A bird’s bill can tell you a lot about the breadth of its diet. The strong, tapered bill of a Eurasian Starling is a great tool for extracting insect larvae off leaves, grabbing grasshoppers and other insects, manipulating fruits, crushing seeds and probing in the ground for prey. Starlings can generally find food.

At the other extreme are Red Crossbills and White-winged Crossbills. Their upper and lower bills cross like a pair of scissors. The bill serves well to separate adjacent scales of the cones of conifers. Once the scales are separated, the hard harpoon-like tongue of the crossbill extends to the base of a scale to extract a nutritious seed. This specialized tool does its job well but is poorly designed for foraging on other types of food.

As specialists on conifer seeds, crossbills live a vagabond existence. They travel in flocks broadly in search of rich cone crops. Once such a mother lode is found, the birds often nest. White-winged crossbills can breed in every month of the year.

Red Crossbills are enigmatic as far as their taxonomy occurs. In North America, Red Crossbill types tend to occur parts of the country. The individuals in each type give a distinctive flight call. There are correlated bill shapes and sizes for some of these call types. Some ornithologists argue that we should recognize twelve species instead of one. The types do wander, always in search of a bumper crop of conifer cones.

From late summer in 2023 into the winter through the summer of 2024, Red Crossbills appeared in southern Maine in large numbers. This influx was likely driven by the abundant pine cones of eastern white pine. The white pine cone crop was two to three times higher than normal peak years.

Glenn Hodgkins, Christine Murray, Camden Martin and Gary Jarvis studied this influx of Red Crossbills and published their findings in The Maine Natural History Observer. I’ll summarize their valuable findings here.

Identifying the call type of a Red Crossbill is a snap if you have a recording of the bird. The recording can be converted to a spectrogram, a graphical representation of the notes and frequencies of a call. Red Crossbill calls are usually loud enough that a recording made with your phone is sufficient to identify the call type.

Type 12 Red Crossbills are the most common type in Maine. These birds have a medium-sized bill, well suited to the high diversity of conifers we have in Maine. These birds can extract seeds from small cones like those of eastern hemlock to massive eastern white pine cones.

The research team found evidence of two additional types during this invasion. Type 2 (ponderosa pine) Red Crossbills are centered in the Rocky Mountains westward into the Cascade Mountains of Washington and Oregon and the Sierra Nevada of California. This type is well known for eastward irruptions, extending as far as the Canadian Maritimes.

Type 4 (Douglas-fir) Red Crossbills are mainly found in the Pacific Northwest where Douglas-fir cones are the major food source. These crossbills irrupt occasionally to the Rocky Mountains and even the western Great Lakes region. They rarely make it into the Northeast. However, they occurred in significant numbers in Maine over the study period. This irruption of Type 4 birds is the best irruption in the Northeast in at least 25 years.

Our understanding of Red Crossbill movements in Maine is surely in its infancy. Prior to 2023, only two type 2 records and one type 4 record existed in the eBird database for Maine. All three call types were present in late August 2023 in Auburn. Surely, with the ability to identify birds based on their call types, we will learn more about the movements of the different call types.

Type 12 Red Crossbills were confirmed as breeders in southern Maine in the summer and fall of 2023 while types 2, 4 and 12 were confirmed as breeders in the winter and spring of 2024.

The article in the Maine Natural History Observer has several excellent color photographs of the three types of Red Crossbills that occurred in Maine during the study and other photographs as well.

I urge you to consider becoming a member of the Maine Natural History Observatory (https://mainenaturalhistory.org/). Membership is as little as $10 a year and you will get four issues of the Maine Natural History Observer with accessible natural history articles and moving essays. A membership gives you access to all back issues. Reading through those articles is a great winter-time activity.

Are they coming this winter? This question is on the minds of many birders with respect to the northern finches. Will high latitude species like Common Redpoll, Pine Grosbeaks and Evening Grosbeaks descend on Maine this winter? We know these irruptive species are perfectly capable of overwintering on their northern breeding grounds if the seeds, cones and fruits they depend on for food are adequate. However, in some years, seed and fruit production are poor and these northern finches are forced to move south for the winter, much to our delight.

Beginning in 1999, the late Ron Pittaway wrote a finch forecast every fall to predict the movements of the northern finches. That task has been assumed by Tyler Hoar. Tyler’s records of cone and fruit crops suggest it will be a poor irruption year for redpolls and crossbills. We may get a few Pine Grosbeaks and Evening Grosbeaks. Purple Finches have already started to move south out of Canada.

