Speaker 1: Approximately one percent of all bird species are total jerks. No,
Speaker 1: approximately one percent of all bird species are not seagulls.
Speaker 1: They're what are called interspecific brood parasites. And fine, they're
Speaker 1: not really jerks, but evolution has endowed them with a
Speaker 1: profoundly jerk like strategy. You see, interspecific brood parasites put
Speaker 1: their eggs into the nests of other species, often without
Speaker 1: them knowing it, and to add insult to injury, the
Speaker 1: parasitic birds often damage the host nest as well. For example,
Speaker 1: just in case the parents of the parasitized nest can count,
Speaker 1: the brood parasite takes one of the host eggs out
Speaker 1: of the nest and yeats it overboard. Now the nest
Speaker 1: has the same number of eggs as it did before
Speaker 1: the doting parents went out to grab a quick snack,
Speaker 1: but those eggs is not their own, and then the
Speaker 1: brood parasite mom typically SCRAMs, leaving the host parents to
Speaker 1: do the difficult job of raising the kids. How did
Speaker 1: this dead beat parenting strategy evolve? And why can't the
Speaker 1: host species seem to figure out what's happening and fight back.
Speaker 1: On today's episode, We're going to dig into interspecific brood parasitism,
Speaker 1: and I'm going to be absolutely thrilled to be combining
Speaker 1: some of my favorite topics, animal behavior and parasitism. Welcome
Speaker 1: to Daniel and Kelly's parasitic Universe. Hi.
Speaker 2: I'm Daniel. I'm a particle physicist, and I have zero
Speaker 2: tolerance for parasites.
Speaker 1: Hello. I'm Kelly Waitersmith. I study parasites and space, and
Speaker 1: I have all the time in the world for parasites.
Speaker 2: Right, Kelly, with then my question for you today is
Speaker 2: how many non human species are there in your brood?
Speaker 1: Oh, you're asking me about pets. You've already asked me
Speaker 1: about pets. You just found a different way to ask
Speaker 1: or I guess you know you need an update, right
Speaker 1: because you asked me this a couple of weeks ago,
Speaker 1: and the number changes regularly.
Speaker 2: But now I'm framing them as parasites on Kelly's goodwill.
Speaker 1: Oh, Oh, probably just my dog Biscuit, because she's been
Speaker 1: she's been a real handful lately. But no, she's a
Speaker 1: good girl. I've got a goose that's been trying to
Speaker 1: bite me lately. I don't appreciate.
Speaker 2: That that wasn't in the terms of service you got
Speaker 2: when you got the goose.
Speaker 1: Now, yeah, we used to call him Jacques Goostow and
Speaker 1: we thought that was really cute. But now we call
Speaker 1: him Schmaltz because we're thinking he might become Christmas dinner
Speaker 1: because he has become very aggressive, So just Schmaltz.
Speaker 2: Wow, what lesson do you think your kids take from
Speaker 2: that sort of change in status based on behavior?
Speaker 1: Well, hmm, that's interesting, based on I don't necessarily want
Speaker 1: them to take the message that based on behavior these
Speaker 1: things happen. But I am okay with the fact that
Speaker 1: they live on a farm and they need to understand
Speaker 1: where their food comes from, although they've insisted that they
Speaker 1: won't eat it. But will I was gonna make a
Speaker 1: joke about them going hungry on Christmas, but I wouldn't
Speaker 1: do that to them.
Speaker 2: Well, I think that's a pretty powerful incentive. You know,
Speaker 2: behave well or you're not going to be here for dinner.
Speaker 2: You're going to be part of dinner.
Speaker 1: Yeah, but you know, this isn't an episode on cannibalism,
Speaker 1: so it really doesn't extend to the family eiting.
Speaker 2: We already got the pull out.
Speaker 1: Your bingo cars. But I am under the impression that
Speaker 1: all of your pets are cherished family members and that
Speaker 1: none of them you would consider parasites.
Speaker 2: No, none of our pets are parasites. Currently. We have
Speaker 2: a dog who lives in our house, and we have
Speaker 2: a horse who doesn't live in our house. But my
Speaker 2: daughter Hazel considers part of the family.
Speaker 1: Oh yeah, I do. I I shouldn't. Well, I'm not
Speaker 1: going to go down that. I shouldn't have said anything
Speaker 1: bad about Biscuit. She's been chewing on her feet a
Speaker 1: lot lately, but we got to get her to the vet.
Speaker 1: That's my fault.
Speaker 2: They're doing their best.
Speaker 1: Yeah, yeah, yeah, yeah, Bescaus, she's a good girl.
Speaker 2: She's the best girl.
Speaker 1: Yeah yeah yeah.
Speaker 2: But today we're not talking about pets we love, who
Speaker 2: we've welcomed intentionally into our family, even if they do
Speaker 2: cross the species barrier. We're talking about something much more sinister,
Speaker 2: aren't we.
Speaker 1: We are. Actually I should have talked about my livestock
Speaker 1: guardian dog who choose on our goats, because that's that
Speaker 1: shouldn't happen.
Speaker 2: That's sort of how the goats feel about that.
Speaker 1: They don't they don't love it. Although we've got one
Speaker 1: goat who kind of spaces out when it's happening, and
Speaker 1: it doesn't really seem to mind so much because she
Speaker 1: really likes food and she's just kind of chewing on
Speaker 1: the grass and he's just playing. But anyway, okay, So, yes,
Speaker 1: interspecific brood parasitism.
Speaker 2: Interspecific is a complicated word. It just means cross species.
Speaker 1: Right, yes, it does. It means yeah, between species. And actually,
Speaker 1: so when you know, when you say interspecific brood parasitism,
Speaker 1: it's fun to watch people try to break the different
Speaker 1: pieces down to try to figure out what it means.
Speaker 1: And so this is a perfect transition actually to the
Speaker 1: questions that we asked the listeners. So let's go ahead
Speaker 1: and see how they broke it down. So I asked
Speaker 1: our listeners who are willing to volunteer to answer questions
Speaker 1: for us, what is interspecific brewed parasitism? And I'd like
Speaker 1: to mention here that you're probably not going to hear
Speaker 1: as many voices from women as I would like for
Speaker 1: us to be hearing. And so I would like to
Speaker 1: make yet another plea for women to please go ahead
Speaker 1: and answer these questions. It's okay if we don't know
Speaker 1: the answers, or you know, some of us probably do
Speaker 1: know the answers. But even if you don't know, add
Speaker 1: your voice to the chorus of or you know, just
Speaker 1: go ahead and guess I would like some more women voices.
Speaker 1: So anyway, let's go ahead and hear what answers we got.
Speaker 3: It is when a animal family builds up a herd
Speaker 3: immunity to a certain parasite.
Speaker 2: I have no idea, you guys got me.
Speaker 4: Look sure where it is, but it sounds like a
Speaker 4: parasot that invites the nest and the zombifores the young
Speaker 4: ones in there.
Speaker 1: I think the bird lays into eggle, moves its egg
Speaker 1: into a different bird's nest, and gets that other bird
Speaker 1: to raise its young, or something like that.
Speaker 2: I think.
Speaker 5: I think interspecific brood parasitism is when a parasitic animal
Speaker 5: fools a different animal species into taking care of its
Speaker 5: eggs are offspring. And I only know this because my
Speaker 5: daughters and I watched the PBS Nature documentary on this
Speaker 5: subject a couple of years ago.
Speaker 6: I think of broods like egg clutches of species relying
Speaker 6: on the egg clutches of other species in order to
Speaker 6: exist and thrive.
Speaker 7: Probably an interspecies specific parasite or a parasite that goes
Speaker 7: after a specific species. But the word brood makes me
Speaker 7: feel like the parasites.
