The Science of Birds - Cooperative Breeding in Birds

Episode Date: February 1, 2025

In this episode—which is number 110—Ivan explores the fascinating world of cooperative breeding in birds, a system in which multiple adults help raise young in a group setting. He begins with an intriguing story from the Kalahari Desert, where Southern Pied-Babblers resort to “chicknapping” during droughts to bolster their flock size. Ivan then broadens the discussion, examining the global distribution of cooperative breeding among bird species and the evolutionary mechanisms that drive this behavior. He introduces key scientific concepts, such as inclusive fitness and kin selection, to explain why some birds delay their own reproduction to assist relatives. Additionally, he covers various hypotheses, from ecological constraints to life history strategies, that influence the evolution of this breeding system. Featured examples of cooperative breeders in the episode include the Florida Scrub-Jay, Acorn Woodpecker, and Superb Fairywren, each of which showcases the complexity and diversity of this strategy in different environments.  ~~ Leave me a review using Podchaser ~~Link to this episode on the Science of Birds website Support the show

The Kalahari Desert in Botswana is always a harsh environment to live in. Water and food are scarce in the sandy savannah with its sparse vegetation of grasses, shrubs, and acacia trees. But in particularly dry years, drought can force birds and other animals in the Kalahari to the very edge of desperation. Things can get pretty dramatic. Like the following scenario, for example. Two neighboring flocks of southern pied babblers are facing off in a noisy territorial dispute. They're hopping and flapping around in some bushes. One group is large with about ten individuals.

The other group is only half that size. The southern pied babbler is roughly the size and shape of an American robin. This species has a mostly white body, but its flight feathers in the wings and tail are black. The eyes are yellow and the pointy black bill curves down slightly. Both males and females look the same. Anyway, while the two groups are busy squabbling over the border between their territories, hurling insults at each other from their respective shrubs, there's a covert operation underway.

A few members of the smaller flock have formed a black ops team. in order to infiltrate the territory of the larger flock. They use the distraction of the dispute as cover while they slip behind enemy lines. Their mission? To kidnap one or more of the chicks from the larger group. The scrappy olive-brown chicks are hidden in the shadows between the leaves and branches of the shrubs. The kidnappers stealthily locate and then lure the chicks away.

The young, naive birds are enticed by tasty treats. and with a soft purring call that adult Pied-Babblers use when feeding their chicks. You know, this is sort of like with humans, when a shady guy in a windowless van pulls up to the sidewalk and says, Hey, kid, do you like candy? Streetwise kids see through this ruse and run home to tell their parents about the creeper in the van. But these southern Piedbabbler chicks, well, they're not always that smart. A chick just can't resist the offer of a tasty morsel and the siren song of an adult making that purring call.

So inch by inch, the kidnappers lure the chicks away back across the border into their own territory. Having accomplished their mission, the pied babblers in the smaller group drop the border dispute. It was just a ploy anyway, and they withdraw. They high-five each other and celebrate because they've just successfully increased the size of their fly. by one or two members. The adults in that flock will raise these kidnapped recruits as they would their own offspring. Kidnapping, or I guess we could call it, chicknapping, is a desperate behavior that southern Piedbabblers resort to, predictably, during severe drought conditions. That's because this species is a highly social, cooperative breeder. Multiple individuals in the

group help to feed the chicks, defend the tent. territory, and keep an eye out for predators. Larger cooperative groups are better at all of these tasks, so they have better chances of making it through a lean year in the Kalahari Desert. If they can't scrounge up enough resources to hatch chicks on their own, they might just steal some chicks from their neighbors. Hello and welcome. This is a little. This is a little. 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. I'm happy to say that I'm back home in Portland, Oregon. If you've been keeping up with the latest episodes of the podcast, you'll know that I was recently working in Asia. I traveled through five countries, birding all along the way. and having a great time. I made several episodes to share those experiences with you. It was a glorious, epic trip overall, and I feel an immense amount of gratitude for the experience. So, having done the experiment of making those from the field podcast episodes, I feel confident

that I can do that again when I go on longer trips. For example, I'm heading down to Patagonia in a few weeks. I'm thinking it would be really cool to make a from-the-field episode about the birds and other natural wonders of Patagonia. But what is this episode about? This is episode 110, and you might guess the topic is kidnapping. But no, it's actually cooperative breeding. The typical breeding scenario with birds is that one male and one female pair up, and they raise a brood on their own. It's just them versus the world. But in cooperative breeding, chicks are raised by more than just their parents. They're raised by multiple adults in a group setting. The group might have three adults, 10 adults, whatever. Those extra adults help to feed, protect, and clean up after chicks that

aren't their own. They act as helpers to the actual breeding pair. So a key feature here is that these helpers delay their own dispersal and breeding opportunities for a year or more. And during the time they stick around, they help raise the chicks of the breeding pair. That's nice of them, isn't it? These birds would rather help others than go raise their own families. They're being altruistic. They deserve a pat on the back. But there's a big question that should be screaming in our heads right now. Why? Why do these birds really do this? Are the helpers at a nest truly being selfless? Are they saint-like altruists?

