Changes in Maine’s Birds over the 200 Years of Maine’s History – I

By in Bird Conservation, Population Dynamics

In honor of Maine’s bicentennial, I want to devote four posts to changes in Maine bird populations over the last 200 years. The 1820 federal census recorded almost 300,000 people in Maine. Our population now has increased a bit more than four-fold.

We obviously don’t have census data for birds dating back to the 19th century but I think I can make a case for a strong decline in our total bird population since 1820.

Let’s start with birds that were found in Maine in 1820 but are no longer with us. The Great Auk, a puffin relative, was a flightless seabird found along the coasts of North America and western Europe. They were large birds, weighing up to 11 pounds with had large fat deposits. Great Auks were common along the Maine coast outside of the breeding season. In the western Atlantic, they nested in Newfoundland and a few other sites well to the north of Maine.

Great Auks were easily captured by sailors. The slaughtered auks were used for human food and for fish bait. Their fat and feathers were also harvested. Great Auks were taken in large numbers as well on the breeding grounds.

These human impacts clearly accelerated the demise of the Great Auk. The last two seen in the wild were killed in Iceland in 1844 for someone’s bird collection.

The Labrador Duck was an enigmatic diving duck found along Atlantic coast from fall to spring as far south as the mid-Atlantic states. We don’t know where they nested. The reasons for their extinction are equally murky. The last Labrador Duck sightings were on Long Island in 1875 and Elmira, New York in 1878.

The Greater Prairie-chicken is a member of the grouse family, found in the middle of the country. The Heath Hen was a subspecies that occurred in the northeast. They preferred scrub-oak habitat as one can see in the Kennebunk Plains region. Heath Hens barely made it into southeastern Maine but were present in 1820.

Heath Hens were extinct on the mainland by 1870. A population on Martha’s Vineyard in Massachusetts persisted until 1932.

And now for the big one. Passenger Pigeons were easily the most abundant bird in North America and in Maine in 1820.  Their population at peak was between three and five billion birds, accounting for 25% of all the birds in North America.

They were nomadic birds, wandering in massive flocks in search of beechnuts, acorns, chestnuts and other forest seeds. They nested in colonies involving hundreds of thousands of birds.

Their gregarious nature led to their doom. It was easy for hunters to kill large numbers of birds to sell for human consumption. Hunters invented horribly efficient punt guns about eight feet long that could fire a pound of bird shot at once.

This over-hunting started the Passenger Pigeons on a downward spiral. Deforestation diminished the pigeon habitat, hastening their demise.

The last Passenger Pigeon in the wild was seen in Ohio in 1900. The last one in captivity, Martha, died in the Cincinnati Zoo in 1914.

Maine regularly hosted large numbers of these birds. Their extinction deprived Maine of its most abundant bird species. Just from the removal of that species, we can say that there were more birds in Maine in 1820 than there are today.

Humans intentionally introduced three species of Old World species into North America that are now part of Maine’s avifauna.

Rock Pigeons were brought by European colonists in the early 17th century for food. These birds are now found throughout the U.S., never very far from human-altered landscapes.

European Starlings were introduced illegally into Central Park in New York City in 1890 and 1891. Starlings have spread throughout the lower 48 states,  southern Canada and even southern Alaska.

One hundred House Sparrows were introduced into Brooklyn in 1851. This species is now almost as widely distributed as starlings in North America.

Winter Finch Forecast

By in Migration, Population Dynamics

Our feeders here in Waterville are being overrun by Purple Finches. Although Purple Finches nest in Maine, their population can swell in the non-breeding season by finches from elsewhere. Of course, there are some winters where our Purple Finches depart and we have to without these cheerful birds.

Have you noticed a relative dearth of the raspberry-breasted males at your feeder? The brown females with their bold white stripe above the eyes (lacking in the similar House Finch) seem to dominate our feeders.

However, it is virtually impossible to tell adult females from first-year birds in the field. A good percentage of the “female” Purple finches are actually first-year males. Next summer, these young males will sport the purple head and breasts of older males.

