The Science of Birds - Bird Subspecies: Another Layer of Diversity

Episode Date: October 2, 2025

👕 Bird Merch —  Get yourself some bird shirts!~~~In Episode 123 Ivan Phillipsen explores the fascinating world of subspecies—the diversity that exists within bird species. Learn how these populations arise, why ornithologists sometimes struggle to define them, and what makes the concept so important for both science and conservation.From the record-breaking Island Thrush, once thought to have more subspecies than any other bird, to chickadees, sparrows, and hawks closer to home, Ivan shares examples that highlight just how complex and surprising intraspecific variation can be. Along the way, he touches on genetics, evolution, and the challenges of naming and classifying birds in a way that truly reflects reality.Whether you’re a birder, a naturalist, or just curious about how new species begin, this episode offers a clear and engaging look at the “gray zone” between populations and species—and why it matters for birding, science, and conservation.Link to this episode on the Science of Birds websiteSupport the show

Let's say that you are about to begin a grand birding tour of the Indonesian archipelago. Borneo, Sumatra, Java, Sulawesi, and New Guinea are just some of the tropical islands you'll be visiting. How exciting, right? Well, imagine you're sitting on the plane heading to your first destination. In anticipation of all the avian wonders ahead, you're studying a bird field guide. You land on the page featuring a bird called the island thrush, tortoise poliocephalus. The illustrations show that this bird has some plumage variation. Some forms are darker, some have rusty red tones, some are more gray, and so on.

But you soon lose interest. You think, enough with the island thrush already. And you flip the page, hoping to find some pretty pictures of more colorful birds, birds that seem more exotic than the island thrush. But what's this? The next page shows more variations of the island thrush. And so does the next page and the next. It just keeps going.

You can't believe it. You flip back to the beginning and count all the variations of this species. You end up with 52. This bird has 52 subspecies. It's as if your book should be titled, a field guide to the island thrush. Little did you know that the island thrush is actually famous for having more subspecies than any other bird in the world.

Or I suppose I should say that the island thrush was famous for that particular superlative. Things have recently changed for the thrush. Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted exploration of bird biology for lifelong learners. This episode, which is number 123, is all about the diversity of birds below the level of species.

the way that populations within a single species can come to look and sound different and how those differences reflect genetic divergence. Another way to say this is that we're looking at intra-specific diversity, diversity within species rather than between species. Specifically, no pun intended, we're talking about subspecies today, like those 52 different flavors of island thrush strewn across, the many islands of Indonesia and the Pacific. If you're a birder or naturalist, you've probably noticed the different photos or illustrations

of birds showing plumage variations in your field guide. A bird species might show geographic variation in things like overall color tone, degree of spotting or streaking in the plumage, bill color, eye color, crest size, tail length, and so on. Now, we're not talking about variation from one individual to the next. No, the variation in this case is divided into different populations, where every individual in a single population is similar, and they share distinct features. But that population has different features than other populations, and each of the populations is located in a specific geographic area. For example, in a field guide for North American birds, you might see that the species, black-capped chickadee, piscily atricapilus, has nine subspecies.

One of them, Piscily Atricapilus Turner Eye, lives in the northwest of the U.S. and northwestern Canada. This subspecies has relatively pale plumage without a lot of buff color on the flanks. Meanwhile, another subspecies, Pissaly Atchapilus Atricapilus Atchipilus is found in eastern Canada, south, to the Central U.S. It has a deep buff color on its flanks. A species with multiple subspecies like this is called polytypic. It has multiple forms, multiple types. If a species has no subspecies, we call it monotypic, one type.

Notice that when we give the full name of a subspecies, like in the black-capped chickadee, there are three words. subspecies is a formal taxonomic rank below species. So the first word is the genus. Then the second is the specific epithet, and the third word is the sub-specific epithet, like peaceily, atricapilus, turner-eye. So that second chickadee subspecies I mentioned was peaceally atricapilus-atricapilus.

That wasn't just me stuttering, the subspecific epithet is the same as the specific epithet in this example because this subspecies was the first one formally described by an ornithologist. So we call it the nominate subspecies. But this is arbitrary. It's not biologically meaningful because the nominate subspecies isn't somehow higher or lower, more awesome or less awesome than any other subspecies. It just happened to get named first. Also, some subspecies are so well known and distinct that we've given them a common name, in English. For example, in the red-tailed hawk, there's Harlan's Hawk, beautio-jamakensis Harlanai, a northern subspecies found in Alaska and northwestern Canada.

