The Physics of Birds and Birding: The Sounds, Colors, and Movements of Birds and Our Tools for Watching Them, by Michael Hurben
Pelagic Publishing, 2025
264 pages, paperback
When I was invited to review this book, I was unfazed by its title. However, I realized rather quickly that it would be a rather intense, though not incomprehensible, exploration of the seen and unseen mechanisms underlying how and why birds do so much of what they do: song, pigmentation, flight, underwater locomotion, prey location, navigation, and thermoregulation. I will admit, I became a bit daunted, as I’ve always viewed physics as challenging ever since my college training in the subject.
Despite my subsequent misgivings, I pressed on, digesting the information bit by bit. I’m glad I did because I can honestly say that my eyes have been opened to a whole new world, one that continually plays out before us all, whether we are aware or not. While this book hasn’t inspired me to return to my formal study of physics, it certainly has galvanized a newfound desire to pay closer attention to the nuances of bird behavior, morphology, and physiology.
In the preface, Hurben poignantly explains just how fundamental physics is. All facets of nature, be they animate or inanimate, tangible or intangible, within reach or light years away, are interconnected, and physics, whether we like it or not, underlies all of it. Physics is what makes everything in nature work; physics and nature are inextricably linked, and there is no way to decouple the two. Although none of the lengthy formulas with the unfamiliar symbols had yet been introduced, I knew I was in for a challenging read. I also knew that the potential reward would warrant the difficulty, especially as Hurben elaborated on how much more satisfying birding—and nature in general—can be when seeking deeper answers.
I’ve been birding since the age of nine, and I still remember how enamored I was at the sight of a Northern Flicker landing in an oak tree in my front yard; and how excited I was to see my lifer Spotted Towhee, at the time known as the Rufous-sided Towhee). At that time, it was all about seeing the birds, and the thought of learning their sounds seemed like an insurmountable challenge. Over the years, however, I learned to identify their sounds, which made birding far more exciting for me. For many years, that was how I enjoyed my birding: watching the birds go about their daily lives in their natural habitats and listening for their various songs and calls. Now, after reading The Physics of Birds and Birding, it is as though another layer has been added. Instead of merely observing in awe as a male Black-chinned Hummingbird flashes its gorget or a Red-tailed Hawk power-dives after prey, I now have a new sense of appreciation for why and how birds look and behave the way they do.
I look back on an incident that took place several years ago. I was observing various ducks and shorebirds from the edge of a tranquil pond, when suddenly, a Peregrine Falcon flew in from out of nowhere and completely disrupted the calm. While I cannot remember exactly how everything transpired, I can still picture the birds on the pond flying off frantically as the falcon made its way toward them at breakneck speed. One unlucky duck—a Mallard, if my memory serves me correctly—was not able to escape, and it lay helplessly at the feet of the peregrine. What I did not know at the time is that when pursuing prey, Peregrine Falcons are known to fly in a logarithmic spiral instead of flying straight toward the prey. Hurben discusses two main reasons for this: The first is due to the location of their fovea; raptors, not just Peregrine Falcons, have the sharpest vision when looking to the side; and secondly flying in a straight line would actually increase resistance, causing them to fly slower! When I’m able to observe such an interaction again, I will definitely be sure to pay closer attention to the peregrine’s flight pattern.
I live in California, and I’m fortunate to see hummingbirds year-round. I’m especially lucky because my husband is an avid gardener, and no matter the time of year, there are plants blooming on our patio, which, of course, keep the hummingbirds—mostly Anna’s but occasionally Black-chinned—coming back. While I’ve always enjoyed their presence, I have new reasons to watch them more closely. After reading The Physics of Birds and Birding, I now have knowledge of the mechanics of how they achieve lift and the figure-eight pattern made by their wingtips during a complete wingbeat cycle, and I’ve also learned that their primaries comprise approximately 75 percent of their wing surface compared to approximately 50 percent in other species.
Another intriguing topic that Hurben touches on is the effect of electrical charge on pollination. Hummingbirds and other pollinators are positively charged, and when they come close enough to flowers, the negatively charged pollen is sometimes attracted enough to leap to the pollinator with no physical contact occurring. Taken together, all this information gives me a new sense of awe and wonder when watching hummingbirds.
As I previously mentioned, I began birding at the age of nine. It all started one day when a stunning male Western Tanager landed in a mulberry tree in my backyard. The bright yellow body and red head caught my attention immediately. Less than a year later, my jaw dropped yet again when an unexpected Summer Tanager landed in the same tree. While the more brightly colored birds certainly struck my fancy, I also had a strong appreciation for those who were less vibrantly colored, such as the California Towhee (then known as the Brown Towhee) and the Oak Titmouse (then known as the Plain Titmouse). However, as much as I’ve always admired the array of colors in the birds I observed, I never gave a lot of thought to their origin. I never thought about why we perceive color in birds the way we do. I now understand how true pigmentation generates color at the molecular level and how structural colors (which in some cases are visible only at certain angles, such as in the reds in a hummingbird’s gorget) are the result of the scattering of light. I now know that while other birds generate reds and yellows from carotenoid pigments, parrots produce them via psittacofulvins! Another insanely cool fact is that structural feathers, like those of a Blue Jay, if ground up, will produce a colorless substance, whereas pigmented feathers will produce a pigmented substance.
