Maine Birds

Entries Tagged as 'Migration'

Bird Orientation, Navigation and Smuggling by Pigeons

October 15th, 2017 · No Comments

The fall migration is on the decline now with most of our flycatchers, swallows and warblers gone for the next seven months. All of these birds depend on insects for their sustenance, a resource in short supply now.

Sparrows and other seed-eaters have a more leisurely migration. They can find seeds, at least until the first snows arrive. Even so, by the end of the month most of our sparrows will be gone to more moderate southern areas.

As I discussed in the last column, we know that the majority of migratory bird species have an innate knowledge of where they should go to spend the winter. It boggles the mind to realize that many first-year birds find their way unaided by adults to their wintering habitat they have never seen. Travel instructions are encoded in their genes.

Considering how migratory birds find their way, we need to recognize two different abilities of birds. First, the birds have a well-developed sense of navigation. In other words, they can set a course and follow it, barring the intervention of hurricanes or other weather phenomena.

Second, some birds have well-developed abilities of orientation. A bird endowed with good orientation abilities knows where it is. Most migratory birds can navigate well but fewer can orient.

A famous experiment done with European Starlings in eastern Europe nicely distinguishes navigation and orientation. Some starlings were captured and placed in a cage in the spring. This particular population of starlings is migratory. In the spring, the caged birds attempted to depart on a northwesterly vector to reach their breeding grounds.

Some birds were transported several hundred miles to the west. Again, the direction that the captive birds chose was recorded. The transplanted birds again tried to migrate to the northwest. They were unable to correct for the fact that they had been moved westward. The starlings showed a good sense of navigation but a poor sense of orientation.

Contrast that result with the abilities of White-crowned Sparrows. A wintering population of birds in southern California migrates each spring to Alaskan breeding grounds. Wintering birds that were either flown to New Orleans or to Maryland ultimately found their way to their Alaskan breeding grounds. These birds were able to compensate for their eastward displacement by biologists. These birds are great at both navigation and orientation.

The abilities to orient and navigate are not restricted to migratory birds.  During the nesting season, birds need to be able to find their way to their nests. The need is particularly acute for birds like Bald Eagles that maintain huge territories or Ospreys or albatrosses that may fish miles away from their nests.

Domestic pigeons have been the subjects of the most illuminating studies on navigation and orientation. Pigeons can home to their roosts from distances as far as 1100 miles.

They use multiple cues for navigation. Pigeons have an internal clock that allows them to determine direction from the position of the sun in the sky. This so-called sun compass is the most important cue. They also can sense the earth’s magnetic field. On cloudy days, magnetic cues become important. We even have evidence that pigeons can smell their home over the last few yards.

Pigeons are able to fly steadily at 50 miles per hour. It’s not surprising that  competitive homing pigeons beat their owners home from a release point.

Homing pigeons played important roles in carrying messages in World War I and World War II. The messenger pigeons were particularly important in the Normandy invasion because the Allies did not want to use radio signals to keep the D-Day invasion a secret.

Pigeons can be used for nefarious purposes as well. Recently, a pigeon whose roost is in an Argentinian prison was caught smuggling 8 grams of marijuana and a memory stick.

[First published on October 1, 2017]

 

Tags: Behavior · Migration

June Vagrants in Maine

September 17th, 2017 · No Comments

Roger Tory Peterson once quipped that birds have wings and they use them. One of the thrills of birding is seeing birds that are either passing through or lost. A vagrant bird can really spice up a daily bird list.

We are accustomed to seeking out rarities during the concentrated spring migration or the more leisurely fall migration (August into November).  In June, most birds should be on their breeding grounds.

Contrary to this logic, June brought some remarkable rare birds to Maine this year. On June 7, a Burrowing Owl was photographed near the Katahdin Inn in York. At this time of year, Burrowing Owls should  be in the western half of temperate North America, nesting in abandoned prairie dog burrows on the plains. There is also a disjunct population in Florida. Unfortunately, the owl was a one-day wonder. If accepted by the Maine Bird Records Committee (hereafter, MBRC), this bird will be only the second ever found in Maine. The first Burrowing Owl lingered for over a month in late summer in Washington County in 2006.

On June 9, an apparent drake King Eider was sighted off Potts Point in South Harpswell. The written description and fuzzy photographs (taken from a long distance) support the identication. These birds breed in the high Arctic; an adult male in Maine in June is peculiar, indeed.

On June 12, a Magnificent Frigatebird was photographed while perched on Stratton Island and was seen later that day from Prouts Neck as well as Pine Point. The bird could not be relocated the following day.  The MRBC lists eight records of this tropical species in Maine, none of which have been reviewed to date.

A Magnificent Frigatebird was seen off Salisbury Beach on the North Shore of Massachusetts on June 14. Perhaps it was the same bird that was found in Maine.

In an amazing contrast, a Snowy Owl was photographed on June 13 in a driveway in Freeport, near Hedgehog Mountain Park. Snowy Owls should be nesting on the arctic tundra at this time of year. Normally, more than 2,000 miles separate frigatebirds and Snowy Owls in June.

Why not add some western vagrants to add to the mix? On June 13, a Snowy Plover was found with Piping Plovers at Reid State Park.  If accepted by the MBRC, the Snowy Plover will a new addition to the official Maine bird list. On the same day, a Townsend’s Solitaire was photographed in Whitneyville. Townsend’s Solitaires do wander regularly to eastern North America but a June record is quite unusual.

