Maine Birds

Aberrant Plumages

February 13, 2017 · No Comments

This snowball of a House Sparrow has been frequenting Peggy Blair’s feeders in Clinton for the past four years. A number of birders got to see this sparrow as they made the trek to Peggy’s feeders to see the two Dickcissels that spent two weeks there, starting in late November.

This sparrow has been the subject of a lot of discussion among birders. Is it an albino? A partial albino? A leucistic bird?  I thought the white House Sparrow would provide a good jumping off point for a discussion of aberrant plumages in birds.

In college, I had a professor who said that nature has no interest in being classified. To be sure, trying to pigeon-hole odd plumages of birds is fraught with problems. Nonetheless, Han van Grouw took a crack at classifying different kinds of aberrantly white-plumaged birds.

To start, we need to know that two major types of feather pigments occur in birds. Carotenoids are the feather pigments that make some birds so colorful.  Carotenoid pigments vary from pale yellow to scarlet red. Birds cannot make carotenoids but rather acquire them from their diet. The pink of flamingos is produced by pink carotenoids obtained from the small shrimp the birds prefer.

Melanins provide the blacks, grays, dark-browns and reddish-browns in feathers. Birds are able to synthesize their own melanin using the amino acid tyrosine, one of the constituents of proteins.

Let’s start with albinism.  An albino bird lacks the enzyme tyrosinase so is not able to convert tyrosine to melanins. An albino bird will have no black or brown feathering on the body at all. Furthermore, the eyes and skin are colorless.  They appear red because of the blood that can be seen through the skin.

Peggy’s white House Sparrow is clearly not an albino. The eyes are dark and you can see some black feathering on the head.  This bird is clearly capable of making melanins.

Albinism is actually one of the least common aberrant white plumages. And here’s a fact to bend your mind. It is possible to have a bird like a Summer Tanager with beautiful red plumage that is an albino.  If that bird cannot produce melanins, it can still acquire carotenoids from its diet to make red feathers. But that bird will have colorless skin and eyes. So, a male Summer Tanager with red eyes is an albino!

The life span of an albino is usually much shorter than average. The reason is bad vision. The lack of eye pigments means that albinos are extremely light-sensitive and also have poor depth perception.

The phrase partial albino is frequently applied to birds from colorful species with some but not all white feathering. I agree with van Grouw that this phrase needs to be stricken from our vocabulary. If a bird can produce some melanin, like our House Sparrow, it is not an albino. Partial albino is self-contradictory, like “very unique” or “slightly pregnant”.

Leucism describes the condition where some or all of the feathers of a bird lack melanins. A leucistic bird can synthesize melanins but it lacks the ability to transfer the melanin to its feathers. This description fits our white House Sparrow perfectly. We know that the bird can produce melanins because the eyes are dark and a few dark feathers appear on the head.

Leucism can vary from fewer than a quarter of the feathers being white to totally white feathers. A leucistic bird does not have the defective eyesight of an albino so its expected life span is not shortened like an albino.

I’ve just touched the surface of aberrant plumages here. Some birds appear to have washed-out feathers but not white. Reductions in the quality (Brown mutation) or quantity (dilution) can yield abnormally light-colored birds.  Some birds overproduce melanin (melanism) and appear much darker than normal. And yes, there are shades of gray!

[First published on December 25, 2016]

→ No CommentsCategories: Genetics · Morphology

Bullock’s Oriole and Dickcissel; Feeding Behavior at Your Feeder

February 13, 2017 · No Comments

The late fall sometimes brings unusual birds into Maine. Whether storm-tossed or directionally challenged, such birds find themselves far removed from others of their species. We have a couple such species represented in Maine late this year.

