In this episode, you’ll hear about:

• What “species” means (and why it’s messier than it sounds)

• The split vs. lump process and why your life list isn’t safe

• Who actually makes the call (committees, checklists, and gatekeepers)

• The kinds of evidence that move the needle (DNA, song, plumage, etc.)

• 00:07 - The Comparison of the Cassia Crossbill to the Bear

• 01:30 - The Redpoll Conundrum: Species and Confusion

• 10:23 - Exploring Hybridization in Species Definitions

• 16:15 - Evolution of Bird Species Classification

• 20:43 - Exploring Genetic Research in Ornithology

• 25:05 - Exploring Bird Complexity

  Timestamp Disclosure
  These timestamps were generated using AI and may contain errors or omissions. They are provided for accessibility and reference purposes only and may not perfectly reflect the original audio.

Dr. Dave Towes
You've watched the bear, right? Yeah, it's just a fantastic show.

Dr. Scott Taylor
It's a great show.

Dr. Dave Towes
I don't know the process of the Emmys, but it's not a comedy. And so I feel like the Cassia crossbow is kind of like the bear. You know, it's like it checks all the boxes. Amazing work.

No one would take that away from, but it's like the gut check, is this a species? I know. I'm not totally convinced by that. Okay, Okay.

Dr. Scott Taylor
So you're at brunch, basking in the glow of finally nabbing a hori, Redpool, that tiny winter finch with the frosted cap and candy red forehead. You tell the table about your hard won id, log into ebird later for the official victory lap, and poof. Your lifer has changed categories.

It's just Redpool now. Yesterday's hard earned hori got cozy with common. Maybe lesser got shuffled too. And your life list has deflated.

Your brain immediately wants the culprit who killed the mood. Was it a shadowy committee in a windowless room? A grad student with a pipette and an agenda? Some mustache twirling tyrant known only as Clements?

If you've ever had that feeling, this. Episode is for you.

Okay, but why did my life list just shrink? And who's the villain in this story?

To help us answer it, I'm talking with Dr. David Toews, an associate professor at Penn State who works right at the intersection of species, genes, and confusion.

To understand what happened to your lifer, we need to step into the Redpole cinematic universe, where three lookalike finches, common hori and lesser, tour the north like a boy band. Same songs, slightly different outfits. Some years they erupt south in big numbers. Other years they barely show up at all.

And right when you finally learn the difference between fluffy brownish snowball and fluffy white snowball with a red forehead, the taxonomy updates and your checklists change. If this were a movie, the villain would be easy. Cape monologue, death ray. In the bird world, the villain is always evidence.

The genomic data that says these two are one were the field studies showing gene flow across what we thought was a hard boundary. And in the case of redpolls, it is personal.

Back in 2013, I was a postdoc at the Cornell Lab of Ornithology, the kind of place where a rare warbler in the parking lot can derail an entire morning that winter, the lab was buzzing because redpolls were everywhere. Flocks were hammering the feeders outside the big picture windows, and coffee breaks Frequently turned into hori versus Common. Show and tell.

One morning, my friend Nick Mason and I were standing there with our coffee mugs, watching this blur of brown streaky finches with red caps and saying what everyone was are these really different species or just different outfits on the same bird? Some were paler, some were darker, some almost ghost white. So we did what you do in. A place like that.

We went down the hall and let the genetics have a say using the tools we had. Then we asked whether hori and common were truly different species.

Across the genome we found no clean split, just birds turning the same pigment genes up or down. Interesting, but not the tidy answer anyone was hoping for. Fast forward to 2019.

My then PhD student Eric Fung sequenced whole genomes for birds that looked hoary and birds that looked common.

Most of the genome was nearly identical, but one chunk of one chromosome lit up a region dramatically different between brown birds and white birds that slice. That tiny slice is the genomic switch for those plumage differences.

Hoary looking and common looking birds differ there, but are basically the same everywhere else in their genome.

Redpolls in North America are more similar to each other regardless of how they look than to birds that look exactly the same but live all the way in Russia. One widespread species with a tiny genetic. Toggle for color and shape.

So if your life list drops a digit, take a deep breath and repeat after my birds are fine, my labels evolved. No one stole your finch. The evidence just told us the story was different and almost all always more interesting than we initially thought.

After the break, My fellow Canadian, Dr. Dave Taves joins us to walk through how DNA, song and behavior help us draw and redraw the lines and why, in the case of the redpoll finch saga, the only real villain is evidence. Not me. Stay with us.