Purple Finches belong to the group of birds we call the northern finches or irruptive finches. These are birds of the boreal forest and taiga that may winter on their breeding grounds if the seeds on which they depend are plenteous. In other years, poor seed crops force them south to the delight of birders where these species don’t occur every year.

Poor seed production forces the birds to erupt (move out) of their nesting areas for the winter and irrupt (move into) areas where food can be found.

So, this year looks like an irruption year for Purple Finches. They may well push well south of us. I remember occasionally seeing irruptive Purple Finches in North Carolina when I was a lad.

Red Crossbill abundance varies wildly in Maine. Some nest regularly in the northern forestland and mountains of Maine. They depend on large conifer cones like white pine. Their crossed bill is the just the ticket for scissoring apart the overlapping scales of a cone so that the seed can be extracted.

Throughout much of their range, Red Crossbills are nomadic, wandering widely in search of a good seed crop. They typically nest from late January to early April, feeding on the seeds from conifer cones that opened in the fall, and from early July to early September, feeding on seeds from newly formed cones. A good conifer set doesn’t guarantee Red Crossbills in your neighborhood but a bad seed set guarantees you will not see these wandering opportunists.

We had a nice influx of Red Crossbills into central and southern Maine late this summer, south of their typical range. Breeding was confirmed in Augusta and at four sites in western Oxford County. Perhaps, these Red Crossbills will stick around for the winter but you never know with crossbills.

We are seeing what I hope will be a strong irruption of Pine Siskins. Large flocks have been seen in early October in Gardiner, Harpswell and Bangor. Siskins depend on smaller cones like those of eastern hemlock and tamarack for most of their energy.

For many years, Ron Pittaway in Ontario has been producing an irruptive finch forecast based on the abundance of cones and other seeds. Some of the birds that irrupt into Maine originate from eastern Ontario so his forecasts are always of interest to New England birders. Ron has passed the torch to Tyler Hoar.

A couple of Tyler’s predictions have already come true: the irruptions of Purple Finches and Red Crossbills. We’ll review his take on some other species.

Pine Grosbeaks are unusual finches in that they rely on fruit, particularly mountain ash berries. The berries of these trees are abundant to our north so sadly we will likely not see  a Pine Grosbeak invasion this winter.

Common Redpolls and Hoary Redpolls specialize on birch seeds. COVID19 restrictions have limited travel to the northerly breeding areas of these species so we don’t have a good handle on the swamp birch production there. A bit further south, paper and yellow birch seed production is poor so we’ll keep our fingers crossed for a redpoll winter. Fill your thistle feeders!

Migration Mortality

By in Migration, Population Dynamics

Ornithologists estimate that migratory birds of many species have about a 50% chance of living through a year. That year requires two migrations and two stationary periods for nesting and  for overwintering in some reasonably moderate climate. We believe that much of the annual mortality occurs during the stressful migrations.

One of the few studies that examined mortality over the course of a year of a migratory focused on black-throated blue warblers. The population studied nested in the Hubbard Brook Experimental Forest in New Hampshire and overwintered in Jamaica. A year in the life of one of these warblers consists of a three-month stationary period in New Hampshire during the nesting season, a six-month stationary period in Jamaica during the winter and three months devoted to the two migrations

The researchers found that the survival rate of the summer period was 99% and winter survival rate was 93%. Survivorship in the migratory periods was only 50%. This result means that 85% of the annual mortality in these warblers occurred during the three months of migration. Weekly mortality during migration was about 15 times higher than weekly mortality in the stationary periods.

What are the factors increasing mortality during migration? First off, a bird migration demands a herculean effort. A flying bird increases its normal metabolic rate five times or even more in some birds. That effort requires a tremendous amount of energy. A significant number of migrating birds perish because of starvation. Scarce food poses a real threat for birds that are living on the edge as they migrate.

