flight – Rae Spencer

Focusing on Mallards, Part II

September 14, 2024September 29, 2024Rae SpencerLeave a comment

Content warning: This blog post contains references to the hunting, agriculture, and research practices of killing birds. If you choose not to read on, I respect and admire your choice.

Part of my purpose in writing this Mallard series is to highlight the price that has been paid (and continues to be paid) for the knowledge we have about Mallards and other birds. I might have constructed these posts, as a younger writer, without acknowledging the deaths behind the data. But as I’ve aged, I’ve grown more aware of the cost of knowledge.

In this photo, the Mallard hen who inspired this series of blog posts swims with her brood of day-old ducklings in our dragonfly pond. The ducklings are gathered around a grassy seed head that the hen tugged down to within their reach. The hen nested in our neighbor’s yard, during spring 2024, and brought her brood to the dragonfly pond the morning after they hatched and again the next day. I wondered, during and after her long inactivity on the nest, if she experienced the kind of changes in muscle mass that I might experience if I spent most of a month in bed. I didn’t find a good answer for that question, but I found adjacent answers to adjacent questions. Enough adjacent questions and answers for this multi-part blog post.

What I mean by “knowledge”

It’s one thing, for me, to observe our yard and its visitors. To slip away from human concerns and simply watch. To sate myself with wonder. These hours shift my perspective. They build new connections between old memories. I sometimes emerge with splintered metaphors to sand and patch and paint. Sometimes with fine-grained phrases that liven up a drab idea. On the rarest and best days, I emerge with blueprints for new knowledge.

Observation and wonder are one thing. But knowledge is an entirely different state.

Separate and distinct from the metaphysical implications of knowing, my definition of knowledge is an inventory of education and experience. The nouns of my past and the context in which I encountered them, indexed by subject and era. A cross-referenced heap of biology, shuffled around the edges with chemistry. A shelf of style guides and writing advice. A few notebooks of math, physics, and cosmology. A faded box of recipes, crochet patterns, and needlework hints. Stacks of genre reading. Great aisles of emptiness where business, economics, and law failed to catch my interest.

I was recently asked to list my areas of expertise. I wanted to respond that I have none. I am a worksite traced with utility locator flags, not a finished library. I might claim my main parlor, biology, but even there the framework is incomplete. And, to align the metaphor with my theme, construction materials are expensive.

For many long decades I failed to appreciate the cost of knowledge, with its scaffolds of data. In this post, I’ve chosen to pull back the curtain I so blithely ignored as a young science student. Much of what I find behind that curtain forces me to stock those great empty aisles of business, economics, and law. Because the dimly-lit ledger of science history, written mostly by rich old white men, seldom accounts for cost. But every so often, jotted in the margins or tucked between the pages, the writers left remnants of their invoices.

In this photo, sleepy Mallard ducklings bask on a sun-warmed rock beside our dragonfly pond. One of the ducklings is yawning. From many perspectives, these ducklings are resources to be managed and controlled. For me, here in my middle years, these ducklings are downy singularities of wonder and charm far more valuable than mere resources.

The capitalism behind the curtain

During my brief foray in the humanities silo, I chafed over intense criticisms of science and science writing. But I couldn’t deny the foundational weakness. Science motored along for centuries, impervious to criticism, fueled by colonialism and capitalism. For the most part, it still does.

What would it look like, if science and science writing discarded the curtain and directly acknowledged the capitalism? The colonialism? Not just here and there, but in every published report? If the ledger was complete and brightly lit?

I don’t expect a humanities-approved (and strengthened) science literature would look like anything I can imagine. I am neither scientist nor science writer. What’s more, my little graduate certificate in professional writing is not a stamp of humanities approval. So I can’t answer the questions that followed me home from the humanities silo.

But I am an avid science consumer. As such, the word cost is not chosen lightly. Whenever I look behind the curtain of knowledge, no matter the era or discipline, I find the busy (and visible) hands of capitalism.

As ubiquitous as hunger, questions are free for anyone who has the energy and time to ask them. But answers? Answers are capital. They are expensive. And, weighed in the hands of capitalism, answers are expected to reap a profit.