Another red-tailed hawk subspecies is called Cridershawk, Boutio-Gemakensis Crideri, found in the northern Great Plains. Now, this is all fine and dandy, but what exactly is a subspecies? Like, how is a subspecies defined by ornithologists? And I'd say it's even reasonable to ask, do subspecies even exist? Well, the answers are more complicated than you might think. This has been a controversial issue for at least 150 years. We won't get into all the gory scientific details, but I hope that,

today's episode will give you a helpful overview of this topic. And along the way, I want to explain how the concept of subspecies is important in the realms of not just ornithology, but also conservation and birding. Before we get into what a subspecies is and whether or not a subspecies is, and whether or not subspecies are real things, we first have to talk about the next level up from there, the species. It was a long time ago now, but I covered this topic in episode 15 of the podcast, which has the title, What is a Species, really?

Let's review the most well-known definition. A species is made of groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups. Put another way, a species is a group of organisms that can successfully interbreed and produce fertile offspring. Now, this is just one way to define a species. It's called the biological species concept, first proposed back in 1942, and it's the definition you're most likely to find in a biology textbook.

At the heart of the biological species' concept, concept is the idea of reproductive isolation. It works like this, more or less. If two organisms can mate to produce healthy, fertile babies, those parent organisms are members of the same species. But if their offspring are not fertile, that means the parents are not of the same species. Those parents in the latter case came from populations that are reproductively isolated. The evolutionary process of one species splitting into two or more species over time is called speciation. It's a gradual process that usually takes hundreds of thousands or millions of years. There are two ways to look at something like the species concept.

First, does it help us humans make sense of the world? Does it allow us to organize our understanding of nature, even though under the hood, So to speak, nature is often kind of messy, fuzzy, or even bewilderingly complex. Most of us would agree that, yes, this is true for the species concept. We can give names to birds and other living things, call them species, and the category of species is what forms the core of taxonomy. Taxonomy is the science of sorting living things into categories and naming them to understand how they're related. So the species concept and taxonomy are helpful. The second way of looking at the

species concept is to ask whether or not it reflects something real. Are bird species discrete biological things out there in the world, regardless of whether humans are paying attention to them and making life lists out of them? Or is the idea of species simply a convenience for humans, one that doesn't actually reflect reality. I would agree with countless scientists and naturalists from the last few hundred years to say that, yes, birds are real, in case you were wondering, and yes, species are real. Diverging populations can and do eventually reach a point where they are reproductively isolated. One thing splits into two things, one species becomes two.

But this is usually a slow, gradual process, right? If you could watch a single population of, let's say, a kingfisher species, splitting apart over a million years, there will be many points during that process where the borders will be blurry. The two diverging kingfisher populations will still share so many physical and genetic traits that you'd have a hard time figuring out where to draw the line between them. The truth is, there are a number of biological and even philosophical realities that can make it hard to delineate species. We won't get into all of that here.

But yeah, even though pretty much everybody agrees that species are real things, it can be hard to define and identify them in practice. Now at last we come to the concept. of the subspecies. If you thought it was hard to define species, well, buckle up, sister, because things are going to get more chaotic when we talk about subspecies. Okay, not really. It's really not that bad. While there's no single universally accepted definition, a subspecies is generally understood to have the following traits. One, it's a diagnosable, geographically discrete population within a species. Two, it shows consistent variation,

often morphological, but it could be behavioral. And three, it is not reproductively isolated from other such populations. And since I said the magic phrase, reproductively isolated there, that tells us this definition is based on the biological species concept. Here's another way of wording the same definition. A subspecies is basically a group of birds or whatever in a single population that live in a particular place. And even though they can still have healthy babies with other birds of the same

species, they look or sound a bit different. A subspecies is like an early step in becoming a completely new species. There are more than 11,000 bird species in the world today, and there are at least twice that many subspecies that ornithologists have given names to. So, of those 22,000 or so subspecies in the world, was every one of them carefully studied and described by an ornithologist according to the definition I just gave you? A diagnosable, geographically discrete population within a species that exhibits consistent variation but is not reproductively isolated? Yeah, not so much.