Speaker 2: Are brooding within their.
Speaker 3: Host interspecific parasit a brudhism is a tongue twister and
Speaker 3: something to do with I don't even know what a
Speaker 3: brood is, like an ipa.
Speaker 4: I think we're talking about animals like cuckoos. I remember
Speaker 4: hearing them a lot when I was a child. I'm
Speaker 4: thinking there was something a bit ikey about their nesting behavior. However,
Speaker 4: I expect the science here is really interesting.
Speaker 6: Maybe it's how parasites select for specific characteristics in a
Speaker 6: host population, or maybe even that parasites doing that guide
Speaker 6: the evolution of the host population. Either way, I'm sure
Speaker 6: Kelly's gonna tell us really excitedly.
Speaker 2: These are great answers, and I'd have to say I
Speaker 2: don't think I would do very well either here because
Speaker 2: the phrase interspecific to me hits on the specific instead
Speaker 2: of species, and so I'm thinking like interspecific as opposed
Speaker 2: to like inter general, Like what does that even mean?
Speaker 2: Interspecific is hard for my brain, and brood is not
Speaker 2: a word I typically use to describe, like people in
Speaker 2: my species. Who I'm taken care of.
Speaker 1: Oh, well, you know I went was that an Ohio thing? No,
Speaker 1: I guess not. But like, so, you know, when I
Speaker 1: was an undergrad, I thought I was going to go
Speaker 1: to med school, and then I was like, you know what,
Speaker 1: I could never deliver to someone the news that like
Speaker 1: their kid didn't make it. That's not for me. Yeah,
Speaker 1: And then I decided I was going to go to
Speaker 1: VET school, and then I was like, you know what,
Speaker 1: I could never deliver to someone the news that their
Speaker 1: dog didn't make it, so like, that's not for me either.
Speaker 1: And then I took an animal behavior class, and I
Speaker 1: was like, this is what I'm going to do with
Speaker 1: the rest of my life. And then I ended up
Speaker 1: going to grad school for behavioral ecology, which is trying
Speaker 1: to understand, you know, why animals do what they do
Speaker 1: in the wild. And so that's where I came across
Speaker 1: the word brood. And so I do think of, you know,
Speaker 1: my children as my brood. But I probably would not
Speaker 1: have thought of that had I not gone to grad
Speaker 1: school for behavioral ecology.
Speaker 2: Because brood to me implies some sort of like dark
Speaker 2: Gothic mood, like he stands at the parapet of his castle,
Speaker 2: brooding over his future or something.
Speaker 1: Yes, as a goth kid, I had heard the word
Speaker 1: yes in that way. Yeah.
Speaker 2: So this is an especially tricky phrase because each word
Speaker 2: on its own has several meetings with very different contexts,
Speaker 2: and so putting them all together in the right order,
Speaker 2: it's tricky stuff. So tell us, Kelly, what the heck
Speaker 2: is this? Break it down for us in basic English.
Speaker 1: Okay, So, first of all, I want to note the
Speaker 1: reason that we are enjoying this amazing topic today is
Speaker 1: because a listener named Daniel saw a New York Times
Speaker 1: article on brown headed cowbirds that have this strategy and
Speaker 1: he wanted to know more. So that's what we're going
Speaker 1: to talk about today. So, interspecific brood parasitism is when
Speaker 1: one organism tricks or coerces a parent of a different
Speaker 1: species into caring for their offspring.
Speaker 2: So this is not Biscuit being taken care of by you,
Speaker 2: because that's something you did intentionally. Yeah, add Biscuit to
Speaker 2: your brood.
Speaker 1: That's right. I knew that I was adding Biscuit to
Speaker 1: my brood. I love Biscuit very much. I wish she
Speaker 1: didn't have allergies. We're working on it. She's great.
Speaker 2: What about the fact that dogs are like selected for
Speaker 2: to be cute and to like, you know, pull on
Speaker 2: your heart strings and effectively emotionally manipulate their way into
Speaker 2: your Does that count?
Speaker 1: No, it doesn't. Like you still you're still choosing to join,
Speaker 1: you know, and like kids are well, I was gonna
Speaker 1: say kids are cute, but not all kids are cute,
Speaker 1: but we still love them.
Speaker 2: I can't believe you just said that on the record.
Speaker 2: I mean, I totally agree with you. Some kids to
Speaker 2: collect Winston Churchill or Richard Nixon, but I would never
Speaker 2: have said that. Oh my god, I just said it.
Speaker 1: Also, yeah, yeah, yeah, but we love them anyway, right,
Speaker 1: you don't have to be cute to be absolutely amazing
Speaker 1: and loved. And so the point with parasitism is you're
Speaker 1: essentially being tricked or coerced. And Okay, so we're gonna
Speaker 1: start with my favorite example, and almost all examples involve birds,
Speaker 1: and so the bird people out there are going to
Speaker 1: be like, how dare you start with an example that's
Speaker 1: not birds? But look at people. The fact of the
Speaker 1: matter is, like number one, I'm a parasite person. But
Speaker 1: after being a parasite person. I'm a fish person, and
Speaker 1: so it's gonna be a fish example. So we're going
Speaker 1: to talk about the cuckoo catfish. All right. So down
Speaker 1: in Africa there are these cicklids and these are the
Speaker 1: host species.
Speaker 2: So this is what's a clid.
Speaker 1: A cyclid is a fish, and like Africa is sort
Speaker 1: of famous for their ciclids, these are species that sort
Speaker 1: of like radiated. There's loads of different species. A bunch
Speaker 1: of evolutionary biolog just go down to Africa to try
Speaker 1: to figure out why there's so many different species of
Speaker 1: this kind of fish in Africa and how they've managed
Speaker 1: to like fill all of these different niches. So it's
Speaker 1: just a species that you find in lakes in Africa.
Speaker 2: Okay, what does it look like? Roughly?
Speaker 1: H it looks like a fish. You may have gone
Speaker 1: to a pet store and you can you've seen convict cyclids,
Speaker 1: Like there's ciclids are a very popular fresh water fish
Speaker 1: species that you can find at pet stores. And this
Speaker 1: is like a different species than what you've seen at
Speaker 1: pet stores, but it's got like the same body shape.
Speaker 2: Okay.
Speaker 1: One of them does this amazing thing where they lay
Speaker 1: eggs and then they stick them in their mouths.
Speaker 2: On purpose, on purpose, hold them in their mouth to like,
Speaker 2: you know, keep them safe or something.
Speaker 1: Yes, they're called mouth brooders.
Speaker 2: Whoa.
Speaker 1: And so like these mouth routers they pick up the eggs.
Speaker 2: Not the same as mouth breathers, right, that's a totally
Speaker 2: different kind of thing.
Speaker 1: That's me when I have a cold. These are mouth ruders, okay.
Speaker 1: And so they pop the eggs in their mouth. The
Speaker 1: eggs hatch and the fish can swim in and out
Speaker 1: of the mouth. And so when the fish want to go,
Speaker 1: like get some food, they'll swim out and they'll like
Speaker 1: eat little things that are in the water. And then
Speaker 1: when a predator comes, they swim into mom's mouth for safety.
Speaker 1: And sometimes Mom will like open her mouth and create
Speaker 1: an inflow of water to like, you know, help them
Speaker 1: get in when she sees a predator. And so, like
Speaker 1: the mouth is a safe place for these little babies.
Speaker 2: And how do they avoid being eaten? Or how does
Speaker 2: mom eat with her babies in her mouth?