A Bullock’s Oriole has been visiting a feeder in Camden since November 23.  Bullock’s Oriole is normally found in western North America during the nesting season and mostly in Mexico during the winter. Here is a photo of this beauty: http://tinyurl.com/zjdb7hz

The ranges of Bullock’s Oriole and Baltimore Oriole meet in the Great Plains. Sometimes individuals of the two species hybridize, producing viable young. Based on this interbreeding, the American Ornithologists Union lumped the two species into one species, the Northern Oriole, but recently reversed their decision based on genetic information.

The Maine Bird Records Committee presently accepts only one prior record of this species, an individual photographed on October 31, 2012 by Jan Pierson in Phippsburg.

On November 30, an adult male Dickcissel was found in Clinton, consorting with a flock of House Sparrows. A few days later, a first-year male Dickcissel was spotted in the flock as well.

Dickcissels are birds of grasslands, abundant in the Midwest. They winter in Central and northern South America.  Dickcissels are not mega-rarities in Maine like Bullock’s Oriole but are uncommon enough to be a thrilling sighting.  Here are some pictures: http://tinyurl.com/gofqneh

Watching Birds at a Feeder

Attracting birds to our yards is a source of joy.  But have you looked carefully at how the birds handle the seeds we provide?

House Finches, Evening Grosbeaks and other large-billed finches are adept at cracking seeds to separate the tasty kernel from the nutritionally poor husk.  These finches do not crush the seeds with brute force but rather do so with an efficient delicacy.

Most seeds have a suture line where the two sides of a seed cover are joined. Such sutures are easily seen in a sunflower seed.

If you look carefully at a feeding finch, you can see that the surface of the upper bill narrows to a tip.   The lower bill surface is a groove.  The point of the upper bill fits nicely in the groove of the lower bill.

To eat a sunflower seed, a finch will manipulate a sunflower seed so that the point of the upper bill bears down directly on the suture line.  As the bill is closed the seed is secured in the groove of the lower bill and the “tooth” of the upper bill splits the seed at the point of least resistance.

Using its tongue and bill, a finch casts out the halves of the sunflower seed husk and swallows the heart.

Some seeds have a second covering, like the reddish skin of a peanut. A finch has the beak dexterity to remove these coverings as well.

Chickadees and titmice are fond of sunflower seeds as well but their short, pointed bill is not an effective crushing tool.  Rather, a chickadee uses its pointed bill to chip away at the seed.

A chickadee will come to your feeder, grab a sunflower seed and then fly off to a nearby branch. The chickadee’s long toes are perfect for holding the seed tight against the branch.  Seed secured, the chickadee attacks the suture of the seed with its bill.

More than one inexperienced birder has been confused by a chickadee seeming to peck repeatedly at its toes. Rather, the morsel-to-be receives the pecks of the bill.

It takes longer for a chickadee or titmouse to open a seed compared to a finch.  But sometimes a chickadee will take a seed and then come back almost immediately.  In all likelihood, the chickadee is caching seeds in a bark crevice for use later in the season.  Chickadees have phenomenal memories so can retrieve most of their cached seeds. Keep your eyes peeled for this behavior.

[First published on December 11, 2016]

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Migration Talk at the University of New England

December 21, 2016 · No Comments

I was invited to speak at the Center for Global Humanities of the University of New England on December 12.  My talk was recorded and posted to YouTube by the Center.  I spoke on the arrival date project I have been working on for the past 22 years, thanks to several hundred birders who have contributed data. If you would like to watch the talk, here’s the link: https://www.youtube.com/watch?v=VzNxu_kWnd8&feature=em-upload_owner

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Evening Grosbeaks

December 17, 2016 · No Comments

Additional reports of Evening Grosbeaks from across the state are arriving daily. Perhaps you have been one of the lucky ones to have them in your yard.   Members of this species are awfully restless in the winter so count yourself fortunate if Evening Grosbeaks linger for more than a week at your feeder.