What happens when answers are not synonymous with capital gain? When hunger lingers or multiplies because the investment outweighs the return? In very short order, the hands of capitalism divert resources and time toward less costly questions and more profitable answers. Or, at least, toward questions perceived to be less costly and answers anticipated to be more profitable. The question I should have been asking for years, the question I am asking now, is this: Whose perceptions and anticipations control the resources?

In this photo, a day-old duckling stretches upward to sample a mostly bald dandelion head. During their brief time in the yard, the ducklings stripped all the seeds from all the dandelions within several feet of the pond. I don't know if they ate the seeds or merely pulled them off as part of their exploration process — In this photo, a day-old duckling stretches upward to sample a mostly bald dandelion head. During their brief time in the yard, the ducklings stripped all the seeds from all the dandelions within several feet of the pond. I don’t know if they ate the seeds or merely pulled them off as part of their exploration process.

Some practicalities about Mallards and other waterfowl

Historically, Mallards had value (and have value, still) because they were and are hunted and farmed. When it comes to funding research, and to collecting data for research, hunted and farmed species are valuable, easy resources. “Valuable” in the capitalist sense of being actual capital, but also in the academic sense of data. “Easy” because these species live and die in larger, more accessible numbers than similar species that are neither hunted nor farmed.

Hunted waterfowl (and other game birds) live and die in their large numbers within easy reach of researchers. I can’t write a path around the pragmatism of this system, but I am increasingly uncomfortable with such pragmatism.

As capital, a Mallard’s value is tethered to its food and sport potential. Driven by this food and sport value, research funding adds further value to a Mallard. Each bird is data. Whether hunted, farmed, or recorded into a set of measurements, a Mallard’s value peaks with its death. (Perhaps this is true of every individual, of every species, but I’ll leave that notion for a later post.)

What of this spring’s next-yard hen, with her downy brood? When I perceive them as more than units of capital, when I anticipate their ongoing existence as more than a value that peaks when they die, my ability (and desire) to control them as resources wanes. For me, this feels like a good and useful adjustment of my perceived and anticipated place in the world.

The older I get, the less comfortable I am with capitalism and its pragmatisms. Far from being an agriculture, research, or policy pragmatist, I want the next-door hen and her offspring to have an embodied value separate from their muscle mass and plumage. I want empathy to count. My still and quiet moments in the yard. The silly antics of ducklings in a dragonfly pond. The charm of infant proportions and curious hungers. I want to measure value as a sense of shared life, a shared world, and shared safety or peril.

Photo of the next-yard Mallard hen sleeping at the edge of the dragonfly pond. She is asleep standing up, the equivalent of a duck cat-nap, beak tucked under the feathers of her wing. Her babies are nestled in her shadow, all except one duckling that has edged out onto the warm rocks in the warm sunlight.

Aside: the literature’s euphemisms for “kill”

According to Google’s default dictionary, the word euphemism is derived from the Greek roots eu-, meaning “well”, and -phēmē, meaning “speaking”. I was taught, somewhere in my education, to translate euphemism as good word. But in my more recent years I have come to view euphemisms as veiled words. Intentional deflections. Syntactical high ground for writers (and researchers?) who wish to describe expanses of quicksand without getting mired. I sympathize with the impulse to build polite nomenclatures. To write around shock words and trauma words. But we’re all in the quicksand, no matter what we write.

(Remember the opening content warning? I do understand the need, the profound and pressing need, to protect victims of shock and trauma from experiencing further shock and trauma. This is why I embrace the practice of content warnings. The remainder of this blog post contains frequent references to the research, agriculture, and hunting practices of killing birds. If you choose not to read on, I respect and admire your choice.)

Policy, agriculture, and hunting literatures shy from the words kill and slaughter. “Kill” is rather imprecise, I suppose, for research literature. And “slaughter” is a bloody word, even with its Merriam-Webster finesse—“the butchering of livestock for meat”. In that sense, I acknowledge that “slaughter” is imprecise, as well. The birds (including Mallards) that populate policy, agriculture, and hunting literatures are resources. They are capital and data, not meat. Does it matter how we describe their deaths? (Yes! Of course it does.)

In the literatures, birds (including Mallards) are hunted, shot, collected, harvested, culled, sacrificed, and euthanized. Dead birds are examined, necropsied, and sampled. Wings are placed in the mail.

