Human-related Mortality of Birds – III

By in Bird Conservation

This post is the last of three leading up to Earth Week in which I compare the human-related causes of bird mortality.  Much of this information comes from a 2013 volume of the journal, Avian Conservation Ecology, wherein these various sources of bird mortality are assessed for Canada.  The proximity of Canada to Maine makes the Canadian findings relevant to bird impacts in our state.

The effect of wind turbines on bird mortality, described in the previous column, is always a hot-button topic.  Not surprisingly, I received emails on the one hand dismissing wind turbines as a significant risk to birds.  Others wrote to claim the reported deaths are vastly underestimated because the correction factors for unfound carcasses and removal by scavengers are too low and that the bird mortality studies are conducted by biologists hired by the wind power companies.

As a long-term opponent to wind turbines on mountain ridges, I am at least heartened that the wind industry acknowledges wind turbines can pose a significant threat to birds and bats.  A consortium of wind power companies in Norway is experimenting with putting black stripes or stripes that reflect ultraviolet wavelengths (birds can see those wavelengths but humans cannot) to mitigate White-tailed Eagle deaths (55 since 2005) at one site.

Yes, there is uncertainty about how many birds die from wind turbine collisions.  But even the highest reasonable estimates of that bird mortality pale in comparison to two other sources of bird deaths.

The second-most important cause is collisions with building windows.  Craig Machtans and colleagues used some field data and some modeling to estimate this source of avian mortality.  They calculate that about 25 million birds are killed annually in Canada from window collisions.  One might think that tall buildings would be the deadliest structures but only about 1% of collision-related deaths occur at this type of building.  Collisions with house windows are responsible for 90% of the mortality.  The remaining deaths occur from collisions at low-rise commercial or institutional buildings.  The importance of houses stems from the fact there are far more houses than other types of buildings.

The reasons for these collisions are two-fold.  Sometimes birds strike clear glass when a breezeway or other narrow glassed-in structure is in their flight path.  The birds think they can fly directly through the transparent glass.  At other times, birds strike reflective glass when they are trying to reach vegetation or the sky reflected in the glass.

The authors’ model predicts the number of birds killed at houses ranges between 0.3 and 16 per house each year.  Houses with bird feeders have more window kills because of our feeding stations attract so many birds.

I wrote a column in 2009 that offered suggestions for reducing window collisions at your home.  That article can be read at http://bit.ly/1i3c51w

The most important source of human-related bird mortality is almost certainly cats.  Peter Blancher in his article estimates that between 100 and 350 million birds per year are killed by cats.  The majority of this predation stems from feral cats (cats that live their entire lives apart from humans).  Canadians own about 8.5 million pet cats. The feral cat population lies somewhere between 1.4 to 4.2 million additional cats.

Blancher finds that between 2 and 7 percent of birds in Canada die each year from cat predation.  When you realize that many birds live to be several years old and some live much longer than that, a 2-7% reduction per year is huge.

About 70% of pet cats spend some time outdoors and hence contribute to bird mortality.  Blancher’s work suggests urban cats account for about one-sixth of cat-related bird deaths.  Feral cats make up roughly 25% of Canadian cats but cause 59% of the cat-related bird deaths.  The remaining bird mortality comes from pet cats in rural areas.

[First published on April 27, 2014]

Human-related Mortality of Birds – II

By in Bird Conservation, Toxicology

This column is the second of three leading up to Earth Day in which I describe the human-related causes of bird mortality.  Much of this information comes from a 2013 volume of the journal, Avian Conservation Ecology wherein these various sources of bird mortality are assessed for Canada.

Keith Hobson and colleagues evaluated the impact of industrial forest harvesting and management on avian mortality.  These industrial forest practices have two major effects: destruction of nests and elimination of suitable habitat.  Hobson calculated that between 600,000 and two million nests are destroyed each year by log cutting.  Habitat destruction is harder to quantify because birds in older growth forests like Swainson’s Thrushes, Scarlet Tanagers and Blackburnian Warblers may be replaced by Chestnut-sided Warbler, Mourning Warblers and Lincoln’s Sparrows in cut-over areas.

Farming practices take a toll on bird populations.  Mowing, tilling, seeding and harvesting in agricultural fields may destroy nests or reduce suitable breeding habitat.  Joerg Tews and colleagues provided estimates of mortality from agricultural activities of some grassland species in Canada.  They estimated that 138,000 Horned Larks, 249,000 Savannah Sparrows, 667,000 Bobolinks, and nearly a million Savannah Sparrows meet their demise from agricultural practices.