For the northern finches that do appear, you will have a wonderful new field guide to increase your knowledge of those finches. The book is The Stokes Guide to Finches of the United States and Canada, authored by Lillian Stokes and Matthew Young.

Lillian, with her husband Donald, has written 35 photo-based field guides. The first was on eastern birds of North America. Others cover butterflies, dragonflies and damselflies, hummingbirds, winter ecology, bird behavior, and more. Lillian is a highly skilled nature photographer as well.

Matt Young is the founder of the Finch Research Network. Broadly interested in all finches, Matt has a particular interest in the vocalizations of the many ecotypes of Red Crossbills. He has worked for many years at the Cornell Laboratory of Ornithology on bird vocalizations and helped develop the Merlin app.

Common names of birds sometimes confuse us as far as their taxonomy is concerned. For instance, the Rose-breasted Grosbeak is in the cardinal family while the Evening Grosbeak is in the finch family. The famous Darwin’s finches are actually in the tanager family, not the finch family.

For this book, the authors restrict themselves to the family Fringillidae, which includes our familiar finches as well as 17 species of Hawaiian honeycreepers. The finches are arranged into three groups in this book: the 18 North American species, eight species of Eurasian vagrants, and the 17 Hawaiian honeycreeper species.

Each account begins with a lyrical Quick Take section, offering an overview of the species with delicious tidbits about the bird. Other sections are Identification (covering subspecies and similar species), Distribution, Language, Habitat, At Your Feeder, Movements and Irruptions, Breeding Behavior, and Conservation. Each account has at least half a dozen superb photographs, many taken by Lillian.

Our understanding of the taxonomy of groups of organisms is always changing. Between submission of the final copy for this book and its publication, the Check-list Committee of American Ornithologists Society decided to merge the two redpolls we have in North America, the Common Redpoll and the Hoary Redpoll. These morphs have their own species account. That’s not a big problem; the two morphs are identifiable in the field and have different behaviors. We just need to realize they are now a single species.

The book ends with general chapters on Feeding and Attracting Finches (include gardening tips), Movements and Irruptions and Research and Conservation. An extensive bibliography for each species concludes the book.

The Language section of each account is impressive, covering the calls and songs of each species in greater detail than in other field guides. The red crossbill section is particularly useful in presenting the call types of the eleven ecotypes of the species. Annual variation in use of various seed trees by each ecotype is shown in cleverly designed graphs.

I was particularly delighted by the coverage of the Cassia Crossbill, a species recognized as a distinct species in 2017. Cassia Crossbills occur on two sky islands in Idaho, the peaks of high mountains, so are isolated there. These crossbills have particularly large bills to allow them to extract cones from lodgepole pines and have unique vocalizations.

We have a local connection to this species. Patrick Keenan, Director of Outreach at the Biodiversity Research Institute in Gorham, studied Red Crossbill vocalizations for his Master’s degree at the University of Wyoming. His research was instrumental in building the case that Cassia’s Crossbill should be split from Red Crossbill.

The appearance of a vagrant bird instills wonder, causing us to ask how such an out-of-place bird got to Maine. Vagrants are also exciting to birders, giving us a chance to see a bird that would normally require us to visit other states or countries.

Maine has its fair share of vagrant species. Of the 475 species of Maine birds, 107 species have been sighted five or fewer times. Forty-nine species have only been recorded a single time and another 29 only twice. May is the most likely time for one of these vagrants to appear with October close behind. March is the most vagrant-poor month.

We are coming up on the 37^th anniversary of what I consider to be Maine’s most mind-boggling vagrant. On November 5, 1977, a flycatcher with bold streaking was seen and photographed in Biddeford. The bird lingered until November 11.

It was initially identified as a Sulphur-bellied Flycatcher, a bird whose northern breeding limit is in southeastern Arizona. These Arizona birds migrate south for the winter. Such a record would be amazing.

However, closer examination of the bird in the field and from photographs indicated that this vagrant was a Variegated Flycatcher, a South American bird. In November, Variegated Flycatchers move south to Argentina and adjacent South American countries to nest.

Variegated Flycatcher photographed in northwestern Argentine, November 12, 2023

Somehow, a Variegated Flycatcher made a major orientation error and ended up flying north all the way to Maine. This record was the first for North America. A likely explanation for this vagrancy was reverse migration, a genetic mutation that causes a bird’s internal compass to be off by 180 degrees.

