Maine Birds

Molting

April 1, 2014 · No Comments

Now is the time of year when I start looking closely at American Goldfinches.  During the winter, females and males are difficult to tell apart.  The dark on the wings is black in males and dark brown in females.  The wing bars, particularly the upper one, are a bit more yellow in males.  In a month, telling males from females will be easy.  The bright yellow body and the black cap on the forehead leave no doubt that such a bird is a male in his summer finery.

The transformation occurs through the process of molting, the replacement of older worn feathers, pushed out by newly formed feathers from below.  Molting is essential because feathers, marvelously light and strong, do wear down.  These feathers must be replaced as they abrade or flight would be difficult and insulation poor.

With over 11,000 species of birds in the world, generalizations about molting are hard to make.  Most birds do molt their contour feathers (their wing feathers, tail feathers and the large body feathers) twice a year.  A bird usually molts all of its contour feathers in a sequenced fashion in the fall, leading to its basic plumage.  In the spring, another molt occurs leading to the alternate plumage, the plumage of the breeding season.  Our American Goldfinches will soon be molting into their alternate plumage.  The spring molt is often with the head, body and sometimes tail feathers replaced.

The distinction between basic plumage and alternate plumage can be dramatic as in the warblers, tanagers, and Rose-breasted Grosbeaks.  The two plumages are similar in other birds such as gulls, sparrows, wrens, chickadees and nuthatches.  Those birds with similar alternate and basic plumages still undergo two molts a year, despite their seemingly unchanging appearances.

Molting requires a significant amount of energy.  The only activities in a bird’s life that rival the energetic cost of molting are nesting and migration.  Each activity pushes a bird to its limit.  No bird can do two of these three activities at once.  A typical pattern for a migratory bird is molt into alternate plumage (often a partial molt), migrate north, nest, molt into basic plumage, and migrate south.

Here are a couple of examples that demonstrate the energetic demands of molting.  Some Peregrine Falcons breed on the arctic tundra.  The short arctic summer is not long enough to allow the falcons to nest and then molt into basic plumage.  After nesting, the falcons begin a molt, replacing some of their flight feathers.  They then migrate to their wintering quarters, forced south by the deteriorating weather.  Once in their winter quarters, they resume their molt.

Yellow-breasted Buntings have a broad breeding distribution in Europe and Asia, stretching from the arctic tundra to central China.  They winter in Southeast Asia and India.  Like the arctic Peregrine Falcons, the brief arctic summer does not allow enough time for the buntings to nest and then molt before migration.  Those high latitude birds migrate immediately after nesting to the lower Yangtze area of China.  In that moderate climate, the birds undergo a complete molt and then continue their migration south on fresh feathers.  Buntings nesting in the southern part of the breeding range have plenty of time to nest and then molt before they embark on their southward migration.

Two of our local bird species transform themselves from basic to alternate plumage without molting.  The dorsal black coloration of breeding Snow Buntings is actually present in basic-plumaged birds. As the winter proceeds, the back feathers of a Snow Bunting erode, exposing the black coloration along the middle portion of each feather.  The black is hidden in the winter by the shingle-like arrangement of overlapping feathers.  The white spangles on winter Eurasian Starlings are eroded in the same way, leading to the black alternate plumage.  Ornithologists call this phenomenon molt by wear.

[First published on March 16, 2014]

→ No CommentsCategories: Physiology

Roosting in Birds

April 1, 2014 · No Comments

A bird chooses a roosting site, a place to sleep and rest, with care.  The roosting site can mean the difference between life and death on a cold winter night.

You know from watching your bird feeders that birds quit coming to feed about a half hour before dusk.  In the dim twilight, birds find a roost site and hunker down for the evening.  Of course, nocturnal birds like owls have a topsy-turvy schedule so go to roost around dawn.

Particularly in the winter, the roost site should provide some protection from the elements.  Heat is easily lost to convection, the movement of a cold fluid over a solid structure.  Meteorologists are always warning us about wind-chill; convective heat loss provides the explanation of wind-chill.

The obvious way to minimize wind-chill is to get out of the wind.  Many birds choose a roost site in a conifer where the needles reduce the wind.  Roosting close to the trunk has triple benefits.  The area next to the trunk will experience the least wind because of the dense foliage extending outward from the trunk.  A central roost in a conifer maximizes the safety of a roosting bird from owls or other nocturnal predators.  Finally, the trunk of a tree emits a modest amount of infrared radiation (sensible heat) that can provide just enough heat to get a chickadee through the night.