Christine Bishop and Jason Brogan summarized data on birds killed by automobile collisions on roads passing through a variety of forested and unforested habitats.   Each year, 1,167 bird carcasses are found along every 100 km (about 62 miles) of road.  The authors adjusted their estimates to account for the removal of auto-killed bird carcasses by foxes, American Crows and other scavengers.  The revised estimates suggest that nearly 3,500 birds are killed each year for every 100 km.  Extrapolated to include all of the roads in Canada, nearly 14 million birds die from collisions with automobiles.

Ryan Zimmerling and colleagues provided estimates of avian mortality from collisions with wind turbines.  Their estimate was based on carcass searches at 43 wind farms in Canada.  A carcass count underestimates the mortality because scavengers remove some of the carcasses before a researcher can find them, some carcasses will be overlooked by researchers and some carcasses fall beyond the search area.   Applying a correction factor, Zimmerling estimates that eight birds on average are killed by turbine collisions each year.  The range of effects varied from no birds to 27 birds killed by each turbine.  Turbine collisions account for about 23,000 bird deaths across Canada.  Birds seem to be better at avoiding wind turbines than bats.  Reducing bat mortality from turbine collisions is proving more difficult than reducing avian collisions.  See this recent New York Times article.

Zimmerling and colleagues also considered the effect of habitat loss from wind turbine construction and maintenance on breeding birds.  They estimate that 5,700 nests are lost each year across Canada due to this habitat loss.  With wind farms predicted to increase ten-fold in the next decade, look for a ten-fold increase in this type of mortality.

Joanne Ellis and colleagues assessed the impact of offshore gas and oil production on bird mortality.  They found that between 2,700 and 46,000 birds die each year in Canadian marine waters as a part of the by-catch.  In other words, diving birds get tangled in nets and drown.

These authors also assessed the impacts of oil slicks and sheens (impairing the ability of birds to fly and thermoregulate if coated with oil) and collisions with platforms and ships.  The estimated mortality from these effects is modest: 200 to 4,500 birds year.

Van Wilgenburg and colleagues provided comparable mortality estimates for land-based fuel exploration and extraction.  Human-related activities leading to bird mortality include seismic exploration, habitat loss from the creation of pipelines and the mining processes themselves.  Their estimates for all of these effects range from 10,000 to 41,000 birds killed each year.

[First published on April 13, 2014)

Human Related Mortality of Birds – I

By in Bird Conservation

In 2013, the ornithological journal Avian Conservation and Ecology (ACE) published a special issue documenting human-related sources of bird mortality in Canada.  Since Maine abuts Canada, the Canadian research has broad applicability to Maine.  I will devote the next three posts to a discussion of some of the papers as Earth Day approaches.

A variety of human or human-enabled impacts result in significant bird deaths or injury.  These impacts are usually additive to natural deaths.  In other words, the human-related factors caused the demise of birds that would have otherwise survived. The value of the work published in the ACE special issue is that the relative importance of the various human impacts is evaluated.  These rankings will allow conservationists and environmental managers to most effectively target their efforts and resources to reduce bird mortality stemming from human direct and indirect effects.

In Canada, several billion birds of over 400 species nest each year.  These birds breed in a broad range of habitats, each of which may have its own particular human-related threats.

Sébastien Rioux and colleagues examined the importance of collisions with transmission lines on bird mortality.  Getting accurate estimates of this impact is difficult because of the dearth of studies and the certain underestimate of mortality because some of the birds killed by collisions are scavenged by foxes and other animals before they can be found and counted by researchers.

The high level of uncertainty is evident in a recent study in the United States where estimates of bird deaths from line collisions ranged from hundreds of thousands to 175 million.  Rioux and colleagues presented their most realistic estimates for Canadian bird mortality from these collisions as 2.5 million to 26.5 million birds per year.  At the high end, those deaths kill about 0.7% of Canadian birds each year.

Some groups of birds are particularly susceptible to colliding with transmission lines, particularly during migration.  Birds at most risk include grebes, waterfowl, shorebirds and cranes.  Some waterfowl species are increasing in population size in Canada. While regrettable, line collisions do not seem to be limiting population growth of those waterfowl.  But a collision-related death for an endangered Whooping Crane is a major blow.

[Originally published on March 30, 2014)

Molting

By in Physiology

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]

Roosting in Birds

By in Behavior, Physiology

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.

Review of Maine Christmas Bird Counts – III

By in Christmas Count Summaries

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.

Review of Maine Christmas Bird Counts – II

By in Christmas Count Summaries

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.

Reducing Bird Mortality from Cat Predation

By in Bird Conservation

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  [email protected]

Review of Maine Christmas Bird Counts – I

By in Christmas Count Summaries

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]

Black-capped Chickadees and Feeder Visits

By in Banding, Behavior, Species Accounts

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]

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