For this post and its subsequent parts (I’m not certain how many parts there will be), I’m choosing the word slaughter. Because I added up the numbers behind the data. The research numbers in the tiny subset of articles referenced here run into the thousands. The hunting numbers, hundreds of thousands per year. I feel the word slaughter fits.

The rest of my multi-part Mallard post draws heavily from work done by and for the research, agriculture, and hunting industries. Birds died for these questions and answers. For better or for worse, this is the world we have shaped for Mallards and their avian kin.

In this photo, a day-old Mallard duckling sleeps in a patch of clover and grass at the foot of one of the stones lining our dragonfly pond. The duckling is slumped forward, having nodded off after slipping down from the stone where most of its siblings were sleeping. Other siblings have slipped off of the stone, too, and are nodding off in a stair-step heap behind the sleeping duckling.

The research numbers

The following section, which deals with variations in the relative sizes of flight muscles, leans heavily on an article by D. C. Deeming, PhD.: “Allometry of the pectoral flight muscles in birds: Flight style is related to variability in the mass of the supracoracoideus muscle.” Deeming’s article pulled data from three primary sources: two tracts (1961 and 1962) from the Smithsonian Miscellaneous Collections and a 2016 survey out of Romania.

Greenewalt, C. H. (1962). Dimensional relationships for flying animals. Smithsonian Miscellaneous Collections 144(2).
- Greenewalt collated pectoral muscle weights from a 1922 French publication: Magnan, A. (1922). Les caractéristiques des oiseaux suivant le mode de vol. Annales des sciences naturelles, Series 10, Volume 5, 125-334. (Yes, that is the same Antoine Magnan responsible for the urban legend that bees should be mathematically incapable of flight.) Magnan’s work used captive birds and, as Greenewalt cited, “…those which appear to be in bad health were discarded” (Greenewalt, 40). Some 228 birds, representing about 223 species, were slaughtered for this data. (I’m hedging my numbers because counting=math=possibility of error.)
Hartman, Frank A. (1961). Locomotor mechanisms of birds. Smithsonian Miscellaneous Collections 143(1).
- Hartman’s tract drew from more ambitious work that took place in Florida, Maine, Ohio, and Panama. Birds were “collected” (or, even more euphemistically, “obtained”) from January to March, mostly before 11 AM (p. 3). The method of collection isn’t specified, nor the method of slaughter, though the authors specify that birds and their dissected muscles were weighed in “fresh condition” (p. 2). The pages and pages of data (pp. 38-91) represent more than 360 species. Individual numbers range from 1 (i.e., a solitary Bicolored Hawk of unknown sex and a single male Ruddy-capped Nightingale Thrush) to 50 or more (i.e., 55 House Sparrows, 51 White-breasted Nuthatches, 52 Rufous-tailed Hummingbirds, 50 Smooth-billed Anis, and 103 Brown Pelicans). In total, more than 6000 birds. (Again, hedging because math.)
Vágási, C. I., Pap, P. L., Vincze, O., Osváth, G., Erritzøe, J., & Møller, A. P. (2016). Morphological adaptations to migration in birds. Evolutionary Biology 43, 48-59.
- Vágási et al. captured and banded live birds in Romania, but also “[c]arcasses from natural deaths (e.g. road kill, building collision, electrocution, starvation) were collected in Romania and Denmark for taxidermy” (p. 50). The authors clarify, “Numerous bird specimens were brought frozen to JE, more than 95% of them being found dead and the remaining were shot by hunters” (p. 51). The dataset, here, includes some 115 species. Sample sizes ranged from single individuals (i.e., one Grey Wagtail , one Peregrine Falcon, and one Whinchat) to more than 100 (i.e., 824 House Sparrows, 228 Eurasian Blackbirds, and 193 Eurasian Sparrowhawks). In total, more than 3800 birds. (This article models a practical and effective approach to science without fresh slaughter, primarily sourcing data from carcasses submitted for the study. Granted, “natural deaths” from road kill, building collision, and electrocution are hardly “natural”, but I appreciate the distinction between carcass repurposing and the slaughter of otherwise healthy birds for research purposes.)