Some birds roost in cavities.  Woodpeckers maintain a roost cavity, often separate from the nesting cavity, were they spend the night in relatively cozy comfort.  Ruffed Grouse and Common Redpolls take advantage of the remarkable insulating properties of snow by roosting beneath the snow surface.  Having a grouse fly up from the snow as you walk by on a nighttime snowshoe hike is a heart-stopping experience.  To get into the snow, the grouse flies into a snow bank to create an instant den for the night.

Some birds roost alone.  Black-capped Chickadees provide a local example.  Others huddle at a roosting site.  The energetic advantage is clear.  By huddling with other birds, some of the heat lost to the cold can be absorbed by a neighboring bird in the huddle rather than lost to the atmosphere.

My favorite anecdote of huddling in birds comes from an English garden.  After a particularly cold night, a homeowner checked the contents of a small nest box measure 4x4x5 inches.  What a surprise it must have been to find 61 Common Wrens (similar to our Winter Wren) huddled together to snugly pass the night.

I have received lots of questions this winter about the massive American Crow roosts that are often in heavily populated areas.  I wrote a column about crow winter roosts last year.  You can read it at: http://bit.ly/1cIYz0f

American Crow roosts vary in size from several hundred birds to two million.  Crows are one-upped by the Red-billed Quelea, an Old World sparrow related to the House Sparrow.  Quelea roosts reach the tens of millions of birds.  Alas, the most social of roosting birds is not longer with us.  Roosts of the extinct Passenger Pigeon numbered in the billions and covered many square miles.

Communal roosts may involve several species.  Several species of herons and egrets may roost together.

For any roosting bird, you may wonder if they ever fall off their perch at night.  Birds have special flexor tendons that cause the toes (usually three pointing forward and one pointed back) to lock into place when the legs are bent.  The weight of the roosting bird keeps the legs bent and the flexor tendons firmly locked through the night.  When the bird awakes in the bird, it straightens its legs and the flexor tendons relax, freeing the toes from the perch.  The same flexor tendons in birds of prey prevent prey from escaping by locking the talons into the unfortunate prey item.

→ No CommentsCategories: Behavior · Physiology

Review of Maine Christmas Bird Counts – III

April 1, 2014 · No Comments

This column is the third of three in which I describe some of the notable sightings of selected Christmas Bird Counts (hereafter, CBC’s) conducted in Maine from mid-December until early January.

We’ll travel all around the state today.  The general results confirm the patterns seen for previously described counts: poor year for irruptive finches and Bohemian Waxwings, great year for Snowy Owls, some remarkably hardy birds that should by rights be far to our south.

Let’s go way Down East to the Mooseport-Jonesport area.  The CBC there on December 21 yielded 56 species.  American Black Ducks are a species of concern.  On this count, they outnumbered Mallards by a count of 679 to 89.  Fifteen species of waterfowl were tallied including a couple of Harlequin Ducks and 1,395 Common Eiders.

A Merlin was a nice find.  About 800 gulls were found, but not a single Iceland Gull or Glaucous Gull among them.

Three Bohemian Waxwings, a Northern Shrike, two Northern Mockingbirds and 2 Swamp Sparrows were notable.  The only finches were American Goldfinches.

Up in the County, intrepid Caribou counters welcomed the New Year with a count of 24 species, starting their day with -27 degree cold, warming to a balmy 7 degrees.  The two most common species were introduced Rock Pigeons (277) and European Starlings (2,625).  Good sightings of native birds included 241 Snow Buntings, four Horned Larks, a Gray Jay and a lone Pine Grosbeak.

Just a bit south, Presque Isle participants found 35 species on December 28.  Some open water must have been available because of the nice count of 132 Mallards and 12 American Black Ducks.  Raptors included a Rough-legged Hawk and six (!) Snowy Owls.  Three Northern Shrikes were also found.

The flat, open terrain of the area is great for ground-dwelling birds so the 1,058 Snow Buntings were not unexpected.

Other notable finds were six Cedar Waxwings, seven Common Redpolls and seven Pine Siskins

We’ll head south now to the Bangor region.  The Bangor-Bucksport count on December 28 yielded a fine count of 52 species.  Eight species of waterfowl were detected including five Bufflehead and two Barrow’s Goldeneye.  A Red-throated Loon is always a good find away from the coast.