Bad weather certainly claims the lives of some migrating birds but it is difficult to get a handle on the magnitude of this effect. Birds are pretty good at evaluating the current weather before embarking on a migratory leg. If inclement weather arrives during a flight, birds generally abort their flight and seek shelter. We know that songbirds hunker down effectively during hurricanes and other storms.

Predation by raptors is minimal for nocturnal migrants while they are flying. However, exhausted birds end their migratory leg around dawn and raptors are often lurking by. A migrant may not have the energy to avoid that sharp-shinned hawk.

Sadly, many migrating birds die because of human alterations to the landscape. Migrating birds passing over cities become disoriented by lights and get lost in the urban canyons. The birds circle endlessly, exhausting themselves, and often fatally colliding with windows or the buildings themselves.

Toronto has been a leader in trying to reduce this mortality with their Lights Out Toronto program. The lights in municipal buildings go out after work and on weekends to reduce confusing light for birds.

Communication towers, required to have lights to make them visible to aircraft, can cause large kills of birds. Birds seem to mistake the tower lights for the moon and proceed to fly in circles, often colliding with the tower. In western Kansas, 10,000 Lapland longspurs were found dead beneath a 400-foot tower after one fateful night. An even taller tower in Florida had as many as 4,000 carcasses of 62 bird species on the ground below in the early morning.An alarming number of migrating birds are dropping dead across southwestern states including New Mexico, Arizona, Colorado and Nebraska. Wildlife biologists estimate hundreds of thousands of birds have died.

Observers report that birds on the ground are lethargic and often fearless when approached by humans. Many of these birds are flycatchers and swallows, which feed on insects caught on the wing. Resident birds like great-tailed grackles and white-winged doves do not seem to be affected.

The rampant western fires may be the reason for the die-offs. Perhaps the smoke is affecting the migrants. The fires may be forcing the birds to alter their migratory route over areas where insects are scarce. A cold snap throughout the southwest may have grounded flying insects, inducing starvation of the insectivorous birds. It’s clearly a disaster.

Diurnal Migration of Birds

By in Migration, Weather

The earlier sunsets and the nip in the air at night usher in autumn. Although the cold of winter is sure to come, I welcome this season because of the phenomenon of the fall bird migration.

Fall and spring migration differ in some striking ways. Spring migration is more compressed. There is an urgency in spring migrants as they rush to get to the breeding grounds and set up shop in a prime territory. The birds are dressed in their best finery and the males sing vigorously, practicing for their performances once they acquire a territory.

Fall migration is more leisurely. Most of our swallows depart by early August and some sparrows will linger into December before moving south. Fall migrants have often molted into their dull basic plumage and males don’t sing.

Nonetheless, the fall migration has some advantages over the spring migration. More birds are found in the fall migration, thanks to the reproduction of our migratory breeding birds. Ornithologists estimate that two billion birds migrate into North America in the spring but about twice as many migrate south.

Rarities are more likely to be seen in fall migration. Many of these rarities are juvenile birds, embarking on their first migration. Some are navigationally challenged and end up in unexpected places. One good example is the Clark’s grebe that appeared on Togus Pod in Augusta on August 8 and delighted dozens of birders for almost two weeks.

Clark’s grebes nest in lakes and freshwater marshes in western North America. The eastern-most breeders are in Wisconsin. These grebes are very rare in eastern North America. Maine has one prior record, an individual that spent three weeks at Owls Head in 2005.

As one would expect, the Togus grebe was a young bird.

It is possible to see some birds migrating south during the day. A minority of our migrating species are diurnal migrants. The sight of vee-formations of Canada geese or double-crested cormorants lifts our spirits.  

Falcons, eagles and hawks migrate during the day as well. These birds are skilled in using thermals, the vertical winds that form during the day because of uneven heating of the surface of the earth. Rocky terrain warms more rapidly than adjacent forested land. The rocks absorb heat from the sun and heat the overlying air. The air rises and is replaced by cooler air from the forested region. That cool air is heated above the warm rock and the cycle continues. These birds are adept at soaring from thermal to thermal, scarcely having to flap their wings.