Speaker 1: I believe mom ejects the babies when it's time for
Speaker 1: her to eat ice. And so yeah, like, so the babies,
Speaker 1: you know, when they're in the egg stage, she might
Speaker 1: sort of like spit them under a rock for a
Speaker 1: little while and then go and get a snack and
Speaker 1: then suck them all back up again. And I'm not
Speaker 1: an expert on the mouth bruders.
Speaker 2: It's amazing to me though, that like things other species
Speaker 2: do sound gross to me, like spitting your babies under
Speaker 2: a rock from your mouth, but things that our species do,
Speaker 2: like you know, creating milk from your body and feeding
Speaker 2: it to your baby, that's not gross to me at all.
Speaker 2: So it's amazing how your instincts are just like totally parochial.
Speaker 1: Yes, I will note that Zach stayed on the side
Speaker 1: of the blanket near my head when labor was happening,
Speaker 1: and so human birth is pretty gross too.
Speaker 2: So well, I guess it depends on the husband, because
Speaker 2: when Hazel was being born and Katuna was having a
Speaker 2: c section, they were like, please stay on that side,
Speaker 2: and I was like, you're opening up my wife to
Speaker 2: pull out my daughter, like I'm gonna watch, and I did,
Speaker 2: and it was fascinating.
Speaker 1: I would have been watching, Yeah, yeah, I would have
Speaker 1: been watching. And then they went to hand Zac the
Speaker 1: umbilical cord and they're like, do you want to cut?
Speaker 2: And he was like, yes, that's what I pay you
Speaker 2: guys for.
Speaker 7: Yeah.
Speaker 1: No, wipe that thing off and give it to me
Speaker 1: when it's clean. But he was very supportive through the
Speaker 1: whole thing.
Speaker 2: Interesting for a man whose office is a disaster that
Speaker 2: he only wants clean things handed to.
Speaker 1: Yes. Yes, well we're all still trying to understand the
Speaker 1: emotional support Dorito's bag. But anyway, yes, exactly.
Speaker 2: All right, So we have this mom who has babies
Speaker 2: and keeps them in her mouth. Yes, and then that's
Speaker 2: the host.
Speaker 1: That's the host. Yes. And so the parasite is called
Speaker 1: the cuckoo catfish. Who And you know, I think a
Speaker 1: lot of us have seen catfishes. They've got those like whiskers,
Speaker 1: they move around on the ground.
Speaker 2: This one they're good and sandwiches.
Speaker 1: Hell, sure, sure. This one's kind of tiny. It's like white.
Speaker 1: It's got some speckles. That doesn't really matter. The point
Speaker 1: is it's like a tiny catfish.
Speaker 2: Okay.
Speaker 1: And so these catfish try to eat the host eggs. Okay.
Speaker 1: So like when the hosts are first laying the eggs,
Speaker 1: they have to lay them on the sand before the
Speaker 1: mom can get them in her mouth. And so well,
Speaker 1: the eggs are being laid on the sand and getting fertilized.
Speaker 1: The catfish are going around and trying to eat them,
Speaker 1: and the parents are freaking out and they're trying to
Speaker 1: get the catfish to leave, and they're like, go away,
Speaker 1: go away. And while they're distracted and trying to chase
Speaker 1: the catfish away, the catfish lay some of their own
Speaker 1: eggs in amongst the host eggs. Wow, And so then
Speaker 1: the catfish go away, and so the mom is like, okay, fine,
Speaker 1: they're gone, Thank goodness. And of course I'm being super
Speaker 1: anthropomorphic here. Who knows what the mom is thinking. It
Speaker 1: might just be like, I don't know how smartfish are.
Speaker 1: So anyway, the mom eventually goes to acquire all of
Speaker 1: the eggs and she sucks them all up into her mouth,
Speaker 1: and she has accumulated her eggs and the eggs of
Speaker 1: the parasitic catfish.
Speaker 2: I see. So they're not replaced, they're just in addition.
Speaker 1: They're in addition, right. But the catfish eggs hatch first,
Speaker 1: so they're like set to hatch faster, and so the
Speaker 1: catfish eggs hatch before the host eggs hatch. But when
Speaker 1: the host hatch, the catfish are there ready for a snack.
Speaker 1: Oh yeah. And so as all the host eggs are hatching,
Speaker 1: the catfish are eating them one by one.
Speaker 2: Oh my gosh.
Speaker 1: And so in a lot of cases, none of the
Speaker 1: host babies will survive. They will all become catfish snacks,
Speaker 1: and the parents will spend a significant amount of their
Speaker 1: energy protecting the catfish babies. So the catfish babies will
Speaker 1: like leave the mouth. But then when a predator comes,
Speaker 1: they'll swim towards the you know, the parasitized mom, and
Speaker 1: the mom will open her mouth to give them a
Speaker 1: place to hide. Because the mom, you know, recognizes anything
Speaker 1: that swims out of her mouth as her offspring, and
Speaker 1: so she has been tricked.
Speaker 2: Wow. Crazy, that is crazy. Can I ask you how
Speaker 2: I'm supposed to feel about this? Because I have all
Speaker 2: of these emotions. When I watch like nature documentaries, I
Speaker 2: always end up like rooting for one animal. But I
Speaker 2: find that like, if I'm watching the documentary about cheetahs,
Speaker 2: I'm rooting for the cheetah as it chases the antelope.
Speaker 2: If I'm watching the antelope documentary, I'm rooting for the antelope.
Speaker 2: And I'm like, you, dang, cheetah, what are you doing?
Speaker 2: So what am I supposed to feel here because it
Speaker 2: feels like one of these is getting tricked. It feels unfair.
Speaker 1: Yeah, in all cases, you should be rooting for the
Speaker 1: tapeworm that lives in all of those animals. But no,
Speaker 1: you didn't see it coming. But yeah, I'm nature is
Speaker 1: just it's complicated. There's no clear answer, like I you know,
Speaker 1: I feel that way also, like when you know, when
Speaker 1: I'm watching the antelope documentary and the antelope gets away,
Speaker 1: I'm like, oh, you know, I'm happy with that antelope,
Speaker 1: but that cheetah maybe had babies that aren't getting fed,
Speaker 1: and nature is you know, it's not Life isn't fair,
Speaker 1: especially if you are, you know, living out in the wild.
Speaker 2: But I feel like parasitism is especially emotionally fraught. Was
Speaker 2: that what attracted you to this field? Or are you
Speaker 2: totally impervious to all of that emotion?
Speaker 1: Oh? Interesting, No, I'm not impervious to the emotion. And like,
Speaker 1: you know, especially when it's humans who are getting infected,
Speaker 1: Like I'm totally on board with, yeah, trying to eradicate
Speaker 1: the parasites that are her people, and.
Speaker 2: Not just trying to eradicate them, but like feeling angry
Speaker 2: at them.
Speaker 1: Yes, yeah, feeling angry at them judgmental, yes, But I
Speaker 1: also but I still have like a begrudging respect for
Speaker 1: for example, a species like what was the speci. John
Speaker 1: Hawden was telling us about a species of parasite that
Speaker 1: is in our body and is able to essentially like
Speaker 1: rip proteins off of like our cells and stick it
Speaker 1: on itself and essentially we're like, uh, you know, host
Speaker 1: coat to escape from us. And in our Zombie Fish episode,
Speaker 1: we were talking about trematodes that go through snails and
Speaker 1: fish and birds, and then they also have a phase
Speaker 1: where they're swimming through the water. Like imagine being able
Speaker 1: to succeed in environments that are that different.
Speaker 2: It's impressive.
Speaker 1: And you've got immune systems that are trying to attack
Speaker 1: you in those different kinds of hosts, Like, that's kind
Speaker 1: of incredible that evolution has come up with solutions in
Speaker 1: all of those different environments. And so I am begrudgingly
Speaker 1: impressed with their abilities. And so anyway, I'm amazed with
Speaker 1: the solutions evolution has come up with for complicated problems.