Red-bellied Woodpeckers, Tufted Titmice and Carolina Wrens are expanding their range northward.  All were found on the Bangor CBC with the 64 titmice being particularly impressive.

Seven Purple Finches were a nice count of a hard-to-find bird this winter.

Just a bit north, the Orono-Old Town CBC produced a count of 49 species on December 14.  Thirteen Barrow’s Goldeneye and a Northern Harrier were excellent sightings.  Two Red-bellied Woodpeckers, 32 Tufted Titmice and a Carolina Wren were nice counts.

Five Cedar Waxwings graced this count.  A lone Red-winged Blackbird was perhaps reconsidering its decision to not move south.  The only finches were House Finches (2) and American Goldfinches (490).

Farmington counters braved -20 degree temperatures on January 4 and found 37 species.  Highlights included a Northern Shrike, two Horned Larks, 48 Bohemian Waxwings, 22 Cedar Waxwings and a Lapland Longspur.

Lingering birds included a Hermit Thrush and three Rusty Blackbirds.  A Northern Mockingbird was a nice find as well.

Finches were hard to come by but the diversity was pretty good for this finch-poor winter.  Counters found four Purple Finches and a Common Redpoll to go along with four House Finches and 137 American Goldfinches.

The Hartland CBC is one of the newer counts in Maine.  On December 21, Hartland participants found 39 species.  Highlights included two Northern Goshawks, two Northern Shrikes, 72 Snow Buntings and 35 Common Redpolls. Lingering birds included a Northern Flicker, two Rusty Blackbirds and a Common Grackle.

Finally, the Sweden count on December 27 yielded 33 species.  Highlights were two Red-bellied Woodpeckers and 116 Snow Buntings.  The 176 American Goldfinches were the only finches found.

→ No CommentsCategories: Christmas Count Summaries

Review of Maine Christmas Bird Counts – II

April 1, 2014 · No Comments

This column is the second of three, describing some of the highlights of the Audubon Christmas Bird Counts (CBCs).  Over 30 Counts are conducted in Maine so I can’t cover all of them but we can detect general patterns of bird abundance from a sampling of the Maine CBCs.  In this column, we will look at five coastal counts.

I will discuss the Bath-Phippsburg in some detail because of the intriguing mix of lingering species, winter visitors from the north and a genuine rarity.  Altogether the participants found 79 birds on the December 14 count.

The rarity was a Pink-footed Goose, a European species whose closest breeding population to North America is found in Greenland.  What a find!

Other northern visitors included two Rough-legged Hawks, 15 Dunlin, a Snowy Owl (not surprising in this invasion year), a Northern Shrike, 15 Pine Siskins and a Savannah Sparrow of the Ipswich race.  The Ipswich Savannah Sparrows breed only on Sable Island, off the coast of Nova Scotia.

Late December in Maine is still in a transition bird-wise between summer and winter.  Despite all the northern visitors, take a look at all these summer birds that were found on the Bath CBC: three Belted Kingfishers, two Yellow-bellied Sapsuckers, a Northern Flicker, eight Eastern Bluebirds, three Hermit Thrushes, 11 Yellow-rumped Warblers (regular wintering birds in this area), a Common Yellowthroat, two Red-winged Blackbirds and a Brown-headed Cowbird.

Throw in a nice count of Red-throated Loons, Common Loons, Horned Grebes, Red-necked Grebes and four Northern Gannets to ice the cake.

Not far away, the Brunswick-Freeport CBC produced 80 species on December 29.  Two Snowy Owls put in an appearance.  The nine Ruddy Turnstones and 33 Dunlins were nice totals.

Lingering birds included a Northern Pintail, a Northern Flicker nine Carolina Wrens, 46 Eastern Bluebirds, seven Hermit Thrushes and a Common Grackle.

Three northern finches were found: a singleton Common Redpoll and two Pine Siskins.  The sharp-eyed observers found one Bohemian Waxwing among 126 Cedar Waxwings.

Heading north, the North Penobscot Bay CBC on December 28 yielded 55 species.  The Stockton Springs are is perhaps the most reliable place in the state to find Ruddy Ducks; 59 were found on the count.

Grebe abundance was low with only seven Horned Grebes and no Red-necked Grebes.  A single Red-throated Loon was found along with 25 Common Loons.