Sustained flight is an energetically demanding activity. Migrating birds wait until winds are blowing in a favorable direction. So, observing hawk migration is a boom-or-bust activity. When winds are blowing from the north, a strong hawk migration can occur.

Most smaller birds migrate at night but swallows, swift American robins, blue jays and some finches are daytime migrants. Look for them as part of the diurnal fall migration.

You can predict good days for migration by looking at a weather map. Specifically, you want to look at the relationship of low- and high-pressure systems in your general area.  High-pressure systems alternate with low-pressure systems, moving from west to east across the continent. 

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

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

Look for the nearest cold front (indicated on the weather map by a line with triangles). 

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

 

 

The Physics of Color in Hummingbirds

By in Morphology

The Ruby-throated Hummingbird has to be one of the most eagerly awaited spring arrivals for Maine birders. Their small size, aerial antics and general feistiness are all endearing qualities. And how stunning the iridescent red on the throat patch, the gorget, is.

I’ve been contacted several times in the past few weeks by people who describe a hummingbird with a black throat. Although some hummers do have black gorgets, none regularly occur in eastern North America. Why would the gorget of a Ruby-throated Hummingbird appear to be black?

Physics explains how the gorget feathers of a hummingbird show that sparkling iridescence. Hummingbird feathers have black melanin granules that function as color pigments. In most birds, the melanin granules are randomly scattered in the feather structure.

In hummingbirds, the melanin granules are hollow and flattened like pancakes. Furthermore, they are stacked neatly in seven to 15 rows.

When light enters a gorget feather, some colors are absorbed by the black melanin granules and others (red in the case of our ruby-throated hummingbird) are scattered back out to an observer’s eye.

The angle at which the light passes through the stacks of melanin granules changes the distance photons of light will move. Consider a cube. If light enters exactly perpendicular to the cube, it will travel a minimum distance to the other side. But if light enters at an angle, it will have to travel a greater distance to pass through the cube.

The changing angles alter the red color that is reflected back. So, when a hummingbird turns its head, the gorget  seems to change from one shade of red to another in a shimmering fashion.  That is how iridescence works in hummingbirds.

If the sunlight hits the gorget at a particularly flat angle, the color that is reflected is dark, almost black. When the hummer turns to a more favorable angle with the sun, the red pops out.

The shape and size of the melanin granules determine the color that is reflected iridescently. The Blue-throated Hummingbird found in Arizona and points south has granules that produce a breath-taking blue iridescence.

Iridescence is not restricted to hummingbirds. Shimmering colors are produced in birds of paradise, trogons and some starlings.

In many birds, melanin pigments produce feathers that are black, brown or tan.  Carotenoid pigments produce the red feathers of a cardinal, the orange of an oriole and yellow of a goldfinch.

Iridescence is said to be a product of structural coloration. Feather pigments do not produce the color but rather interfere with light to reflect a particular portion of the visible spectrum.

No bird has blue pigment. The blue of a blue jay or eastern bluebird is produced by structural coloration. Photons of white light enter a feather and only the blue wavelengths are reflected back out.  Jays and bluebirds do not have their melanin granules arranged in tiers as in hummingbirds so they do not show iridescence. The blue color is always the same.

If you take a blue feather and hold it up to the light, it will appear gray because the blue light is scattered on the opposite side of the feather but not to your retinas.

If a bird combines a feather that produces blue structural color with yellow carotenoid pigment, the feather will be green. With a few exceptions, birds cannot produce green feathers using a pigment.

Structural coloration is also used in bird skin and eyes. Blue or green skin produced by structural coloration is known in at least 50 families of birds. Arrays of collagen fibers rather than melanin granules do the trick here. (Collagen is a common protein providing structural support in tendons, ligaments and skin of birds, mammals and other animals.)

In similar fashion, chemical pigments interact with structures in the eye to produce the often striking iris color in birds.