Well, welcome back everyone. I'm super excited to have Dave Toews in the studio with me today. Well, virtually at least.

Dave and I have been friends for a really long time now and it's great to have a chance to chat about this really exciting topic. So welcome Dave and thanks for coming.

Dr. Dave Towes
Yeah, thank you. I was just trying to do mental math and what it was, I think it was 2009, so.

Dr. Scott Taylor
Oh yeah, yeah, Philadelphia, right? Yeah, yeah, the Philadelphia AOS meeting and.

Dr. Dave Towes
Then, oh yeah, American Ornithological Society at the time, the American Ornithological Union. Very critical distinction. There was lots of critical distinction.

Dr. Scott Taylor
We're not going to focus on the name of the society this morning.

Start off by talking about a question that I Think, a lot of people think, has a very simple answer, a very clear answer, which is actually a little bit more or a lot more complicated, depending on how you think about it. But let's start off our conversation before we get into splits and lumps and all of those things, with the broader question, what is a species?

Dr. Dave Towes
I mean, yeah, getting right into it. I mean, that's usually like the question at a conference, someone asks at the end and everyone kind of rolls their eyes and it's.

But it's, you know, it's an important question. As you know, it goes back to a definition, early 50s Ernst Meyer, who came up with the biological species concept.

And he defined species as groups of individuals that only interbreed with other individuals of that group. And he gave it a special name. He called it reproductive isolation.

And that are, you know, in the intervening 50 some years, we, there's other definitions that have arisen and debates about how broad and applicable that definition is, but at least in the bird world, that's the one that is most often used.

Dr. Scott Taylor
Yeah, definitely, I agree. The biological species concept, this, this reproductive isolation question, which we're going to be talking a lot about today.

And in the context of that, like a lot of the birds that you and I study are not reproductively isolated, but we still consider them species sometimes, but not all the time. Can you talk a little bit about that?

Like for you specifically, and you're generating research questions and working with your students, what's the functional definition that you're going by?

Dr. Dave Towes
Yeah, I mean, like in all of biology there are like gray areas and fuzzy edges and there's no exception for species. And so there are certain species that have fuzzy edges.

And you know, we call those actual areas where they, you know, make mistakes and they do interbreed with another species as contact zones and hybrid zones, where you get, you know, these mixed up individuals, you know, species. One makes a mistake and a female of one mates with the male of another and you get a hybrid.

And that's one of the things that has changed over the last 50 years.

Like how do we treat things that otherwise look like a good species in that for all other intents and purposes, they act like a distinct species, but actually sometimes make mistakes and produce hybrids.

And so studying these hybrid zones, how wide they are, how big they are, how extensive the hybridization is, is part of the piece that plays into whether we actually describe something as a distinct species or not, even if they do form hybrids.

Dr. Scott Taylor
I think if it was mare deciding that if there was any reproductive activity between two lineages, he would say, oh, this is not a species. And according specifically to the biological species concept, that's correct. But, yeah, hybridization adds this interesting wrinkle.

I guess the way I think about it, and I know the way we've talked about it, is if the hybrids have something wrong with them, like they can't reproduce themselves or they have a weird signal, maybe they're the wrong color, or their behavior is screwed up and they're isolated from the parents, then maybe we would still consider those parently lineages species. Right. Kind of separate evolutionary trajectories.

But if the hybrids can mate back and forth, it gets even more complicated and it's harder to draw a box around something which we like to do, but is, as you said, very hard to do in most of biology.

Dr. Dave Towes
I think it was the early 70s. The nuance that you just described wasn't part of the conversations, the taxonomic authorities.

It was called the big lump, where any species that was found to hybridize with another species was lumped, regardless of all the nuance you just described. And so it meant that what we now know, a lot of species that were merged together because, oh, they made a mistake, they're not species.

On further investigation, we actually. They're probably distinct species. When you look at a.

When you look at a trajectory of like the named species and it goes up and up and up, and then the early 70s just tanks and it's like, oh, my God, was there like an extinction event? Was there? You know, some. Did an asteroid hit the Earth and it's like, no, no, they just changed the definition of species.

Dr. Scott Taylor
But yeah, at least we didn't have EBIRD back in the 90s 70s. And a record of that. That would be.

Dr. Dave Towes
Didn't have Flame wars on Twitter at the time.