Speaker 1: But you know, I don't think that the suffering is
Speaker 1: funny or wonderful, and especially when it's people, but it
Speaker 1: still is kind of amazing. It is amazing unless it's
Speaker 1: happening to people, then it's sticks.
Speaker 2: Yeah, And I think it's probably misguided to put yourself
Speaker 2: on one side of it or the other, or to
Speaker 2: assert like moral superiority or inferiority to one side of
Speaker 2: these battles, because you know, who knows what these animals
Speaker 2: are thinking, that they really have choices to make anyway.
Speaker 2: In the end, we're like really imposing a lot of
Speaker 2: human values and emotions on these things, which is something
Speaker 2: weirdly we do, right, Like I impose human emotions on
Speaker 2: my dog. I interpret my dog's emotions in the context
Speaker 2: of humanity, And so here I'm like really feeling for
Speaker 2: the mom, Like not only has she lost her babies,
Speaker 2: she ended up taking care of the babies that killed
Speaker 2: her babies.
Speaker 1: Yeah, I know. And you know what's kind of weird
Speaker 1: is that, you know, we have all of this human baggage,
Speaker 1: and we sort of care differently depending on what species
Speaker 1: we're talking about. So when I was talking about the fish,
Speaker 1: I didn't feel that bad for the cicklid. They kind
Speaker 1: of got like empty, vapid looks in their eyes.
Speaker 2: Your impersonation of the sicklid mom was not especially empathetic.
Speaker 1: I have to say, yeah, I'm sorry, but like, but
Speaker 1: we're about to talk about birds and when I when
Speaker 1: I see the bird babies getting yeated out of the nest,
Speaker 1: then I feel bad and I don't know why, and
Speaker 1: it's kind of arbitrary, and humans are arbitrary.
Speaker 6: I guess.
Speaker 2: Well, then let's take a break and when we come back,
Speaker 2: we'll hear about more examples of interspecific brood parasitism, ones
Speaker 2: that make even Kelly feel bad.
Speaker 8: Even Kelly, Okay, we're back, and we're talking about species
Speaker 8: that trick other species.
Speaker 2: Moms into taking care of their youth for them. Why
Speaker 2: can't they take care of their own babies, Kelly? What's
Speaker 2: wrong with them?
Speaker 1: Well that's a great question. So you know, evolution has
Speaker 1: now sent them down this path where they can't take
Speaker 1: care of them anymore because they don't need to. There's
Speaker 1: this other strategy where they can get somebody else to
Speaker 1: do it. And so to me, the question isn't why
Speaker 1: can't they take care of their own babies anymore? The
Speaker 1: question is why are the host parents allowing this to
Speaker 1: happen to themselves? Which sounds very much like victim blaming, but.
Speaker 2: It why were you wearing that?
Speaker 1: Huh oh? Yeah right, I'm feeling uncomfortable about the phrasing already,
Speaker 1: But so let's walk through. So a big part of
Speaker 1: the way scientists think about this question is how much
Speaker 1: pressure does it put on the host in terms of costs,
Speaker 1: like how much how many babies essentially are they losing
Speaker 1: in a season because this is happening to them, okay,
Speaker 1: And it turns out the answer is it depends a
Speaker 1: lot on what a surprise, Yeah, right, on the details.
Speaker 1: So let's talk about the common cuckoo first, because this
Speaker 1: is one of the most well studied examples, and for
Speaker 1: a common cuckoo, you lose a lot if a common
Speaker 1: cuckoo lays eggs in your nest. Some folks may have
Speaker 1: seen videos of this, because these videos kind of really
Speaker 1: make the rounds when they start getting some traction. But so,
Speaker 1: a common cuckoo will lay an egg in the nest
Speaker 1: of a bird that's much smaller than it is when
Speaker 1: that bird is like off collecting food or something, okay,
Speaker 1: And when the egg hatches, the egg tends to hatch
Speaker 1: again before the host egg hatches, and while that chick
Speaker 1: is still like completely naked, no feathers. It's at the
Speaker 1: stage where it's still like sort of trembling, trying to
Speaker 1: get its body in order. Like its eyes are still closed.
Speaker 2: It feels like a helpless babe or something.
Speaker 1: Yeah, right, you'd imagine like, well, this couldn't do any
Speaker 1: harm at all. Someone needs to take care of this
Speaker 1: poor little bit. It fumbles around the nest and when
Speaker 1: it feels another egg, it puts its back up to
Speaker 1: the egg, lifts its butt up.
Speaker 2: Uh oh, the music just got dark.
Speaker 1: Yeah, gets the egg up on its back, lifts it
Speaker 1: up over the side, and then pushes its neck back
Speaker 1: to throw it over the side of the nest. What
Speaker 1: And it does that over and over and over again
Speaker 1: until it is the only thing in that nest.
Speaker 2: I'm imagining like security footage of some hospital where they
Speaker 2: have the babies in those little trays and like one
Speaker 2: baby is crawling around like pushing all the other babies
Speaker 2: out of the trays. That's the moral equivalent of what's
Speaker 2: happening here, right.
Speaker 1: Oh, yeah, that sounds somehow, that sounds way worse. Again.
Speaker 1: We're back to the humans having different sets of values
Speaker 1: depending on the species. You're talking about, but yes, that
Speaker 1: would be the equivalent.
Speaker 2: So here the cuckoo doesn't just want to be taken
Speaker 2: care of by the mom. It wants like exclusive access.
Speaker 2: Is that because of the food limitation. It's like want
Speaker 2: a bigger share of breakfast?
Speaker 1: Yeah? Yeah, And it is going to grow to be
Speaker 1: much bigger than its host parent, and so it needs
Speaker 1: a lot of food. And if it does happen that
Speaker 1: some of the eggs do hatch before the baby gets
Speaker 1: a chance to push the eggs out, then it will
Speaker 1: just go ahead and push the babies out of the nest.
Speaker 1: It's kind of horrible.
Speaker 2: Is there no limit to what these cuckoos will do?
Speaker 1: I know, I know, darn you cuckoos. And so sometimes
Speaker 1: these babies will grow to be like three times bigger
Speaker 1: than the parents that are frantically trying to feed it. Wow,
Speaker 1: which is crazy, Like you'll see it. It's like, you know,
Speaker 1: the baby cuckoo is like spilling out of the nest
Speaker 1: and the parents are still frantically trying to shove food
Speaker 1: in its mouth as it screams at them like.
Speaker 2: Fe me me, and there's nothing in the parent's brain.
Speaker 2: It's like something is weird here. Or trigger some sort
Speaker 2: of response to it recognizes that it's not its own baby.
Speaker 1: Yeah, all right, So here is where evolutionary biologists gets
Speaker 1: super excited about this system, right, because that should be happening. Yeah,
Speaker 1: and so this has become a really sort of exciting
Speaker 1: system for studying co evolution. And so that is when
Speaker 1: you get evolution happening with both the host and the parasite.
Speaker 1: So what should be happening here is that the host
Speaker 1: should be figuring out some way to detect the cuckoo
Speaker 1: egg so they can throw it out of the nest.
Speaker 1: And then the cuckoo should end up with some way
Speaker 1: to make it harder for the host to detect the
Speaker 1: cuckoo egg, and then you should ends up with this
Speaker 1: arms race where you keep getting the host getting better
Speaker 1: at evicting the cuckoo and the cuckoo getting better at
Speaker 1: tricking the host, and back and forth.
Speaker 2: Yeah, that makes perfect sense. And so is that what
Speaker 2: happens is the cuckoo like developing techniques that it knows
Speaker 2: will take advantage of like weaknesses in the host bird brain.