On many occasions, I’ve watched a Belted Kingfisher dive beak-first into a body of water after a fish or some other aquatic prey. While I always found this to be an enthralling sight, I hadn’t thought much about the mechanics behind it. The shape of the kingfisher’s beak is very tapered, which is a perfect adaptation for minimizing the drag coefficient to prevent damaging compression to the birds’ upper bodies as they dive into the water. The tapered beak shape also serves to minimize deceleration upon entering the water, allowing them to reach prey more quickly. Hurben explains that diving kingfishers—there are over 100 species across the globe and not all of them dive—have beaks that are on average 10 percent narrower than those that do not dive.
A few years ago, I stood on a sandy beach in southern California with a tour group I was co-leading. Through a scope, we watched in awe as a distant swarm of Black-vented Shearwaters flew low over the water’s surface. I remember wishing then, as I do now, that we could have seen them more closely. I have always found seabirds to be both mysterious and enchanting, not only because of where they live, but also because of the adaptations to their environment. Hurben goes on to discuss one such adaptation: the ability to consume saltwater without experiencing dehydration. Like other living things, seabirds have a cellular composition that makes them vulnerable to dehydration when exposed to highly saline environments. To circumvent this issue, they possess specialized glands which remove excess sodium and chloride ions, the mechanics of which Hurben explains in marvelous detail. Now having a greater understanding of this function makes seabirds even more intriguing to me and deepens my desire to partake in more pelagic adventures!
While I’ve lived most of my life in the San Joaquin Valley of California, where summers are blazing hot and winters are mild, I went to college in Iowa, where winter weather is not mild. Having lived in these two very different environments, I’ve witnessed many instances of avian thermoregulation, both in very hot and very cold temperatures. I remember a particularly hot July day this past summer when I watched a Rufous-crowned Sparrow hold its beak agape, and I can remember countless times that I’ve watched cormorants performing a behavior known as gular flutter—vibrating their throat muscles with their mouths open, for anyone unfamiliar with this term. When living in the Midwest, I marveled at how birds as small as Black-capped Chickadees and Tufted Titmice could withstand bitterly cold temperatures. I found Chapter 11 of The Physics of Birds and Birding, where Hurben takes a deep dive into thermoregulation, particularly interesting—especially discussion of the underlying mechanisms of the counter-current exchange for keeping birds’ legs from freezing in colder temperatures. When reading this chapter, I learned many new and exciting facts: larger beaks correlate with warmer temperatures, especially in areas where water is scarce; portions of feathers closer to the body have randomly-arranged barbs, which serve to trap air pockets that provide insulation; and the dark wing tips in birds with white coloration serve to improve flight efficiency by releasing heat. Having a better understanding of how and why birds thermoregulate the way they do has made it the behavior more fascinating to observe.
Each winter, I can reliably find Hooded Mergansers on local streams, ponds, and lakes. I’ve always enjoyed watching them dive into the water after aquatic prey, but I did not know until reading Chapter 9 of The Physics of Birds and Birding that mergansers have an amazing adaptation for being able to see while submerged: their lenses undergo a significant shape change to compensate for the loss of corneal refraction under water. In this same chapter, Hurben explores the myriad similarities between cameras and eyes, as well as multiple facets of avian vision. I had previously assumed that all raptors have visual acuity greater than that of humans, but I now know that this isn’t true. Even some raptors have weaker visual acuity than humans. It is typically the raptors that hunt from high places which require exceptional vision, and, as Hurben explains, that comes at a high biological cost. Hurben further elaborates that while most birds—like humans—have eyes with only one fovea, some prey-pursuing species have a second fovea, which gives enhanced binocular vision in a forward direction.
While living in the Midwest, I looked forward each year to spring migration, when droves of colorful species came through as they made their way to their more northerly breeding grounds. I still cherish by first encounters with birds like the Yellow-throated Vireo, Northern Parula, Blackburnian Warbler, and Chestnut-sided Warbler. At the time, I was just so enamored by the sight of them that I gave little thought to the amazing journeys that they were still embarking on. The mere fact that their tiny bodies can fly such long distances is remarkable enough, but the fact that they know when and where to go is perhaps even more incredible. In Chapter 4, Hurben gives an in-depth explanation of one of the adaptations that enable these extraordinary feats of navigation: Some birds sense the Earth’s geomagnetic field by means of cryptochromes, magnetic sensors found in their retinas; some species produce more of these during migration. Understanding the intricate structure and chemistry fundamental to these sensors is something I had trouble with, but I was nevertheless well-impressed with the take-home message that birds are capable of astounding navigational feats.
I have barely scratched the surface of what Hurben covers in The Physics of Birds and Birding. For example, the remarkable story of how birds produce sound. Instead, I have highlighted a few case studies that were particularly fascinating. The Physics of Birds and Birding wasn’t the easiest read, and there was much that I struggled to understand—especially when complex equations came into play. But it is certainly a worthwhile read, particularly for those who love to take the time to observe birds closely.
For me, it has added an entire new dimension to my birding adventures. No longer am I simply watching and listening to the birds, I’m now paying much closer attention to their behaviors, their anatomies, and the ways in which their physiology is tailored to their environments and life history strategies. Physics will never be my strongest subject, but I now cannot help but admire the innumerable ways in which it powers the world around us, especially as it relates to birds and birding.
Rachel Clark is a wildlife biologist and guide based in Fresno, California. Her love for birds began at the age of nine after seeing a Western Tanager. Today, she owns and operates a company called Central California Birding Tours. When not working, Rachel can often be found birding in the San Joaquin Valley, Sierra Nevada, and central coast of CA. Connect on Instagram: @tanager_girl or @central_ca_birding_tours.
