in a late arrival.
The web app can be used to investigate these patterns. Choose a species and click on Temperature.Departure.from.Mean. Negative values of Temperature.Dependence indicate a colder than average spring; positive values indicate a mild spring.
Click on Scatterplot to see the relationship. Red-winged Blackbird shows a particularly strong effect.
Lastly, clicking on the NAO.Index radio button allows a user to see the effect of this hemispheric weather phenomenon (analogous to the El Niño effect in the Pacific).
[Originally published on April 16, 2017]
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected]
As a fledgling birder in the 1960’s, my chief source of bird information was my cherished Golden Guide Birds of North America by Chandler Robbins and the artist Bertel Bruun. At the time, the Robbins guide and Roger Tory Peterson’s guide were the only two field guides available. To be sure, Peterson’s illustrations were far superior to those of Bruun but the text, the plates and the range maps were in different parts of the Peterson guide. The Robbins guide had text, illustrations, maps and sonograms of each species on facing pages. Plus, all of the bird species in North America were covered.
These memories spring to mind because Chan recently passed away at the age of 98. His contributions to ornithology and to birding were immense. The Golden Guide was just one of his many accomplishments.
Chan took a job as a biologist with the U.S. Fish and Wildlife Service in 1945. He was based at the Patuxent Research Refuge in Maryland until his retirement in 2005 after 60 years or service! Even in retirement, he continued to work as an emeritus biologist for another 13 years.
Early in his career, he conducted research on the effects of DNA on birds. He worked closely with Rachel Carson, one of Maine’s own, and his work on the deleterious impact of DDT provided scientific support for Carson’s Silent Spring, published in 1962.
Concerned about tracking the effect of DDT on bird populations, Chan realized that we lacked a rigorous method to assess changes in bird populations at the regional and continental level in North America. Chan remedied that problem by designing the Breeding Bird Survey (hereafter, BBS), a citizen-science project that provides a view of the changes of breeding bird populations throughout North America.
A BBS is conducted along a 24.5-mile stretch of secondary roads. Once during the breeding season, an observer starts at the designated starting point about half an hour before sunrise. The observer listens and looks for birds for three minutes, drives 0.5 mile to the next stop, observes for three minutes and so one until 50 stops are sampled.
The observer samples the same route each year, reporting the data to the BBS office.
Nearly 3,000 BBS routes are sampled yearly. Modest contributions from many yield a powerful tool for detecting declines or increases of our avifauna.
The BBS data are available to researchers. Over 400 papers been published with the data. One of the most influential of these papers was a 1989 article written by Chan and his colleagues. They showed that an alarming number of long-distance migrants showed decreasing abundance on the breeding ground in North America. Related species that did not migrate to the tropics were not showing such steep decreases in abundance. Hence, the authors could infer that deforestation and other habitat degradation in the tropical wintering areas of these long-distance migrants could explain lower densities in North America. This work provided a strong impetus to redouble efforts at habitat conservation.
Chan visited Midway Island in the Pacific ten times during this career. His work involved banding Laysan Albatrosses that nest there. In 1956, he banded an albatross, subsequently named Wisdom. Wisdom is still alive and reproducing at the ripe age of 60! Wisdom is the oldest banded bird ever.
I got to know Chan from ornithological meetings. I well remember chats we had after presentations I made. He was a kind, soft-spoken and generous man. He was also a highly skilled observer. His eyes and ears were amazing.
For many years, I conducted BBS routes in Maine. After conducting my 50th BBS census, I received a certificate of appreciation from the BBS Office along with a signed copy of the Chan’s Birds of North America. I am very proud of the book, which sits on my shelf next to my tattered childhood copy.
In the middle of January, my wife, two other couples and I made a 12-day trip to Costa Rica, following by a few months the billions of North American birds that migrated south for the winter.
Waiting to pick up our rental van near the San José Airport, we saw some birds flitting in a few trees adjacent to the building. And our first birds of our trip were . . . . Chestnut-sided Warblers, Tennessee Warblers and a bright male Baltimore Oriole. Not the exotic tropical species were we expecting!