So Deeming gleaned data from more than 10,000 birds, without listing a single slaughter in the Materials and Methods section. This is both efficient science and inefficient communication. The actual numbers were curtained off, in at least one case, two sources deep and a century back. I applaud the reuse of data, but I resent the legwork required to find the birds within the data.

I expect that most of The Journal of Zoology‘s readers feel no need to find the birds. After all, the article’s intended audiences hold greater and deeper knowledge of birds, wings, and flight than I bring to the moment. The author and intended audiences would likely characterize my stroll down the numbers rabbit-hole as a tangent prompted by unrealistic purposes and fueled by OCD. But, was it?

What is the capital, here? Or rather, which capital is more valuable? The answers and knowledge, so satisfactory to my passing curiosity? The data and findings, so neatly packaged for future reference? Or the birds themselves, so fleetingly alive?

Ask a different me, in a different era, and my response to these questions would change. But, for now, my heart yearns toward the birds so fitted for flight as to seem almost magical, winging through yards and migrating over landscapes and dabbling with their downy chicks in dragonfly ponds.

In this photo, the Mallard hen reaches up to strip seeds from an overhanging, overgrown, and unknown species of grass that was growing around the foot of the dragonfly pond. The hen is floating in the pond surrounded by her day-old brood.

Here, the Mallard hen has pulled the overhanging grass down toward her day-old ducklings. One of the ducklings is looking up from its place floating in front of her in the dragonfly pond, waiting for her to pull the grass low enough for the ducklings to sample the seeds.

Variation in the relative masses/sizes of flight muscles

(For specifics of flight muscle anatomy, see Part I of this post. In short, two muscles power bird flight: the large pectoralis muscle, which powers a wing’s downstroke, and the smaller supracoracoideus muscle, which powers a wing’s upstroke. Both muscles stretch across birds’ chests, from wing to sternum. If you eat poultry, these flight muscles are the breast meat.)

An average bird with average flying habits pushes down against air with its downstroke muscle, wing extended and feathers angled to maximize (or to finesse) the lift. How much force is needed depends on the birds’ weight and acceleration. Is it a heavy-bodied duck or a sleek-framed crow? At a minimum, the downstroke muscle is massive enough to lift the bird’s weight against gravity and accelerate according to the bird’s habits. Imagine the initial heaves of a Mallard taking flight. The lazy hop-launch of a crow. Which bird has bulkier downstroke muscles?

Back to the average bird with average flying habits, downstroke accomplished. Now it tucks and rotates its wings, to minimize air resistance for the upstroke.

Push (PUSH) down. Tuck. Pull (pull) up. Flap. Flap.

Large downstroke muscle, for the heavy work of lifting body weight against gravity. Much smaller upstroke muscle, lifting only the weight and feather-drag of tucked and rotated wings against air. Whether Mallard or crow, the upstroke muscle does less work. (Read on for exceptions, because there are always exceptions.)

In average birds with average wings, downstroke muscles are between 8 and 13 times larger than upstroke muscles (Deeming, “Discussion”, para. 1). So much pushing, so little pulling.

But what about not-average birds? What about birds with exceptional flight habits? What about flightless birds?

Some birds need to pull (PULL) as they raise their wings. They need a mightier upstroke muscle. Penguins, auks, and many other diving birds use their wings under water. No matter how much they tuck and rotate, water isn’t air. There’s more drag. These birds’ upstroke muscles are large, both in proportion to their downstroke muscles and in proportion to their body sizes. Their downstroke muscles are still the largest flight muscle, but only about 1 to 3 times larger than the upsized upstroke muscle. No more of those 8 and 13 numbers (Deeming, “Discussion”, para. 2).

Hummingbirds, which actually rotate and invert their wings during the upstroke, generate lift in both phases of the flap: push (PUSH) and pull (PULL). Surprisingly, to me, pigeons also generate lift in the upstroke, via a trick of the wing tip to change their wing shape. Both hummingbirds and pigeons measure in the same range as diving birds that swim with their wings; their downstroke muscles are only 1 to 3 times larger than their upstroke muscles (Deeming, “Discussion”, para. 2 & para. 5).

More special conditions occur for flightless birds, such as Rheas, and for owls and hawks. More special distributions of muscle. The Deeming article is packed with details.

