The Science of Birds - Flocking Behavior in Birds

Episode Date: August 7, 2022

This episode—which is Number 57— is all about the flocking behavior of birds.Birds of many species spend at least part of their yearly cycle hanging out in groups. This could be just a handful of individuals or it could be a gathering of millions of birds.Today, we’ll look at some explanations for why—as the saying goes—birds of a feather flock together. What benefits do birds get from forming groups like this?We’ll also look at how flocks work. As in, their mechanics. For example, how do birds communicate and coordinate their movements in a flock?~~ Leave me a review using Podchaser ~~Links of InterestStarling Murmuration [VIDEO]Boids algorithm demonstrationLink to this episode on the Science of Birds websiteSupport the show

Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners. This episode, which is number of, number of, 57 is all about the flocking behavior of birds. Birds of many species spend at least part of their yearly cycle hanging out in groups. This could be just a handful of individuals, or it could be a gathering of millions of birds. At first thought, we might take this sort of thing as just a simple

behavior in birds, one that isn't very complex, or for that matter, very interesting. Like, here are some birds oh look they decided to fly around together la di da end of story but you and i know that just about every aspect of nature is way more complex than it appears on the surface the same goes for flocking behavior there's a lot going on here today we'll look at some explanations for why as the saying goes birds of a feather flock together what benefits do birds do birds get from forming groups like this? We'll also look at how flocks work, as in their mechanics. For example, how do birds communicate and coordinate their movements in a flock? All right, shall we begin?

Among birds, there's a wide variety of flocks. types. They range from tiny to supermassive, of course. But flocks can vary in more ways than just size. Some flocks are loose and temporary, lasting only for a season or only during migration. Others are more enduring. The American Robin, tortoise migratorious, is territorial in the summer breeding season. But this bird is gregarious in the winter, often forming. large foraging flocks. So the American Robin is an example of a species that forms flocks only temporarily, seasonally. The opposite seasonal pattern occurs for some bird species that nest in large colonies.

Puffins, for example, breed in dense colonies during the summer. But when winter rolls around, these birds often scatter, dispersing across the waters of the open ocean. Some other species stick with their flockmates all year. Examples include the Pinyon J and Bush Tit in North America and the European bee-eater of Africa and Europe. These birds are highly social and maintain tight, relatively stable groups. Another way flocks vary is by their composition. We tend to think of all the birds in a flock as belonging to the same species. That's generally the case, sure, but there are plenty of times when birds of multiple species

buddy up and fly around together. I did an entire episode on this phenomenon of mixed species flocks. That was episode 17, so check it out if you haven't already. Today, we'll focus on homo-specific bird flocks. These are the ones that include only a single species. So we've got small versus big flocks, temporary versus permanent flocks, and single versus mixed species flocks. Another interesting variable to think about is the relationships of birds in a flock. Are the individuals all total randos completely unrelated to each other, as in not genetically related, or are they just friends with some common interests? The alternative is that at least some birds in the flock are related to each other. Parents and their offspring, siblings, cousins,

step-uncles, that sort of thing. From the perspective of natural selection and evolutionary theory, the degree of relatedness among birds in a flock should be an important factor. Why do birds form flocks? Biologists have been asking this question for over a hundred years. And they've also been studying similar grouping behavior in other animals, like fish, insects, and mammals. There are multiple theories among scientists about why animals form groups, whether we're talking about flocks, herds, swarms, schools, boy bands, or unruly mobs. From what I can tell, these theories mostly have to do with two major benefits of joining a group.

One, avoiding predators, and two, finding food. In general, a bird in a flock has a better chance of not getting eaten by a predator, and better chances of finding food than it would if it just went solo and lived alone. The bird would know that if it had ever watched the Walking Dead TV show, or any other zombie show. some character tries to be a tough guy and leave the group and another character pleads with them you'll never survive on your own out there it's too dangerous so how exactly does being in a flock protect a bird from predators you already know that the answer is in its simplest form safety in numbers if you're flying around in a flock of let's say twenty thousand other birds that look just to like you, well, the chance that a swooping falcon is going to single you out of the crowd is pretty dang low. This is one way that flock membership protects you. It's a numbers game. For example, in a 1975 study of shore birds and their avian predators, researchers found that

small sandpipers in one bay in California were 3.2 times more likely to get killed by a Merlin when they were hanging out by themselves compared to when they moved in a flock. And FYI, the Merlin is a type of small falcon that eats mostly birds. The flock also provides many more pairs of eyes to detect sneaky predators. In a large enough flock, there are always some birds looking around warily for danger. If this is true, then each individual in the flock can relax a little. and let their guard down from time to time. Spending less time being nervous and vigilant,

a bird has more time for stuffing its hot little mouth with food. Now, I should point out that each bird in the flock is most likely acting purely in its own self-interest. Just because birds are hanging out together in a flock doesn't mean they're being altruistic. It's not like they're watching each other's backs out of the kindness of their hearts. I mean, who knows, but they probably don't have a sense of moral obligation or whatever.