This count had very few lingering birds.  No doubt the bitter cold around Christmas Day had something to do with the decision of those half-hardy birds to seek warmer climes.

More northerly birds included a Peregrine Falcon, a Fox Sparrow and a dozen Purple Finches.

The Schoodic Count, held on January 1, yield a count of 52 species.  Like the North Penobscot Bay CBC, few lingering birds from the fall were found. A Northern Harrier and six Yellow-rumped Warblers were about it for lingering birds.

Highlights included a Merlin and three Northern Shrikes.

The York County CBC on December 16 produced a tally of 86 species.  Sixteen species of waterfowl were counted.  The 68 Harlequin Ducks must have been a treat to see.

Shorebird diversity was impressive: 115 Purple Sandpipers, a Ruddy Turnstone, 189 Sanderlings, and a dozen Dunlin.

Only two species of alcids were found with Razorbills outnumbering the normally more common Black Guillemots, 18 to 1.

Three Snowy Owls were found.  A single Purple Finch was the only irruptive finch found on the count.  It’s a poor winter for the northern finches in Maine.

Three American Pipits were nice finds.  A Clay-colored Sparrow and three Fox Sparrows were also notable.

We expect more lingering summer birds in this most moderate of Maine counts and the birds did not disappoint on this count.  Highlights were three Great Blue Herons, 113(!) Eastern Bluebirds, a couple of Hermit Thrushes, a Baltimore Oriole and 16 Brown-headed Cowbirds.

→ No CommentsCategories: Christmas Count Summaries

Reducing Bird Mortality from Cat Predation

January 21, 2014 · No Comments

This winter, Maine birders get a chance to help prevent bird mortality from cats, by helping get cats sterilized before spring’s unwanted pregnancies begin.  In a February “Beat the Heat” campaign at Freeport’s Community Spay-Neuter Clinic, and with help from a grant from PetSmart Charites, Dr. Elizabeth Stone, Director of Center for Wildlife Health Research, will be spaying an extra 250 female cats above and beyond the 9,600 cats (baseline of 250/month on average) that have been sterilized by Dr. Stone and her team since her spay-neuter program started 3 1/2 years ago.  Female cats will be sterilized for just $20 each. They need help getting the word out to cat owners that need to have this done.

Maine birders are likely well aware of the high numbers of birds killed by cats in the U.S. every year. In their 2013 Nature Communications paper titled, “The impact of free-ranging domestic cats on wildlife of the United States”, authors S.R. Loss, T. Will, and P.P. Marra concluded that an estimated  1.3–4.0 billion birds and 6.3–22.3 billion mammals are killed by cats annually. They go on to state, “Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals.”

Dr. Stone and her staff target unsterilized cats belonging to low-income households, where timely spay-neuter is unlikely to happen. Spay-neuter that targets low-income households can help to reduce the number of free-ranging cats that were identified by Loss et al. as causing the majority of bird mortality. In the 2009 paper, “Population Characteristics and neuter status of cats living in households in the United States” (JAVMA 234(8)) by K. Chu et al, only 51.4% of cats in households with annual incomes of $35,000 or less were neutered. U.S. Census data (http://factfinder2.census.gov/faces/tableservices/jsf/pages/productview.xhtml?src=bkmk) show that 36.8% of households in Maine fall in this income bracket.

Owned cats that are allowed outdoors are a source of free-ranging and feral cat populations. Preliminary data collected by Dr. Stone through client surveys show that 45% of cats brought to CSNC for sterilization are allowed outdoors. On average, 1 of 3 females have already had 1 litter (averaging 6 kittens per litter), and 23% of resulting kittens have been lost to the wild, potentially adding to the feral cat population. Approximately 71% of female cats presenting for sterilization were likely or highly likely, according to their owner, to become pregnant or pregnant again without affordable and convenient spay-neuter services such as we provide.

Loss et al. (2013) state that scientifically sound conservation and policy intervention is needed to reduce the impact on birds from cats. While we agree, at the same time, high-volume spay-neuter is a tool that can help towards the goal of reducing the population of unwanted cats. Affordable spay-neuter (not to include trap-neuter-release, or TNR) has the advantage of being immediately available in Maine, and having high acceptance among animal welfare, veterinary and wildlife professionals as an acceptable method for cat population control.

