The Science of Birds - Vagrancy: Why Some Birds End Up Far From Home

Episode Date: March 17, 2026

👕 Bird Merch —  Get yourself some bird shirts!~~~In this episode—which is number 130—Ivan Phillipsen explores the fascinating phenomenon of vagrancy... those surprising moments when birds appear far outside their normal range.Learn about the forces that send birds off course, including navigation errors, weather, social behavior, and more. The episode goes beyond the mystery of lost birds to ask a deeper question: are these wayward journeys simply mistakes, or can they shape the future of species?Along the way, the episode reveals how vagrancy connects to migration, ecology, and evolution in ways that are more important than they might first appear.Link to this episode on the Science of Birds websiteBirding Tours with Wild LatitudesCheck out our line-up of awesome tours in 2027! Support the show

You may or may not know this, but I'm the co-owner of a birding and nature tour company called Wild Latitudes, based here in Portland, Oregon, where I live. My business partner and I have been leading tours around the world for about 10 years now. Honestly, a lot of what I talk about on this podcast comes from my own experiences in the field, seeing birds in their habitats, traveling to amazing places, and guiding people through some of the most interesting natural environments on Earth. Well, we've just announced our 2027 lineup of tours, and I wanted to let you know about it here because if you've ever thought about doing a birding trip or traveling with me, or just with a

wonderful birding guide in general, this might be a great time to take a look. Our approach at Wild Latitudes is a little different from the super intense, hardcore birding trip. Now, we absolutely love birds, of course, but we also care deeply about the whole natural world. The landscapes, the plants, the mammals, the reptiles, the geology, and the cultural side of travel, too. We like to move at a comfortable pace and see as much as we can and really enjoy the experience to savor it. So the goal is not to just rack up species and cover as much ground as possible. Instead, we want you to have a genuinely fun and memorable time on the tour.

And I should mention that our 2026 tours are sold out. So if this is the kind of experience that sounds super groovy to you, I'd encourage you to check out the new 2027 trips sooner rather than later. I just want to highlight a couple trips in the 27 lineup. We have a tour to India, led by my friend and business partner Steve Robertson, who has run this trip at least five times, and he absolutely loves it. Our India tour offers an amazing mix of birds, wildlife, and culture, with chances to see amazing things like multiple hornbill species and countless other special birds,

Indian rhinos, Bengal tiger, leopards, and of course, the Taj Mahal. We're also heading to Baja, California, Mexico at the southern tip of the Baja Peninsula. This is one of my favorite places in the world. It's this incredible meeting of desert and ocean with fascinating birds, beautiful desert plants, marine life, and some spectacular whale watching opportunities. with possibilities including dolphins, gray whales, sperm whales, and even the world's largest animal to ever have lived, the blue whale. So if any of this sounds like your kind of adventure,

head over to Wild Latitudes. The website is wildlatitudes.com and take a look at the new tours. Maybe you can join me out there somewhere in the world. All right, let's get on with the show. The red flanked blue tail is a small passerine bird in the old world flycatcher family muscacapady. Adult males in this species are nice looking birds with blue upper parts and a blue tail and a white throat and white eyebrow or supercilium and reddish orange sides. So, you know, like the name says, red flanked blue tail. For those of us in North America,

we might see a red flanked blue tail and think it looks a bit like a western or eastern bluebird. This species has a large breeding range, not in North America, but in northern Eurasia, extending from Finland to the far east of Russia. In winter, red-flanked blue tails normally migrate south to places like southern Japan, South Korea, Southern China, and Southeast Asia. They don't normally migrate to the state of Virginia in the United States. And yet, on January 1st, 2020, A red-flanked blue tail showed up at Great Falls Park in Virginia,

about a 40-minute drive northwest of Washington, D.C. This is not normal. In fact, I think this is only the second time ever that this bird species has been found east of the Rocky Mountains in the U.S. For many American birders, such a rare event is worth dropping everything you had planned for the day and tearing off on a frantic search for the bird. Leave your work unfinished on your desk and risk getting fired.

Let your kids find their own way home from school and let your dog destroy the furniture in frustration because it didn't get to go for its daily walk. I mean, who cares about all of that when you have a chance to add a mega rarity like the red-flanked blue tail to your life list? This particular individual bird in Virginia has been hanging around and causing

a stir among birders for a couple months now. It appears to be a female or maybe a first winter male, so it's not as brightly colored as an adult male, as I described a moment ago. This is just one example of a bird showing up far beyond where we would expect to find it. Ornithologists call such an individual a vagrant. The appearance of a rare vagrant can make the news in the U.S. or in Canada, the UK, and many places around the world. Another recent-ish example of a famous vagrant in the U.S. was the individual Stellar's sea eagle that wandered across North America, turning up from Alaska to Texas to eastern Canada and New England.