Since 1977, nine other variegated flycatchers have occurred in North America in Florida, Texas, Tennessee, Michigan, Washington and Ontario.

In 1977, this record captured my imagination. In college in North Carolina then, I had no chance to see it. I did make a trip to Argentina last November and the Variegated Flycatcher, a common bird there, was on my list of most-desired species. I saw and photographed many.

Although Maine has two records of Kirtland’s Warbler, I regard those vagrants to be highly noteworthy. Kirtland’s Warblers nest in jack pine forest in northern Michigan with satellite populations in Wisconsin and Ontario. The population fell to only 400 birds by 1971 due to Brown-headed Cowbird brood parasitism and habitat loss. Conservation efforts have been effective, but the population now is only around 4,000 birds. 

This species winters in the Bahamas. You can picture a northwest to southeast trajectory for the migration of this species. Somehow, two have been sighted in Maine. One was on the Kennebunk Plains in June 2008 and another on Matinicus Rock in September 2023. The rarity of the species combined with the fact that Maine is far removed from their migration path makes our records wonderfully unlikely.

The Great Black Hawk is a raptor found in Central and South America. Texas and Maine share the only record of this species in North America. In April 2018, a Great Black Hawk appeared on South Padre Island, Texas. In August, the same bird as judged by details of its plumage showed up in Biddeford. The bird appeared in Portland on October 29 and stayed until January 30, 2019. It spent most of its time in Portland in Deering Park where the abundant squirrels provided a steady food supply. Unfortunately, the hawk developed frostbite in late January. Efforts to nurse it back to health by rehabbers failed so the bird was mercifully euthanized. Certainly, a Maine winter is tough for any displaced tropical bird.

A list of the most amazing Maine vagrants must include the Steller’s Sea-eagle that first appeared in Maine in Georgetown on December 30, 2021, and stayed until March 5, 2022. It put in another appearance from February 4-14, 2023. Since then, it has been hanging out in Newfoundland.

The species is found along the western Pacific coast from Russia south to Japan and Korea. There are a few records for the Aleutian Islands and western mainland Alaska. But the one we saw in Maine was first sighted in Alaska and then southern Texas. The eagle then made the rounds in Massachusetts, Maine, Nova Scotia and New Brunswick.

This bird was easily the most observed rare vagrant in Maine history. Hundreds of birders came to the Georgetown-Boothbay area to try to see this remarkable bird.

I think these four species are the most amazing vagrants we have on the Maine bird list. There is plenty of room for argument with so many other remarkable vagrants in the Pine Tree State.

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected]

The bird checklist for Maine currently stands at 475 species. A complete listing is available on the Maine Bird Records Committee website.

The list includes resident birds who grace us with their presence all the year. Downy Woodpeckers, American Crows and Black-capped Chickadees are good examples.

Over 100 species are migratory breeding birds, moving from wintering areas to our south to nest here and then departing before winter sets in. Killdeer, Eastern Phoebes and Yellow Warblers fit the bill.

We look forward every spring and fall to passage migrants, birds that breed to our north and winter to our south. Many plovers and sandpipers are passage migrants.

Some species on the Maine list are irruptive species, northern species that move south to winter in Maine when their food at high latitudes is hard to find. Although we can’t depend on seeing them every year, we can consider species like Snowy Owls, Common Redpolls and Pine Grosbeaks to be expected members of the Maine avifauna.

The remainder of Maine bird species are vagrants, birds that only occur rarely and unpredictably in Maine.

Some vagrants like White-eyed Vireo and Hooded Warbler occur annually in Maine. However, we do have 107 species in Maine that have been sighted five or fewer times. Forty-nine species have been seen only once and another 29 only twice. The sighting of such a bird leads to an onrush of birders anxious to see one of these out-of-range birds. But how did they get here in the first place?

Some birds like swans, geese and cranes migrate as family units so young birds are shown a migration route by their parents. Most songbirds and some other groups of birds have their migration direction encoded in their genes. A first-year Ruby-throated Hummingbird or Black-and-white Warbler finds its way to the species’ wintering ground on its own.

Genes, however, are subject to mutation. Mutated migration genes of birds may direct the bird in the wrong direction. In most cases, the direction is 180 degrees opposite the correct direction. Such reverse migration can lead a bird to head north instead of south or east instead of west. Less commonly, mutations may misguide a bird but not in the exact opposite direction.