Dr. Stone’s team transports cats to the Freeport clinic from as far away as Waterville, Dover-Foxcroft and Rockland for day surgery for a subsidized fee ranging from $10-$60. Please help us get the word out about spaying and neutering cats. If you want to help, “Like” us (search Community Spay-Neuter Clinic) on FaceBook and consider posting fliers for the Beat the Heat campaign. Donations are also accepted. For more information, visit www.communityspayneuterclinic.com or write to Elizabeth Stone at  communityspayneuter@yahoo.com

→ No CommentsCategories: Bird Conservation

Review of Maine Christmas Bird Counts – I

January 19, 2014 · No Comments

The National Audubon Christmas Bird Count season has begun. This column is the first of three in which I will describe some of the notable sightings of some of the Christmas Bird Counts (hereafter, CBC’s) conducted in Maine.

In a recent column, I wrote about the phenomenon of irruptions of northerly birds into Maine.  From the first CBC data, this winter does not appear to be an irruption year.  Perhaps I may change my tune by the end of the CBC season on January 5.

Saturday, December 14 was a bitterly cold but clear day.  Intrepid birders braved the weather, encountering a nice diversity of birds.  We’ll look at the highlights of three counts conducted on that day.

The Lewiston-Auburn CBC yielded a count of 47 species.  The cold weather over the past week caused most open water to freeze with only the Androscoggin River and the middle of Lake Auburn available to waterbirds.  Despite the reduced open water habitat, three Common Loons were found.  Five species of ducks were found with the 479 Mallards far outnumbering the Common Mergansers, Hooded Mergansers and Common Goldeneyes.

Seven species of birds of prey were pretty impressive, headlined by a Snowy Owl and three Peregrine Falcons.

Lingering birds included two Carolina Wrens, six Eastern Bluebirds, an Eastern Towhee and two Field Sparrows.

The only waxwings were 4 Cedar Waxwings.  The only finches were 33 House Finches and 81 American Goldfinches.

A quick glance at the totals of any CBC reminds one of the impact that humans have on bird diversity and abundance.  The two most common birds on this count were introduced birds: 875 European Starlings and 825 Rock Pigeons.  The 765 American Crows were the most common native birds.

The Augusta CBC produced a total of 46 species.  Waterfowl were hard to come by with 40 Mallards and American Black Ducks the most common.  A single Common Goldeneye, three Common Mergansers and 27 Hooded Mergansers rounded out the list.

Four species of finches were found with a lone Pine Siskin and nine Purple Finches joining the more common American Goldfinch and House Finches.

Lingering birds, soon to depart I am sure with the arrival of snow and extended cold, included Belted Kingfisher, a Northern Flicker, five Eastern Bluebirds (spectacular against the snow), two Hermit Thrushes, and two Northern Mockingbirds.

The Greater Portland CBC usually takes pride of place with the most species of any CBC in Maine.  This year, 46 counters found 92 species.  The seabird counts were a bit low, in large part because of the sea smoke that limited visibility over the ocean water.

Twenty-two species of waterfowl were found.  Highlights included a pair of American Wigeon, three Northern Pintail, two Ring-necked Ducks, six Barrow’s Goldeneye, and a singleton Ruddy Duck.

Grebe and loon numbers were on the low side: six Red-throated Loons, 118 Common Loons, 31 Horned Grebe, and 30 Red-necked Grebe.

Lingering birds included three Double-crested Cormorants, six Turkey Vultures, three Northern Harriers, an American Coot, a Killdeer, six Belted Kingfishers, three Yellow-bellied Sapsuckers, 11 Northern Flickers, eight Carolina Wrens (all-time high for this count), a Ruby-crowned Kinglet, 40(!) Eastern Bluebirds, five Hermit Thrushes, two Gray Catbirds, five Yellow-rumped Warblers, four Savannah Sparrows, a Lincoln’s Sparrow, and a White-crowned Sparrow.  Whew!  That is a remarkable list of birds, most of which are surely struggling to survive in Maine while other members of their species are in much more equitable climates.

The eight Snowy Owls were a high total for this count.  Three Peregrine Falcons were nice to see.

Six species of gulls were found with only one Bonaparte’s Gull found.  Both species of white-winged gulls were found: two Iceland Gulls and seven Glaucous Gulls.

No irruptive finches were found; American Goldfinches and House Finches were the only finches tallied.