Or is there something else going on? Let's see if we can find some answers in today's episode. First, we'll look more closely at the Southern Piedbabbler, as a great example of a cooperatively breeding species. Next, we'll look at the extent of cooperative breeding in birds, both geographically and among taxonomic groups. Then we'll consider some hypotheses about the evolution of cooperative breeding in birds. And along the way, we'll talk about some other interesting examples of bird species that breed cooperatively.

So let's look at the southern Piedbabbler in more depth, as a case study, because A, it's an excellent example. of a species with cooperative breeding, and B, because scientists have done a lot of research into its breeding behavior and social structure. The southern Piedbabbler's scientific name is Terdoides bicolor. The genus name Terdoides means resembling a thrush. Remember earlier when I said this Piedbabbler species is roughly the size and shape of an American Robin? Well, the American Robin is actually a thrush, and its genus is turdus, T-U-R-D-U-S. So Tirdoides means resembling a thrush. When you see the suffix oides, O-I-D-E-S, that means like or resembling.

The species name for the southern pied babbler is bicolor, and that, of course, means two colors. This bird does indeed have plumage with a pied color pattern, black and white. Terdoides bi-color is a member of the Laughing Thrush family, Leothricody. I talked about laughing thrushes a lot in my last three episodes, since I saw quite a few species across Asia. This has become one of my all-time favorite bird families, Leothricotie. Anyway, the southern Piedbabbler lives in the arid and semi-arid parts of Namibia, Botswana, Zimbabwe, and South Africa.

They live in groups of three to 15 adults. adults, and they defend territories year-round. The members of a group stick close together as they go about their business every day. They forage together, preen each other, play fight by wrestling and chasing each other, and they roost together. They also make a lot of noise. Their calls alert other birds in the group to the threat of predators, or to the presence of rival groups, hungry chicks, or birds in distress. interactions between groups, like the territorial dispute I talked about in the intro, are common. Scientists have reported that these interactions occur about once every three to four hours, on most days.

The two rival gangs line up and face off. They make some ritualized threat displays at each other. They call and chatter, fluff up their feathers, and, pump their wings up and down. Thankfully, these disputes rarely lead to actual physical violence. Each group of southern pied babblers has a single breeding pair that's in charge. The rest of the adults in the group, the subordinates, are helpers. They're usually the offspring of the dominant pair. The subordinates do a lot of work. They help incubate the eggs, brood the nestlings, provide food for the chicks, protect the chicks and even teach behaviors to the chicks. And it seems there's a pay-to-stay rule in the

group, because when a subordinate shirks its duties, when it doesn't pull its own weight, it might get thrown out on the streets, so to speak. Because each group has just one pair of monogamous breeding adults, the southern Piedbabbler is an example of a bird with singular cooperative breeding. The alternative, seen in some other species, is plural cooperative breeding. That's where multiple breeding pairs in a group cooperate in raising the offspring, often with the help of some non-breeding adult birds. The Piedbablers in a group are usually all closely related, except that is for the dominant breeding pair. At least one of them is likely to have been born in another group. The adult helpers are usually the offspring or the siblings of the breeding pair.

Pied babblers avoid inbreeding through dispersal and by being able to recognize their own relatives. Kin recognition like this seems to be based on the ability of a pied babbler to recognize the calls of the birds it grew up around. Life is challenging for these birds in the harsh environment of the Kalahari Desert. The survival of a group and its ability to gain and hold territory against rival groups is mostly a function of group size. The bigger the group, the more successful it is. Southern Pied Bablers seem to have evolved their cooperative breeding system and complex social structure in order to maintain large group sizes. A lot of what we know about this species comes from the research of Dr. Mandy Ridley, a professor at the University of Western Australia. In 2003, Dr. Ridley and her colleagues began a long-term

study of southern Piedbablers. She was able to habituate dozens of Piedbabler groups, get them used to people, so that the birds would tolerate the presence of her and the other scientists. Dr. Ridley could observe the birds at close range, and she followed them around all day, day after day. The researchers could recognize each individual bird by the unique bands or rings on its legs, and they would routinely weigh each bird on a scale to assess. its health. Dr. Ridley's painstaking research of following pied babblers around for years has revealed just how complex the social lives of these birds are. In one article, she describes a group of pied babblers she named The Outsiders and the many dramas that unfold within this

group over a couple of seasons in the Kalahari. The individuals in the group have names like tomboy, patch, Little Mixie, and Muppet. And seriously, there's a lot of so much social drama among these birds, someone could make a reality TV show about them. I would totally watch that. The last thing I want to point out about Southern Pied Bablers has to do with their sneaky kidnapping behavior. Remember that the adult birds on a black ops team use not only food to entice the chicks away from another group, but also a specific purring call. Well, that combo of a call and food is even more.