 

 

More on Habitat Selection

By in Behavior, Habitat Selection, Reproduction

In the last post, we explored the phenomenon of habitat selection in birds. We saw that birds choose habitat at different scales. For instance, Yellow-rumped Warblers prefer coniferous forest but, at the level of individual trees, are typically in the lower parts of a spruce, firm or hemlock.

But, not so fast. Generalities about habitat preferences in birds don’t always hold. We’ll explore a couple of cases of changing habitat selection in birds in today’s column.

Let’s start with Red-winged Blackbirds. Males are polygynous; they may have more than one mate at the same time. Some males have five or more mates, meaning that some males remain unmated.

Red-wings nest in marshes. Although a marsh looks rather homogenous to our eyes, they are often quite patchy in terms of food resources. A male wants to grab one of those better patches for its breeding territory. The competition for the best territories is really intense in red-wings, probably explaining why males return to Maine in the spring a month ahead of the females.

During that month before potential mates return, the males duke it out with the top males getting the best territories. They aggressively proclaim their ownership by singing “konk-a-ree” while flashing their red epaulets.

When the females arrive, they began considering males as a possible mate. The females are not interested in the quality of a male’s song or the redness of his epaulets. Rather, they are interested  in real estate.

How do we know that? Some researchers captured male red-wings and painted their red epaulets black. When they exposed their epaulets as they sang, the red signal was no longer there and they were attacked by other males. The lack of red epaulets didn’t weaken them; they repelled the attacks but had to endure more of them.

But the females didn’t care. A red-wing male with blackened epaulets was perfectly acceptable provided his territory was a rich one.

To keep the example simple, we’ll consider a marsh with four males on territory. The first female to arrive has an easy choice; she’ll become the partner of the male with the best territory.

Now, a second female arrives. She will either bond with the male with the second best territory or perhaps will become the second female on the best territory, if the top territory is particularly rich. Let’s say she chooses the male with the second best territory.

Now a third female arrives and the relative habitat quality has changed because of the presence of two females. She may decide to become the second partner of the top male, leaving two males with no mate yet.

And so it continues in this dynamic system where the relative value of each territory changes. Talk about complicated. So, we may end up with the fourth male in the hierarchy with no mate, male three with one female, male two with two females and male one with four partners. Birds are better at math than we think.

I did a study one winter in Maine on habitat selection in wintering birds. I divided the Maine landscape up into four categories: coniferous forest, deciduous forest, edge habitat (including suburban yards) and agricultural fields.  I had 50 stops that I censused once a week. Nine of the 16 most common species showed a preference for one or more type of habitat. For instance, European Starlings preferred edge and agricultural habitats to forested habitats.

One of the deciduous forest sites had a feeding station and seven edge sites had feeding stations. When I excluded those sites from the analysis, four species showed different habitat preferences.

Downy Woodpeckers preferred edge habitats when feeders were present but switched to a preference for deciduous forest when feeders were absent.

Blue Jays, House Finches and American Goldfinches preferred edge habitats when feeders were present but that preference disappeared if feeders were absent.

The closer we look at biological interactions, the more complicated they become. It’s no wonder habitat selection is such a rich research topic.

Habitat Selection in Birds

By in Behavior, Habitat Selection

The natural world is a mosaic of habitats. An aerial photo of Maine will show patches of forest, marshes, lakes, grasslands, and blueberry barrens along with human-altered patches of towns and farms. Each of these habitats offers a particular set of food and other resources available for animal use. All animals need to find and occupy the habitat that best meets their own needs.

The choice of habitats occurs by a process that ecologists and animal behaviorists call habitat selection. Research on habitat selection is important for crafting methods to help protect and conserve animal populations.

We know that habitat selection operates at different spatial scales. Ecologists use the term grain to describe the spectrum of habitat selection. For instance, we can speak about coarse-grained habitat selection to describe birds that nest in forests. Most of our wood warblers, Winter Wren and Scarlet Tanager are good examples.