[First published on December 29, 2013]

→ No CommentsCategories: Christmas Count Summaries

Black-capped Chickadees and Feeder Visits

January 19, 2014 · No Comments

Today, let’s think about chickadees. These endearing birds are regulars at any feeding station.  Sometimes, ten or more may be seen at a feeder at once.  However, the total number of individuals visiting your feeder is far more than that.  I’ll describe some of my own research to demonstrate that point.

During the winter, Black-capped Chickadees form season-long flocks.  The flock is made up of a local pair of adults joined by usually between eight and twelve juvenile birds (none of whom are the kids of the adult pair).  Often this cohesive flock is joined by one or two White-breasted Nuthatches, Red-breasted Nuthatches, Tufted Titmice, Golden-crowned Kinglets or Downy Woodpeckers.

The flock defends a large territory (10-25 acres) against incursions by neighboring flocks.  A flock makes sure it has exclusive access to the food in its winter territory.

But what happens when we put out well-stocked bird feeders through the winter?  Ecologists know that territorial behavior is only seen when the benefit of having sole access to resources is greater than the cost of defending those resources.  If food is essentially unlimited, what is the benefit of defending a territory?  Shouldn’t there be enough food for all?

To explore these questions, I set up a number of feeding stations in the spruce-fir forest on the eastern bank of Flagstaff Lake.  Few people live along the upper part of Long Falls Dam Road in the winter so I knew that the chickadees there would not have access to other feeding stations.

At each feeding station, I captured chickadees with a mist-net.  Each bird was fitted with a numbered, aluminum band and two plastic color bands.  I used a number of different colors of bands and each bird was given a unique combination of bands.  Therefore, I could recognize individuals at the feeders without having to recapture them to read the band number.

Over the course of the winter, I conducted four 30-minute observations each week at each of the four feeding stations.  For each half-hour, I recorded each visit to the feeders by chickadees, identifying the color-band combination of banded birds and identifying other birds as unbanded.

These censuses got manic at times.  Once I had 374 visits in a half-hour!  I could only keep up by recording the data into a hand-held recorder with my other hand holding by binoculars to determine the color-combinations of visitors.

At the end of each weekly census, I refilled the feeders.  The feeders had sunflower seeds continuously from late October until the end of March.

At the end of the study, I used a technique called mark-recapture analysis to determine the total number of chickadees visiting each feeder.  I knew how many banded birds I had at each station (15-20) but I had to use the mark-recapture technique to estimate how many unbanded chickadees were taking advantage of my sunflower handouts.

Mark-recapture is a straightforward technique.  One marks some individuals of a population (the color-banded chickadees in my case).  Future sampling should yield a mix of marked and unmarked individuals.  If most of the individuals subsequently sampled are marked, one can infer that the unmarked individuals are relatively few in number.

In my case, feeder visits by unmarked birds greatly exceeded visits by banded birds.  The mark-recapture software I used indicated that between 80 and 120 chickadees were visiting my feeders each week!  However, the birds still maintained their flock integrity so I rarely would have more than a dozen birds present at any time.  Territories broke down when food became unlimited.

[First published on December on December 22, 2013]

→ No CommentsCategories: Banding · Behavior · Species Accounts

Irruptions

January 19, 2014 · No Comments

What will the winter bring?  Birders frequently ask this question each fall.  We know we can count on seeing our resident birds this winter like Black-capped Chickadees, American Crows and Hairy Woodpeckers.  We also know that most species of migratory breeding birds are gone now but will be back next summer.  You can count on seeing Eastern Phoebes, House Wrens and Yellow Warblers come the summer.  Passage migrants (birds which breed to our north and winter to our south) seldom linger in Maine for the winter.  Snow Geese and Semipalmated Sandpipers are two examples of Maine passage migrants.

The last category of birds, winter migrants, inspires excitement in birders.  These birds breed to our north, some as far north as the arctic tundra. Some of our winter migrants like American Tree Sparrows are expected every year.  But many winter migrants are unpredictable; in some years, they may be common and in other years scarcer than hen’s teeth.  These birds include Snowy Owls, Bohemian Waxwings and a suite of finches commonly called the northern finches.

Why the variability?  The answer is quite simply food availability.  Snowy Owls are perfectly capable of making it through a winter on the arctic tundra if the lemming population is sufficient to provide food.  Similarly, Common Redpolls can survive an arctic winter given sufficient birch seeds.

However, lemming abundance, birch and conifer seed production, and soft fruit production vary from year to year.  When the requisite food is scarce, birds must migrate south to find food.  The result is an influx of northern birds.  Who is not thrilled by flocks of Common Redpolls at our feeders or Bohemian Waxwings in our fruit trees?