interesting because southern pied babblers teach their youngsters to associate food with that call. And this is really cool because it's a rare example of teaching behavior in birds. It all begins when an adult pied babbler shows up at the nest with food, and it makes that call and then feeds the nestlings. Just like the proverbial Pavlov's dog, repeating this process over and over eventually teaches the young birds to get excited every time they hear that purring sound. The adults end up using the call to encourage the youngsters to leave the nest, to fledge. The chicks enthusiastically follow any adult making that sound.

After fledging, this behavior continues to be useful. The adults can sort of heard the fledglings around, luring them from one foraging area to another or to a safe roosting site. So this pur-call that the chicks learn to find so irresistant, was probably a necessary precondition for the evolution of kidnapping behavior in adults. And that's pretty cool, right? Now, let's get back to focusing on cooperative breeding itself. I just wanted to give you a little window into the lives of these pied babblers,

but it's time for us to consider the distribution of cooperative breeding among birds, both taxonomically and geographically. Do you remember how many bird species there are in the world? Well, if you listened to me back in the day, I told you to remember the number 10,000. And then that was very rough approximation because ornithologists keep discovering new species, so really the number is about 11,000 and some change. Of those 11,000 species, only about 1,000. 1,000 show some cooperative breeding tendencies. So we're talking roughly 9% of all birds are

cooperative breeders. But those 1,000 species are not evenly distributed among all bird families. In total, there are about 250 bird families in the world. How many of those include some cooperative breeding species? Well, different sources give different answers. For example, one source I found says there are 28 families. Another says 62 and another 84. Who knows which number is closer to the truth? Some of this disagreement probably has to do with researchers using slightly different definitions of what cooperative breeding actually is. I should point out that there's also disagreement about the percentage of bird species that breed cooperatively. I just said it was 9%, but some researchers, for example, would say it's more like 5%.

Scientists are still learning a lot about cooperative breeding in birds, so hopefully we'll get a better idea about all this stuff someday. In any case, it's clear that cooperative breeding has independently evolved many times across the branches of the avian tree of life. And some lineages have gone from independent breeding to cooperative breeding and back again, and vice versa. So cooperative breeding has been a very fluid social trait in the evolution of birds. A few bird families comprise only cooperative breeders. For example, there's the family Pomatostomody. These are the pseudo-babblers of Australia and New Guinea. There are five species in the family, and as far as I know, they're all cooperative breeders. Other avian families have a large

proportion of cooperative breeders mixed in with species that are independent breeders. Some examples here are the families of bee-eaters, wood hoopoos, New Zealand wrens, and Shrikes. In general, cooperative breeding seems to be most common in small families of tree-dwelling birds, and most of these represent relatively ancient lineages. That suggests that cooperative breeding appeared fairly early in the evolution of birds. So that's a little about how cooperative breeding is distributed taxonomically among species and among families. Now let's look at how this breeding system is distributed geographically among birds around the world. If we look at the regions where we find a high number of cooperatively breeding bird species, we see a couple of patterns.

First, there's a broad tendency of cooperative breeders to be concentrated in tropical environments. But maybe that's not too surprising, since those are the places where we find the highest species diversity of birds in general. The second pattern, which is stronger, is that sub-Saharan Africa and Australia are the biggest hotspots where we find this breeding behavior. not just in absolute numbers of cooperative breeders, but in the proportion of cooperative breeders among the bird species. For example, roughly one-fifth of Australia's bird species are cooperative breeders, so 20%. Now, if you're like me, you're wondering why that might be.

Why are there relatively more cooperative breeders in Africa and Australia? Well, I don't know the answer. It might have something to do with the often harsh, unpredictable environments of those continents. And or it might have something to do with the particular bird families found on those continents. If those families tend to be the relatively ancient ones with more cooperative breeders, that might explain the pattern. It could be mostly a consequence of the evolutionary legacies of the birds in those places. So maybe what looks like a geographic pattern is, might actually be more of a taxonomic pattern at the heart of it. What do you think about that, Mr. Spock?

Fascinating. In any case, if you're out wandering around in the bush, in Africa, or Australia, you're more likely to bump into a cooperatively breeding bird species there than in many other parts of the world. Now, let me just point out a few bird species across the continents. Here in North America, notable examples of cooperative breeders include Harris's Hawk, Acorn Woodpecker, Red Cockaded Woodpecker, Florida Scrub Jay and Brown-headed Nut Hatch. A couple species in South America are the Greater Ani, which is a member

of the Kuku family, and the grayish Bay Wing, a member of the Blackbird family. In Europe, there's the long-tailed tit and Iberian magpie as two examples. Representative Cooperative Breeders in Asia include the white-crested laughing thrush and the jungle babbler, both members of the family Leothricody. Africa has lots of examples, including the white-fronted bee-eater, pied kingfisher, southern ground hornbill, superb starling, sociable weaver, and green wood hoopoo. And hey, just because it's fun, let's listen to a small group of green woodhupus moving through some trees on a wooded slope in South Africa.