However, not all forest tracts are the same. So, looking at a finer grain reveals that some birds prefer deciduous forests, others like old-growth coniferous forests and some like forests that are regenerating after a fire, strong winds or clear-cutting. So, to find a veery or wood thrush, head to a forest dominated by maple, beech and oak. Swainson’s Thrushes and Winter Wrens will be in old-growth coniferous forests. Mourning Warblers and Lincoln’s Sparrows will be in regenerating stands.

We can look at bird habitat at a yet finer grain. One of the first and most influential studies of fine-scale avian habitat selection was done on Mt. Desert Island and in Vermont by Robert MacArthur for his doctoral research at Yale University. He published his work in 1958.

MacArthur later joined the faculty at Princeton and became one of the leading ecologists of the 20th century, using his mathematical skills to advance theoretical ecology. But he was also a crackerjack naturalist. Sadly, he died in 1972 of renal cancer at the age of 42.

For his doctoral research, MacArthur studied habitat selection at the level of a single conifer by five species of wood warblers. Picture a conifer as a triangle on a stick. Five species of warblers tend to be found in particular parts of the tree. Cape May Warblers occur at the top of conifers. Yellow-rumped Warblers occupy the lowest level of our triangle, both on the periphery and in the center of tree. Blackburnian and Black-throated Green warblers like the periphery of the middle third of the tree, with the latter also found toward the middle. The central upper two-thirds of a tree is the bailiwick of the Bay-breasted Warbler.

You can confirm these patterns when you are birding in the boreal forest. The information is useful in finding that sneaky Bay-breasted Warbler skulking in the middle of a conifer.

Some ornithologists take issue with MacArthur’s explanation of this division of habitat by the five warbler species. He claimed the five species are reducing competition among themselves by occupying different parts of a conifer. He did not demonstrate aggressive behaviors of these birds, defending their part of the tree and driving off that Yellow-rumped Warbler that tried to feed in the top of a conifer.

We do have some evidence for competition between species in conifers. Doug Morse studied warblers in coastal Maine forests and on islands where species diversity was lower. On the mainland, Northern Parulas prefer to feed at the tops of conifers but are frequently attacked and displaced by Golden-crowned Kinglet (feisty birds half the weight of a parula!). On off-shore islands where kinglets are absent, the parulas forage happily in the tree tops.

In another study, Morse found patterns of habitat use similar to those described by MacArthur but further noted a difference between the sexes within a species. Male Magnolia Warblers, Black-throated Green Warblers, Yellow-rumped Warblers and Blackburnian Warblers foraged higher than females, usually above the nest location. Females foraged at the level of the nest.

The Physics of Hummingbird Colors

By in Morphology, Physiology

The Ruby-throated Hummingbird has to be one of the most eagerly awaited spring arrivals for Maine birders. Their small size, aerial antics and general feistiness are all endearing qualities. And how stunning the iridescent red on the throat patch, the gorget, is.

I’ve been contacted several times this summer by people who describe a hummingbird with a black throat. Although some hummers do have black gorgets, none regularly occur in eastern North America. Why would the gorget of a ruby-throated hummingbird appear to be black?

Physics explains how the gorget feathers of a hummingbird show that sparkling iridescence. Hummingbird feathers have black melanin granules that function as color pigments. In most birds, the melanin granules are randomly scattered in the feather structure.

In hummingbirds, the melanin granules are hollow and flattened like pancakes. Furthermore, they are stacked neatly in seven to 15 rows.

When light enters a gorget feather, some colors are absorbed by the black melanin granules and others (red in the case of our ruby-throated hummingbird) are scattered back out to an observer’s eye.

The angle at which the light passes through the stacks of melanin granules changes the distance photons of light will move. Consider a cube. If light enters exactly perpendicular to the cube, it will travel a minimum distance to the other side. But if light enters at an angle, it will have to travel a greater distance to pass through the cube.

The changing angles alter the red color that is reflected back. So, when a hummingbird turns its head, the gorget  seems to change from one shade of red to another in a shimmering fashion.  That is how iridescence works in hummingbirds.

If the sunlight hits the gorget at a particularly flat angle, the color that is reflected is dark, almost black. When the hummer turns to a more favorable angle with the sun, the red pops out.