And the hits keep on coming. On June 20, a Brown Pelican was photographed off the Prouts Neck Yacht Club. The bird was seen regularly through June 23 by many birders. The bird split its time among Prouts Neck, Stratton Island, Bluffs Island and Pine Point.

The plumage and the presence of a pale stripe on the lower part of the throat pouch indicate this bird was in its second year of life.

The MBRC lists one accepted record for Brown Pelican in the state, a bird seen on June 16 in Harpswell. Four older records from 1826, 1914 (2 records) and and 1922 have yet to be reviewed by the MBRC.

Despite diligent searching on June 24, the pelican could not be located in Maine. However, a Brown Pelican was seen in Rye, New Hampshire on that day. This bird was also a second-year bird and may well have been the same bird seen in Maine. Two additional Brown Pelicans were reported from Salisbury Beach in Massachusetts.

New Hampshire birders enjoyed the first record of another tropical vagrant, a Brown Booby. This cooperative bird was found at Cobbett’s Pond in Windham. Here’s a remarkable YouTube video of this delightful bird http://bit.ly/2sk2dJE They are normally found no further north than the Caribbean.

[First published on July 2, 2017]

 

 

Tags: Behavior · Migration

Migration Physiology II

September 13th, 2017 · No Comments

Spring bird migration has run its course. Birds are busy attracting mates, establishing territories and building nests. Before I put migration to rest, I want to add a bit on the remarkable physiological demands of bird migration and the adaptations birds have to meet those demands.

In the last column, we explored the engineering problem migrating birds have of how much fuel (fat) it bird should carry. Carrying extra fat for insurance means a bird’s mileage will be reduced because of the excess weight. Cutting the fat stores too close might mean running out of fuel and perishing.

Thanks to the work of Dr. Scott McWilliams and his students at the University of Rhode Island, we know many migrating birds have a trick up their wing to improve their flight performance.

In preparation for migration, a bird enlarges and lengthens its gut to allow it to feed more rapidly and put on weight. It’s an adaptation for gluttony. The cells of the intestines become larger and new cells are formed.

However, the physiological demands of the gut are high. So during migration, once fat stores have been loaded, a bird essentially shuts down its gut and the gut decreases in size and weight. The diversion of energy from the gut can be used to fuel the flapping of the wings for a migrating bird.

Once a bird has stopped after completing a leg of its journey, it is unable to feed efficiently because its gut has shut down. It must rebuild the gut to allow food to be digested properly.

McWilliams showed that proteins are essential to get the digestive tract functioning well. Birds that only have access to fruit at a stopover will refuel more slowly, often entailing a delay in their migration.

Let’s revisit the Semipalmated Sandpipers discussed in the last column. To fuel their four-day migration over the Atlantic Ocean from the Bay of Fundy to Suriname, the birds pig out on small crustaceans called Corophium in the upper Bay of Fundy mudflats. Dr. Jean-Michel Weber of the University of Ottawa noted that the Corophium are high in omega-3 fatty acids. He found that the efficiency of the sandpipers’ muscles increased over the two weeks or so that birds spent fattening on the mudflats.  Weber suspected that the omega-3 fatty acids might be the reason for that increase in efficiency. However, he could not rule out other reasons (hormonal changes, exercise) to explain the muscle improvement.

He resorted to some lab experiments with Bobwhite quail. These birds rarely fly and do not migrate, eliminating exercise and migration-related hormonal changes as possible factors. By supplementing the diet of the Bobwhite with omega-3 fatty acids, he found a direct increase in muscle efficiency between 58% and 90%.  These changes are similar to ones noted in Semipalmated Sandpipers shortly before they embarked on their 2,400-mile jaunt to South America. Remarkable!

Switching gears, we know that migrating birds often overshoot their intended breeding destinations. Summer Tanagers, Hooded Warblers and Kentucky Warblers occasionally appear in Maine in the spring but presumably withdraw to their more southerly breeding grounds.  These birds likely made a navigation error.

A different explanation may explain the appearance of some out-of-range birds. Recently in southeastern Florida, a number of Caribbean birds appeared to the delights of Florida birders. These birds included Bahama Mockingbirds, a LaSagra’s Flycatcher, a Fork-tailed Flycatcher, a Thick-billed Vireo, two Cuban Vireos and many Bananaquits and Western Spindalis (a type of tanager).

Why this influx of rarities? Some ornithologists believe that these appearances were driven by the devastation wrought by Hurricane Matthew last fall that hit eastern Cuba and the Bahamas with its full fury. Lots of bird habitat was destroyed. The hypothesis is that some Caribbean birds returned to their normal breeding grounds, found it to be destroyed, and kept on trucking to Florida.

[First published on June 11, 2017]

Tags: Migration · Physiology

Migration Physiology I

September 11th, 2017 · No Comments

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.

[Originally published on May 28, 2017]

Tags: Migration · Physiology

Passage Migrants

August 28th, 2017 · No Comments

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.

 

[First published on May 14, 2017]

Tags: Migration

Web App to Explore the Phenology of Bird Migration in Maine

June 5th, 2017 · No Comments

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 whwilson@colby.edu

 

 

 

Tags: Migration · Software

Migration Talk at the University of New England

December 21st, 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

Tags: Migration

Evening Grosbeaks

December 17th, 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]

 

 

Tags: Foraging · Identification · Migration · Species Accounts

Northern Finches

November 28th, 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]

Tags: Foraging · Migration

Swainson’s Hawk in Millinocket!

November 28th, 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.

Tags: Foraging · Identification · Insects · Migration · Species Accounts