I didn’t mean to write this much. But I’m fascinated. And I have OCD. It’s a dangerous combination, where tangents are concerned. But in the next part of this post, I’ll move on to flight muscle changes during a bird’s life cycle, as there is plenty of evidence regarding changes in flight muscle mass during molt.

Photo of a Mallard hen walking through the mown grass and weeds that make up our back yard. She is followed by her day-old brood of nine. Here, they were beginning their first stroll away from our tame-ish yard, toward the big waters running through our Tidewater area. — Photo of the Mallard hen walking through the mown grass and weeds that make up our back yard. She is followed by her day-old brood of nine. Here, they were beginning their first stroll away from our tame-ish yard, toward the big waters running through our Tidewater area.

Publication Announcement!

If you’re still here, I very much appreciate your time and attention. And, while I do feel a pang of irony as I promote my own writing while complaining about capitalism, my second poetry collection is now available!

Alchemy (Kelsay Books, 2024)

Photo of the front cover of Alchemy, which features trinkets and jewelry (many passed down from my mother) arranged on a cloth background. Each broach, bracelet, pendant, earring, and trinket illustrates a theme or topic from the poetry. Featured in the center, a Noah's ark pin and a globe-and-animals pin are connected by an antique miniature watch on a chain. Other items show mammals, birds, insects, fish, reptiles, amphibians, plants, and a fossilized seashell. Text on the cover reads "Alchemy, poems, Rae Spencer". — Photo of the front cover of Alchemy, which features trinkets and jewelry (many passed down from my mother) arranged on a cloth background. Each broach, bracelet, pendant, earring, and trinket illustrates a theme or topic from the poetry. Featured in the center, a Noah’s ark pin and a globe-and-animals pin are connected by an antique miniature watch on a chain. Other items show mammals, birds, insects, fish, reptiles, amphibians, plants, and a fossilized seashell. Text on the cover reads “Alchemy, poems, Rae Spencer”.

Alchemy is a different kind of collection than my previous Watershed. The poems in Alchemy are arranged in five sections after the style of academic articles: Introduction, Methodologies, Results, Discussion, and Conclusion. The poems celebrate my fascination with science and the history of science, but also express my yearning for the kind of metaphysical knowing I referenced earlier in this post. I hope readers feel their own celebrations and yearnings, as they read. Alchemy is available in paperback ($20) from Kelsay Books and in paperback ($20) or Kindle ebook ($9.99) from Amazon.

References

Deeming, D. C. (2023). Allometry of the pectoral flight muscles in birds: Flight style is related to variability in the mass of the supracoracoideus muscle. Journal of Zoology 319(4), 264-273. https://doi.org/10.1111/jzo.13043

Greenewalt, C. H. (1962). Dimensional relationships for flying animals. Smithsonian Miscellaneous Collections Vol 144(2).

Hartman, F. A. (1961). Locomotor mechanisms of birds. Smithsonian Miscellaneous Collections Vol 143(1).

Vágási, C. I., Pap, P. L., Vincze, O., Osváth, G., Erritzøe, J., & Møller, A. P. (2016). Morphological adaptations to migration in birds. Evolutionary Biology 43, 48-59. https://doi.1007/s11692-015-9349-0

Focusing on Mallards. Part I: The Flight Muscles

May 22, 2024September 29, 2024Rae Spencer2 Comments

While the yard didn’t have its very own Mallard nest, this year, we had regular visits from a hen who nested in the neighbor’s yard. Throughout April, the hen stopped in to graze and have a bath in the dragonfly pond. Then, on the morning of April 30, she brought along her brood of nine.

*Photo of a Mallard hen standing beside our dragonfly pond. Almost hidden in her shadow are nine ducklings, huddled for a nap after a busy excursion in the pond.*

*A Mallard hen (far right) swims with her nine ducklings in our dragonfly pond on April 30, 2024. The hen is mostly in shadow, her head in silhouette as she forages with her brood.*

Where I started this multi-part post, and why

Spring often brings Mallards to our yard. March after March, April after April, May after May, pairs of Mallards wander in for a nap or a drink or a meal. Last spring, one pair stayed to nest. This year, there was the next-door nest.