Ecologists refer to these incursions of birds as irruptions.  An irruption is movement into a particular place, just the opposite of movement out in an eruption.  We can think of Common Redpolls erupting from northerly areas when food is not available and irrupting into Maine where birch seeds may be more plentiful.

This winter is shaping up to be an irruption year for Snowy Owls.  Over 20 of these magnificent raptors have been sighted in Maine already this winter, mostly along the coast.  On December 1, two birders in Newfoundland saw 138 on an all-day birding trip.  Keep those eyes peeled!

A couple of flocks of Bohemian Waxwing were seen in the past week. Look for these fruit-eaters at apple orchards or in stands of fruit-bearing trees or shrubs.

The irruptive finches show weak correlations in their abundances because they rely on different types of tree seeds for their sustenance.  Ron Pittaway prepares predictions of irruptions each fall based on the production of various species of trees in the vast stretches of boreal forest to our north.

Pittaway reports that mountain ash produced an abundant berry crop to the north of us this fall.  Therefore, we are not likely to see very many Pine Grosbeaks (fruit-eating finches) this year.

Birch and alder seeds are abundant in boreal forests to our north.  We should not expect a major irruption of Common Redpolls.

Red Crossbills prefer to extract seeds from the cones of Red Pine and White Pine.  Red Pine cone production is fair to good this year and White Pine production is poor.  Look for occasional Red Crossbills in Maine where ornamental conifers or pines are laden with cones.

White-winged Crossbills prefer spruce cones.  Good to excellent spruce production is seen in the boreal forest, extending down into northern New England and the Adirondacks.  These crossbills are likely to be broadly dispersed so we should not expect high populations this winter.

Pine Siskins with their small bills rely heavily on hemlock and spruce cones.  Fair numbers of siskins are expected in northern New England this winter.

[First published on December 10, 2013]

→ No CommentsCategories: Migration

White versus Dark Muscles in Birds

January 19, 2014 · No Comments

White meat or dark?  This question will be asked thousands of times as families and friends gather around the Thanksgiving turkey.

But why are there two kinds of muscles?  We’ll need to explore some muscle physiology to answer the question.  Muscles are made of many elongate cells called muscle fibers.  Each fiber is capable of contracting, causing the muscle to shorten.  The muscles are attached to bones via a piece of connective tissue called tendons.  When all the fibers of a muscle contract, the muscle is capable of remarkable force, causing movement in the part of the body to which the muscle inserts.

All muscles contain a mixture of two types of fibers: white and dark (or red).  They differ in their metabolism and their contractile properties.  Dark fibers are sometimes referred to as slow-twitch muscles or aerobic muscles.  As the name implies, aerobic fibers require a constant supply of oxygen to continue to function.  This oxygen supply is enabled by the myoglobin molecules in the muscle fibers.

Like the related hemoglobin in the blood, myoglobin is a molecule that readily binds to oxygen.  Oxygenated blood courses through muscles and oxygen is transferred from the hemoglobin in the red blood cells to the myoglobin molecules in the muscle fibers.  The more myoglobin within the muscle fibers of a muscle, the darker the muscle appears.

Dark fibers are great for activities involving endurance.  Walking and running are generally powered by the contraction of aerobic fibers.

White fibers, also called fast-twitch fibers or anaerobic fibers, are used for rapid, short-term activities like fleeing from danger.  These fast-twitch muscles are able to contract more quickly than the dark, slow-twitch muscles.  However, they fatigue very quickly.  These fibers operate in an anaerobic mode, a mode not requiring the continuous input of oxygen.  To fuel their contraction, white fibers take up the starch glygogen, stored in the muscle fibers.  The glycogen stores are quickly depleted so the rapid contraction of the white fibers is necessarily limited in duration.

In life, muscles made mostly of white fibers appear translucent and glossy.  When cooked, the proteins in the muscle fibers denature and coagulate, resulting in the white, opaque appearance we associate with a chicken or turkey breast.

The myoglobin in the dark muscles also breaks down during cooking, imparting the brownish color to the meat.  The breakdown of myoglobin also makes a steak brown when it is cooked.