We can say that a bird's behavior in a group is the product of natural selection acting over millions of years. A bird's behaviors serve to increase its fitness. Some of those behaviors may also be helpful to other birds in the group. if all the birds in the flock share these behaviors then everybody wins now if we're not careful here we could stumble into a discussion of altruism group selection game theory and stuff like that those are much bigger topics in biology and today is not the day for them so let's keep cruising here let's look at one more thing about the anti-preditor function of flocks that thing is a mobbing. This is where several smaller birds join forces to harass a predator that's lurking around. The predator is usually a large raptor, but it could be a mammal like a fox or something. The little birds scream at and generally harass the predator until it gives up

and retreats. Having lots of flockmates around for a good old mobbing party is an advantage of living in a group. You've probably seen crows, gulls, or blackbirds chasing a hawk like this. I know it's a stressful situation for all the birds involved, but I can't help but find it kind of funny when I see mobbing in action. I'm usually rooting for the smaller birds, but I also kind of feel sorry for the large bird being harassed. Ornithologists hypothesize that it's the smaller bird species that are more likely to form flocks in the first place. They're more vulnerable to predators because they're relatively bite-sized, so they can greatly improve their chances of survival by gathering in flocks.

Flock behavior is an adaptation for avoiding predators. But the second major reason birds form flocks is to find more food, right? Imagine a food source that's distributed across the landscape unevenly, in other words, in clumps. This would be true for things like insects, fish, berries, and seeds. To find foods like these, having more eyes searching the landscape should increase the likelihood of discovery. So more birds in a flock should result in higher foraging efficiency. One model that biologists have come up with to explain how this works is called the

information sharing model. In this case, every bird in the flock is searching for tasty morsels of food. Simultaneously, each bird is keeping an eye on its nearby flockmates. When one bird finds a nugget of food, the other birds around it notice and they come hopping over to share in the bounty. So the birds are sharing information about where the good stuff is. Then we have the producer scrounger model. This is another way to explain foraging in bird flocks.

In this model, some birds in the flock are producers and others are scroungers. Producers are the ones who find food. They hop around on the ground with their heads facing down. They're searching. Scroungers don't look for food Instead, they keep their heads up and just watch the producers to see what they find

When a producer hits the jackpot Here come the lazy scroungers to join the feast So scroungers be like Are you gonna eat that? Oh, oh you are Oh well, oops, too late, I ate it, sorry If these scroungers were humans we might call them deadbeats, freeloaders, or worse.

But birds can and do switch between the roles of producer and scrounger. A producer today might be a scrounger tomorrow, depending on a variety of factors like food distribution and flock size. Scientists have studied this sort of behavior in a tiny bird called the scaly-breasted munya, Lankura punctilada, also known as the Spice Finch or Nutmeg Manikin.

This species is found throughout India and Southeast Asia. Scaly-breasted munias forage in flocks of up to 100 birds. They eat a lot of grass seeds. In experiments with captive munias, the birds tend to adopt the scrounger approach when food is distributed in clumps. You also get more scroungers when the flock size increases. But if the balance shifts so that the flock is mostly lazy scroungers, then it can take a lot longer for any food clumps to be discovered.

The birds are all watching each other rather than looking for food. Silly little spice finches. There's food right there on the ground, but you don't see it because you're too busy scheming on how to steve your friend's lunch. But your friend doesn't have any lunch to steal because he was planning to swipe yours. And that's how all the scroungy little scaly-breasted munias died of starvation. What a senseless tragedy. Anyway, I hope you're getting an appreciation that life in a flock is dynamic and complex.

So far, we've been looking at the primary reasons why birds join flocks. Safety in numbers, a reduced need for vigilance, and sharing information about food. These are some of the pros of living in a flock. Other pros include improved flight aerodynamics while migrating in formation and huddling on the roost with your flockmates to stay warm in winter. Also, birds of some species need to spend time in a flock when they're young in order to learn their proper songs, other vocal sounds, and some social behaviors. But as you've probably guessed, there are some major downsides to being part of a flock.