*Photo of three downy, day-old Mallards swimming in our dragonfly pond. One duckling faces the camera lens, a drop of water hanging under its bill. The light pink remnant of its egg tooth is visible.*

Watching the next-door hen sit her nest day after day, watching her amble into our yard to bathe and eat, I wondered about her flight muscles. All told, with about a month on the nest and maybe two months more until her ducklings can fly, she’s grounded for three months. That’s a quarter of her year. What happens to her vital flight muscles during that time? Are stretching and flap-bathing enough to keep a Mallard’s muscles in flight condition?

As I’ve noted before, I can’t resist a bit of research…

Photo of the Mallard hen enjoying a vigorous bath in our dragonfly pond on April 30, 2024. Here, her head, chest, and wings are lifted out of the water as she flaps furiously against the surface, churning the water into sprays. One of her ducklings (far right) is just visible through the splashes.

Photo of the Mallard hen, still indulging in her vigorous bath. She has moved to the other end of the small pond as she continues to splash with her wings. A duckling watches from the foreground (lower left), safely anchored on the surrounding rocks.

*Another photo of the Mallard hen, still bathing. Here she is leaning into her bath, wings clapping against the water hard enough to throw spray under her feathers.*

Yet another photo of the Mallard hen, here nearing the end of her bath. She is standing tall in the water facing the camera, wings extended behind her, showing the white feathers on the underside of her wings.

Photo of the Mallard hen stretching her wings after enjoying a splashy bath. She is standing tall in the water, facing away from the camera, both wings at full extension. The tops of her wings are visible, complete with patches of deep blue feathers on each wing.

I haven’t found any research into the changes (or lack of changes) in the flight muscles of nesting Mallard hens. That doesn’t mean this research isn’t out there. I simply haven’t found it. (I’m still searching.) But I did find a lot about flight muscles, and an article about flight muscle changes in molting, captive barnacle geese. (I’ll get to the geese in a later post.)

I’ll start with anatomy, because that always seems a reasonable place to start.

Unless you’re a duckling, then maybe start with the duck version of situational awareness. The world is a dangerous place for Mallards.

Photo of the Mallard hen teaching her ducklings to look overhead for danger. Whenever a crow or hawk flew over, she tilted one eye toward the sky (as seen in this photo) and gave a sharp quack. The ducklings froze in place, when they heard that quack, and they soon began to mimic her skywatching behavior.

Photo of the Mallard hen teaching her ducklings to look overhead for danger. Here, one of the babies is copying its mother's tilt of head, one eye turned to the sky. — *Photo of the Mallard hen teaching her ducklings to look overhead for danger. Here, one of the babies is copying its mother’s tilt of head, one eye turned to the sky.*

Photo taken the next day, May 1, 2024, after the Mallard hen and her brood returned from spending their first night on the big water. They basked and bathed in our little water for one last calm day, but were not completely free of danger. Here, the hen has flattened herself in the grass at the pond's edge, her wide and wary eye skyward, while a Bald Eagle passed high overhead. This was her most extreme reaction, while I was watching, but it was the ducklings' least attentive response. A few of them glanced upward, but they didn't freeze in place. Instead they continued to fidget and stretch in preparation for a nap. I wondered if they couldn't see the eagle, as it was too high for my camera to find with autofocus. — Photo taken the next day, May 1, 2024, after the Mallard hen and her brood returned from spending their first night on the big water. They basked and bathed in our little water for one last calm day, but were not completely free of danger. Here, the hen has flattened herself in the grass at the pond’s edge, her wide and wary eye skyward, while a Bald Eagle passed high overhead. This was her most extreme reaction, while I was watching, but it was the ducklings’ least attentive response. A few of them glanced upward, but they didn’t freeze in place. Instead they continued to fidget and stretch in preparation for a nap. I wondered if they couldn’t see the eagle, as it was too high for my camera to find with autofocus.

Flight muscles in birds

Bird flight is powered by chest muscles. Each wing needs one muscle to raise the wing and another muscle to lower the wing. Two wings, two muscles per wing, four muscles in total. All in the chest.

Pretend your arms are wings. Now try mimicking flight. Can you feel your chest and back muscles moving? Now imagine you are a bird. All that flying, with only chest muscles at work.