But more about that in a moment when we talk about the history of subspecies name. In any case, a subspecies is a population that has already started to go its own way. Whether you name something a species or a subspecies just depends on where it is along the continuum of divergence, the continuum of speciation. If you're looking at the early stages, it's probably best to call it a subspecies. However, if you're looking at the final stages of splitting, where reproductive isolation is complete or nearly complete, then you probably have a species. But often the challenge is figuring out where a population is along that continuum. For example, how do you actually

know that two populations are reproductively isolated? The process of subspecies and species formation is driven by the evolutionary forces, natural selection, gene flow, genetic drift, and mutation. We can't get into all of that right now, but I want to say a few things about these forces. One, natural selection acting differently on two diverging populations can make them look, sound, and act differently. Two, genetic drift and mutation can also contribute to the accumulation of genetic and physical differences between the populations. And three, gene flow, which is the movement and interbreeding of individuals between the populations, has the effect of homogenizing the populations, making them more rather than less similar. The more birds are

moving between the populations and interbreeding each generation, the more similar those two populations will be. So, for subspecies to exist and to be recognizable to us, selection, drift, and mutation must have made the populations less and less similar over time. And gene flow must be low enough that it hasn't erased the dissimilarity generated by the other three evolutionary forces. The most common way gene flow is limited or cut off

is by geographic barriers, something that creates a divide between two populations, a mountain range, a big river, a desert, or the ocean. If birds on either side, have a hard time crossing such barriers, gene flow will be limited and it's possible for subspecies and eventually species to form. If you look at the range maps for birds in your field guide, you'll often find species with disjunct distributions. A species with a disjunct distribution exists in patches across its range, some of which are completely isolated. In many cases,

the birds in an isolated patch will represent a subspecies found only in that patch. For example, the Golden Parrot Bill, Sothora Varroai, is an East Asian species. Its distribution is discontinuous across its range. It's broken up into multiple separate patches. The Golden Parrot Bill has four subspecies, and these are divided into four geographic clusters. One in Central China, one in Taiwan, and so on. Knowing what we know about geographic barriers, gene flow, and all that, it's not surprising to learn that a species with a vast range that spans multiple continents has a bunch of subspecies.

For example, the horned lark has 42 subspecies scattered across North America, Europe, and Asia. But under the right conditions, subspecies can evolve even at relatively small spatial scales. A great example is the Song Sparrow, Melaspeza Melodia. This North American species is highly polytypic, with 25 subspecies recognized. Some of these occupy remarkably small ranges. For example, three distinct song sparrow subspecies occur around the San Francisco Bay in California, each confined to different tidal marshes only a few dozen miles apart. That's pretty crazy. Next we have the idea of the subspecies

complex. This refers to a set of closely related subspecies that are especially similar. Scientists and field guide authors sometimes group subspecies into complexes as another way for us to get our heads around this intraspecific variation. To illustrate, I've got another Sparrow example for you, the Fox Sparrow. It has 19 subspecies. Ornithologists have grouped these into four subspecies complexes. Their names are red, sooty, slate-colored, and thick-billed. Each complex contains multiple subspecies that share traits and geography. Right? You've got 19 subspecies and those are divided into just four subspecies complexes. A subspecies complexes. A subspecies complex is just a scientific slash taxonomic convenience for practical use. It isn't any kind of

formal rank below species. Okay, let me make a little sidebar now. I want to talk briefly about morphs. Just as you find different subspecies illustrated in your bird field guide, some species also have morphs, M-O-R-P-H-S. An example is the eastern screech owl. which has two color morphs, gray and rufus. These two morphs exist in the same population. They are not at all the same thing as subspecies. A single brood, a single group of siblings in the eastern screech owl, can include some chicks that are Rufus morphs and others that are gray morphs.

Now, the eastern screech owl does have subspecies, six of them. But each of these represents a unique population. and there can be Rufus and gray morphs within each of those subspecies, in each of those populations. So again, the words subspecies and morph refer to very different things. They are not synonymous. But even ornithologists have been confused at times. Sometimes what we now know to be morphs in a species were once treated as subspecies. Okay, so that's all I wanted to say about morphs for today.