Weather can disperse birds to areas beyond their normal range. A hurricane or tropical storm can spirit seabirds or coastal birds long distances. Strong winds can bring Gull-billed Terns or Black Skimmers to Maine from southern coastal areas.

Hurricanes do not play much of a role in transporting landbirds. Most landbirds hunker down before a hurricane hits. But winds associated with weather fronts can explain some vagrancy. Songbirds migrating south from areas to our south on favorable winds may encounter a front with strong winds blowing to the northeast. Those poor birds are buffeted northward until they can find landfall. The slight easterly direction of those winds means that birds are sometimes blown out to sea. It’s no wonder that places like Monhegan Island, Matinicus Rock, Mount Desert Rock and Petit Manan Island have so many extraordinary records of southern vagrants.

During spring migration, some species that nest just to our south may overshoot and land in Maine. They may linger for a day or two but then correct their overflight by flying south to their normal range. We can usually count on a few Hooded Warblers, Worm-eating Warblers or Summer Tanagers every spring.

Some species engage in post-breeding dispersal. Egrets, herons and ibises are particularly known for this behavior. One should never be surprised to see an egret or Glossy Ibis inland at this time of year. Just last year, a flock of White Ibis visited Maine in August in Wells.

These birds may be prospecting for good future nesting sites. In the 1970’s the northern breeding limit of Glossy Ibis was in North Carolina in the Morehead City area. This species has expanded its nesting range to southern Maine. I can’t help but think that post-breeding dispersal facilitated this rapid range extension over the past 50 years. Finally, some species expanding their ranges first trickled into Maine only to become established breeders. This expansion is driven by either population increases in source populations or by climate change. Fifty years ago, Turkey Vultures, Red-bellied Woodpeckers, Tufted Titmice and Carolina Wrens were regarded as vagrants. Now they are established nesters in the state.

Humans are a noisy species. Think about our amplified music, our cars and trucks, construction equipment, chain saws, construction projects, aircraft, windfarms and snowmobiles. There is no doubt that humans alter the natural sonic environment in profound ways.

Our noise production is not restricted to terrestrial habitats. Boat motors represent insults to the soundscape of aquatic habitats. Interference of those sounds with whale song is well known.

This column will draw from a recently published article by a team of European ornithologists, led by Margret Engel, who reviewed the literature on human-caused sounds on birds. The authors develop a valuable framework for assessing the impact of such noises.

People have mused about the effects of noise on animals over the course of history. Aristotle wrote about the effects of human noise on aquatic organisms. Leonardo Da Vinci considered the effect of noise on marine mammals. However, it was not until 1960 when audio-cassette recorders were invented that scientists had ways to assess changes in the vocalizations of birds and other animals in response to anthropogenic noise.

The authors were guided by known effects of noise on humans. Loud noises can be a nuisance, forcing us to speak louder to be heard and straining to hear other people. But loud noises can cause more serious effects like sleep disturbance, cardiovascular and metabolic problems, and adverse effects on learning in children.

The Engel article is a synthesis of the literature on known effects of human-caused noise on birds. The 50 articles reviewed were published in the past 60 years. Of course, with over 11,000 bird species, we have no information on the effect of noise on most bird species, but the reviewed articles do include data from 12 orders of birds. Birds are the best-studied group of animals in terms of the effects of human-produced noise.

The authors divided the impacts of human-caused sounds on birds into three basic categories: Acoustic Perception, Physiological Response and Behavioral Response.

As birders, we are aware of the diversity of the vocalizations of bird species. Black-capped Chickadee males give a song with the cadence of “cheeseburger” or “hey curly”, used to attract a mate and deter competing males. Soft chip notes serve as contact calls to keep a flock together. The “chick-a-dee” call is an alarm call and the number of “dee” syllables indicates the perceived risk. “Chick-a-dee” puts other chickadees on mild alert but “chick-a-dee-dee-dee-dee” means high alert.

One can understand how human-produced sounds might interfere with the acoustic signals of a chickadee. The frequency of traffic noise is quite close to the frequencies of many bird sounds and calls. Furthermore, these low-frequency sounds can travel long distances and penetrate through vegetated areas.

Human-induced sounds can mask portions of a bird’s vocalizations. Bird sounds may not be heard by other birds, making it difficult to procure a mate or to repel an intruding male or to alert other members of a flock to a Sharp-shinned Hawk.