I strongly encourage you to learn the distinctive flight calls of Evening Grosbeaks.  Sometimes the note given (often translated as “cleep”) is sweet and other times burry.  In either case, it is instantly recognizable once you train your ears. Visit this site for good recordings of the calls: http://bit.ly/2fiPyiO

As satisfying as it is to detect an unseen flock of Evening Grosbeaks overhead, seeing these robust beauties is even better. The males with their yellow bodies, brown heads with yellow eyebrows and a large patch of white on each black wing, are stunning.  The understated females, with tones of bluish-gray on their body and a large white patch on each black wing, have a beauty of their own. They love sunflower seeds so keep your feeders stocked.

The scientific name of this finch is Coccothraustes vespertinus.  The genus name “Coccothraustes ” means “kernel breaker”, certainly appropriate for a bird with a stout, conical beak.  The species name “vespertinus”  refers to “evening”, a puzzling claim since these birds are active all day long as anyone lucky enough to have them at a feeder can attest!

The evening reference comes from observations made by a Major Delafield, a United States boundary agent in 1823:

“At twilight, the bird which I had before heard to cry in a singular strain, and only at his hour, made its appearance close by my tent, and a flock of about half a dozen perched on the bushes in my encampment . . .. My inference was then, and is now, that this bird dwells in such dark retreats, and leaves them at the approach of night”.

Perhaps Delafield heard some Evening Grosbeaks as they were going to roost but they certainly do not call only at twilight. Nevertheless, Delafield’s claim of calling restricted to the twilight hours was accepted by ornithologists who dubbed Coccothraustes vespertinus the Evening Grosbeak for its standardized common name.

Evening Grosbeaks are relatively recent arrivals in Maine.  This species is originally a bird of western North America. The imminent Massachusetts ornithologist, Edward Forbush, claims that until the winter of 1889-1890, Evening Grosbeaks were virtually unknown east of Ohio.  During that winter, an eastward invasion brought these birds into eastern Massachusetts.

A second large invasion came in 1910-1911, leading to the gradual establishment of Evening Grosbeaks as breeding birds in southeastern Canada and the northeastern United States.

Some have suggested that the immigration of Evening Grosbeaks into the east was facilitated by the spread of box elder (Acer negundo) trees.  The seeds and buds of box elders are highly favored by Evening Grosbeaks.  The planting of these trees as ornamentals may have contributed to the invasion of Evening Grosbeaks to Maine.

Evening Grosbeaks were fairly common birds in the 1960’s and 1970’s in the northeast. Their success may have resulted from the widespread spruce budworm outbreaks then.  Evening Grosbeaks feed their young protein-rich insects and spruce budworms are among their favored prey.

Spruce budworm populations go through decades-long patterns of growth and decline. A decline in spruce budworm abundance in the early 1980’s is correlated with a steep decline in Evening Grosbeak abundance. The grosbeak populations continue on a downward slope begun around 1980.

Human impacts are certainly responsible for some Evening Grosbeak mortality. This species is the tenth most likely species to be killed from window collisions.  Many Evening Grosbeaks are killed by cars because the birds come onto roads to collect grit for their gizzards as well as road salt.

[Originally published on December 4, 2016]

 

 

→ No CommentsCategories: Foraging · Identification · Migration · Species Accounts

Northern Finches

November 28, 2016 · No Comments

Are they coming this winter or not?  One hears this question a lot in birding circles at this time of year.  The question centers on the group of birds called the northern finches or winter finches, higher-latitude birds that grace us with their presence in some winters but not in all.  The only predictable feature of northern finch abundance is unpredictability.

The northern finches include Purple Finch, Pine Siskin, Evening Grosbeak, Pine Grosbeak, White-winged Crossbill, Red Crossbill and Common Redpoll.  Although some of these species nest in Maine, most individuals of these species nest well to our north.

All of these species depend on the seeds from trees for their sustenance, particularly during the winter. Redpolls are fond of birch seeds and the rest specialize on conifer seeds (firs, hemlocks, spruces, larches and pines).  Pine Grosbeaks have a taste for fruit as well.