Where does this leave us? How about we ask this question? Are subspecies biologically real entities in nature, the way we agreed that species are? I would say yes. But that said, we're trying to put names to things that don't necessarily fit into tidy little boxes or categories. Rather than a clean dividing line existing where a subspecies ends and a species begins, there is often a fuzzy gray area instead. In any case, what features should ornithologists use to identify a real subspecies? One that meets the criteria of divergence at the physical and genetic levels, being geographically discrete, and all of that. Well, ornithologists and other biologists have been trying to answer that question for hundreds of years. It's time for a brief history lesson. Yay! The concept of geographically distinct variation, varieties, races, forms, came around as early

as the mid to late 1700s. That's when Linnaeus and his pals were running around naming everything. Many of those naturalists wanted a way to classify variation below the species level. Ornithologists were actually among the first scientists to develop the idea of subspecies, an idea which we now apply not only to birds, but just about every living thing. The term subspecies was at first used to designate geographical varieties. However, subspecies were often defined as though they were constant, well-defined groups, and these were based on a purely physical or morphological definition.

plumage differences and that sort of thing. But there wasn't really a formalized set of rules or quantitative measures to define subspecies. During this sort of Wild West free-for-all in the 1700s and early 1800s, some naturalists were recklessly naming species and subspecies all over the place, without much science to back up what they were doing. They just wanted the fame, glory, and groupies that came with being a distinguished natural. And then something interesting happened in 1859. Can you guess what it was? Now I know probably the first thing that comes to your mind is the Second Italian War of Independence, fought in 1859 between

the Austrian Empire and the Allied forces of the Kingdom of Sardinia and France. But no, I'm talking about that other thing that happened in 1859. That's right, the publication of Darwin's book on the origin of species. Once that revolutionary book hit the shelves, subspecies began to be seen as incipient species, representing the early stages

of the speciation process. And subspecies were also seen as evidence of a species adaptive response to local climatic conditions. Darwin himself recognized the importance of such variation, but also the challenge of describing it.

He pointed out that no clear lines divided species from subspecies. He saw these things as continuous steps in the process of divergence. And boy, was he right. And then in the early 20th century, so about 100 years ago, many ornithologists enthusiastically adopted the biological species concept. This caused a frenzy of lumping. By applying the biological species concept, ornithologists reclassified a bunch of birds, knocking them down from species to mere subspecies. Two or more species were, in many cases, lumped into one species. In North America alone, this mass hysteria of lumping, occurring through the 20th century, resulted in about 315 bird species being downgraded to

subspecies. For example, the species we now know as the northern flicker has two subspecies called the red-shafted and yellow-shafted flicker. Well, before 1973, those subspecies were treated as full species. But these two populations have a broad geographic area where they interbreed, so ornithologists lumped them into a single species. There were some reasonable attempts to come up with a way to rigorously, quantitatively, defined subspecies, but none of them really stuck. Ornithologists couldn't agree on the best way to do this. So for a long time, designating subspecies seemed more like an art form rather than a rigorous science. But over the last 75 years or so, new scientific tools have been developed. New statistical methods, for sure, but most importantly, new methods that

could reveal the genetics of individuals and of populations. So it's now possible for an ornithologist to get DNA sequences for the entire genome of many individuals. By comparing those genomes, it's possible, at least in theory, to see where a population is along the continuum between being a species or a subspecies. So now a researcher can look at a combination of genetic, morphological, behavioral, and geographical data when studying subspecies.

Genetic data from DNA also allows us to study the connection between populations. We can quantify the amount of interbreeding between two populations, for example. In other words, we can estimate the amount of gene flow. That's super helpful when you're trying to figure out if those populations represent different species. If they do, there should be very little or no gene flow between them. But if there's a moderate amount of gene flow, maybe those populations represent two subspecies. Or if it turns out there is rampant interbreeding and therefore high-demeanor, gene flow, well then, maybe every bird in those populations actually belongs to the same species