The shape and size of the melanin granules determine the color that is reflected iridescently. The Blue-throated Hummingbird found in Arizona and points south has granules that produce a breath-taking blue iridescence.

Iridescence is not restricted to hummingbirds. Shimmering colors are produced in birds of paradise, trogons and some starlings.

In many birds, melanin pigments produce feathers that are black, brown or tan.  Carotenoid pigments produce the red feathers of a cardinal, the orange of an oriole and yellow of a goldfinch.

Iridescence is said to be a product of structural coloration. Feather pigments do not produce the color but rather interfere with light to reflect a particular portion of the visible spectrum.

No bird has blue pigment. The blue of a Blue jay or Eastern Bluebird is produced by structural coloration. Photons of white light enter a feather and only the blue wavelengths are reflected back out.  Jays and bluebirds do not have their melanin granules arranged in tiers as in hummingbirds so they do not show iridescence. The blue color is always the same.

If you take a blue feather and hold it up to the light, it will appear gray because the blue light is scattered on the opposite side of the feather but not to your retinas.

If a bird combines a feather that produces blue structural color with yellow carotenoid pigment, the feather will be green. With a few exceptions, birds cannot produce green feathers using a pigment.

Structural coloration is also used in bird skin and eyes. Blue or green skin produced by structural coloration is known in at least 50 families of birds. Arrays of collagen fibers rather than melanin granules do the trick here. (Collagen is a common protein providing structural support in tendons, ligaments and skin of birds, mammals and other animals.)

In similar fashion, chemical pigments interact with structures in the eye to produce the often striking iris color in birds.

Variation in Clutch Size Within and Between Species

By in Physiology, Reproduction

A highly variable feature of bird reproduction among species is clutch size, the number of eggs laid in a nest. Ruby-throated hummingbirds and mourning doves always have a clutch size of two. herring gulls lay two or three eggs. Most songbirds have clutch sizes in the single digits. For instance, chestnut-sided warbler and black-throated green Warblers lay three to five eggs.

Some birds are more ambitious. The clutch size of ruffed grouse varies from nine to 14.  A female wood duck lays six to 16 eggs.

Why the variation? The explanations are complicated but food availability is a major driver. Let’s start with grouse and ducks. These birds have precocial development; the chicks hatch out fully feathered and can begin foraging for their own suppers soon after hatching. The adults provide watchful eyes but are not burdened with feeding hungry babies. So, clutch sizes of precocial birds can be large.

At the other end of the development spectrum, we have altricial birds that hatch out naked and blind. The nestlings are utterly dependent on their parents for food and warmth. Most songbirds, hummingbirds, owls and woodpeckers are good examples.

Because the adults must keep their rapidly growing chicks fed, clutch sizes are smaller than clutches in precocial birds.

But within altricial birds, we see variation among species. How can we explain this variation?

That question was tackled by the British ornithologist, David Lack, over 75 years ago. He studied blue tits and great tits, relatives of our chickadees. These two tit species readily nested in nest boxes that Lack erected in a local woodland in England.

He used an experimental approach to study the success rate of nests with different clutch sizes by taking some eggs from nests and placing those eggs in the nests of other birds. So, he reduced the clutch size of some tits, left others the same and augmented the clutch size of others.

Lack found that the normally observed clutch size was the most productive, resulting in the highest number of fledged young. For great tit, eight eggs is the most common clutch size. Nests with five or six eggs did not tax the parents as much as a clutch of eight eggs. However, starting with fewer eggs led to fewer fledged young. Pairs with ten or eleven chicks simply couldn’t keep up and some of the nestlings starved.

Pairs with eight eggs found the happy medium. Pairs with five or six eggs could have worked harder and those with ten or eleven eggs were taxed beyond their abilities to feed that many young.

Lack’s work is commemorated as Lack’s Hypothesis, claiming that a female bird should lay the number of eggs that will result in the maximum number of fledged young.