Huh?

Birds have one upstroke muscle per wing…

Photo of the Mallard hen stretching her wings. In this photo, both wings are raised, meaning the upstroke muscles for each wing are contracting (shortening) while the downstroke muscles are relaxing (lengthening). — *Photo of the Mallard hen stretching her wings. In this photo, both wings are raised, meaning the upstroke muscles are contracting (shortening) while the downstroke muscles are relaxing (lengthening).*

…and one downstroke muscle per wing…

Photo of the Mallard hen, stretching her wings. Here she is shifting from a completed downstroke into an upstroke. The downstroke muscles are beginning to relax and lengthen, while the upstroke muscles are beginning to contract and shorten. Her wings and flight feathers are positioned to minimize air resistance on the upstroke.

…groups of smaller muscles coordinate fine movements of flight feathers and joint angles, but power for flight lies in the muscles of the chest. The downstroke and upstroke muscles stretch, one on top of the other, between the sternum (the breastbone) and the humerus (the first and largest wing bone). One downstroke muscle and one upstroke muscle on the left side of the chest, for the left wing. One downstroke muscle and one upstroke muscle on the right side of the chest, for the right wing. If you eat poultry, these muscles are the breast meat.

Photo of the Mallard hen watching over her brood as they settle for a nap after an excursion in our dragonfly pond. I'm not here to preach against meat-eating, or against hunting. Both are part of the world, and both have been part of my world. But baby duck cuteness is part of why I am happier, here in my middle years, as a herbivore. — Photo of the Mallard hen watching over her brood as they settle for a nap after an excursion in our dragonfly pond. I’m not here to preach against meat-eating, or against hunting. Both are part of the world, and both have been part of my world. But baby duck cuteness is part of why I am happier, here in my middle years, as a herbivore.

Birds’ outermost chest muscles, the ones closest under the skin, are the downstroke muscles. They’re called the right and left pectoralis. They connect the sternum to the humerus on each side. When contracted, or shortened, these muscles pull the wings down. This anatomy is as straightforward as muscular anatomy gets. Sternum to humerus. When the muscles contract, they pull each humerus toward the sternum and the wings go down. A simple mechanism for a simple downstroke.

Flight anatomy gets its magic in the other flight muscles, the upstroke muscles. They’re called the right and left supracoracoideus. These muscles, nestled beneath the right and left pectoralis, also connect the sternum to humerus. But each upstroke muscle condenses into a tendon, as it nears its associated shoulder, and threads through a triosseal canal. A “three bone canal”. This canal lets each tendon emerge behind and over its associated shoulder, essentially passing from chest to back, before attaching to the top of the humerus.

This anatomical upstroke slight-of-hand, accomplished via the shoulder’s “three bone canal”, allows a pair of chest muscles to function like a pair of back muscles. When the upstroke muscles contract, or shorten, they pull the humerus away from the sternum so the wing goes up. An elegant mechanism for a simple upstroke.

Photo, from May 1, 2024, of the Mallard hen taking another vigorous bath in the dragonfly pond. Her ducklings (right foreground) bob on rough water and scatter to avoid being swamped as she churns up waves and spray with her strong wings. All of her wing power rests in her chest muscles.

If you think of a mechanical pulley system, the upstroke tendon would be the rope that runs over the wheel, while shoulder bones would be the wheel. Contracting, or shortening, the upstroke muscle is like pulling down on your end of the rope. The tendon slides over the bones, like the rope sliding over the wheel, and the wing (or the load you are lifting) rises up.

Presto.

The following video makes it much clearer (animation of the supracoracoideus and pectoralis starts at 3:59 and ends at 4:36).

Embedded YouTube video from medical illustrator Kelly Kage. A thesis video about the mechanics of bird flight, the video begins by describing skeletal anatomy, then moves into an animation of flight muscles at about three minutes and fifty seconds. Animation of the supracoracoideus and pectoralis begins at about 3:59 and ends about a minute later, at around 4:36. The entire video is nine-and-a-half minutes long. (I recommend the entire video, when you have time. The animations and narration are excellent.)

Bird flight isn’t exactly magic, but it’s mighty magical.