Those three species were the first of many Neotropical migrants we would see on our trip. We tend to think of Chestnut-sided Warblers and Baltimore Orioles as “our” North American birds. But they spend less of the year in North America than they do in tropical areas. We get them on loan for the breeding season.
We spent our first night at the Hotel Bougainvillea, north of the airport. The ten acres of gardens there were delightful for a pre-breakfast bird walk. Clay-colored Thrushes, the national bird of Costa Rica, were common. Other highlights were Lesson’s Motmots, Crimson-ringed Parakeets and some old friends, three Yellow Warblers.
On to the La Selva Biological Station in northeastern Costa Rica, a center of rain forest research in the New World tropics. We took advantage of the extensive trail system there for a glorious three days.
Neotropical migrants included Broad-winged Hawks, House Wrens, Wood Thrushes, abundant Chestnut-sided Warblers, and Summer Tanagers.
Toucans were abundant, loud and easy to see. We found three species: Yellow-fronted Toucan, Keel-billed Toucan and Collared Aracari.
We saw small flocks of Great Green Macaws in flight several times and once had the delight of watching two perched macaws through a spotting scope. Fewer than 300 individuals of this species exist today.
Bronze-tailed Plumeleteers, Rufous-tailed Hummingbirds and Steely-vented Hummingbirds were the most common hummers. We also had great looks at a Rufous-tailed Jacamar. This woodpecker relative has a long, thin bill for capturing insects on the wing. It looks like a giant hummingbird!
We had the pleasure of seeing a number of Green Ibis. They are so different from the Glossy Ibis that nest along the southern Maine coast. Glossies are rather quiet birds, sedately probing in the mud with their long decurved bills.
Green Ibises like to perch in treetops and they are extremely vocal, giving an accelerating hooting call. They are most active at dawn and dusk.
Numerous species of tanagers delighted us, each gaudy and spectacular in its own way. But sometimes, an understated appearance can be the most beautiful. For me, that applies to the Snowy Cotingas we saw: white (male) or light gray(female) feathering with a dark eye and bill. Stunning birds!
We had long looks at a perched Rufous Motmot. Another beautiful bird with subtle coloration.
Birds of prey included a Semiplumbeous Hawk, a Gray-headed Kite and a Laughing Falcon (whose call really does sound like a person laughing).
On our final afternoon at La Selva, we signed up for a boat tour of the Rio Sarapiquí that flows through La Selva.
Greater Yellowlegs, Spotted Sandpipers, Great Blue Herons and Little Blue Herons were foraging on the banks. Most of the swallows wheeling overhead were familiar Northern Rough-winged Swallows. Some had gray rumps indicating a different species, Southern Rough-winged Swallows. A few Mangrove Swallows with their blue-green upperparts were mixed in.
Our guide spied a well-hidden Green Kingfisher, only 7.5 inches in length. A delightful imp! We also had a good view of the much larger Amazon Kingfisher.
We had a brief view of a soaring bird that came back into view for a good look. It was a King Vulture. We knew it was a particularly good sighting because our tour guide was so excited to see it.
We saw several Anhingas as well.
Anhinga
We departed westward from the tropical rain forests in La Selva to higher elevation. En route, we passed many cow pastures with Cattle Egrets, Great-tailed Grackles and an occasional Crested Caracara consorting with the bovines.
Ultimately, we arrived at the Arenal Observatory Lodge. The lodge is at the base of the Arenal Volcano, the youngest and most active volcano in Costa Rica. Standing nearly, 5,400 feet high, this cone-shaped volcano is a wonder to behold. Steam and other gases emanate from several craters. The last eruption was in 2010.
The lodge has an expansive deck with chairs with a full view of the volcano. It’s also a great platform for birding. A fig tree only 30 feet away is a magnet for many fruit-eating birds. The lodge staff also puts out fruit on a large feeder to attract birds.
The highlight was the diversity of tanagers, each seemingly more colorful and beautiful than the next. You can get an idea of the colors from the names: Blue-gray Tanager, Blue-and-Gold Tanager, Crimson-collared Tanager, Emerald Tanager, Silver-throated Tanager, Golden-hooded Tanager, Green Honeycreeper and my favorite, the Bay-headed Tanager.
Montezuma’s Oropendolas, large members of the blackbird family, were abundant. The males continually performed their bow display.