When seed abundance is adequate on the breeding grounds, these finches will forgo a southern migration and spend the winter on their breeding grounds.  The birds spare themselves from the significant cost of migration. However, seed production by the trees the finches depend on varies dramatically from year to year. In a year of low seed production, the northern finches are forced to be nomads, wandering south until they encounter the seeds they need.

These southern migrations are called irruptions.  The birds irrupt or move into areas away from their breeding grounds.

In our neck of the woods, three conditions have to arise for us to see an irruption of Common Redpolls, White-winged Crossbills or other irruptive species. First, seed production on the finches’ breeding areas has to fail. Second, seed production of those trees has to be high in Maine. Third, the irruptive finches have to happen upon our abundant seeds in their wanderings.

For the past 20 years or so, Ron Pittaway in Ontario has been putting out a winter finch forecast.  He gathers data on the cone production of various conifers, birch and fruit trees.  He has been remarkably good in predicting flights of irruptive finches.  His data for southern Ontario mirror abundances in neighboring provinces and states.

According to Pittaway, this winter will likely be poor in Maine for Pine Grosbeaks. Mountain Ash in the boreal forest produced many berries this summer.  Pine Grosbeaks will have no need to irrupt.

On the other hand, cone production by several species of conifers across the boreal forest was modest at best.  Pittaway expects White-winged Crossbills, Red Crossbills and Pine Siskins to stage irruptions.  Purple Finches have already started to appear in Maine in good numbers at feeders.

The Evening Grosbeak has had a couple of excellent breeding years so their population seems to be on a bit of an upswing after several decades of declines.  Pittaway thinks these birds are likely to be seen at feeders in southern Ontario and northern New England.

So far, he seems right on the money.  In the past week or so, I have heard reports of Evening Grosbeaks in Machias (100 birds!), Newcastle, Bangor, Wells, Skowhegan, Gardiner, Milbridge, Pittsfield, Biddeford, and Yarmouth.  You get the picture; it is an irruption!  I am not alone in hoping we have an abundance of these beautiful finches here all winter.  Keep those sunflower feeders filled.

Red-breasted Nuthatches depend on conifer seeds during the winter as well. Unsurprisingly, their irruptions tend to coincide with those of Purple Finches, Pine Siskins and White-winged Crossbills.  I’ve seen more Red-breasted Nuthatches this fall than I have in the past few years.

Blue Jays also show irruptive behavior, responding to the abundance of their preferred winter food, acorns. Acorn production has been low this year in central Maine, perhaps due to the dry summer we had.  Many of our Blue Jays will move south for the winter.

[First published in mid-November, 2016]

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Listing and Competitive Birding

November 28, 2016 · No Comments

Grocery lists, to-do lists, bucket lists.  Making lists is a common human behavior.  Birders engage in this practice, keeping lists of birds seen on trips or birds seen at their feeders.  But the most common such list is the life list, a compendium of all the species of birds one has seen in one’s lifetime.

Some birders keep a life list but don’t even bother to count how many species are on their list. Others keep close track but keep their totals to themselves. Yet others are interested in publishing their list totals and comparing their lists to others.

Let’s step back in time to 1970. Jim Tucker of Texas had envisioned a birding publication that would focus on the publication of top species lists for different areas, identification tips for hard-to-identify birds and descriptions of sites where rare species might be seen. The first issue of his brain-child, Birding, was published in February, 1970 and soon thereafter the American Birding Association (ABA) was created with Birding as its flagship journal. The early members of the ABA thought Birding should not contain articles on ornithological research or on conservation efforts but rather should fill a perceived void for competitive birders and birding hobbyists.  Thus, a formal mechanism for competitive listing began.  Birders submitted their list totals and could see how they stacked up against other birders. The game was on!

The ABA has thousands of members now.  The mission has expanded considerably to cover avian conservation, book reviews and ornithological history. However, maintaining members’ list totals is still a mainstay of the organization.