Physiological responses are less obvious impacts of anthropogenic noise but often dramatic. Human-produced noises can raise a bird’s heart rate. This overexcitation results in reduced fledging of Muscovy Ducks, Great Tits and Eastern Bluebirds.

Noise can produce stress responses, resulting in release of stress hormones, leading to DNA damage. Such damage causes an increase in the number of infertile eggs produced.

Other physiological effects include suppression of the immune system and a reduction in overall health of birds. Noise can produce hearing loss, particularly of higher frequencies.

Behavioral responses include forcing some birds to move out of areas subject to human-caused noise. Local bird diversity then falls. The foraging of birds may diminish in loud environments. Loud noise can affect a bird’s brain, leading to reduced vigilance against predators.

The authors conclude with a fourth type of effect, impact on fitness, that combines the first three impacts to measure the overall effect of survival and reproduction as a function of  human-produced noise. Their sophisticated data analysis showed two clusters of effects. One cluster included acoustic perception and behavioral responses, usually negative, indicating an interaction of these two responses. The second cluster involved physiological responses, nearly all negative.

This work is valuable in providing a solid framework from which to study the impact of human-associated sounds on birds. Mitigating those effects is a huge challenge.

With several billion birds migrating south, understanding the destination of birds is a daunting task. Banding birds is a tried-and-true technique but rather inefficient. For a bird banded in North America that winters in South America, the chances of capturing that banded bird in South America is slim because banding stations are few.

We now have techniques that do not require a marked bird to be recaptured. Satellite transmitters continue to be miniaturized so that even a small bird’s travels can be tracked from a computer desktop. The Motus Wildlife Tracking System, a project directed by Birds Canada, uses radio telemetry whose signals can be picked up by strategically placed radio antennas. Ultimately, the Motus team would like to have a dense network of antennas from North America to South America so that any tagged bird would be detected regularly on its migration. See more on this great program at https://motus.org/about/

Geolocators are small devices that can be fitted to most birds. The locator continuously records light-levels and time. By calculating daylength, researchers can determine the latitude and by calculating solar noon, researchers can determine longitude. The downside of this technique is that the geolocator must be recovered. The best way to do so is to band a bird at its breeding site and then recapture the bird the following spring. Fortunately, many bird species show breeding site fidelity.

Let’s consider the Red-eyed Vireo. This woodland songbird occurs broadly throughout North America. Its population is thought to exceed 125 million birds. As a bird of the treetops, this abundant bird is rarely seen by the non-birding population. However, its incessant song, “here I am – over here – in the tree”, alerts a birder to its presence.

Red-eyed Vireos spend the winter throughout a broad area in South America, including Venezuela, Colombia, Ecuador, Perú, Bolivia and Brazil. It would be great to know where the vireos nesting in Maine spend the winter, where the vireos nesting in Oregon spend the winter and so on. Perhaps, satellite transmitters, Motus transmitters and geolocators will provide that information.

Thanks to banding projects, we do have a few examples of an intriguing migratory system called leapfrog migration. A great example is the Fox Sparrow along the Pacific coast of North America.

These sparrows nest from the eastern Aleutian Islands in Alaska south along the mainland Pacific Coast to southern Oregon.  But the various populations of birds reverse their position in the winter. The birds nesting in Washington and Oregon do not migrate at all. Those in southern British Columbia leap over the Washington and Oregon birds and migrate to central California. The Alaskan nesters migrate all the way to southern California.

An Old-World example of even greater geographic scope is the Common Ringed Plover. These birds nest from the high Arctic down to Portugal. In the winter, the Ringed Plovers in the United Kingdom, Spain and Portugal don’t migrate at all. German, Polish and Belgian birds migrate only a short distance to Spain and Portugal. Scandinavian nesters winter in northwestern Africa and the arctic nesters winter broadly through Africa, some as far south as South Africa.

So, what is the explanation for this migration pattern? The current explanation is that competitive exclusion is occurring. In other words, birds that get to a more northerly wintering area first stake out a territory there and exclude later arrivals. For a Fox Sparrow in southern British Columbia, their best choice of territory is just south of Washington and Oregon. This area offers a reasonably moderate winter climate and a relatively quick flight back to their nesting grounds in the spring. The residents in Washington and Oregon force them south. The Alaskan birds with farther to go fail to reach the central Californian wintering sites before they are occupied by British Columbian birds and move all the way to Southern California.

Humans have a propensity to organize, to put things into boxes. People who try to pigeon-hole nature often do not fare well with their efforts. I still remember the admonition of one of my biology professors who said that nature has not stake in being classified.