Montezuma’s Oropendola
From a perch on a branch, a male rotates on the perch to put its head down and tail sticking up, all the while giving a distinctive, loud metallic gurgle.
Great Currasow male
From the deck we had great looks at a Great Curassow, a distinctive ground-dwelling bird as well as a Black-and-white Becard.
Long-nosed Coati
Delightful long-nosed coatis, a raccoon relative, roamed around in small packs.
We hired a guide to take us on an early morning bird walk along some of the many trails and roads of the Lodge property. The highlight was a Yellow-eared Toucanet. Our guide had not seen one at Arenal in over a year. Other goodies included a Laughing Falcon, a Violet-headed Hummingbird, Blue-black Grosbeaks and a Black-cowled Oriole.
We departed Arenal for three days in Monteverde, one of the most popular birding sites in Costa Rica. This area has some large tracts of cloud forest with a distinctive bird fauna.
We hired a guide for a morning walk. Usually the cloud forest is foggy with water dripping from the trees. For our walk, the weather was clear and dry.
We enjoyed the beautiful songs of Ochraceous Wrens and Gray-breasted Wood Wrens, eventually getting a good look at each. An Azure-hooded Jay gave us great looks. Slate-throated Redstarts, mostly yellow and black, darted around at eye-level.
We heard the dry trill of a Silvery-fronted Tapaculo, a small songbird that mostly forages on the forest floor. Our guide told us that seeing one of these birds is extremely difficult.
The highlight of the walk was a sighting of a male Resplendent Quetzal. The male we saw was perched in the top of an avocado tree, calmly digesting a meal of avocados.
Resplendent Quetzal male
The word spread quickly about the quetzal and many tour groups converged. Everyone got a good view through a spotting scope. With an iridescent emerald-green head, back and chest, red belly and a long tail with green and white feathers, this species is the most beautiful bird I have ever seen. The quetzal is the national bird of Guatemala as well as the name of their currency.
Lesson’s Motmot
We also had a fine look at a Lesson’s Motmot high overhead.
Some of us went on an afternoon walk on our own. I saw a bird flitting about on the ground. It was a Silvery-fronted Tapaculo. I was ecstatic!
At the Café Calibri just outside the reserve, hummingbirds visit the many feeders hanging there. We saw seven species including the stunning Violet Sabrewing and Green Hermit. Bananaquits, currently classified into the tanager family, competed for their chance at the sugar water.
Now that 2016 has ended, it’s time to check on the Big Year efforts. John Weigel shattered the old North American record of 749 species seen in a calendar year by finding 781 birds! Three of his species are new to North America and must be accepted by rare bird committees before their official inclusion.
Olaf Danielson did nearly as well, finding 778 species (two pending). Danielson also spent time birding in Hawaii and has set a new record of 827 species in a year in the United States.
Laura Keene ended her Big Year with 759 species and Christian Hagenlocher exceeded his goal of 700 species by documenting 750 species. I’m sure all four of these birders are glad to get a chance to rest!
On a more local level, Josh Fecteau of Kennebunkport did a Big Year in Maine in 2016 and found 305 species. An extraordinary effort! You can read about Josh’s Big Year at joshfecteau.com
The Effects of Bird Feeding
Feeding the birds is a common practice for hundreds of thousands of Americans. Over 40% of American households maintain a bird feeder. We know that bird feeding does increase the survivorship of birds and improves their physiological condition. Birds do not become dependent on our handouts. What’s the downside of feeding birds?
Jenn Malpass and two colleagues have recently published a paper describing their more nuanced perspective on impacts of bird feeding. Jenn is a Colby College alumna who recently completed her Ph.D. at Ohio State University.
Jenn’s work investigated the impact that bird feeders have on nest predators over the period of 2011 through 2014. On the one hand, if bird feeders increase the abundance of Blue Jays, American Crows or gray squirrels, other birds nesting in the area may be at a higher risk of losing their eggs or nestlings to those nest predators. On the other hand, providing food to Blue Jays may satiate them, reducing their tendency to take eggs or nestlings.