Speaker 1: Okay, so I sent a picture to you in the outline, Oh,
Speaker 1: and I want you to scroll down.
Speaker 2: Okay, scroll and scroll and scroll in.
Speaker 1: I've shared with Daniel a photo where the top row
Speaker 1: are all eggs that were made by cuckoos, and it's like.
Speaker 2: A bunch of different eggs, is like green and orange
Speaker 2: and ones with squiggles on them and spots, very very
Speaker 2: different kinds of eggs.
Speaker 1: Very different kinds of eggs. And then the bottom row
Speaker 1: are all the host eggs that they're trying to match.
Speaker 2: Wait, those are not from the same species. That's crazy.
Speaker 2: They match exactly. They look like, detail for detail the
Speaker 2: same as the original eggs are.
Speaker 1: Are you just being nice to me or do you
Speaker 1: mean it? Because I think they're pretty good matches.
Speaker 2: They're incredible matches.
Speaker 4: Yeah.
Speaker 2: I mean maybe they're a little bigger or a little
Speaker 2: smaller or whatever. And I don't know what the variation is,
Speaker 2: but the difference between the host and the cuckoo is
Speaker 2: much smaller than the difference between the different species. Yeah,
Speaker 2: so they're pretty good matches, you know.
Speaker 1: Yeah, they're pretty good matches. And there are stories about,
Speaker 1: you know, evolutionary ecologists going out into the field and
Speaker 1: looking at a nest and being like, Okay, I just
Speaker 1: saw a cuckoo lay an egg in here, which one
Speaker 1: is the cuckoo egg and which one is the one
Speaker 1: you know that was laid by the hosts?
Speaker 2: All right, So the cuckoos know that the hosts are
Speaker 2: looking out for this, and they're doing their best to
Speaker 2: camouflage their babies.
Speaker 1: Yeah, and by doing their best, essentially, what we mean
Speaker 1: is that, you know, there's a lot of cuckoos laying
Speaker 1: a lot lot of eggs. Randomly, a cuckoo will lay
Speaker 1: an egg that happens to be a shade or two
Speaker 1: that's a little bit closer, and that egg is less
Speaker 1: likely to be rejected, so that female makes a lot
Speaker 1: more babies that make it to the next generation, and
Speaker 1: their egg also tends to match a little bit more.
Speaker 3: Right.
Speaker 2: There's no intentionality or design here, it's just natural selection, right.
Speaker 1: Yes, exactly, And so over time, these cuckoos have ended
Speaker 1: up with eggs that do an amazing job of matching
Speaker 1: these increasingly complex eggs that their hosts are making, and
Speaker 1: so they have essentially made it very costly for the
Speaker 1: moms to eject an egg from the nest. And so
Speaker 1: there have been cases where, you know, scientists have been
Speaker 1: watching a nest and a mom has looked at the
Speaker 1: eggs in the nest, and you know, presumably you know,
Speaker 1: we don't know what the moms are thinking, but they've
Speaker 1: ejected an egg, and we've seen that a cuckoo has
Speaker 1: laid an egg. We know which one was the cuckoo egg.
Speaker 1: And she ejected her own egg and not the cuckoo egg.
Speaker 2: Oh that's even more tragic.
Speaker 1: I know, right, So mistakes get made, Mistakes get made.
Speaker 2: Well, so when the dad comes back and the mom
Speaker 2: is like, by the way, I killed one of our babies.
Speaker 2: Mistakes were made. Do you think he's could accept that
Speaker 2: passive voice?
Speaker 1: Well, you know, the secret at Daniel is they don't
Speaker 1: actually talk to each other like that.
Speaker 2: Oh I see, So you're saying that's the secret to
Speaker 2: marital harmony is just stop talking to each other.
Speaker 1: That's right. Low communication ability, that's the key.
Speaker 2: This is not a marriage advice podcast, by.
Speaker 1: The way, that's right, that's right. Yes, please go somewhere
Speaker 1: else for that where we're going to get you in trouble.
Speaker 1: But parents will start using other information in the environment.
Speaker 1: So you know, scientists will go out there and they
Speaker 1: will like put a mimic cuckoo egg in a bird's
Speaker 1: nest and they'll note that, like the birds won't respond
Speaker 1: to it. They'll like look at their nest and they
Speaker 1: won't eject any eggs. But if you put a stuffed
Speaker 1: cuckoo near their nest, they'll be like, oh, those jerks
Speaker 1: are around, they might be, and then they'll start ejecting eggs.
Speaker 1: And so, you know, they're trying to collect at your information,
Speaker 1: like how high is the risk are there cuckoos in
Speaker 1: the area. If so, maybe I'm going to have to
Speaker 1: take a closer look at my eggs boy, And so
Speaker 1: you know, it's not like they're just sort of passively
Speaker 1: accepting things. They're constantly looking collecting information about risk. Sometimes
Speaker 1: they're making mistakes. It's getting increasingly complicated.
Speaker 2: Wow, but what about the scenario we talked about originally
Speaker 2: where now you have this cuckoo and it's growing and
Speaker 2: it's like much bigger than your own babies. Isn't that
Speaker 2: a clear signal? How can the cuckoos continue to be
Speaker 2: fed by the mom when they're so outrageously big.
Speaker 1: Yeah, So there are examples in some systems or with
Speaker 1: some of the two hundred plus hosts of common cuckoos
Speaker 1: where the hatchling will get rejected at that stage where
Speaker 1: like a mom or dad or whatever will be like, ah,
Speaker 1: darn it, you know, we thought we had this figured out,
Speaker 1: but you are clearly not our own, and the just
Speaker 1: abandon the nest. But there's also selection for cuckoo offspring
Speaker 1: to like have the features that the parents are looking for. So,
Speaker 1: for example, some offspring have very particular markings inside of
Speaker 1: their mouths that the parents queue in on when they're
Speaker 1: bringing food, and they can be you know, like orange splotches,
Speaker 1: and so sometimes cuckoos will have like these very species
Speaker 1: specific markings on the inside of their mouths. And I
Speaker 1: forget if this is common cuckoos in particular or other
Speaker 1: species of cuckoos, because there's a lot of cuckoo species
Speaker 1: with a lot of different strategies. But there is also
Speaker 1: an arms race at various other stages. So yes, there's
Speaker 1: the egg recognition stage, but then there's also the hatchling
Speaker 1: recognition stage. Yeah, there's a lot going on. And so
Speaker 1: not only does it vary depending on like how well
Speaker 1: the eggs match or how well the hatchling matches, but
Speaker 1: there's also pressure depending on how bad the situation is
Speaker 1: for the parents. So like if you've got a common
Speaker 1: cuckoo hatchling that's going to throw all your eggs out.
Speaker 1: There's a lot of pressure to get that right. But
Speaker 1: sometimes there are some other species of birds that will
Speaker 1: like lay one egg in your nest, they won't throw
Speaker 1: your eggs out, and their offspring will take about as
Speaker 1: much energy as the rest, and so the parents still
Speaker 1: get all of their babies that will hatch out. Maybe
Speaker 1: they all get a little bit less food than they
Speaker 1: would have otherwise, but in that case there's a lot
Speaker 1: less like selective pressure to figure out which egg doesn't
Speaker 1: belong and kick out the intruder, because you know your
Speaker 1: babies are still going to survive. So we see a
Speaker 1: lot of variability depending on what the parasite species is
Speaker 1: and what it does to the host, on whether or
Speaker 1: not hosts are just like they tolerate what's going to
Speaker 1: happen to them, or if they're like actively trying to
Speaker 1: fight back against you know, the presence of parasites in
Speaker 1: the area.