As this fall migration proceeds, we can see how our attempts to sort out different migration strategies may lead us astray. One dichotomy that is often used for migratory birds is to contrast long-distance with short-distance migrants. Usually, a North American long-distance migrant describes a species that moves south out of the continent to Central America, South America or the Caribbean islands. A host of our nesting birds fall into this category: Ruby-throated Hummingbirds migrating to Central America, Red Knots to Argentina and Scarlet Tanagers broadly across South America.

In contrast, short-distance migrants typically move south to areas with more clement winter weather but do not leave the continent. Some of our breeding birds, like the American Robin, travel only short distances. Some may only go as far as Massachusetts. Other short-distance migrants like our yellow-Rumped warblers may go as far as the coastal regions of the mid-Atlantic states. American Tree Sparrows nest on the taiga and high altitudes and migrate to Maine for our “mild” winters.

We can see the messiness of this system by comparing a short-distance migrant like Lincoln’s Sparrow that may winter in the Rio Grande Valley (that’s where I saw the species for the first time) with a long-distance migrant like the Rose-breasted Grosbeak that spends its winter in Mexico. Hardly a difference there in distance traveled.

Let’s compare that same grosbeak to another long-distance migrant, the Arctic Tern, some of which migrate from pole to pole every spring and fall. The differences in migration length are huge but both are classified as long-distance migrants.

Another contribution to the inadequacy of our classification is the phenomenon of partial migration. Our Field Sparrows nesting in southern Maine head south to the Carolinas or beyond for the winter. The Field Sparrows that nest in North Carolina do not migrate so there is a mix of resident and migrant sparrows in the winter. It turns out that the resident sparrows outcompete the migrants and have a higher survivorship over the winter.

Blue Jays are a local example showing partial migration. In some years, some but not all our Blue Jays migrate south in the fall. In years where oaks have high acorn production, the jays stick around to enjoy their favored food. In years where acorn production is meager, many jays move south.

American Goldfinches, Purple Finches, Red-breasted Nuthatches and Black-capped Chickadees may show partial migration as well.

As surely as temperatures decrease as you travel toward higher latitudes, so does temperature fall as you climb a mountain. Altitudinal migration is an underappreciated yet common type of migration.

One can find information on most aspects of a bird species by consulting The Birds of North America. This work is a series of species accounts, each written by an expert or experts on that species, reviewing all that is known about a particular species. In a 2017 paper, Alice Boyle scoured the 603 species accounts for North American breeders in search of evidence for altitudinal migration. She found that altitudinal migration was reported for 163 species (27%).

As you might imagine, most of these species occur in the western part of North America where many of the Rocky Mountains, Cascade Mountains and Sierra Nevada are over twice as high as the tallest mountains we have.

Nevertheless, we do have altitudinal migrants in Maine. Here is a partial list: Hairy Woodpecker, Pileated Woodpecker, Northern Flicker, Canada Jay, Brown Creeper, House Wren, Dark-eyed Junco, Purple Finch and Evening Grosbeak. These birds may only migrate a few miles as measured along the surface of the earth.

Just to add to the complexity, some species show partial altitudinal migration with some species sticking out the winter at high altitude and others descending where temperatures are more moderate.

What about really tall mountains? Using eBird records, researchers found that 70% of the 302 species that breed at high altitude in the Himalayas engaged in altitudinal migration. Who’s surprised?

Defining a species is, like any other scientific endeavor, subject to revision as we learn more. The provisional nature of taxonomy is surely evident in birds. The American Ornithological Society (AOS) has a committee, the North American Check-list Committee (NACC), that maintains the official checklist of North American birds.

Ornithologists who believe that a taxonomic change (combining two species into one or splitting one species into two or more) is in order, submit proposals to the NACC. The proposal may include observations on interbreeding or lack of interbreeding, morphological differences and, increasingly, comparisons of genes. The committee considers the proposals throughout the year and publishes a committee report in July, updating the North American check-list.

Bird listers eagerly await these yearly reports. It is possible for birders to get a life bird on their life list if a split is accepted. For instance, the Pacific wren was split a few years ago from our eastern Winter Wren. On the other hand, lumped species diminish one’s life list.

This year’s supplement has many changes that affect Caribbean or Central American birds that I will not cover here. However, there are three decisions that affect Maine birds.