Again, that was the green wood hoopoo. And finally, on our tour of the continents, Australia has cooperatively breeding species like the superb fairy wren and noisy minor. Decades of research on cooperative breeding has shown us that this behavior is widespread among birds, and that roughly 5 to 9 percent of species breed this way. And there's evidence that cooperative breeding has evolved independently many times. It's been gained and lost in multiple lineages over millions of years. But how exactly does this behavior evolve? What is the

underlying drive for a group of adult birds to work together to raise a family, rather than go off on their own. Among scientists, not just ornithologists, but biologists in general, cooperative breeding has been a hot topic of research for a long time. It's a profoundly important social behavior to investigate. And that's because of what it can teach us about natural selection and evolution. The way Charles Darwin laid it out, natural selection works at the level of the individual. Individuals with traits better suited to their environment are more likely to survive and reproduce, so they end up passing on those advantageous traits to their babies, and they tend to leave behind more babies. This process repeats generation after generation, and it's what drives the adaptation of species over time. Beneficial traits accumulate,

less favorable ones get stripped away. With that understanding of Darwinian natural selection, then, we would predict that individuals should develop breeding behaviors that maximize their own reproductive output. And indeed they do. Birds and other critters have powerful instinctual drives to make babies. But what about cooperative breeding? This behavior seems to fly in the face of Darwinian natural.

selection. Individual birds are delaying their own reproduction or skipping it altogether to help other birds reproduce. These helpers appear to be making a sacrifice for the benefit of others. And this seems like a paradox. It doesn't jive with how we think natural selection works. Because how could helping behavior be advantageous if what it does is reduce the reproductive success of the helper? Well, thankfully, smart scientists have been working on questions just like that for a long time. They've come up with some concepts and mechanisms that help explain what's going on. First up, we have the concept of inclusive fitness. British evolutionary biologist William Donald Hamilton came up with this idea in 1964. It states that an individual's success isn't just based on their own

direct reproductive output, on just the babies they crank out themselves. With inclusive fitness, an individual's fitness, their total genetic contribution to the next generation, also takes into account the reproductive success of their relatives. The closer your relative is to you, the more their success is your success. You, the individual, are getting an indirect measure of success every time one of your relatives has a baby. The reason for this is that relatives share some of their genes. That's what makes them related, right? The more closely related to individuals are,

the greater the proportion of their genomes they're likely to share. For example, you share, on average, 50% of your genes with each of your parents. And you share 50% of your genes with each of your full siblings. But you share only 12.5% of your genes with your first cousins. And speaking of cousins, fun fact, Darwin's wife, Emma Wedgwood, was his first cousin. Yes, I know. In our modern Western culture, we tend to think of marriage between first cousins as kind of icky. There are laws against it and whatnot. The underlying reason for this sort of taboo is that inbreeding can lead to health issues in the children of such unions.

That's why many bird species that breed cooperatively have behaviors, such as kin recognition, that help them minimize in breeding. Anyway, marrying one's cousin was a common and acceptable practice in Darwin's time, especially among the middle and upper classes of Europe. But Darwin being Darwin, he was acutely aware of the possible genetic problems that his kids might have to deal with. Nevertheless, he and Emma ended up having ten of them. Interesting stuff, but I digress.

This concept of inclusive fitness helps explain cooperative breeding. Helpers gain indirect fitness benefits by assisting relatives like siblings in raising offspring. By doing so, they help pass on shared genes to the next generation, even if they don't personally have any offspring. And you know, inclusive fitness would be a great name for a gym. It's like, Inclusive Fitness Gym, the place where a bunch of nerdy biologist types go to get totally shredded. Also, the word inclusive has the positive connotation of an environment where everyone feels welcomed and respected regardless of their differences. I mean, come on, this is a great business idea.

Inclusive fitness. Give me just a sec here while I do a quick Google search. Dang it! There's already a place called Inclusive Fitness. inclusive fitness. For real, it's in Roxbury, Massachusetts. They took my idea. Well, good for them, I guess. Anyway, operating on this concept or framework of inclusive fitness, we have the actual mechanism that leads to these seemingly altruistic behaviors in birds and other animals. That mechanism is called kin selection. This is a special form of natural selection that favors behaviors or other traits

that increase the reproductive success of relatives, of kin. Over many generations, kin selection strengthens any behaviors that promote inclusive fitness. Yes, an individual helper bird sacrifices its own direct reproduction, and that's a cost it must pay. But helping behavior emerges and persists through evolution as long as the cost paid by the helper is outweighed by the reproductive benefits received by the helpers' relatives. So helping your relatives is just an alternative way to get your genes passed down into the next generation. As far as evolution is concerned, that's all that matters.