The research team used seven study areas in residential neighborhoods in Columbus, Ohio. Each neighborhood was about nine acres in area. The team got permission from most home owners to visit their yards. The team carefully canvased each area and noted the location of every American Robin and Northern Cardinal nest. The nests were checked every one to four days for evidence of nest predation. This project was an ambitious one; nearly 1,000 nests were monitored. The researchers also did visual searches for 18 different potential nest predators.
Unsurprisingly, multiple houses in each area had feeding stations. The research team placed additional bird feeders in three of the seven neighborhoods, essentially doubling the number of feeders. This supplemental food provided a direct test of the influence of bird feeding on nest predator abundance. Many of the potential nest predators could take advantage of the bird seeds (squirrels and several bird species). Others, like cats and raptors would not be directly attracted by tasty sunflower seeds, peanuts or millet.
As you can imagine, the statistical analysis is complicated. The authors first tested the effect of year-to-year variability and the amount of supplemental food available on the abundance of the various potential nest predators. Next, they tested the effect of nest predators and bird feeders on nest success.
The results showed that bird feeders do increase the abundance of American Crows and Brown-headed Cowbirds. However, this increase in nest predator abundance did not translate into reduced nesting success of robins or cardinals. The one negative effect was a reduction in robin nest success in the presence of high American Crow abundance and high bird feeder density. The main effect of bird feeders on nesting success is neither a positive or negative effect. Our joy in feeding birds, at least for two species, does not entail unintended negative consequences.
This post concludes the overview of the National Audubon Society Christmas Bird Counts conducted in Maine between mid-December and early January.
The Orono Christmas Bird Count (hereafter, CBC) was held on December 17. A Gray Jay was perhaps the least expected of the 44 species tallied. Tufted Titmice were represented by 28 individuals.
A hardy Northern Mockingbird was unexpected. A whopping 1,467 Bohemian Waxwings were found, an excellent count for this early in the winter.
Irruptive finches were well represented with 65 Pine Grosbeaks, 25 Purple Finches, 54 Common Redpolls and 103 Evening Grosbeaks.
Just eight miles south of Orono, the Bangor Christmas Bird Count was held on December 31. The effort yielded a fine count of 58 species. Careful looks at the Common Goldeneye flocks on the Penobscot River yielded two Barrow’s Goldeneyes.
Two Red-bellied Woodpeckers and a lingering Northern Flicker were the most notable woodpeckers. Two Peregrine Falcons and a Northern Shrike were delightful finds.
Tufted Titmice continue to increase in the area; a total of 96 were found this year. Lingering songbirds included a Carolina Wren, two Northern Mockingbirds and a Yellow-rumped Warbler.
The Bangor counters found 311 Bohemian Waxwings along with 79 Cedar Waxwings.
Northern finches put on a good show: 146 Pine Grosbeaks, six Purple Finches, three Pine Siskins and nine Evening Grosbeaks.
Let’s head over to the downeast coast to Machias and then work our way south along the coast.
The Machias Count yielded 59 species on December 31. A Common Pintail and four Harlequin Ducks were the most notable of the 14 species of waterfowl.
Lingering birds included a Northern Harrier, three White-throated Sparrows and a Song Sparrow.
A Red-bellied Woodpecker was unusual for this part of Maine. Rough-legged Hawks have been scarce in Maine so far this winter so the two found here were great finds.
Red-breasted Nuthatches were well represented with 363 individuals. Irruptive birds included 38 Bohemian Waxwings, 74 Pine Grosbeaks, 61 Purple Finches, 55 Pine Siskins and 27 Evening Grosbeaks.
Counters on the Schoodic CBC started the new year off right, finding 59 species. Twelve species of waterfowl appeared, none out of the ordinary.
Six Northern Gannets were delights along with two Rough-legged Hawks.
Black Guillemots are expected on any coastal Maine CBC. Counters here found 36 along with two other less common alcids: two Thick-billed Murres and a quartet of Razorbills.
Less common gulls included five Black-legged Kittiwakes and singleton Iceland and Glaucous gulls.
Two Northern Shrikes graced the area with their presence. Lingering birds included nine American Robins, a Northern Mockingbird, a White-throated Sparrow and three Song Sparrows.
Winter finches included 55 Purple Finches and an excellent total of 24 Red Crossbills.