You can check out list totals at the Listing Central page on the ABA website (http://listing.aba.org/). For Maine, the top lifetime lister is Doug Hitchcox with 374 species seen.  The top year list for Maine (the total birds seen in a calendar year) is also Doug Hitchcox for his 2011 effort.  Frank Paul has the largest life list for Cumberland County.

Keep in mind that not all birders submit lists to ABA Listing Central. The popular eBird site (http://tinyurl.com/c8atyh) has the capacity to generate lists at different geographic levels and for different time intervals. I see that Pat Moynahan has a Maine life list of 380 species. I know there is at least one other birder in Maine whose lists do not appear in the ABA or the eBird database who has seen even more species in Maine.  Some top listers simply choose to not play the game.

I’ve been thinking about listing lately because of the success of four birders who are doing a Big Year in North America. These hard-core birders are traversing the continent to try to surpass the total of 749 species seen in 2013 by Neil Hayward.

Completing a successful Big Year requires finding all of the 671 species that occur regularly and widely in North America.  One must target another 82 species that occur in North America each year but are rare.  Finally, one has to make trips to places like the Aleutian Islands, southern Texas and southeastern Arizona to find vagrants.  The time and money to be able to jump on a plane at a moment’s notice to see a rare bird is essential.

It turns out that 2016 has been a phenomenal year for rarities. Four birders have broken the 700 species mark, the first time that has ever happened in a calendar year. Furthermore, the record of 749 species was shattered in July!  John Wiegel, an Australian, saw a Buller’s Shearwater on July 16 for his 750th species. Olaf Danielson, a physician from South Dakota, racked up his 750th with a Red-faced Cormorant in Alaska. Currently, Wiegel is in the lead with 770 species to Danielson’s 765. Wow!

Laura Keene has found 737 species to date, besting the prior women’s record. Finally, Christian Hagenlocher has tallied 734 species.

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Swainson’s Hawk in Millinocket!

November 28, 2016 · No Comments

On September 29, Rhonda Little-Aifa posted photographs of an unfamiliar hawk on the Maine Birds Facebook page.  The bird was at the Millinocket Airport on Medway Road, first seen a few days earlier.

Doug Hitchcox, the Naturalist at the Maine Audubon Society, recognized the bird as a Swainson’s Hawk.  Swainson’s Hawks nest on cliffs near grasslands in western North America and spend the winter in South America, as far south as Argentina.

Clearly, this was a bird out of place.  The Maine Birds Checklist Committee recognizes only two prior records for the state, one seen on May 3, 2009 in Pownal and on seen on September 23, 2013 in Harpswell.  Eight other reports of this species, dating from 1883 to 2005, have not yet been reviewed by the Checklist Committee.

A major migration of birders to Millinocket began on September 30. Dozens of birders got to see this cooperative bird, particularly over the weekend.  The hawk was last soon on the morning of October 4.  You can see pictures at: http://ebird.org/ebird/view/checklist/S31826769

Swainson’s Hawk belongs to the genus Buteo, the genus that also includes the familiar Red-tailed Hawk and Broad-winged Hawk.  Swainson’s has proportionally longer wings and a smaller bill than the similarly-sized Red-tailed Hawk.

Swainson’s Hawk has colloquial names of locust hawk and grasshopper hawk.  The hawks feed often on the ground, chasing grasshoppers, a favored food.  The Millinocket Bird spent most of  its time perched on the fence surrounding the airport or walking/running on the ground, chasing down grasshoppers. Louis Bevier made a video of the hawk capturing a grasshopper: You can watch the video at: https://vimeo.com/185072912

Swainson’s Hawks will also catch dragonflies and other large insects on the wing.

Normally, Swainson’s Hawks migrate south from their western breeding grounds, through Central America and then spread out in South America. Like most Buteo hawks, Swainson’s Hawks are averse to migrating over water.