Dr. Scott Taylor
Yeah. Oh, man. Bringitback or whatever. Recently in the news is this GRU Jay.

I don't know if you've seen the coverage of the green jay blue jay hybrid that was discovered. Some news coverage of the grue jay is calling it a hybrid species or unprecedented evolutionary event.

What's your take on this green J blue jay hybrid discovery, given that you've discovered some really weird hybrids yourself?

Dr. Dave Towes
Yeah. So what I would say is, like, first, unlike a lot of the potential cool, crazy hybrids, they actually had genetic data for this.

Dr. Scott Taylor
Yeah. Which is great.

Dr. Dave Towes
Which was great. I think that's cool. But the problem, I think, comes, like, in the term species.

I can't remember the Latin derivation, but it's like describing a thing. And we use it in our colloquially. And so when we talk about, you know, a new thing, people will call it like, oh, it's a new.

It's a new thing, it's a new species, but it's not. It's just a weird, oddball hybrid between two otherwise distinct species.

Dr. Scott Taylor
Right.

Dr. Dave Towes
You know, some of the confusion comes. I mean, you were referring to ebird and, like, where you've got a list of species that you can select, you can also select, which is cool.

Hybrids between them. Right. And so I think the.

The fact that you can select it, these hybrids, just like you select another species, can sometimes leak into the way people think about a hybrid between species and a distinct species itself.

Dr. Scott Taylor
Okay, I want to take a minute to set the record straight. So earlier in the episode, I added myself as one of the villains responsible for removing a bird from everyone's life list.

The hoary Redpoll is no longer an ebird because of work that I and others have done. I want to also point out that I have played a role in adding a species.

The Chihuahuan meadowlark, which is a new species for North America, was added to everyone's list based on work that Johanna Beam, who was a PhD student actually with Dave, did while she was an undergrad in my lab. But, Dave, I know that you've only ever been a hero in this saga of taking species away and adding species. You've only ever added them. Can you talk to us a bit. About your research and how you determined what was once thought as a single species to actually be two?

Dr. Dave Towes
Yeah. So this is work way back during my master's degree, and we were.

I was working with Darren Irwin at the time, and we were studying what at the time were known as winter wrens across North America.

But previous genetic work had suggested that they were, you know, the eastern form of winter wren and the western form of winter wren were pretty genetically distinct. And, well, they. They looked almost identical, right?

Dr. Scott Taylor
Yeah. Little brown.

Dr. Dave Towes
Exactly. Little brown jobs. That's the derogatory term we use in the birding world. Super cute, though.

Like, I mean, like little mice in the forest that can fly. But they, you know, traditional taxonomy was usually working with what they had in front of them.

And a lot of that time it included, like, a specimen in a museum drawer. And one thing we know about songbirds is they, you know, song is really important in, you know, their. Their communication.

A bird in a door does not sing. Um, and so one of the things that. One of the main differences between these eastern and western winter wrens was the song that they sing.

And so I went out, we did recording of birds.

We found an area where we got eastern and western birds that were singing basically in neighboring territories, did the genetics and showed that, like, they seemed to be treating each other, even where they occurred together in the same spot in this cool town, Tumblr Ridge, up in northern British Columbia.

Dr. Scott Taylor
Oh, yeah. I was wondering where it was. That's nice.

Dr. Dave Towes
Yeah, yeah. So it's like where the kind of boreal forest meets the Rocky Mountains. So you get a lot of, like, cool east meets west stories there.

And this seemed to be one. So it was like genetically very distinct. They seem to not breed with each other where they came into contact.

While they looked very similar, they sang very different songs. And so we kind of all put that into a package together to split them.

The eastern form retained the original name winter wren, but then we named the western form the Pacific wren, which wasn't. I don't know, with now 20 years on, I might have come up with a more creative name, but it stuck. I think I'm glad I didn't name it after myself, but.

Dr. Scott Taylor
Yeah, right. That wouldn't have been the right move for folks listening. It is poor form to name anything after yourself. If you ever describe a new species.

So those that do it. Yeah, you can judge them.

You used genetics and song because the plumage really wasn't distinguishable, and that's why these birds hadn't been described as different species. And some people would call that kind of a cryptic speciation event or something that we as humans couldn't visually detect originally.

So in general, are people using genetics and song and plumage, or a combo of a few of them. How has that changed since you. Because you were saying you did this work when you were a master's student, which no shade was a while ago. I mean, it was for me, too. How have things changed in that context? What are people using now to kind of ask these questions?