This presents a problem for me, though. I don't have any kids, and I don't plan to have any. But hypothetically, let's say my biggest priority in life was still to pass down a bunch of my genes. I suppose I could be like a helper at the nest in a cooperatively breeding bird species. Helping to take care of my younger siblings, I would increase their chances of survival and reproduction. I could pay for their piano lessons, teach them how to drive, maybe even pay for their weddings, whatever it takes to make them successful. Everyone would think I'm a

noble, selfless person, a loving and generous and handsome big brother. But I fooled you all. I wasn't being altruistic. This was all just a selfish, fiendishly clever scheme to maximize my own inclusive fitness. There's one flaw with this evil plan, however, and that's that I don't actually have any siblings. I'm an only child. So I guess the success of my genes, making it into the future, depends entirely on the reproductive success of all my more distant relatives. My cousins second cousins and so on. Well, good luck you guys. Make lots of babies and stuff. Okay, so in a cooperatively breeding group of birds, we have the breeders and the non-breeders. The non-breeders are the helpers. As we've been talking about, helpers are often related to the chicks

they're feeding and protecting. The helpers are young adult birds, and in most cases they're helping to raise their younger brothers and sisters. And multiple studies have shown across a range of species that all the hard work put in by helpers really does increase the health and survival of the chicks. It's a win-win situation for everybody in the group. But here's a twist. Sometimes the helpers at a nest are not closely related to the chicks they're caring for. Say what? Right, because didn't I just say that kin selection based on inclusive fitness is how all of this is supposed to work? I did. But the presence of non-kin helpers in some cooperative groups tells us that kin selection isn't the only game in town. There must be other mechanisms that lead to the

evolution of cooperative breeding. When a helper takes care of a related chick, it gains indirect genetic benefits through the magic of inclusive fitness. But when helpers, are not closely related to the chicks, their behavior is often motivated by direct benefits rather than indirect genetic ones. One direct benefit is increasing your chances of reproducing in the future. Unrelated helpers may eventually gain access to breeding opportunities or territories within the group in exchange for their good service. Be a useful member of the group now so that you improve your chances of mating in the future. For example, take the Brown J.

This member of the family Corvody lives from southern Texas down to Panama. Brown Jays are large, and yes, their plumage is mostly brown. They live in large groups that include both extended families and some immigrants. The immigrant helpers are basically. unrelated to the rest of the birds in the group. So getting indirect benefits by way of inclusive fitness isn't an option for the immigrants. But an immigrant male can get a direct benefit if he makes himself useful for long enough, because then he can increase his chances of eventually replacing the dominant male to partner up with the dominant female. Another direct benefit,

in a more general sense, is that by being in a group, even as an unrelated helper, you increase your likelihood of survival. For example, with southern pied babblers, an individual doesn't have much chance of surviving alone in the harsh landscape of the Kalahari Desert. These birds feed on the ground, looking for invertebrates by tossing leaves aside and digging in the dirt. A lone bird foraging this way is highly vulnerable to attacks from predators like the yellow mongoose. Staying in a group, even when you get no reproductive genetic benefit from it, is a better option than dying out there on your own. You might still get a chance to breed someday, somehow, if you're lucky. But first, you have to stay alive.

Okay, so we're talking about the evolution of cooperative breeding, right? A lot of what I've been covering so far is the most basic and widely understood mechanism that drives a species towards cooperative breeding. The dynamic duo of inclusive fitness and kin selection, all of that. That's the classical way to look at the evolution of this breeding system. This model or hypothesis focuses on indirect benefits. With kin selection at work, even a helper individual that never personally breeds, never has any of its own babies, that individual still wins in the game of evolution if, because of its helping behavior, more of its genes get transmitted into later generations through its relatives.