Swainson’s Hawks are one of the most abundant species migrating through the Isthmus of Panama. Hawk watchers in Panama City counted 900,000 soaring migrants (mostly Swainson’s Hawks and Turkey Vultures) passing overhead on a single day in November of 2013.  That record was eclipsed on November 2, 2014 when 2.1 million birds passed over.  What a spectacle that must have been!

This hawk joins a long list of vagrants to Maine from western North America.  These birds include White-winged Dove, Western Flycatcher, Calliope Hummingbird, Hermit Warbler, Brewer’s Sparrow, Black-throated Sparrow and Western Meadowlark.

I think it is significant the the Millinocket Swainson’s Hawk was a young bird, born in the summer of this year.  Many birds that appear in unexpected places during migrations are naïve, inexperienced birds.  Young birds are much more likely to make navigational errors than more experienced birds.

Navigation during migration involves two abilities. Most migrants are capable of vector navigation, maintaining a particular compass direction for a specified length of time or distance.  True navigation requires that a bird knows exactly where it is, even if it is displaced by a storm or wind.

Experiments demonstrate differences between the navigational abilites of juvenile and adult birds. Imagine Yellow-rumped Warlers banded on their breeding grounds in Maine that normally would migrate south to North Caroina for the winter. Vector navigation in a south-southwest trajectory will get those birds to their wintering grounds.

Some ornithologists have experimentally captured such birds and displaced them eastward or westward.  Let’s fly some warblers from Maine to Minnesota and release them there in the fall.  Adult birds have true navigation; they realize where their displaced position is and will migrate in a southeasterly direction to get to North Carolina.  The young warblers are poor at true navigation.  Most will use their vector navigation skills and head south toward Texas. Vagrant birds therefore tend to be young birds that are much more likely to get lost.

→ No CommentsCategories: Foraging · Identification · Insects · Migration · Species Accounts

Fall Migration Tips – II

November 28, 2016 · No Comments

In the last column, I provided some tips on how to predict when migrating birds are likely to be seen in your local patch. Experiencing a fall-out of migrants is exhilarating. In today’s column, we will explore ways that you can experience migrating birds while they are in flight.

Some birds migrate during the day.  We have all thrilled to skeins of Canada Geese or Double-crested Cormorants, winging their way in V-formation to more favorable areas.  Hawks, eagles and falcons are diurnal migrants as well.  They are adept at taking advantage of the vertical winds, called thermals, that form during the day due to uneven heating of the earth’s surface. A rocky outcrop will warm more rapidly than an adjacent forest. The rocks warm the air, the air rises and is replaced by cooler air from the adjacent forest.  That cool air warms, rises and you get the picture.  Hawks are masters at soaring from thermal to thermal, scarcely beating a wing.

A sunny day with winds in the right direction produces spectacular numbers of these soaring migrants.  Mt. Agamenticus in the Ogunquit area and Cadillac Mountain in Acadia National Park have several thousand raptors migrating over them each fall.  Bradbury Mountain in Pownal can be great for spring hawk migrants.

Hawk watching is a boom-or-bust activity.  Make sure the weather conditions are right and you may be rewarded with more hawks than you can follow.

Shorebirds and most of our songbirds are nocturnal migrants.  Advantages of night-time migration are three-fold. The risk of predation from raptors is low. The air is cooler; migrating birds raise their metabolic rate so high they must constantly dump heat or they will overheat. The cooler air helps them balance their heat budget. Finally, the air is less turbulent at night, making powered flight more efficient.

Migrating songbirds mostly migrate at altitudes of 2,000 to 4,000 feet. Shorebirds may fly a bit higher.

How can you see these birds at night? Get your binoculars or, better yet, a spotting scope and train it on the surface of the moon. If migration is occurring, you will see the silhouettes of birds passing in front of the moon’s image.  Don’t expect to see birds flying at their normal migrating height but as birds take off or descend, they are easily seen against the moon.  The technique works well for birds that are no more than several hundred feet above the surface of the earth.