Dr. Dave Towes
Yeah, I mean, you know, a hundred years ago, when people were describing these things, they didn't even have the ability to, like, record the songs. Like they could.

Dr. Scott Taylor
Right? Yeah. You had to write it down.

Dr. Dave Towes
Yeah. You'd have to, like, you know, make a qualitative assessment and, like, hear all the.

Anyway, so that's something that's changed over the last hundred years. Over the last, I would say, two decades. Yeah. It's more of a holistic approach to delineating species.

So you use, you know, the, you know, lots of measurements, plumage.

But now it's not just like a qualitative plumage score, you can actually, you know, use spectrophotometers and measure the wavelengths of light that may not be able to be seen by the human eye because, you know, birds can see in a broader visual spectrum, in some cases in the UV light. And then in addition to that, you can use recordings and songs.

And our ability to use genetics, I mean, I think there's some reticence there because interpreting, understanding, explaining genetic data can be challenging. It's one of the most important tools in the toolbox these days.

Dr. Scott Taylor
Okay.

So in terms of using large genetic data sets to ask long standing questions about species differences, one project that we've both been involved with and started being involved with as postdocs at the Lab of Ornithology was this question about blue winged and golden winged warblers.

And, you know, being able to sequence whole genomes allowed us to discover that really there are just these handful of regions in the genome that differentiate them, and at least some of them underlie plumage differences. So can you talk a little bit about what that means, you know, and what your journey has been with this vermivora complex?

Dr. Dave Towes
Yeah, I mean, it was a fun journey to share with you.

Dr. Scott Taylor
Yeah.

Dr. Dave Towes
And it was, you know, that is like a mystery that goes back to like the 1800s, you know, John James Audubon raising questions about their species status, that the hybrids between them were actually thought to be distinct species and still retained their names. Like the Brewster's warbler and the Lawrence's warbler are not actually species, they're just hybrid named hybrids between them.

And it was only until we were lucky enough to be able to sequence their whole genomes that we actually found those handful of regions.

But I share with my students there's the idea of some Eureka discovery moment with a scientist running down the hallway screaming to her colleagues like, eureka. And it's like, yeah, 21st century, we don't do that.

I was drinking red wine in my basement and I like made the graph and I sent you a screen cap on imessage and I was like, holy, this is, this is crazy. Anywho.

Dr. Scott Taylor
Yeah, but who actually do we ask to make these decisions?

Dr. Dave Towes
In North America, the main taxonomic committee for birds is called the North American Classification Committee.

Dr. Scott Taylor
Yeah.

Dr. Dave Towes
And they have, I think like 12ish members. I think it's. It varies.

And proposals are submitted by committee members and other scientists presenting evidence to whether to split or lump a species. And then they discuss it, vote on it. I think there needs to be like a, for some change to the Status quo.

There needs to be like a two thirds vote to pass and they make the decision. And honestly, I mean, you've probably disagreed with some of their decisions.

I've disagreed with some of their decisions because the other side of the coin, like herpetologists and folks who study, like snakes and lizards and things, it's the Wild west. There's no committee, so anyone in any paper can write something and, oh, I found some distinct population. We're going to call it a new species.

And so it means the benefit of having a standard to work from is gone.

Dr. Scott Taylor
Yeah, we've been talking about splits and lumps and the decisions that are made and who makes those decisions, but what impact do those have on conservation? And what are your thoughts on the way these decisions should relate to conservation? Or.

Dr. Dave Towes
So, for example, the question is, like, if golden wing and blue winged warblers were lumped.

Dr. Scott Taylor
Ooh, controversial.

Dr. Dave Towes
I know, right?

So, yeah, I mean, I have been approached by people to write a proposal to lump them, not just based on our genetic data, but the fact that they hybridize extensively. The laws that are used in the context of species conservation, in the US it's the Endangered Species Act.

In Canada, it's the Species at Risk act, protects even things that aren't genetically distinct, that are distinct in a number of ways that aren't necessarily named species. In reality, we're trying to conserve diversity, and it doesn't necessarily need to be at the species level.

It can be at lower levels as long as it passes certain bars.

Dr. Scott Taylor
In the context of all of this, I mean, we pay attention to the research being done, we go to the conferences, we see what studies people are doing, and then we know usually what's being proposed to be split or lumped in a given year. What's to you, is there like a surprising split or rump?

Dr. Dave Towes
Split or rump? Yeah.