The first decision addresses a proposal to combine Common Redpoll with Hoary Redpoll. Hoary Redpolls are paler with a very short, conical bill. They have less streaking on the breast and lack any dark streaking on the undertail coverts. The NACC decided to lump the two species into one species, Common Redpoll. Many of you, like me, have just lost a species on your life list.

The evidence that convinced the NACC to lump the two species is based on a genetic phenomenon that I find fascinating. Stick with me for a little cell biology. Birds like us, have a number of paired chromosomes in their cells. The thousands of genes of a bird are lined up along the chromosomes.

To form reproductive cells (sperm or eggs), cell division must occur to produce cells with a single copy of each chromosome. The single chromosomes in a sperm cell combine with the single chromosomes of an egg to make an embryo with two copies of each chromosome, half from mom and half from dad.

Before a cell divides to form eggs or sperm, the tips of paired chromosomes may overlap and trade a portion of the tip of each chromosome. Imagine each of your arms is a chromosome. Cross your arms at the wrist. Now imagine that your left and right hands switch arms. That process, called crossing over, happens about half of the time and promotes greater diversity among the chromosomes of the reproductive cells.

Occasionally, the process goes awry. One of the tips of the chromosomes that is exchanged flips around before it attaches to the opposite chromosome. This time, one of your hands that is exchanged is attached by the fingers to the forearm with the wrist at the tip. 

For birds that inherit one chromosome with the inversion and one without, crossing over is not possible in that region of the chromosome because the corresponding genes do not line up. So, the genes in the inversion are linked together to make a supergene. And guess what those inverted genes produce? Pale plumage, short bills, limited streaking – the marks of a Hoary Redpoll.

Since all the other genes of redpolls are freely exchanged between Hoary Redpoll and Common Redpoll, the NACC chose to lump the two species, recognizing there are two distinct forms based on the presence or absence of the inversion. Pretty cool!

The Barn Owl, rarely found in Maine, has been regarded as a cosmopolitan species, found on all continents except Antarctica and on many oceanic islands. A proposal to split Barn Owl into three species was headed up by Maine’s own Louis Bevier and colleagues. The proposal was accepted and now we have American Barn Owl in North America. The other barn owl species are Eastern Barn Owl and Western Barn Owl.

The committee made one change based on grammar. They removed the hyphen from night-heron so that we now have Black-crowned Night Heron and Yellow-crowned Night Heron.

You have certainly noticed how a dog will suddenly respond to a sound that you can’t hear. When you take a dog for a walk, it will frequently stop to sniff a smell that you can’t detect. A cat can see a mouse in a dark room that is pitch black to you.

The acuity of the senses of different species varies. It is a challenge to try to understand the behavior of a species whose senses differ so much from our own. The limitations of our senses constrain how effectively we can understand another animal’s behavior.

This constraint was first recognized in prescient work written by the German biologist Jakob Johann de Uexküll about a century ago. He proposed the concept of Umvelt, best translated as self-centered world.  Uexküll argued that organisms in the same environment may have quite different Umwelts. In other words, animals in the same habitat may experience the world in quite different ways because of the relative strength and weaknesses of different senses. Animal behavorists must avoid pitfalls by not recognizing their study animals sense the environment in ways that our own senses can’t.

Let’s compare the Umvelts of birds to our own Umvelt. In some ways, birds perceive their environment in ways we cannot sense or comprehend.

Many birds sing so it is no surprise that the sense of hearing in birds is pretty good. Our hearing acuity is similar. Our ears can hear some low frequencies birds can’t hear, and birds can hear some frequencies that are higher than we can detect.

However, birds are better at us in hearing the detail in a sound. We hear the characteristic call of an Eastern Whip-poor-will as three notes rather than the five notes a bird hears. A Winter Wren can produce a hundred notes in a single song to our ears, but birds hear far more. Those extra notes matter to a bird.

Among mammals, our vision is well developed. We have three types of cones in the retinas of our eyes that are sensitive to blue, red and green colors. Most mammals only have two kinds of cones, so the acuity of their color vision is limited.

Birds outdo us. They have four kinds of cones in their retinas and one of them can detect ultraviolet light, invisible to us. We can use technology to render objects in the environment that reflect ultraviolet light as color visible to us but, alas, we have no way to sense the world as birds too.

Armed with this information, we now know that some birds like Eurasian Starlings have patches of feathers that reflect ultraviolet light that are used in identification of individual birds. To us, they all look the same. These differences among individuals seem to be important in mate selection.