You can also appreciate migrating birds at night from radar images. In the early days of modern radar in the early 1940s, mysterious blips were detected on radar screens. They proved to be no threat to military aircraft.  These echoes were called angels.  Now we know that the angels are small flocks of birds.

The Doppler radar used now for weather forecasting is perfect for detecting bird migration.  Here is the URL for a great tutorial on how to use the freely available NEXRAD radar images to monitor migration: http://www.woodcreeper.com/videos/NCAR_Tutorial-desktop.m4v

Yet one more way to appreciate nocturnal migration is to use your ears.  Nocturnal migrants are noisy, regularly emitting short flight notes.  In some cases, the flight notes are similar to the calls the birds give while they are on the ground.  In many cases, however, the flight notes are only given during a nocturnal flight.

Bill Evans has been a pioneer in the study of nocturnal flight calls.  Visit his website at  http://www.oldbird.org/ He has sonograms for a number of warblers and sparrows.

On a night that is not too windy, you can hear the flight notes above.  However, a microphone will capture many more of those vocalizations.  Evans provides directions on how to build a microphone system using cheap materials like a plastic flowerpot, saran wrap, a dinner plate and an inexpensive microphone.

→ No CommentsCategories: Migration · Weather

Fall Migration Tips – I

November 28, 2016 · No Comments

The southward migration of five billion birds in North America is a staggering phenomenon.  These migratory movements provide us with the chance to see a diversity of birds, often in very high numbers.  I will devote the next columns to ways to fully experience the fall migration.

Migrating birds are flying right on the edge of survival.  Flight is energetically taxing, requiring that a bird’s metabolic rate be raised five times or more above its resting rate.  With the exception of birds like swallows, swifts and kites that feed on insects on the wing, migrating birds cannot refuel during flight. One way migrating birds try to maximize the length of a migratory leg is to take advantage of favorable winds.

A weather map offers you a tool to predict when migrations will be strong by looking at the relationship of low- and high-pressure systems.  Generally, high-pressure systems alternate with low-pressure systems, moving from west to east across the continent.

A high-pressure system has winds that circle the center of the system in a clockwise pattern.  The leading edge of the high-pressure system therefore has winds that flow from north to south.

A low-pressure system has winds that flow counterclockwise.  The winds on the backside of a low flow to the south.

To determine when conditions are perfect for a wave of fall migrants, all you have to do is find the nearest cold front (indicated on the weather map by a line with triangles).  At the cold front, an area of cool air from a high-pressure system moves underneath the less dense, warmer air of the low-pressure system.  The rising air cools, usually causing a line of precipitation.

As the front passes, a strong flow of wind blowing to the south occurs with the interaction of the trailing edge of the low-pressure system and the leading edge of the high-pressure system.  Depending on the rate at which the high-pressure system moves, spectacular migrations may be seen for several days.

If you see a warm front passing across your neighborhood, you do not need to worry about getting up at the crack of dawn to look for migrating warblers or sparrows.  A warm front (indicated by a line with semicircles on your weather map) is caused when a low-pressure system slides over and above a high-pressure system.  In this case, the winds at and behind the front will flow to the north.  Birds migrate mostly when the winds are favorable and will stay put if the winds are opposite their migratory trajectory.

On a favorable night, birds will fly as long as they can, settling down sometime in the wee hours of the morning.  Sometimes, precipitation can cause birds to land en masse.  By luck, a given spot may be hopping with birds.

Where is the best place to look for a fallout? Frankly, serendipity plays a huge role here. Sometime fallouts are broad, occurring over a county-sized area; at other times, the fallouts may be quite restricted.