and there are no subspecies. Because when gene flow is high enough, any differences between the populations disappear. What you've got is really just one big population in that case. Let's go back to the island thrush we talked about in the intro. You know, the species that has 52 subspecies in your field guide? As I mentioned, some of those subspecies have pretty wildly different plumage patterns. This level of intraspecific variation in the island Thrush has fascinated and bewildered ornithologists for decades. Well, in 2023, there was this paper published about the island Thrush in the journal Evolution Letters. The study was conducted by Andrew Hart-Reeve and colleagues. Their paper-used genomic data from over 70 individual thrushes sampled across the

species' vast geographic range. It turns out that a lot of the plumage color and pattern variation we see among island thrush populations does not closely match the underlying genetic relationships of those populations. What seems to have happened is a little thing we call convergent evolution. Some island thrush populations, even those separated by large geographic and genetic distances, have ended up looking similar because they've experienced similar pressures from natural selection. Their plumage patterns have converged because of evolution. That 2023 study revealed an evolutionary history in the island thrush where, over the last 1.3 million years or so, new populations were founded on one island after another.

It was a stepping stone pattern of colonization, going from west to east, and then natural selection kicked in for those relatively isolated populations scattered across Indonesia and the Pacific. Selection made some of them look different, but where convergent evolution happened, selection made the populations look similar,

despite not being all that closely related anymore. In 2024, ornithologists took the genome data from the 2023 study, and they considered that data along with morphological, behavioral, and geographical data to make a dramatic decision. They split the island thrush from one species into 17 new species. So I guess we have to rip out the page in the Guinness Book of World Records that says the island, Thrus is the most polytypic bird, that it has more subspecies than any other. That's no longer true because the island thrush is no longer true. It doesn't exist. Instead, we have 17 newly named species, like the white-headed island thrush, Samoan Island Thrush, Tasman Sea Island Thrush, and so on. That is just one example of a modern study on subspecies. The criteria used in the island

Thrust study involved genetic, morphological, behavioral, and geographical data. In the case of that species, some subspecies were elevated to full species status. But in other birds, similar combinations of data might give us a good way to discover the existence of subspecies, of introspecific variation that we didn't know was there. Even though scientists are better equipped than ever to detect subspecies, doing so isn't always easy or straightforward. There still isn't agreement among ornithologists on what should be used to define a subspecies. Is it visible field marks, behavioral cues, songs, genetic differences?

And for each of these things, what is the quantitative degree of difference that should separate two populations if we're going to call them subspecies. You know, with a bird formerly known as the island thrush, the authors of that 2023 genomics study did not make the case for splitting the species into multiple species. They seemed content to keep the island thrush as a single highly polytypic species. But some other ornithologists came along, looked at the same genetic data, and they were like,

Nope, this bird should be split into no less than 17 new species. And this kind of process is fairly common, actually. Many genomics papers or genetics papers stop at phylogeny, at the genetic revolutionary relationships among populations. They just lay out the genetic relationships for all to see. Formal species and subspecies delimitation, however, is a policy choice made by ornithologists, belonging to checklist committees.

They weigh multiple lines of evidence and aim for global consistency. In the Island Thrush case, the checklist committees judged that the deep genomic structure plus diagnosable differences warranted species status across those 17 populations.

An interesting challenge in detecting and naming subspecies arises when we find statistically significant genetic differences among some populations of a species, but we don't find any visually detectable differences among them. Like they all look the same,

even though we know they are different at the genetic level. This is what we call cryptic subspecies diversity. For example, there is the least turn, sternula and tellerum. This bird has three subspecies found in separate geographic regions, California, the North American Interior, and eastern North America. But these subspecies are morphologically so similar that you can't reliably separate them by sight in the field. And yet, data from DNA reveal significant population differences among those subspecies.

Another example is the European Storm Petrol, Hydrobates Pelagicus. The two genetically distinct subspecies, one in the Mediterranean and one in the Atlantic, are indistinguishable at sea for all practical purposes. So sometimes subspecies exist, but it's almost impossible to tell them apart in the field, at least visually. And then we have the opposite situation. Sometimes there are obvious morphological or behavioral differences

among populations in a species, and these even correspond to specific geographic regions. These populations seem like excellent candidates for subspecies. But then we do some lab work, and we find that these birds have almost no genetic differences among the populations. A good example of this is the white wagtail, Motocilla Alba. This songbird has a vast range across Europe, Asia, and Alaska. The nine recognized subspecies vary in their plumage pattern and coloration, and these differences are easy to see in the field.