Speaker 2: And for birds, is it both moms and dads that
Speaker 2: are feeding the babies. Do they both need to evolve
Speaker 2: this or the dad's involved? How does that work?
Speaker 1: Depends on the species. Sometimes the dads are involved. Sometimes
Speaker 1: the dads aren't involved. I think in general the pressure
Speaker 1: is more on the moms. And so there's a big
Speaker 1: question in the field how do the parents figure out
Speaker 1: what their eggs should look like? So initially there was
Speaker 1: this idea that maybe moms figure out what their eggs
Speaker 1: should look like by like the very first egg they
Speaker 1: see in their nest. They will like imprint on that
Speaker 1: and use that as a template for the rest of
Speaker 1: their lives. But if they make the nest and the
Speaker 1: very first thing that shows up in their nest is
Speaker 1: a cuckoo egg, is that going to mess things up
Speaker 1: for the rest of their lives. And it turns out
Speaker 1: that's probably not how it works. It looks like maybe
Speaker 1: at the beginning of every season for like this, for
Speaker 1: some of the species that we've looked at the very
Speaker 1: first egg that they lay, they turn around and they're like,
Speaker 1: that's what I do.
Speaker 2: That just came out of me. So that's that's a me.
Speaker 1: That's a me. That's a me. Uh And it's not
Speaker 1: like it's monogrammed or something. But like, and the problem is,
Speaker 1: you know, like you mentioned, there's variability, and so you know,
Speaker 1: you hope that's a pretty good representation of what you're
Speaker 1: going to be doing that season, But that seems to
Speaker 1: be kind of how.
Speaker 2: They do it, and the pressures must be complicated also
Speaker 2: because like, if the cuckoo is too successful, then it's
Speaker 2: essentially going to kill off the host, right then there'll
Speaker 2: be no host babies to grow up to be tricked
Speaker 2: parents to raise the next generation of cuckoos. So isn't
Speaker 2: there pressure for the cuckoos to not push all the
Speaker 2: other babies out of the nest.
Speaker 1: So in situations like that, you can get cycling. So
Speaker 1: if you do end up with a whole lot of
Speaker 1: cuckoos one year, then the next year there's just not
Speaker 1: going to be a lot of parents. Yes, there's not
Speaker 1: going to be a lot of host nests that you
Speaker 1: can lay eggs, and so a lot of cuckoos are
Speaker 1: just not going to be successful. So there won't be
Speaker 1: a lot of cuckoos the year after that or you know,
Speaker 1: five years after that or something, depending on how long
Speaker 1: the cycling takes.
Speaker 2: So it's self regulating that, Yeah, it's.
Speaker 1: Self regulating that way.
Speaker 2: Interesting.
Speaker 1: I'm sure there are some cases where cuckoos, for example,
Speaker 1: have driven local species locally to you know, extinction. Or
Speaker 1: extirpation now, and that at the cuckoos again, that's right,
Speaker 1: But usually my sense is that usually you would get
Speaker 1: something like cycling.
Speaker 2: And I don't even know what a cuckoo looks like.
Speaker 2: Is it cute? Because weirdly that affects my emotional reaction here.
Speaker 1: It's pretty cute. Yeah, I mean, yeah, it's pretty cute.
Speaker 1: It's got like bars on its chest, something that it's
Speaker 1: kind of meant to mimic some raptors, so that warblers,
Speaker 1: we'll leave it alone a little bit rather than mobbing
Speaker 1: it because they're scared of it, at least initially, and
Speaker 1: then they realize, oh, you're a cuckoo. You're not gonna
Speaker 1: eat me. I hate you, and then they'll try to
Speaker 1: chase it away.
Speaker 2: All right, let's take a break, and when we come back,
Speaker 2: we'll hear about why sometimes birds might even tolerate these
Speaker 2: invaders in their nests even when they do discover them. Okay,
Speaker 2: we're back, and we're talking about interspecific breed parasitism, when
Speaker 2: birds or fish are tricked into raising birds of another species.
Speaker 2: And we've heard all about the clever tricks cuckoos use
Speaker 2: and other birds used to avoid being spotted. But you
Speaker 2: were also telling me Kelly about the mafia hypothesis that
Speaker 2: there's an idea for why these birds might actually tolerate
Speaker 2: these invaders in their nest. What is that all about?
Speaker 1: Yeah, so one person noted, like, you know, wow, there's
Speaker 1: a lot of instances where it really seems like a
Speaker 1: host bird should have been able to notice that there
Speaker 1: was a like parasitic egg in its nest, it should
Speaker 1: have thrown it out, but it didn't. What other reason
Speaker 1: could we come up with for why a host bird
Speaker 1: might tolerate it? And one idea that I believe it
Speaker 1: was a matsahave came up with, was that maybe they're
Speaker 1: being coerced. Maybe it's sort of like a mafia sort
Speaker 1: of thing where if they were to kick it out,
Speaker 1: if they were to destroy the parasite eggs, then the
Speaker 1: parents would come back and would like take retribution in
Speaker 1: some way. Oh and there've actually been a couple tests
Speaker 1: of this. So, for example, brown headed cowbirds, which you
Speaker 1: can find in the United States, they parasitize prothenatterie warblers
Speaker 1: I'm just gonna call them warblers because nobody wants to
Speaker 1: hear me stumble over that again. And there was this
Speaker 1: experiment where they had these greased poles with nest boxes
Speaker 1: up top. And the reason it's important to know they
Speaker 1: had greased poles is because snakes and small mammals couldn't
Speaker 1: get up the greased poles to eat the eggs. And
Speaker 1: so now you can sort of control predation and know
Speaker 1: what got the eggs, because the only thing that could
Speaker 1: steal the eggs from the nest would be things that
Speaker 1: could fly up there. Okay, all right, So they had
Speaker 1: three different treatments. They knew that cowbirds had laid their
Speaker 1: eggs in each of the warbler nests. In the first treatment,
Speaker 1: they removed the cowbird egg, so the parasite egg was
Speaker 1: taken out. In the second treatment, they left the cowbird
Speaker 1: egg in there. Their treatment, they took out the cowbird egg,
Speaker 1: and then they narrowed the hole a little bit so
Speaker 1: the warblers could still get in, but the cowbirds, which
Speaker 1: are bigger, couldn't get in anymore.
Speaker 2: All right.
Speaker 1: And then they looked to see what happened to the
Speaker 1: host eggs which had been left in all of the
Speaker 1: nest boxes. And what they found was that the nests
Speaker 1: where they had removed the cowbird.
Speaker 2: Eggs the invading eggs.
Speaker 1: The invading eggs, the host eggs had been destroyed when
Speaker 1: a cowbird egg was removed, but that didn't happen when
Speaker 1: the cowbird egg was removed, But the cowbirds couldn't get
Speaker 1: into the nest because the hole had been narrowed, and
Speaker 1: it didn't happen when the cowbird egg was left in
Speaker 1: the nest. And so it really looked like the cowbirds
Speaker 1: were coming back and taking retribution on the warblers. You
Speaker 1: presume they thought the warblers had removed the eggs and
Speaker 1: they were taking retribution. And why would they do that. Well,
Speaker 1: when the warbler nest fails, they'll remove everything from that
Speaker 1: nest and start over again. And when they start over again,
Speaker 1: they're probably gonna accept the cowbird egg the next time,
Speaker 1: and if they don't, they'll get attacked again. And so
Speaker 1: this is the cowbird's way of saying, Hey, you've got
Speaker 1: another chance, make the right decision the next time.
Speaker 2: Awfully nice nest you've got here, be a shame if
Speaker 2: something more to happen to it.
Speaker 1: That's right, exactly, I see. There have been some other
Speaker 1: experiments that people have done that have gotten similar results.