Birds that migrate long distances have breast muscles made mostly of dark muscle fibers to enable long bouts of strenuous flight.  Ducks and geese have breast muscles made of aerobic fibers and are dark when cooked.  Wild Turkeys do not fly for great distances.  These birds have breast muscles that contain fewer dark fibers than a duck but more dark fibers than a domesticated turkey.

Domesticated turkeys have far larger breast muscles than Wild Turkeys. Selective breeding by turkey farmers has led to the increase in these muscles.  The breast muscles of a male turkey are so massive that the tom turkeys are incapable of getting close enough to a hen turkey to mate.  Domesticated turkeys are produced by artificial insemination.

In a cooked turkey or chicken, you can see two distinct muscles in the breast: the smaller supracoracoideus (closer to the base of the breastbone) and the much larger pectoralis muscle.  Both attach to the upper wing bone, the humerus.  The pectoralis pulls the wing down, providing the power for flight.   The supracoracoideus muscle pulls the wing back up in preparation for the next power stroke.

How does a muscle below the wing raise the wing?  The supracoracoideus runs through a canal between the humerus, the scapula and the coracoid bone to attach on the upper side of the humerus.  With a downward tug, the wing is raised.

[First published on November 26, 2013]

→ No CommentsCategories: Physiology

Herring Gulls

January 19, 2014 · No Comments

The Herring Gull is the most common and the most familiar gull in Maine.  They are typically associated with the shorelines of the ocean, lakes and large rivers.  These birds have readily adapted to human-altered landscapes so small flocks may hang out in parking lots, cadging French fries or other morsels from fast-food restaurant customers.  Hundreds and even thousands of these gulls may be seen at open landfills.

In North America, Herring Gulls breed across most of Canada and in the northern tier of states from Minnesota to Maine.  Many of those breeding Herring Gulls will migrate south for the winter, either along the Pacific Coast from southeastern Alaska to Baja Mexico or to southern states from Texas east to North Carolina.  Some even migrate to Caribbean islands.  Some Herring Gulls breeding along the coast from Massachusetts to North Carolina are year-round residents.

Although we think of Herring Gulls as abundant members of our avifauna, this species was nearly extirpated from North America in the 19th century by plumage hunters and egg collectors.  Thanks to protection afforded by laws, Herring Gull populations have rebounded.  Populations in New England have been reasonably stable since 1970.  Some ornithologists believe that Herring Gulls may be more abundant now than they were historically before the egg and plumage collectors began to take a major toll on the populations.

Adult Herring Gulls are fairly easy to identify.  Look for the pink legs to start with.  The head, neck and undersides are white, often speckled with black in the winter (as seen in the photograph).  The upper wings and the upper back (the mantle) are light gray.  The wing tips are black with white spots (called mirrors).  The eye is yellow.  The massive bill is yellow to light orange with a red spot near the tip on either side.

Herring Gulls require four years to attain sexual maturity and therefore their adult plumage.  The immature plumages of Herring Gulls are a bit trickier to master and separate from other large gulls but a little effort can be quite rewarding.  The timing of the molts varies greatly among individuals of the same age and an incomplete molt leading from winter (basic) to summer (alternate) plumage adds to the challenge of ageing a Herring Gull.

Take a look at your favorite field guide and you will see that the plumage of Herring Gulls gets lighter as they age.  First-year gulls are mostly brown; their bills are dark.  Second-year gulls are usually a bit lighter than first-years, particularly showing some white on the head and some gray feathers on the mantle.  Their bills are black at the tip but are yellow at the base.  Third-year birds still show some brown streaking on the head.  Such a bird appears to be wearing a gray backpack, contrasting with the browner feathers on the outer part of the wing.  The bill shows a bit of black at the tip.

The third-year plumage is the least frequently encountered plumage.  Can you figure out why?  To answer the question, let’s follow four cohorts of gulls over four consecutive years.  Let’s say that 100 Herring Gulls are hatched each year and that 10% of them will die within a year.  After those four years, we will then have 100 first-year gulls, 90- second-year gulls, 80 third-year gulls and 70 fourth-year gulls.  But those fourth-year gulls are now in the adult or definitive plumage and will join the multiple-year class of adult birds.  Herring Gulls typically live to be 15-20 years old, with some exceeding 30 years old.  With this piling up of birds of many ages wearing the same clothes, It’s not surprising that the adult plumage is the most commonly encountered, followed by first-year birds, then second-year birds, and finally the third-year birds.

[First published on November 12, 2013]

→ No CommentsCategories: Identification · Species Accounts