However, research on the white wagtail shows very little genetic difference from one. one subspecies to the next. So it appears there's plenty of gene flow among the subspecies. This comes from a 2018 study of the White Wagtail, published in the Journal of Evolutionary Biology. To explain the existence of visual plumage differences, the researchers suggested that these are the result of natural selection acting on just a few genes within the genome. Selection on those few genes is so strong that it can overcome the homogenizing effects of high gene flow. One more thing I want to mention before we move on to talk about conservation is something called clinal variation, clinal c-l-I-N-A-L. The general definition of the word

Klein is a continuum with an infinite number of gradations from one extreme to the other. Kleins are fairly common in birds when we're looking at their plumage or other morphological differences across broad geographic areas. For some, bird species with large continent spanning ranges, their subspecies actually represent points on a continuum of variation. So they show clinal variation. Sure, populations at the extreme ends of the cline may be easily separable, easily diagnosable. But drawing arbitrary lines between the subspecies along that continuous gradient is a real problem. Because the subspecies smoothly grade one into the next and then into the next. Where does one end and where does the other

begin? Who knows? So does it even make sense to call these end point populations along a Klein, different subspecies, when there aren't really any clear geographic breaks between them? Now let's take a moment to think about the reasons we might care about subspecies. First, there's the scientific goal of knowledge, of truth. We want to discover all the natural variation out there. If subspecies are real biological units, we want to identify them and name them. Second, as birders and nature lovers, we might want to understand all the diversity that exists, so that we can appreciate it and make an effort to see it for ourselves. Knowing about subspecies can help with that.

And third, knowledge of subspecies can help with conservation efforts to protect natural diversity. So let's talk about conservation first. In the United States, we have the Endangered Species Act. This law allows protection not only of full species, but also subspecies. recognizing a valid subspecies can therefore open a direct legal path to a population getting listed as endangered. And that allows for protection of the subspecies habitat and its recovery planning, even if the full species itself is not threatened or endangered. A couple examples are the southwestern willow flycatcher,

Empedanax Tralei Xtymus, and the northern spotted owl, Stricks, Occidentalis, Cowrina. Both of these subspecies are listed under the Endangered Species Act specifically at the subspecies level, and those listings have helped to drive habitat protection and recovery actions for these birds. Similar laws in Canada, the UK, Australia, and other countries explicitly allow for the protection of subspecies.

So in some cases, whether or not a population gets protection from the government depends on whether or not it has been officially recognized by scientists as a subspecies. The scientific pursuit of knowledge is a noble thing, and the protection of endangered populations is, I think you would agree, vitally important. But does the subspecies concept mean anything more to you and me, to the average bird or naturalist out in the field. What does it mean to us that the golden parrot bill has four subspecies or that the horned lark has 42? Well, I can't speak for you, but for me, I like to have access to everything scientists have discovered about bird diversity below the level of species. If there are some subspecies within a species of interest,

I want to know that. What do they look like? Where can they be found? Can I flip open a bird field guide to get that information? Even if I don't really do anything with that info, I like to know that it exists. It makes me feel all warm and fuzzy inside. But knowing that there are, for example, nine subspecies of the Merlin, Falco Columbarius, can be helpful when you're outburning. Let's say you've already seen Merlins before. You wouldn't want to get all excited and or confused when you see a small falcon

that you think might be a new species for your life list, but it's actually just another Merlin subspecies that you're unfamiliar with. Or maybe you're the kind of birder who wants to see and document all of the subspecies variation out there. Instead of just 11,000 bird species, you want to see all 22,000 or so subspecies in the world. And that's great, but good luck. You've got your work cut out for you. And we have to remember that some subspecies are not, identifiable in the field. They are genetically distinct, but not visually distinct. The eBird app and website has an interesting solution to this. This platform uses eBird subspecies groups. This is a categorization that combines similarly appearing