Subsequent work has shown that pairs of birds within a species with altricial development vary in their ability to provide for their young. Some birds are simply better at finding food to bring back to nestlings.

In Sweden, Goran Högstedt examined the quality of parenting in magpies, members of the crow family. He had banded a large number of magpies and recorded each pair’s clutch size in the first year of his study. The clutch sizes varied from five to eight.

In the next year, he manipulated clutch sizes to produce sizes of five, six, seven or eight eggs within each clutch size class of the previous year. He found that, for instance, pairs that normally laid five eggs fledged the most young with a clutch of five eggs. Pairs that normally had a clutch of seven did more poorly with five, six or eight eggs. Each pair could assess their own ability to raise young and laid the optimal number of eggs. Brilliant!

Maine Breeding Bird Atlas – Year 3

By in Population Dynamics

giAssessing changes in the natural world (including COVID-19 incidence) is difficult without solid baseline data. If you don’t know where you were, how can you measure how far you have traveled?

We know that human memory is often faulty. Our memories fade. We are often selective in our memory retention. We may remember the snowy winters of our youth but not the mild ones, asserting that winters now aren’t what they used to be. Without data, impressions guided only by are memories are suspect.

Establishing a baseline for the distribution of birds of Maine is a major goal of the Maine Bird Atlas project. The third of five years is underway now. The project has two arms, the Breeding Bird Atlas (BBA) to document nesting across the state and the Winter Atlas to map our wintering birds.

For purposes of the BBA, the state is divided into over 4,000 blocks, each a square roughly 3 miles on a side; 974 of these blocks are designated as Priority Blocks. These randomly chosen Priority Blocks, when completed, will insure a thorough coverage of Maine. A minimum goal of the BBA is to complete surveys in all the Priority Blocks.

Birders with the time and energy to devote time to a Priority Block may adopt it on the Maine Breeding Bird Atlas (https://www.maine.gov/ifw/fish-wildlife/maine-bird-atlas/index.html). These birders commit to spending 20 hours censusing the block during the nesting season for evidence of nesting (e.g., gathering nesting material, eggs in a nest, nestlings in a nest, dependent fledged young). A Priority Block is not complete until 20 hours have been spent and at least half of the species have been assigned a Confirmed Breeding Code.

To get all the Priority Blocks covered, the BBA team is relaxing its requirements for unclaimed Priority Blocks that have received little coverage to date. To complete these blocks, 15 hours of birding are required and 60% of the species have to have either a Confirmed Breeding Code or a Probable Breeding Code. Documenting Probable Breeding is often fairly easy. Two criteria for Probable Breeding are the presence of seven or more singing males within the block on a given day and singing by a territorial male on two days, separated by at least a week.

So, here’s where you come in. Even if you do not want to take on the responsibility of adopting a Priority Block, you can still devote time to helping complete a block. Visiting the block a couple of times this summer will certainly provide many Probable and Confirmed Breeding Records. In the last two summers of the atlas, the coordinators of the project will make sure that someone gets that block up to the minimum 15 hours of coverage.

Here’s how to get started. Go to:  https://ebird.org/atlasme/effortmap Zoom in on your area of interest in the state. The Priority Blocks are outlined with thick black marks. The light-colored ones have received little or no coverage. Just click on a block and a pop-up will give you information on the number of hours that have been devoted to that block, the number of species and other information. Since only 347 of the 974 Priority Blocks have been adopted, I daresay that you can find a Priority Block near you that would benefit from your participation.

The state has been divided up into 31 super-regions, each of which has a Regional Coordinator. You can find the name and email address of the Coordinator in your area at: https://www.maine.gov/ifw/fish-wildlife/maine-bird-atlas/regional-coordinators.html

She or he will be glad to suggest blocks near you that need help.

Of course, you may observe breeding behavior in your yard, which may not be in a Priority Block. By all means, submit the record to the BBA at https://ebird.org/atlasme/. However, if you  have some time to devote to the BBA, choose a Priority Block near you and donate a few hour to the Maine Breeding Bird Atlas.

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