Scientists have come up with several other hypotheses to explain the situations that lead to cooperative breeding. I'll do just a quick overview of some of these hypotheses here. First, we have the ecological constraints hypothesis. The idea with this hypothesis is that cooperative breeding tends to evolve in environments where a bird's opportunities to breed independently are limited. The limiting factors are things having to do with the environment. So we call them ecological constraints. These include scarce resources, high predation risk, or a very limited number of suitable territories.

young birds might delay dispersal and become helpers because high-quality territories are limited, making independent breeding difficult or impossible. Better to stick around with mom and dad for a while. Habitat saturation, as in all the good territories are taken, seems to be a consistent predictor of cooperative breeding. So the ecological constraints type of constraints. I have a little trouble with pronouncing constraints. So the ecological constraints hypothesis might explain why cooperative breeding

is often more common in harsh environments where resources are scarce. Next we have the benefits of philipatri hypothesis. Philopatry is spelled P-H-I-L-O-P-A-T-R-Y. This is the tendency of a bird or other animal to stay in or return to the place where it was born, its natal territory. A bird that stays in its natal territory can gain some direct benefits, such as safety, access to resources, or with luck, it might even inherit a high-quality territory from its parents. Evidence shows us that helpers often stay longer in groups with higher-quality territories. Even if a helper doesn't

inherit a territory from mom and dad, staying home for a while might allow it to gain strength and experience in a safe environment before venturing out into the cold, hard world to find its own territory. The benefits of Philippatri hypothesis is pretty much all about direct rather than indirect benefits. Next on our list is the life history hypothesis. Life history is another term I should probably define. A bird's life history is its overall strategy for growth, reproduction, and survival, including things like its lifespan, age at first breeding, and number of offspring. Bird species with certain life history traits appear to be more likely to evolve cooperative breeding. These traits include a long lifespan, raising just one or a few chicks per

year and a long time spent in the immature life stage. Cooperative breeding might be more common in long-lived bird species because individuals have multiple opportunities to reproduce over their relatively long lives, allowing them to invest in helping for a few years before becoming breeders themselves. Okay, so that was the life history hypothesis. We also have the temporal variability hypothesis. The idea with this one is that in unpredictable environments, cooperative breeding acts as a beth hedging strategy. It makes it more likely that at least some offspring survive during adverse conditions. For example, the white-fronted bee-eater Merops Bolochoides lives in semi-arid and savannah environments in southern Africa, where rainfall and insect

abundance can fluctuate wildly from one year to the next. In drought years, bee-eater food, primarily flying insects like bees and wasps, is in short supply. Under these conditions, trying to breed independently is risky. You aren't likely to find enough insects to keep your chicks from starving. So instead, many adult white-fronted bee-eaters delay their breeding and serve as helpers at the nests of their close relatives. In such lean times, this approach may help at least a few chicks survive. Because some members switch from being breeders to helpers, they might prevent total reproductive failure for the entire family group. As a side note, this is an example of facultative cooperative breeding, where individuals can breed independently,

but they sometimes choose to delay their own reproduction to help others, usually their relatives, to raise offspring. And hey, when the good times return, when the rains pour forth from the heavens and the air is so thick with buzzing bees that you can't see your own beak in front of your face? During those times of plenty, some helper birds will try their luck at making their own babies.

They switch back. That's facultative cooperative breeding in action, because facultative means occurring optionally in response to circumstances. And in case you forgot, this last hypothesis we've been looking at is called the temporal variability hypothesis. Temporal as in time, variability over time. Believe it or not, there are even more hypotheses, such as the adaptive delayed dispersal hypothesis. But we'll stop for now, because I have a feeling I've already bombarded you with too much information. Here's the thing.

Most of these hypotheses about why cooperative breeding exists are not mutually exclusive. Many of the factors they speak of, inclusive fitness, life history traits, environmental variability, these could be working together to make birds want to breed cooperatively. The particular combination of factors at work probably varies from species to species. In one species, life history might have the biggest influence. In another, it might be the ecological constraint of limited territory availability. So, research on this topic these days tends to emphasize the integrative nature of all these hypotheses, acknowledging that the evolution of cooperative breeding is shaped by combinations of genetic, ecological, and life history factors.

There's one more idea I want to share with you. about the evolution of cooperative breeding. Research suggests that as a species evolves, as it goes from being a completely independent breeder to a full-blown cooperative breeder, there's an intermediate step in that evolutionary process. And that's family living. This is where young adult birds delay their dispersal from the natal territory.

In your typical independently breeding species, the parents don't put up with that. They chase their kids off. They're like, go on now, boy. Get out of here and don't come back. But family living evolves when the parent birds actually tolerate their offspring staying at home, staying in the territory. The parent birds let their college-age son live in the basement,

where it seems like all he does is eat Cheetos and play video games. He says he's filling out college applications, but has he really? Has he? parent birds put up with such freeloaders for a while but then they put those kids to work doing chores around the house around the territory it soon becomes obvious that having more warm bodies around is beneficial because a family group is better at protecting against predators defending the territory from rivals and finding resources like food only later does helping with rearing the chicks evolve as a behavior.