Over 100 species of birds are now known to reflect ultraviolet colors. Birds that to our eyes have similar male and female plumages like Cedar Waxwings, Barn Swallows and Eastern Meadowlarks, have different ultraviolet patterns making it easy for birds to tell males from females.

Bird eyes are better than ours in seeing details. This ability is tested using images of parallel white and black lines. By reducing the width of the lines, a test animal will ultimately see the image as a black object. Birds are twice as good as us at discerning narrow white and black lines. That means that that a bird like the Wedge-tailed Eagle can detect a rat from a mile away. No wonder that rodents are so skittish!

In general, birds have a more poorly developed sense of smell than us. There are exceptions. Pigeons smell their way back to their roosts once they get close. Albatrosses and other tubenoses can smell the oils given off by their squid and invertebrate oceanic prey. Turkey Vultures locate carrion by smell.

Touch acuity is similar in birds and humans. Humans have more taste buds than birds, so our taste is certainly more important than in birds.

Birds have one sense we lack. Birds can detect the earth’s magnetic field. This sense is particularly important in orientation and navigation for migrating birds. Despite years of research, we still do not where the magnetoreceptors are in birds.

The fall migration is sneaking up on us. Already most of our breeding swallows have departed the Pine Tree State for warmer wintering areas. A diversity of shorebirds can be seen on intertidal sand flats and moist lake and pond edges. They are just passing through.

Most of our migratory perching birds move through North America in fits and starts. They may migrate 50-100 miles south during one night and then linger for a few days until they have refueled and the weather is favorable.

But for those who will winter in Central America or South America, a big hurdle waits for most of them: the Gulf of Mexico. This trans-oceanic route cuts the distance of getting into the tropics compared to flying westward overland and then south into Mexico and beyond. A successful flight over the Gulf is a non-stop flight. Birds that lose their strength and land on the water will perish.

These flights are marvels of endurance but pale in comparison to some of our other species. Semipalmated Sandpipers wend their way from their arctic breeding grounds to get to the Bay of Fundy to fatten up for an arduous trek. Some semipalmateds will make it into New England. Relatively few go further south because most make a non-stop flight over the ocean all the way to the productive mud flats at the mouth of the Amazon River in South America. This flight requires four days of continuous flight.

Blackpoll warblers are the northern-most breeding warblers. They migrate in greatest numbers during the fall along the eastern seaboard. They can be abundant in New England but oddly enough are quite uncommon further south in the United States in the fall. We now know that blackpolls follow the same strategy of the Semipalmated Sandpipers in undertaking one huge flight to get to their South American wintering grounds.

The ability of birds to undertake long migration is astounding. They have several metabolic challenges to meet. First, the resting metabolism of a bird is higher than a mammal (also warm-blooded) of similar size. Smaller birds like hummingbirds, warblers and sandpipers have higher metabolisms than larger birds. When a bird flies, its metabolism increases as much as eight times its resting rate. The best you can do with maximum exertion is to double your resting rate. So, a long-distance migrant needs a lot of fuel and a way to carry sufficient fuel for its flight.

Fat is the fuel of choice for migrating birds. Fat has two big advantages over carbohydrates or proteins as a fuel source. First, the combustion of a gram of fat yields more energy than either a gram of protein or carbohydrate. Second, the breakdown of fat produces more water as a byproduct. This metabolic water sustains a migrating bird that has no way to drink in flight to replace lost water.

The fat for migration is carried just below the skin on the underside of the body. But packing on the right amount of fat is tricky. A bird needs to have enough fat stored to fuel its migratory leg but carrying an excess means that flight efficiency will be low because of the greater weight carried. This calculus is not critical for birds flying over land; they can simply land and feed in the morning.

Trans-oceanic migrants are at more risk. We know that Semipalmated Sandpipers double their weight from 20 grams to 40 grams before embarking on their long migration. Birds captured in Suriname as they end their four-day flight are just about at their lean body weight.

The gut and gonads of migrating birds regress before migration. Every bit of weight reduction helps.

Migrating birds use the wind to their advantage. In the fall, a low-pressure system pushing against a high-pressure system is advantageous for southward migration. The counterclockwise winds of the low-pressure system and the clockwise winds of the high-pressure system both blow south where the two systems come together. That is go time for migrating birds.

Semipalmated Sandpipers and blackpolls leave North America by flying southeastward out to sea! They will ultimately reach the trade winds, dependably strong winds that will help push them to South America.