This rare, massive raptor is normally found only in the far east of Asia. And then there was that yellow-billed loon that showed up in the fountain at the Bellagio Hotel, in Las Vegas. This species breeds in the high Arctic in North America and Eurasia. If you live in Europe, you probably know this species, Gavia Adamzii, as the white-billed diver. In any case, yellow-billed loons normally spend the winter off the coast of Alaska, British Columbia, or Scandinavia. This one, however, was chilling in an artificial pond in the middle of the Nevada desert, being gawked at, or more likely ignored by thousands of drunk humans staggering up and down the Las Vegas strip. This sort of thing happens every year on every continent.

It's the stuff that Twitchers live for. You know, twitchers, passionate birders who go out of their way to see, or as we say, to chase rare birds that someone else has reported. A Twitcher might rush off to find a vagrant in their own town, or the next county over, or even on the other side of the country. Such is their fervor. Now, it's one thing to give you examples or describe instances of vagrancy around the world.

I could do that all day long, because yes, vagrancy happens. But as a listener of this podcast, I assume you want to dig deeper. You want to know why. What are the causes of vagrancy? Is it just random and meaningless? or does vagrancy play an important role in the biology of birds?

Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted exploration of bird biology for lifelong learners. And hey, it's great to have you here with me today, whether you're a longtime listener or this is your very first Science of Birds episode. whether you're a hardcore birder or you just love nature and you want to learn more about birds. This is episode number 130 and it's all about the phenomenon of vagrancy in birds.

In simple terms, vagrancy in birds is the rare event where an individual appears way outside the normal geographic range of its species or of its particular population. When we say normal range, we're talking about the usual breeding areas for the species. that species, as well as its wintering grounds and migratory pathways. You might have heard people saying that a vagrant bird was simply blown off course by the wind or by a big storm. And yeah, sure, such weather events can be the cause of vagrancy, but in many cases there are other forces at work. Another overly simplistic idea about vagrancy that you might have heard is that it's a biological dead end. And by that I mean vagrancy doesn't have any important effects on a population or on a species. Like when a lone bird gets lost and ends up in a weird place, it usually just stays lost,

lives for however long, without ever finding a mate, and then it dies, usually sooner rather than later. So in that scenario, the population that bird came from isn't affected, nor is the species overall. So you could say that in such cases, vagrancy is an evolutionary dead end. The vagrant bird doesn't contribute any genes to future generations of its species. It's doomed to die alone and childless. And I can sympathize because I too am an evolutionary dead end. I don't have kids and don't plan to have any. So future generations of my species will neither benefit from my genes, nor be burdened by them. But again, even though dying young, alone, and childless might often be the case for vagrants,

it's not always what happens. Vagrancy can sometimes play out differently and have enormously important consequences for the ecology and evolution of birds. Okay, but before we jump into all of that, before we go into the deep end on this topic, I want to say that this podcast episode is sort of a part-to-one, Part 1 was the episode I did on Avian Navigation. That was episode 128, published not that long ago. So I'm not going to go into a whole lot of detail about the ways that birds navigate.

I strongly recommend you go back and listen to the Avian Navigation episode first before listening to this one, or listen to it again, maybe, as a review. Also, a lot of what I'm talking about today can be found in the book, Vagrancy in Birds by Lees and Gilroy published in 2022. So if you want to go much deeper into this topic, I recommend checking out Vagrancy and Birds by Lees and Gilroy. Okay, let's go ahead and get into it. Now, I know I just said to go listen to episode 128 about avian navigation,

but I can't help myself. So let's go ahead and do a mini review of that topic here to lay the foundation for our conversation about vagrancy. When it comes to finding their way over long distances, birds are sort of like Liam Neeson. They have a particular set of skills. They have a toolkit of adaptations for orientation and navigation. Remember that there's a difference between orientation, which is knowing where you are and which way you're facing right now, and navigation, which is actually getting from point A to point B. Ornithologists have proposed a mass.

map and compass model to help us understand how all of this works in birds. On the compass side of things, birds can, first of all, use the sun. They can use the sun as long as they can compensate for its hourly movement with their internal sense of time, their internal clock. Birds also have compasses based on the stars, polarized light, and the Earth's magnetic field. So that's four different internal compasses. right? Sun, stars, polarized light, and magnetic fields. The magnetic compass might actually be the default compass for most birds, since it works in most conditions. For example, when it's

cloudy and birds aren't really able to navigate by the sun or stars, they can probably still navigate using the Earth's magnetic field. As for the map in the map and compass model, a bird's sense of where it actually is in the world, well, that's a bit more mysterious. Scientists suspect that birds build mental maps of their world using visual landmarks, patterns of magnetic intensity sensed through their beaks, as well as possibly smells and low-frequency sounds.

Juvenile birds of many species get a head start because they inherit a navigation program from their parents. They're born with a clock and compass instinct, a genetically programmed set of instructions for the direction and duration that should get them to the right place on their very first migration. They do this with no adult supervision whatsoever. Over time, a bird's life experience gets layered on top of its instincts, and it builds an increasingly richer, more detailed mental map. It learns to recognize waypoints, like the magnetic signatures or visual structures of landscape features. Now, even though birds have this amazing toolkit of senses, instincts, and life experience, and they're capable of absolutely astounding feats of long-distance navigation,

some of them still mess up. Some birds end up in a place far from where they thought they were going. Just as a bird can use more than one approach to navigation, navigation, there's more than one way it can get off course, to end up as a stranger in a strange land. You might expect that most vagrants are very young birds who fly around sort of willy-nilly, randomly and more or less aimlessly on their first long-distance migratory journeys. They goof up and get lost because they're silly, naive youngsters. And sure, that probably happens sometimes, and it is true that many vagrants are first-year birds.