Dr. Scott Taylor
To you, is there a surprising split or lump that's recently happened that you want to highlight?

Dr. Dave Towes
Yeah, I mean, I don't know how familiar you are with the Cassia crossbill.

Dr. Scott Taylor
Yes.

Dr. Dave Towes
So this might get me into a little hot water, but this is like, crossbill's amazing birds, like, you know, cool ecology. But there has been, you know, research on certain populations and these populations differ in, like, the call notes that they produce.

Anyway, classic work on one of these, work by Craig Bankman at the University of Wyoming, found that, you know, it did all this, like, fantastic research on the ecology, the genetics and the call variation in these cross bills and found that this one population, confined to like 70km square checked all the boxes in terms of a distinct species. But, like, I don't know. I was asking you before. You've watched the Bear, right?

Dr. Scott Taylor
Yeah, seasons one and two, season three. I haven't quite got through.

Dr. Dave Towes
Would you describe it as a comedy?

Dr. Scott Taylor
I would not. And was shocked when it was listed as a comedy at the Emmys.

I remembered the holiday episode and thought having to pause that because I was so anxious, like, eight times is not funny to me.

Dr. Dave Towes
Exactly. Yeah.

And so I don't know the process of the Emmys and things, but they checked all the boxes, and they got it in as a comedy, won all the awards, and no one would take anything away from all the amazing. Just a fantastic show. It's a great show, but it's not a comedy. And so I feel like the Cassia crossbow is kind of like the bear.

It's like, it checks all the boxes. Amazing work. No one would take that away from. But it's like the gut check, is this a species? I know. I'm not totally convinced by that.

Dr. Scott Taylor
I'm not either. So, Dave, we've reached the part of the show that we call that's BS or that's bird stuff, where our guest.

Dr. Dave Towes
Family friendly.

Dr. Scott Taylor
Yeah, very family friendly. So you get to debunk a myth about birds that you think we should all know.

Dr. Dave Towes
I mean, it's not BS per se, but the.

Dr. Scott Taylor
It's a very Canadian way to start things.

Dr. Dave Towes
Yeah, I know, right? Fair enough. You know, the fact that the. The hybrids between.

I mean, we already kind of touched on this, but the hybrids between golden winged and blue winged warblers, which are named as, you know, what looks like a distinct species. They are not distinct species.

Dr. Scott Taylor
Totally. Yeah.

Dr. Dave Towes
That's why you're doing the podcast, right?

Dr. Scott Taylor
Yeah.

Dr. Dave Towes
To bring these. There you go. That's what we're here.

Dr. Scott Taylor
There you go. It's the reason.

But, you know, I remember as a kid, like, I would just read field guides, and I would think about nature in these very categorical ways.

And it wasn't until, like, I really started learning about natural history and getting out in the field and birding that I realized, oh, man, there's so much more complexity, and it's actually cooler than just, like, these six birds. It's these six birds plus five others that these three could make. And that's all very, very interesting. So. Yeah, I totally agree with you. Well, Dave, it's been awesome to get. To chat with you.

I wish we were still working in the same place, just grabbing pizza at lunch and chatting about all these weird, weird birds that we study. But thanks so much for joining us on the podcast.

Dr. Dave Towes
Yeah, this was great. Yeah, there's an endless story of birds to be told, and no one better to tell it than Scott Taylor.

Dr. Scott Taylor
Oh, man, that's very kind. Well, happy to have you with me on the journey today.

Dr. Dave Towes
Same.

Dr. Scott Taylor
Okay, so birds are dinosaurs, and around here, we like our snacks. So we end each of our episodes with a dinosaur nugget. Today's nugget.

When it comes to your life list expanding or contracting, the only real hero or villain in the story is evidence that may come in the form of. DNA, song or plumage, usually a combination. And when a bird falls off your.

Life list, it probably means something really interesting is happening, something that's confused folks. For a while, sometimes centuries. Maybe that's hybridization or, like, for the red poles. Maybe it's the discovery of a really unique genetic variant.

That's a wrap on our episode. Okay, but why did my life list just shrink? If you liked this episode, leave a.

Comment like and subscribe, and we'll see you next time. Byeee. Okay, But… Birds is hosted by Scott Taylor with production and creative by Zach Karl.

Transcript Disclosure
This transcript was generated using AI-assisted transcription and may contain errors or omissions. Please refer to the audio or video episode for the most accurate representation.