There are some cons. First, you're way more likely to catch diseases and parasites from other birds when you're part of a flock. Second, there's the issue of competition, competition for food mostly, but also roosting sites and whatnot. Competition over resources like these can lead to stress. Likewise, stress can come from fighting to establish or maintain the pecking order, in other words, the dominance hierarchy. Recall that I did a podcast episode on the pecking order a while back. Stress from squabbling with your neighbors over some grass seed

or from getting pecked in the eyeball by a dominant bird might lower your overall health and ability to reproduce so this is a major con of living in a flock despite the potential downsides many many bird species have evolved the behavior of forming flocks these species have through natural selection found that the pros outweigh the cons, at least in their unique situations. For a given flock of a given species, we can imagine that there's an ideal flock size, the optimal number of birds in the

group. In flocks that are too small, individuals have to spend a lot of time scanning for predators. That means they have less time for foraging. On the other hand, if the flock is too large, competition among individuals will lead to a lot of fighting. Any time taken up pecking and clawing at your competitors is time that you can't use to look for food. But there's a happy medium, an optimal flock size where fighting is minimal and there are enough birds to keep a lookout so that vigilance for any individual doesn't have to be super high. At this theoretical, optimal size, life is good because each bird in the flock has the maximum possible amount of time for foraging. What is the optimal flock size, you ask? The answer is, of course, 42.

Not 41 birds or 43 birds. 42 is the optimum. Actually, there's no single optimal flock size we can apply to all birds. The number will be different for each species or for each population or flock. And the optimum number might change from season to season, or even from day to day. The optimum depends on many factors, like food availability, the climate, the local predator population, etc. And anyway, it's probably not something any scientist will be able to calculate with certainty.

This leaves us with one important question. If flocking behavior is generally beneficial to birds, why don't all bird species form flocks all the time? Because, just like the concept of the optimal flock size, one size does not fit all when it comes to the advantages of flocking. Again, there are many variables at play. flocking only makes sense for species with certain habitats, diets, and predators. For example, flocking seems to work best for small, vulnerable birds that live in open habitats.

These include shore birds and many songbirds that live in grasslands. Flocking also works well for species whose food resources tend to be found in clumps, as I mentioned earlier. Here we're talking about birds like parrots, pelicans, gulls, and some finches like crossbills and pine siskins, just to name a few. Okay, so we've looked at why birds form flocks. Some of our discussion has already veered into the hows of bird flock mechanics. Let's dig more into that now. Let's say you're looking at a flock of 5,000 small songbirds. They're flying around in one big swarm over some fields.

The flock is changing directions this way and that. It's a beautiful sight to behold. Then sort of suddenly, the flock zooms off and disappears over some hills. Which of those 5,000 birds was in charge? Who was deciding to change directions and then to leave the scene? The answer is no one. There is no single bird or committee of birds in charge of the flock. With large groups of humans, there's usually one or a few leaders.

So we say that our groups are organized from the top down. But with birds, it works the other way around. Flocks are organized from the bottom up. There's no leadership. Each individual bird is making decisions, and the decisions of every bird in the flock ripple through the flock, causing something to happen. Like the flock was moving to the left,

then because of the collective decisions of all the birds, the flock now turns to the right. Scientists have several terms for this sort of phenomenon. They say that flocks are self-organizing. flocking is described as emergent collective behavior all of the little interactions between birds collectively create the large-scale patterns that we see

swarm intelligence is another term used to describe the way in which decisions are made by large numbers of birds seemingly all at once but how does this actually work don't the birds need to communicate with each other somehow to coordinate their high-speed movements with such precision? Ornithologists struggled for a long time to understand how birds in flocks communicate on the fly. In the 1930s, one British ornithologist named Edmund Sellis

actually wrote a book proposing that birds used thought transference to make their sudden collective decisions. Yes, thought transference, as in telepathy. man i kind of wish that were true that birds could read each other's minds that would be crazy right and what if they could read our thoughts if they could maybe they would finally understand that i love them and just want to be their friend they wouldn't have to be all terrified and scatter every time I come around with my binoculars, as though I'm trying to murder them or something. But sadly, birds don't have telepathy, at least not that we know of. Instead, they use their eyes to watch the movements of their flockmates. That's the primary way they communicate. Each individual

bird uses and responds to visual information from the birds around it. Birds in a flock can coordinate their movements at high speed because, compared to us, they have high temporal resolution in their vision and in their brains. Birds see and respond to things faster than we do. That's one of their superpowers. It's like they see the world around them moving in slow motion. For example, Dunlin fly around in flocks to evade aerial predators like falcons. The Dunlin is a species of sandpiper. A flock of Dunlin in anti-preditor mode moves at high speed and can turn on a dime. The average time it takes for a flock to change direction is just 196 milliseconds. That's only about two-fifths of a second.