The birds in the group are closely related, so there's a good chance the mechanism of kin selection is going to kick into gear and, boom, you've got cooperative breeding. So family living is a sort of evolutionary stepping stone from independent, non-family living, towards cooperative breeding. The social benefits of family living, such as protection against predation, can favor the evolution of delayed dispersal and combined with parental tolerance,

and these in turn promote cooperative breeding. But Ivan, you ask, if cooperative breeding is so beneficial, why isn't it much more common among birds? That is a great question. Cooperative breeding is a complex behavior influenced by a bunch of interacting factors, including ecological constraints, life history, phylogenetic history, kinship, the costs and benefits of helping, environmental factors, and even the influence of brood parasitism. Listen to episode 12 if you want to learn about brood parasitism.

Cooperative breeding can work really well under specific sets of factors, certain conditions, in harsh, unpredictable environments, for example. But not all birds live under such conditions. Most of them do just fine breeding independently. I want to give you a little more info on some of the species I mentioned earlier, just so you can see how cooperative breeding plays out in these unique situations. Each of these species is absolutely worthy of an entire podcast episode, but for now we'll just take a peek at how each of them breeds. First up is the Florida Scrub J, a phylicoma cirrelessons.

It's an endemic species in Florida, where it occupies a very specific habitat, oak scrub that experiences periodic wildfires. This is one of the most intensely studied cooperatively breeding birds in North America. Florida scrub jays live in family groups with one of the ones. breeding pair. So that makes this a singular cooperative breeder, right? The offspring of the dominant pair typically stay with their parents and help raise the next generation of chicks. These helpers are mostly one-year-old adults, but some of them will stay in their natal territory for five years or more. There are between one and six helpers in any particular family. They bring food to their younger siblings in the nest, they watch out for and chase away predators,

and they protect the family's territory. Because of all this help, the breeding pair end up raising more offspring than pairs without helpers. Next is another North American species, one that has also been extensively studied by ornithologists. The Acorn Woodpecker, Melanerpe's Pharmacivorous. This is one of my personal favorites.

The acorn woodpecker has a complex cooperative breeding system, one of the most complex among birds, really. A group of acorn woodpeckers includes three to 15 individuals with an average of about three to four. Cooperative breeding in the group works on two levels. The first is that some birds in the group engage in plural breeding. The second level is that the remaining members of the group are non-breeding helpers. The plural breeders include one to four females who all lay eggs in the same nest cavity. Then there are one to eight males who compete to mate with those females. Despite the competition among males, it's common for more than one of them to breed successfully, and they all share in the parental duties, both males and females.

So this is a species that gives us an example of plural cooperative breeding. Additionally, there are the one to ten non-breeding helpers, which are offspring fledged by the group in previous years. Helpers can be up to five years old. Cooperative breeding works well for acorn woodpeckers because of their unique way of life. As you might guess, they eat a lot of acorns, The woodpeckers in a group work hard during the autumn months to store thousands of acorns in what's called a granary tree. They cooperate to maintain and defend their granary tree. When winter comes, the stored acorns provide a much-needed, reliable food source. Defense of the granary tree year after year means the group's territory is stable over time. In this situation, cooperative breeding is a good

strategy because offspring have a better chance of survival staying in a stable, resource-rich environment. But granary trees are few and far between on the landscape. Helpers delay their dispersal because of limited breeding opportunities and because there's fierce competition for territories that include granary trees. This sounds like a case where the ecological constraints hypothesis applies, doesn't it? The cooperative breeding system, of acorn woodpeckers also enhances the survival rates of everyone in the group by providing better defense against predators and improving their ability to forage successfully. Moving over to the old world, we have a species whose geographic range runs from Western Europe

all the way to the Russian Far East. The long-tailed tit, Igothelos Caudetus, is an adult adorable tiny passerine bird in the family egotality. This is in the same family that the bush tit of North America belongs to. The long-tailed tit has a round body, a short, stubby bill, and a disproportionately long tail. Its feathers are mostly black and white, with some splashes of gray and pink mixed in. A single pair of long-tailed tits is perfectly, capable of breeding independently. And in a good year, they do. But sometimes disaster strikes. Rough weather destroys their nest, or a predator slithers in to eat all their nestlings.

You know, like a slithering raccoon? Oh, wait. Yeah, they don't have raccoons in Eurasia. Oh, well, we're probably talking about a snake, I guess. Anyway, in such situations, the pair of long-tailed tits will often find some of their relatives nearby and just help them raise their chicks, the pair whose nest failed switches into cooperative breeding mode. They redirect their parental energies to become helpers rather than start over trying to raise their own brood. So in that particular year, they don't personally breed, but through the miracle of inclusive fitness, they improve the chances of spreading their own genes by helping their relatives. So breeding in long-tailed tits might be a case where the temporal variability hypothesis applies, and this is also

another example of facultative cooperative breeding. But how do these helpers tell their close relatives apart from just any old randos in the neighborhood? Research has shown that long-tailed tits can tell the difference between their kin and unrelated randos by their calls. They listen for contact calls that have distinct characteristics. Individual tits learn to recognize those characteristics while they're still in the nestling stage. These were the sounds made by adults bringing food to them when they were still helpless babies. And research has also shown that helpers at a nest significantly improve the chances of survival for the chicks they feed and care for.