Speaker 1: There's also some evidence of what we call farming. And
Speaker 1: the idea here is that if a parasitic bird arrives
Speaker 1: too late in a season and the eggs are about
Speaker 1: to hatch, like the host eggs are about to hatch,
Speaker 1: that would be bad for them because their babies need
Speaker 1: that head start, and so they'll go through and they'll
Speaker 1: destroy a bunch of nests, so the parents have to
Speaker 1: start over again. And when the parents start over again,
Speaker 1: they'll go and lay their eggs in those nests. And
Speaker 1: so they call that farming because they're essentially like creating
Speaker 1: resources for themselves that they'll be able to use because
Speaker 1: now they're at the right stage at the right time.
Speaker 2: And this implies somehow that the host bird, the one
Speaker 2: that destroyed the invading eggs the first time and not
Speaker 2: the second time, has like learned this, you know, because
Speaker 2: like in the mafia example, you're very clear, you're like, look,
Speaker 2: I'm going to bust up your shop if you don't
Speaker 2: pay the protection money or whatever. But there's no conversation
Speaker 2: between these birds. So the host has to effectively learn
Speaker 2: this behavior. This is like negative reinforcement of this behavior.
Speaker 2: That's something that these birds are capable of.
Speaker 1: It seems that they are. I would bet that not
Speaker 1: all species catch on, and I would bet that some
Speaker 1: couples need to learn the lesson more than once. And
Speaker 1: I should note that we don't always see this happening.
Speaker 1: Not all bird species that do interspecific breed parasitism use
Speaker 1: this mafia strategy. Yeah, and we don't always even see
Speaker 1: the species that do this using the mafia strategy all
Speaker 1: the time. And so I think a lot of these
Speaker 1: parasitic birds will lay their eggs in a bunch of
Speaker 1: different nests, and so some years maybe they're like, oh,
Speaker 1: you know what, I've laid one hundred eggs and one
Speaker 1: hundred different nests. I don't need to watch them all.
Speaker 1: This was a great year for me, but it But
Speaker 1: in some years where maybe the stakes are higher, they
Speaker 1: might be like watching a little bit more closely, you know.
Speaker 1: So yeah, I'm guessing it doesn't always go according to plan.
Speaker 1: But there are some years where they give it a
Speaker 1: shot and hope that the message sticks and other years
Speaker 1: where it doesn't work as well.
Speaker 2: And so just so that I understand, this is not
Speaker 2: a selection thing where you're just choosing the nests where
Speaker 2: you don't get destroyed by cutting off the reproduction path
Speaker 2: of those that have destroyed it. You're really teaching these
Speaker 2: birds that if you destroy the invading eggs, we will
Speaker 2: also destroy your eggs. So this is like within the
Speaker 2: life cycle of an individual bird, not like within generations
Speaker 2: of that host.
Speaker 1: That's right, Yeah, this is within the So for some
Speaker 1: bird species, they're able to have multiple nests in a year,
Speaker 1: and if their nest gets destroyed early in the year,
Speaker 1: then they're able to start a new nest sooner, and
Speaker 1: maybe they can go through more cycles, or maybe they
Speaker 1: can just do one cycle if their nest goes through
Speaker 1: the normal timing, but maybe they can get two in
Speaker 1: there if the first one is destroyed and they restart.
Speaker 2: And to really convince yourself with this, wouldn't you want
Speaker 2: to do something like analyze the behavior of the birds
Speaker 2: who had their nest destroyed relative to those who didn't,
Speaker 2: to see if they're like less likely to kick out
Speaker 2: the invading eggs.
Speaker 1: Yes, right, So you are wanting to know how well
Speaker 1: this strategy works. Yeah, yeah, it would be great to
Speaker 1: know how well the strategy works, as opposed to just
Speaker 1: saying that like brown headed cowbirds are real jerks. Yes, yeah,
Speaker 1: it would be great to have those data. I'm under
Speaker 1: the impression that we don't have those data, and that
Speaker 1: the people who have done the follow up work have
Speaker 1: been like, wow, well we didn't actually see it happen
Speaker 1: at all this time, and so maybe it's sort of
Speaker 1: a rare thing.
Speaker 2: Interesting. Yes, so we're at the cutting edge of understanding
Speaker 2: mafia behavior in birds.
Speaker 1: Yes, and maybe we will end up discovering actually, this
Speaker 1: is the thing that happens pretty rarely. And maybe it
Speaker 1: happens pretty rarely because birds aren't brilliant. They don't pick
Speaker 1: it up real fast.
Speaker 2: Are you whispering in case birds are listening and you
Speaker 2: don't hurt their feelings?
Speaker 1: Yeah, well I don't want them to attack me, you know,
Speaker 1: like maybe they'll go after my kids.
Speaker 2: Oh my gosh.
Speaker 1: Yeah, yah, it'd be bad.
Speaker 2: And so how rare is this? Like what fraction of
Speaker 2: bird species or fish species do this?
Speaker 1: So it has been most thoroughly studied in birds, like
Speaker 1: it's been a little bit studied in fish. Some insects
Speaker 1: do it. It's like scattered around the animal kingdom, but
Speaker 1: in birds it's gotten the most attention, and about one
Speaker 1: percent of bird species seem to do it. Wow, it
Speaker 1: looks like it's popped up about seven times.
Speaker 2: Seven times? What do you mean?
Speaker 1: So, if you look at like the tree of life
Speaker 1: and you've sort of started at the branch where birds
Speaker 1: pop up or along seven of the branches, this strategy
Speaker 1: of laying your egg in the nest of a different
Speaker 1: species has developed, and then there's been like speciation where
Speaker 1: you get more species that do it and they keep
Speaker 1: this strategy with them.
Speaker 2: Oh I see. So you're saying it's not just like
Speaker 2: one branch of birds do this and all the branches
Speaker 2: of birds that do it today come from that same branch.
Speaker 2: You're saying it evolved independently seven different places on the tree.
Speaker 2: That's incredible.
Speaker 1: Yeah. Right, And so then one of the things that
Speaker 1: people have been trying to figure out is what were
Speaker 1: the birds doing before they started this strategy? And so yeah,
Speaker 1: one of the ideas is that maybe they were doing
Speaker 1: what we call conspecific brood parasitism, which is to say,
Speaker 1: there were laying their eggs in the nest of other
Speaker 1: members of the same species.
Speaker 2: Oh.
Speaker 1: So, for example, wood ducks will nest in tree cavities,
Speaker 1: so like if there's a hole in a tree, wood
Speaker 1: ducks will lay their eggs in there. But if there's
Speaker 1: not enough wood cavities that season and there's too many ducks,
Speaker 1: sometimes two females will lay their eggs in the same tree,
Speaker 1: and one female will evict the other. But maybe she
Speaker 1: can't tell that. I don't know if it's that she
Speaker 1: can't tell the difference between all of the eggs or what,
Speaker 1: but she will sit on and raise all of the
Speaker 1: eggs and the chicks that were in that tree cavity. Okay,
Speaker 1: And so the idea is that maybe over time, you know,
Speaker 1: females started laying eggs and nest cavities, and instead of
Speaker 1: fighting to be the winner, they were just like, oh no,
Speaker 1: I lost, you can you can raise all of these.
Speaker 1: And then maybe they just started like laying eggs in
Speaker 1: other places and letting other maybe even other duck species
Speaker 1: raise their young. So you could imagine it's starting that way.
Speaker 1: Another example are American coots. They're duck like things, but
Speaker 1: they're extra kind of unattractive. Sorry coots, but females that
Speaker 1: can't get nest sites tend to lay their eggs in
Speaker 1: the nest of other females.