Let’s hop on a plane to visit Matinicus Island, 20 miles off shore, like three CBC birders did on January 5. You never know what a far-flung outpost like Matinicus will hold.
The counters found 39 species. This year there were no jaw-dropping finds. The expected coastal birds were present just offshore.
Lingering birds included a Northern Flicker, a Yellow-rumped Warbler, four White-throated Sparrows and two Song Sparrows. The only other sparrow was a American Tree Sparrow and no finches were found at all.
The Pemaquid Count produced a nice total of 64 species on December 17. Three Wood Ducks were the most unusual of 15 species of waterfowl.
Lingering birds included a Northern Harrier, a Belted Kingfisher, five Eastern Bluebirds and a Northern Mockingbird. A Merlin and two Fox Sparrows were notable.
The Bath CBC was held of December 19, producing a fine total of 74 species. Fifteen Northern Pintails were the most notable waterfowl.
Highlights included an American Pipit, four Lapland Longspurs and a long list of lingering species. These ambitious birds included a Great Blue Heron, five Northern Harriers, two Hermit Thrushes, a Savannah Sparrow and five Red-winged Blackbirds.
This column continues the overview of the National Audubon Society Christmas Bird Counts conducted in Maine between mid-December and early January. We’ll concentrate mainly on inland counts in central Maine today.
The Waterville Christmas Bird Count (hereafter, CBC) was held on December 18. A lower-than-normal total of 47 species were detected this time, owing in large part to the freezing rain that delayed the start of the count and restricted birding on foot.
A Northern Pintail, six Barrow’s Goldeneyes and a Bufflehead were the most unusual of nine species of waterfowl. Two Red-bellied Woodpeckers and a lingering Northern Flicker were notable. Thirteen Pine Grosbeaks were the only northern finches. Two Northern Shrikes graced the count with their presence.
The dairy farms in the northern part of the count circle are usually good for ground-dwelling land birds. This agricultural habitat did not disappoint this year, yielding three Lapland Longspurs, six Snow Buntings, six Savannah Sparrows and an all-time high count of 325 Horned Larks.
The highlight of the count was a Buteo hawk that had characteristics of both a Red-tailed Hawk and a Red-shouldered Hawk (the latter rare in the winter in Kennebec County). Louis Bevier re-found and photographed the bird, determining that it was a hybrid between these two species.
The Augusta Christmas Bird Count took place on December 31, rescheduled from December 17 because of snow. This CBC yielded 54 species. Three Sandhill Cranes were a big surprise.
The Hatch Hill Transfer Station is usually good for white-winged gulls. This year one Glaucous and five Iceland gulls were spotted.
Boreal Chickadees are common in the mountains and coastal spruce-fir forests of Maine but rare in Kennebec County. One appeared at a suet feeder in Augusta just after Christmas and stuck around long enough to be tallied on the Augusta CBC.
This count did produce a few irruptive finches: two Pine Grosbeaks, 56 Purple Finches, a Pine Siskin and nine Common Redpolls.
Just a bit north of Augusta, the Unity CBC took place in the snow on December 17. A total of 39 species were found, fewer species than in past years. The heavy snowon that day is no doubt the explanation for the failure to find any Mallards as well as the low numbers of many other species.
A lingering American Kestrel and Savannah Sparrow were nice finds. Northern visitors included 125 Snow Buntings, a Northern Shrike, a Pine Siskin and 27 Pine Grosbeaks.
Evening Grosbeaks staged a modest incursion into Maine in the fall although most seem to have passed through the state. The 36 Evening Grosbeaks in Unity were excellent finds.
Let’s move west to Farmington for highlights of their December 28 CBC. A total of 35 species were detected. With most water frozen over, waterfowl were nearly absent. In fact, a single Snow Goose (an unusual species for this time of year) was the only waterfowl species. A lingering Northern Harrier was a highlight.
Northern visitors included 206 Bohemian Waxwings, 36 Snow Buntings, 42 Pine Grosbeaks and a nice total of 37 Evening Grosbeaks.
Participants tallied 25 Tufted Titmice, a clear indication that this species has established itself in Franklin County. Titmice continue their invasion of Maine. The species was essentially absent in central Maine 25 years ago.