subspecies into groupings that can be reliably identified by birders in the field. It groups described subspecies where the groups can be distinguished, but individual sub-species within a group might not be. The first-named subspecies in a group often lends its name to the group. This is related to the idea of the subspecies complex that we talked about earlier. You can think of it sort of this way. Subspecies complex comes from taxonomy, whereas an e-bird group is meant for data entry, for recording the birds that we observe in the field. Sub-species complexes and e-bird groups might overlap, but they aren't. aren't always identical. The Cornell Lab of Ornithology, the makers of eBird, create groups to help

birders identify and report birds more easily. An eBird group usually corresponds to a particular subspecies complex, but sometimes it's more broad. In other words, eBird doesn't give you every subspecies. It only makes groups where birders can realistically tell them apart in the field. It's entirely up to you to decide how far you want to go with learning the differences between one subspecies and the next. If you have a hard time just being able to identify species, then I'd recommend holding off on worrying about subspecies. Personally, when I record data in eBird, I just report species. There is a little toggle switch in the eBird app settings where you can choose to show subspecies or not. I've had that switch set to off since I started using eBird about nine years ago.

Now, I enjoy being able to recognize subspecies when I see them in the field. It's great to recognize geographic variation. But I like to keep my eBird lists more manageable and straightforward. And I know myself. If I turn on that switch that allows me to tick the boxes for each subspecies, well, I might get obsessed with the goal of seeing all the subspecies, and that could be dangerous. One advantage of keeping track of the subspecies you see,

beyond the contribution to citizen science, is that some of those subspecies might get reclassified someday as full species. So you could get some armchair lifers, bird species that get added to your life list without you having to lift a finger. I mean, you could be sitting on your couch on a Tuesday night, chugging from a two-liter bottle of Pepsi when, suddenly, an official change in taxonomy bumps up a few of the subspecies on your life list to full species. Oh, happy day!

Just don't be surprised when the opposite happens, when some of the species on your list are downgraded to subspecies. You know, like what happened recently to many of us when the three red-pole species, common, lesser, and hoary, all got lumped into one species, the red pole, acanthus flamaya. If nothing else, subspecies remind us that nature doesn't always fit neatly into the categories we come up with. They sit in that gray zone between populations and species, showing us the early steps of divergence. including the influence of geography and the evolutionary forces. Sometimes a subspecies is glaringly obvious in the field, sometimes it's invisible without genetic data,

and sometimes it's just a point along a cline that doesn't have any clear boundaries. Whether we treat them as scientific curiosities, conservation priorities, or birding challenges, subspecies deepen our appreciation for avian diversity and the dynamic processes that shape it. They show us that evolution isn't just something that happened millions of years ago. It's happening all around us right now, sometimes at the scale of a single marsh, mountaintop, or island.

Thanks for hanging out with me today to learn about subspecies. Now, I admit this episode was a bit more on the technical side, but I hope it made sense and that you feel like. like you learned a few things. A massive, gigantic thank you, as always, to the members of my Patreon community. My patrons make this podcast possible, and I'm so grateful for the amazing support. Welcome to my newest members, Elena, chickadee chicks, Will, Runar, Alexander, Antonson, Danny Hermes, and Paul Murray.

Thanks very much to all of you, and again, welcome. If you, dear listener, have some interest in supporting this podcast, you can check out my Patreon page at patreon.com slash science of birds. There's also a support the show link in the show notes on your podcast player app. And you can shoot me an email if you have something you'd like to share with me. Perhaps you've got some hot takes on important questions like, are subspecies real? Our birds real? Is Pluto a planet? Can you believe it's not butter? In any case, my email address is Ivan at Scienceofbirds.com. Again, this is episode 123.

You can check out the show notes for the episode, along with some curated photos of the birds I talked about today on the Science of Birds website, which is at Science of Birds.com. And hey, don't forget about bird merch. If you're looking for some bird and birding themed t-shirts, you can check out the designs I've made at birdmerch.com. I'm Ivan Philipson and

true fact about me, I really can't stand the texture of sandpaper. You know how some people hate the sound and feeling of fingernails running down a chalkboard? Like back in the day when chalkboards still existed? Well, that's how I feel about sandpaper. Just thinking about that gritty texture and two pieces of sandpaper scraping against each other, ugh, it makes me shudder and get unpleasant goosebumps. I've just shared my greatest weakness. Anyway, thanks again, and I wish you a lovely day. Peace. You know,