However, some places are more likely to produce fallouts.  Shrubby areas along the immediate coast are often productive. Birds that are migrating just offshore will seek landfall to rest and refuel. A dawn excursion to a coastal area can produce a stream of tired birds, welcomed by dry land.  Fort Foster in Kittery, Two Lights State Park in Scarborough and the Eastern Promenade in Portland often harbor many fall migrants.  I have experienced fallouts at West Quoddy State Park in Lubec.  Any patch of coastal real estate with some bush and tree cover can be productive.

Migrating birds may look for islands of habitat in areas that are heavily developed.  The Evergreen Cemetery in Portland is one such magnet.

Finally, migrants need water so checking ponds, streams and rivers can produce excellent fall migrant numbers.

→ No CommentsCategories: Migration · Weather

Fall Migration

November 28, 2016 · No Comments

It’s late Augusts and the fall migration is well underway.  Where did the summer go?

Migrations are tremendously expensive undertakings for birds.  They must pack on fat to fuel each leg of their long journey.  To see fall migratory birds, finding an abundant food source is a good strategy.  Putting on fat quickly is an imperative for migrating birds so they know the best places to eat.

My wife and I spend a lot of time in Lubec on Cobscook Bay.  The area is a wonderful birding destination with lots of accessible conserved land.  During the fall migration, my wife and I use the strategy of going to the food to find the birds.  If you want to see diners, go to a restaurant.

The South Lubec Sand Bar can be hopping with shorebirds and other water birds from August into October.  This bar is about a mile long and is adjacent to an expansive sandflat along the South Lubec Road.  This sandflat is the best restaurant in the area for sandpipers and plovers.

Sandpipers forage by rapidly probing into the sediment, capturing invertebrates by feel.  Their bills are well equipped with touch receptors.  The sandpipers prey on small shrimp-like crustaceans called Corophium as well as polychaete worms, marine relatives of earthworms.  These invertebrates are found in the lower to middle part of the intertidal zone.

Plovers use a different feeding technique, relying more on their vision than their touch.  A plover stands and looks for movement in the sediment. The plover then runs to that unsuspecting prey animal and captures the ragworm, bloodworm or other invertebrate.  This form of feeding is called ambush predation or run-and-peck predation.

The plovers and the sandpipers are dispersed broadly across the flat at low tide. Birding at this stage of the tide is fruitless.

The trick is to let the rising tide bring the birds to you. As the tide starts to cover the productive part of the flat, the birds seem to redouble their feeding efforts as they are forced higher and higher in the intertidal zone.  They congregate right along the rising tide line, seemingly oblivious of the humans staring at them.

For an hour or so, large number of shorebirds will be congregated in a narrow swath, affording great views. Eventually, the tide will force the birds to higher ground.  The birds fly off to local fields or other open habitats and the show is over.

I have found that arriving at the sand bar four hours before predicted high tide is optimal.  The birds will start congregating within the next hour.  By two hours before high tide, the birds will have gone to roost.

Of course, it is possible to arrive at high tide and wait for the birds to return.  I have had less success with this method as the birds seem to be more aware of human presence.

We walked the sandbar recently with a group of friends. Diversity and numbers of birds varies from day to day.  We had a corker of a day but not high bird diversity.  We enjoyed stunning close-up views of many Least and Semipalmated Sandpipers. The Leasts with their reddish-brown upperparts and yellow-green legs are lovely birds.

We had fun picking out the occasional White-rumped Sandpiper from the flocks.  These birds are easy to identify in flight by their namesake white rump.  On the ground, they are similar in color to the gray Semipalmated Sandpipers but a bit larger.  The tail of a White-rump extends well beyond the folded wings, unlike the shorter tail of Semipalmated Sandpipers.

A few Semipalmated Plovers and Greater Yellowlegs rounded out our list for the day. We often see a Merlin, Peregrine Falcon and even a Parasitic Jaeger hunting the shorebirds but not that day.

Of course this technique of letting the tide bring the shorebirds to you works on any intertidal mudflat. Give it a try!

 

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