Lingering birds in Farmington included four Song Sparrows and an Eastern Bluebird.
Continuing to the southwest, we’ll cover the Sweden CBC in western Cumberland County. This December 28 count produced 37 species.
Four American Black Ducks and 244 Mallards were the only waterfowl. Gamebirds included three Ruffed Grouse and 194 Wild Turkeys. A lingering Northern Flicker and six Red-bellied Woodpeckers were nice additions to the expected Downy, Hairy and Pileated woodpecker counts.
Northern visitors included a single Northern Shrike, a single Bohemian Waxwing and a lone Snow Bunting.
Hardy lingering birds included a Winter Wren and seven Eastern Bluebirds.
The 117th Christmas Bird Count season is now over. As usual in January, I will discuss the highlights of some of the Maine Christmas Bird Counts. These standardized censuses provide an important tool to monitor the abundance of winter birds throughout North America and beyond.
I’ll concentrate on any changes in regularly wintering birds, the arrival of unpredictable invaders and records of any lingering birds whose wintering areas are well to our south. A rarity or two may pop up as well.
We’ll start with the southern Maine coast. The York County count was held on December 21. Thirty observers found 82 species of birds. Eighteen species of waterfowl were found with the most notable being four Wood Ducks and five Northern Pintail. The York County rocky coast is a stronghold for Harlequin Ducks in Maine; 65 of these lovely birds were counted.
Six species of hawks and eagles were spotted. One Red-shouldered Hawk was a nice find; most winter well to our south. One Rough-legged Hawk, a northern visitor, made a nice geographic contrast. Two Peregrine Falcons added to the diurnal raptor list.
Purple Sandpipers (329 to be exact) were the only shorebirds tallied this year. The only alcids were 22 Razorbills and five Black-Guillemots.
The relatively moderate climate of the York County coast usually has more lingering species than other areas in Maine. This year did not disappoint with a Great Blue Heron, three Belted Kingfishers, a Northern Flicker, 152 Eastern Bluebirds, a Gray Catbird, two Yellow-rumped Warblers and a Rusty Blackbird.
The most remarkable species this year was an Eastern Screech-Owl. I suspect this species will increase in Maine as our climate warms.
Greater Portland usually takes top honors for the most species on their count. Eighty-eight species were tallied this year despite the snowy conditions on December 17. Twenty species of waterfowl were present with the most notable being a lingering Snow Goose and Wood Duck.
Only two Red-throated Loons were present along with 66 Common Loons. No alcids, not even a guillemot, appeared this year.
A lone Glaucous Gull was the only northern gull in attendance. A Merlin and two Peregrine Falcons were found.
Lingering, half-hardy species included a Northern Harrier, an American Coot, two Yellow-bellied Sapsuckers, six Northern Flickers, a Gray Catbird, two American Pipits, a Black-throated Blue Warbler (an extraordinary find), three Rusty Blackbirds and a Common Grackle.
The Pemaquid count was held on the same day as the Portland count. A total of 64 species appeared. Highlights were three lingering Wood Ducks, 80 Purple Sandpipers, 158 American Robins, a Northern Mockingbird, two Fox Sparrows and an Eastern Towhee.
Twelve Black Guillemots were the only alcids found and only three species of gulls were tallied. I expect the heavy snow throughout the day had something to do with that.
The Mount Desert count was also held on that snowy Saturday. Fifty-three species were counted. This count usually has impressive Common Eider counts; this year 1,402 were counted. An American Wigeon was an unusual bird for this time of year.
Other lingering birds included a Northern Harrier and 133 American Robins. A Snowy Owl was a nice sighting.
The Lewiston-Auburn Count on December 18 yielded a total of 44 species. By late December on inland Christmas Bird Count, any still water is frozen. Counters have to seek out running water to find any waterfowl and typically waterbird diversity is low. The L/A counters found five species of waterfowl, with the 436 Mallards representing an impressive total. Five Common Loons were found, always an excellent find on an inland Christmas Bird Count in Maine.
Other notable sightings included a Merlin, a Peregrine Falcon and 82 Horned Larks.
The northern finches (Common Redpoll, crossbills, Pine Siskins) failed to appear on any of these counts. Not a strong irruption year so far.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected]