Speaker 2: What do you mean unattractive? They look cute? Oh yeah, Okay, now,
Speaker 2: I'm zooming it a little bit. Yeah, it's a little
Speaker 2: bit of a vult.
Speaker 1: Yeah, yeah, I still like them. I still like them.
Speaker 1: But anyway, so females who couldn't get their own nest
Speaker 1: will lay their eggs in the nests of other females,
Speaker 1: or females who have gotten their own nest, but they
Speaker 1: like have made a bunch of eggs, and they're like,
Speaker 1: I can't really raise any more kids, but it can
Speaker 1: make more eggs, and they'll go ahead and lay their
Speaker 1: excess eggs in the nests of other females. Like you,
Speaker 1: you know, you could imagine that maybe you could go
Speaker 1: from that strategy where you fill up your nest and
Speaker 1: then maybe you see if you can get some of
Speaker 1: your eggs in the nest of another species, and you know,
Speaker 1: you just try some stuff out and maybe that's the
Speaker 1: path through which interspecific brood parasitism arose.
Speaker 2: But for that to happen, for it to be passed down,
Speaker 2: for that behavior to exist also in your children, it
Speaker 2: has to be genetic, right, So there's something in these
Speaker 2: genes that have been tweaked that chaines the behavior of
Speaker 2: the birds to accept this kind of scenario or to
Speaker 2: attempt this kind.
Speaker 1: Of approach, Yeah, exactly, but you can imagine it being
Speaker 1: less of a jump. If you are genetically encoded to
Speaker 1: lay your eggs in the nest of another individual of
Speaker 1: the same species, and then you lay your eggs in
Speaker 1: the nest of an individual of a different species, then
Speaker 1: to go from I'm laying my eggs in my own
Speaker 1: nest and then jumping to nominal laying my eggs in
Speaker 1: a totally different species nest. But actually, when you like
Speaker 1: look at the genomes of all of these different species
Speaker 1: and you look at where they differ, and you try
Speaker 1: to like make a tree of life based on you know,
Speaker 1: what those codes say, it looks like most of the time,
Speaker 1: maybe every time, but once that jump went through like
Speaker 1: normal parental care, so like they were sitting on their
Speaker 1: own nest, their own babies, and then the next step
Speaker 1: was they were laying eggs in the nest of another species.
Speaker 1: And wow, we're not quite sure how that jump happened,
Speaker 1: and so there's you know, a lot of research going
Speaker 1: into trying to understand that. But for a long time
Speaker 1: we thought there was probably this intermediate step, but we
Speaker 1: don't have any evidence to support that hypothesis. So now
Speaker 1: we're changing the way we think about it and doing
Speaker 1: some more research.
Speaker 2: And there doesn't have to be an intermediate step.
Speaker 3: Right.
Speaker 2: If you can go in one generation from just being
Speaker 2: parental to laying your eggs in another and it works,
Speaker 2: then it's going to be reinforced by selection. Right.
Speaker 1: So it's a little hard for me to imagine that
Speaker 1: in one generation there was a jump, but as long
Speaker 1: as that behavior was somehow encoded in a way that
Speaker 1: could be passed either through learning, like maybe you saw
Speaker 1: your mom do it and so you do it, or
Speaker 1: maybe like imprinting was genetically encoded.
Speaker 2: But how can you see your mom do it if
Speaker 2: you're raised by another mom?
Speaker 1: Right, yeah, right, So maybe it wasn't that you saw
Speaker 1: your mom do it. Maybe it was just when you
Speaker 1: were hatched in the nest of another species, you saw
Speaker 1: that species and you were.
Speaker 2: Like, oh, this is where the eggs go.
Speaker 1: This is where eggs go. Right, And so that was
Speaker 1: like the thing that took one generation for the you know,
Speaker 1: the change to happen.
Speaker 2: Hold on a second, I just had a complete realignment
Speaker 2: of my emotional connection because now I'm like, maybe cuckoos
Speaker 2: think that they are this other species and they're just
Speaker 2: going there because that's how it works, you know, that's
Speaker 2: how they grew up. They were raised by this other
Speaker 2: kind of mom, and so that's what they want for
Speaker 2: their babies.
Speaker 1: But they're still hill and their brothers and sisters. Though
Speaker 1: if they think that that's still that's still not okay. Yeah, right,
Speaker 1: we got like, I don't know, twenty five percent of
Speaker 1: the way there or something. Anyway, I think this is
Speaker 1: fascinating and it's really interesting as a way to study
Speaker 1: like evolution between parasites and hosts and you know, sort
Speaker 1: of like how this arm race works and how one
Speaker 1: sort of tries to counter the effects of the other,
Speaker 1: and it's just kind of crazy the solutions that evolution
Speaker 1: has come up with. Like I will post on our
Speaker 1: blue Sky account and our Discord channel and our Instagram account.
Speaker 1: I'll link to like a picture of the cuckoo eggs
Speaker 1: and the host eggs that I showed to Daniel because
Speaker 1: it is incredible to me how close the match is.
Speaker 1: And we didn't even talk about the genetics, Like it
Speaker 1: looks like genetic information you only get from females, so
Speaker 1: you know, I'll be really quick about this, but like
Speaker 1: in humans, females are have the XX chromosomes and males
Speaker 1: have x Y. But in ducks the males are zz
Speaker 1: and the females are ZW, so they have different chromosomes.
Speaker 1: But the females are the ones that have two different chromosomes.
Speaker 1: So if the females are the ones that are continuously
Speaker 1: like picking a certain kind of host species to end
Speaker 1: up in their nest over time, the genetic information about
Speaker 1: what the eggs look like could get passed on the
Speaker 1: W chromosome. And that's how you can have one species
Speaker 1: that produces eggs that look super different and match a
Speaker 1: bunch of different species host species, egg coloration patterns, and
Speaker 1: you get your genetic information in your mitochondria from your mom.
Speaker 1: So that's another way egg color and pattern information could
Speaker 1: get passed through mom. And anyway, it's absolutely fascinating how
Speaker 1: they manage to color match all of these so closely.
Speaker 1: And I just think it's super neat. Evolution's weird and
Speaker 1: doesn't care about your feelings.
Speaker 2: Yeah, well, let's go out on a limb. What do
Speaker 2: you think is the future of interspecific brood parasitism If
Speaker 2: birds went from like I'm gonna have another mom, take
Speaker 2: care of my babies in the same species too, then
Speaker 2: eventually to another species. In a million years, Are we
Speaker 2: going to have like elephants taking care of bird babies?
Speaker 1: Hmmm, uh, you know, I don't necessarily, it doesn't really
Speaker 1: work necessarily like work that way, Like it doesn't have
Speaker 1: to like become more extreme or more species don't necessarily
Speaker 1: have to do it.
Speaker 2: Over time, We're I'm gonna have antelopes raising cheetababies or something.
Speaker 1: Yeah, No, I don't think so. I don't think that'll happen,
Speaker 1: you know. I think it's it's possible that some interspecific
Speaker 1: brood parasites will drive the hosts that they were parasitizing,
Speaker 1: like to extinction, or maybe they'll switch to a different
Speaker 1: host species if their other host species is like the
Speaker 1: population numbers are getting low. But I'm not expecting that,
Speaker 1: like next year I will be raising cuckoos and I
Speaker 1: won't realize they're not human babies.
Speaker 2: All right, And if any of our listeners are warblers,
Speaker 2: maybe you know, go out there and check on those
Speaker 2: babies and make sure you're not racing cuckoos. And let's
Speaker 2: hate you want to, in which case, more power to you,
Speaker 2: because nature tells us that there's all kinds of families
Speaker 2: out there.
Speaker 1: That's right, all right, Until next time, everyone. Daniel and
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