Why am I so fascinated?

An earlier version of myself, somewhere in my early twenties, taught a single semester of Introductory Zoology lab to undergraduates. (I was technically a graduate student at the time, but only because I needed two graduate courses to complete my prerequisites for veterinary school. I had no intention of finishing a Master’s degree.)

My most vivid memory, from my (thankfully) brief stint as a lab instructor, is the supracoracoideus exercise. I remember the uncanny slip of knowledge and knowing gliding across each other. The cognitive dissonance of trying to imagine a pair of flight muscles on my own chest.

Flex a chest muscle, and the wing goes down. Flex a different chest muscle, and the wing goes up.

Wing down. Wing up.

Chest. Chest.

Photo of a two-day old mallard duckling exercising its wing muscles. Here, with wings raised, the upstroke muscles in its chest are contracting while the downstroke muscles in its chest are relaxed. Photo taken May 1, 2024.

Photo of a two-day-old Mallard duckling exercising its wing muscles. In this frame, the wings are early in the downstroke phase, meaning the little bird's downstroke muscles are beginning to contract while the upstroke muscles are beginning to relax. — Photo of a two-day-old Mallard duckling exercising its wing muscles. In this frame, the wings are early in the downstroke phase, meaning the little bird’s downstroke muscles are beginning to contract while the upstroke muscles are beginning to relax.

[Full disclosure: I was a bad teacher. I was both stupid and ignorant. I feared my human empathy, so I had conditioned myself to ignore the body language, verbal cues, and emotions of people around me. And I never thought to apply imagination to the teaching guide. I never thought to have my students move their own arms and feel their own muscles, then try to imagine the upstroke as a chest muscle, instead of a back muscle. As a tension through the shoulder while a tendon slides. If this post ever reaches any of my unfortunate students, I want to thank them for their patience and attention. They showed up, week after week. They showed up and they tried to learn what they needed, despite being burdened with an incompetent lab instructor. I know an apology is not enough. Even so, I’m sorry.]

Photo of a two-day-old Mallard duckling swimming in our dragonfly pond. The duckling is gazing at the camera lens from behind a rock. The facial markings of a Mallard duckling, with dark eye stripes over yellow down, make the babies look grumpy from this angle. I imagine my students felt grumpy, and likely overwhelmed, after each of my class sessions. I would have felt angry and betrayed, had I been my own student.

The muscular choreography of bird flight is nothing like what I had imagined and mimicked, as a child. Not pushing my arms down with chest muscles and pulling them up with back muscles. Not a rowing cycle, over and over. Every time I pretended my arms were wings, my chest and back muscles cooperated. But for birds, it’s all chest. Chest muscles down and chest muscles up.

Photo of the Mallard hen with her brood scattered about her. In this photo, some of the ducklings are sleeping, some are fidgeting, and some are practicing preening. The hen is watching me and my camera with her head turned to one side, one eye focused directly on me. I can't help but imagine an internal monologue for her. "What is wrong with this human? Why is she so nosy? Should I be afraid?" — Photo of the Mallard hen with her brood scattered about her. In this photo, some of the ducklings are sleeping, some are fidgeting, and some are practicing preening. The hen is watching me and my camera with her head turned to one side, one eye focused directly on me. I can’t help but imagine an internal monologue for her. “What is wrong with this human? Why is she so nosy? Should I be afraid?”

Even today, despite my long familiarity with bird anatomy, I struggle to imagine how flight must feel. When I read about science fiction and fantasy creatures with wings, especially dragons, I usually forget to wonder about the musculature that powers fictional flight. But, in moments when I do pause to wonder, my imagination becomes richer.

A preview of Part II: More about Mallards and their flight muscles

So here is a duckling, with its clever wings and wing muscles, destined for flight. How it proceeds, how it uses those wings and wing muscles, determines how bulky the wing muscles must be. Or, do I have it backward? Do the wing muscles, with their relative bulks, determine how the duckling must use its wings? As with much, when it comes to physiology, the answer is a loop. The relative bulk of wing muscles influences how a duck might use its wings, and the ways a duck uses its wings influences the relative bulk of its muscles. Part II will have more about flight muscles, more about Mallards, and more photos of these ridiculously cute ducklings.