Okay, I've got one more for you. This time from the land down under, Australia. The superb fairy wren, Malurus, Sionaeus, is a well-studied species with a complex social life. A socially monogamous breeding pair of fairy wrens maintains a small year-round territory. They're often joined by a few helpers, and the helpers are usually male offspring from previous breeding seasons. As in so many other cooperatively breeding species, helpers contribute to raising the chicks by providing food, defending the territory, and guarding against predators,

like slithering raccoons. The cooperative behavior of superb fairy wrens is driven by a combination of ecological constraints and the bird's instincts to maximize inclusive fitness. The ecological constraints are that high predation rates and unpredictable food, availability make parental care very demanding. But these male helpers take some of the burden off of their mother. As a consequence, mom will probably live longer and crank out more babies over her

lifetime. So the male helpers are also helping their mom produce more little brothers and sisters. And those little buggers inherit the cooperative breeding behaviors. And so this goes on generation after generation, forever and ever. Interestingly, female superb fairy wrens are known for their promiscuity, often mating secretly with males outside the group, which adds a layer of complexity to this species' genetic dynamics. So because of that, helpers might be unknowingly helping to raise some chicks that aren't even related to them.

That's a waste of energy in time, because it doesn't help with inclusive fitness. And yet, despite that risk, the best bet of a helper is to stay in the group where it was born, where relatedness is generally highest, and where there are still some direct survival benefits that have nothing to do with genetics. As I hope I've explained in this episode, cooperative breeding comes in a variety of flavors. Some species form monogamous pairs and have related helpers. Groups in other species can include some unrelated helpers. Some species have groups that include multiple pairs of breeders.

Other species switch from independent breeding to cooperative breeding in some years if their nest fails, and so on. So it's not surprising that biologists have identified multiple hypotheses to explain the way these behaviors evolve. Cooperative breeding is fascinating because rather than defying Darwin's ideas on natural selection, it actually expands our understanding of how fitness and selection work in complex social and ecological settings. And cooperative breeding still comes back to the interests of the individual. It's still Darwinian natural selection just with a twist. birds don't do this stuff out of the kindness of their little hearts to contribute to the

greater good of the group. No, they cooperate because each bird is driven to get as many of its own genes passed down to the next generation. Yes, sometimes it takes a village to raise a chick, but the seemingly well-intentioned, seemingly altruistic villagers probably have ulterior motives of their own. Thank you ever so much for listening to episode 110. I really hope you enjoyed it. This is the kind of episode that puts the science in the science of birds. We don't just talk about all the fun times to be had looking at pretty birds.

I mean, sure, that's great. I love doing that, but we aren't afraid to wrap our little minds around some higher-level concepts and juicy technical jargon, like temporal variability and faculty. cooperative breeding because we're here to learn right and i'm able to be here to learn with you to keep making this show because i get significant support from the members of my community on patreon so a big thank you to everyone who is making this podcast possible my newest shiniest supporters on patreon are joel eatman elijah willow ayesa dm rm brandon helms

Ben Kehoe, Marcel Haas, Nicole Parafit, Max Roth, Mary H, Michelle Follett, and Chris Heyman. Sorry if I mispronounced your names, but thank you all for helping me make ornithology accessible around the world. If you, dear friend, want to join these folks and become a helper at the nest, if you want to support the podcast, you can check out my Patreon page at patreon.com slash science of birds. There's also a link down at the bottom of the show notes that says something like support the show. And if you decide to join my Patreon community, well, first of all, thank you. But to save yourself a bit of money, I suggest you sign up using anything other than the Patreon app on an iPhone. Because Apple recently added a fat 30% fee on any purchases you make through the Patreon iOS app. Lame, but true. Patreon

doesn't get that money and I don't get it. Apple does. So, Please just use a desktop computer or go to the Patreon website on your mobile browser or use an Android phone. You can always shoot me an email if you have something you'd like to share with me, like if you have any hot tips for how someone can deviously increase their inclusive fitness. Here's my current strategy. Every Christmas, I send Burger King gift cards to all of my second and third cousins. Maybe those extra calories will help them to survive and reproduce more, to keep my genes alive in the world.

But yes, if you want to write to me, my email address is Ivan at Scienceofbirds.com. Again, this is episode 110. You can check out the show notes for the episode, along with some curated photos of species I talked about today on the Science of Birds website, which is at Science of Birds.com. I'm Ivan Philipson, and true fact about me, when I was four years old, I started my first business. selling rocks that I had colored with markers. I displayed them atop a cardboard box, and I would yell,

Rocks for sale, to all passers-by. I made approximately $0. Thanks for listening, and I'll see you next time. Cheers.