Birds in a flock also communicate using sound in some situations. The crested pigeon of Australia, for example, has specialized wing feathers that make a whistling sound, like this. If the bird gets spooked by a predator and takes off in alarm, the other crested pigeons in the flock hear that whistle, and they all immediately take off. Here in North America, we have the morning dove, which also makes whistling sounds with its wings.

The function of those sounds may also. be to work as an alarm. Now, let's consider one of the most amazing natural spectacles when it comes to bird flocks. And that is the murmuration. Mirmeration is the word used for a large flock of starlings. European starlings, sternus vulgaris, are famous for their enormous undulating flocks. These birds gather over fields and other open spaces in Europe and in places they've been introduced to, like North America and Australia. Murmurations often occur during the evening as the birds are getting ready to roost for the night.

Starling murmurations are mesmerizing and beautiful. The flock seems to behave like a single superorganism, pulsing and twisting with a mind of its own. If you've ever seen a murmuration, you, probably remember how impressive it was. I'll put a link in the show notes to a video of a murmuration, so you can also check that out. Ornithologists and other scientists have done a lot of research on starling murmurations, so we know

a bit about how these things work. Their primary function is protection from predators. Peregrine falcons and other birds of prey often try to swoop in to catch starlings. But the starling flock responds rapidly to the threat. The murmuration swirls and changes shape at high speed, seemingly at random. The predator has a hard time singling out just one starling from this confusing vortex of birds. Since there's no leader of the flock, no captain to shout orders, the movements of the murmuration have to come from the bottom up,

from the collective choices of individual starlings. Scientists studying murmurations have come up with some mathematical rules to describe how all this works. One of the early and most famous models is called the Boyd's algorithm. That's Boyd's, B-O-I-D-S, bird-like objects, I guess, like the bird version of Androids or something. this computer algorithm can simulate how a flock works with just a few rules that each bird slash boyd follows first there's a rule of attraction or cohesion each bird in the flock steers towards the average position of its nearby flockmates second there's the rule of repulsion or separation each bird steers itself so that it avoids crowding

or crashing into its nearby flockmates. It keeps a little bit of distance. Third, we have the rule of alignment. This causes each bird to steer towards the average direction or heading of its nearby flockmates. And it matches their speed, too. So, in a computer simulation using the Boyd's algorithm, these three simple rules can be applied

to create flocks that appear to behave like real bird. flocks. I'll put a link in the show notes to a website where you can see this algorithm in action and mess around with the parameters yourself. It's pretty cool. But just how many nearby flockmates does a real bird need to keep track of for this to work? You know I'm tempted to say 42, but actually, research on European starlings has revealed that each bird keeps track of it's seven nearest neighbors. That's right, just seven. So that's one bird in front, one behind, one above, one below, and one on each side. Wait, that's only six. So I guess there's an oddball, seventh bird, also being tracked somewhere in the vicinity. Amazingly,

it seems that the highly effective anti-preditor response of a murmuration is simply the collective result of thousands of individual starlings making decisions as individuals. Each bird is following simple rules of movement and keeping an eye on just a handful of its nearest neighbors. At least that's what seems to be going on, with European starlings anyway. Are the rules different for other bird species? Possibly. Ornithologists have a lot of unanswered questions about how murmurations and other bird flocks behave. This is an active and exciting field of research. Who knows what amazing things we still have to learn about how flocking behavior works in birds.

Your homework assignment this time is to stop and pay attention the next time you see a large flock of birds in the sky. Try to single out one bird and watch what it does. I know, that's not an easy thing to do, right? In any case, I hope that what you learned here today will give you some more perspective the next time you see a flock of birds. This podcast continues to exist in part because of the generous support I get from my listeners.

So I want to thank all my supporters on Patreon for doing their part to make the science of birds more sustainable. sustainable. And I'd like to give a special shout out to my newest patrons, Judy Houston, Johnny Rockadee, Paul, and Freya Noss. Thank you guys so much for joining my Patreon community. If you're interested in supporting this podcast, you can check out my Patreon page at patreon.com slash science of birds. You can also send me an email if you have something you'd like to share, maybe a comment about the show, or you want to tell me about some lazy scroungers you have to deal with in your life. In any case, my email address is Ivan at

Science of Birds.com. You can check out the show notes for this episode, which is number 57, on the Science of Birds website, Scienceofbirds.com. This is Ivan Philipson, wishing you the best of everything. Peace.