However, many long-distance vagrancy events follow more distinct patterns. For example, certain species are more likely to produce vagrants, and those vagrants are more likely to show up in specific areas at particular times of year. And all of that suggests that the underlying causes are not generally random. The causes of vagrancy we'll talk about today include compass errors, getting blown off course by the wind or thrown off by extreme weather, overshooting, and social behaviors. I'll talk about each of these in more detail. And we can categorize any given factor or force that leads to vagrancy as being either external or internal. external forces are things from the outside world that act on a bird, causing it to go astray,

even when its own navigation tools are working just fine. Internal forces are things that sort of short-circuit a bird's biology, functions in the brain like its senses or its instincts, and then these are what lead the bird off course. One of the most important causes of vagrancy appears to be compass errors. something malfunctions with one or more of a bird's internal compasses. So that means we're talking about an internal force or cause of vagrancy. Scientific studies tell us that most compass errors seem to happen in young birds, because in many species, birds in their first year of life have to rely entirely on their genetically

inherited programming to successfully complete their first long-distance journeys. That genetic program is supposed to help the young bird navigate first by correctly identifying where north is. Then the program needs to tell the bird how to orient itself in the correct direction relative to north. So, in step one, the bird figures out where north is, using one or more of its internal compasses. and then in step two it turns to face a particular direction, 60 degrees to the west, for example. And that is the direction it heads for its first migration. Here's a little quote from the Vagrancy in Birds book. Quote, from the point of view of understanding vagrancy,

errors in any part of the inherited migratory program could result in first-year birds moving off in the wrong direction. end quote. So if something is wonky about the bird's genes or about the way its brain developed, it might mess up step one and or step two. Either way, it will probably end up as a vagrant. What seems to happen most of the time when there's a compass error is that a bird gets misoriented. It actually follows a consistent, coherent path, but the problem is that the direction or path is wrong. This misorientation is different from disorientation. With disorientation, the bird would just lose all sense of direction and fly around randomly.

One of the most common hypotheses that ornithologists offer to explain long-distance vagrancy is reverse migration. This happens when a bird mistakes north for south, or vice versa, resulting. in a 180-degree orientation flip. For example, songbirds that breed in the forests of Siberia should fly southeast to Asia, at least certain species. But a compass error may send the bird flying off to the northwest instead, bringing it directly to Western Europe or wherever.

The bird went in the exact opposite direction along the north-south axis. Reverse migration is most common among juvenile birds on their first migrations in autumn. So that's as they head out from where they were born in the breeding season, with the correct goal being their non-breeding site. And again, this kind of compass error might be the result of a genetic mutation or of a developmental problem in the brain. But in some situations, a bird can get confused even if its compass is working well, near the occasional. equator, for example. Earth's magnetic field is, as we've discussed, very important for birds. But as a bird gets close to the equator, approaching from the north or south, it gets harder to tell north from south. The magnetic field only indicates which way is toward or away from the poles,

not specifically which way is north or south. So a bird flying near the equator might get mixed up and think it's flying south when in fact it's gotten turned around and it's flying north. An interesting prediction of the reverse migration hypothesis is that for any given population of breeding birds, there should be a so-called reverse migration shadow. This is the geographic area where we would expect vagrants from that particular source population to end up if they erroneously switch north and south. because we know where birds in that population normally spend the winter, for example, so we can look at a map and calculate where reverse migration vagrants should end up,

180 degrees in the other direction. For example, in the new world, the yellow-green virio breeds in Mexico and Central America. It normally migrates south to South America in winter. However, vagrant yellow-green virios are recorded. every year in California during fall migration. The distance these vagrant birds traveled north to get to California is similar to their normal migratory distance, but with 180 degrees shift in orientation. They end up smack dab in their reverse migration shadow.

Okay, so that is reverse migration. That's one kind of misorientation. Mixing up north and south is just one. kind of misorientation. But what about mixing up east and west? This could happen when a bird correctly identifies north, but then when it orients itself relative to north, it does the old switcheroo and swaps east and west,

left and right. This type of compass error is called mirror image misorientation. And speaking as a left-handed human, I feel like I suffer from mirror image misorientation. I routinely confuse my left from right. Like I'll be riding in the passenger seat of my friend's car, helping him navigate as we drive around at night. We're out late, we're hungry, we're heading to Taco Bell to do some fourth meal. And anyway, I tell my friend to turn left at the street up ahead. He starts to make the turn, and I start yelling, no, no, the other way, stabbing my

finger aggressively to the right. He says, dude, you said left, so I turned left. And now we're in a big argument, and we end up eating our burritos that night while sitting in ill-tempered silence. My mirror-image misorientation has lost me more than one friendship over the years. So a bird that makes this kind of wrong-turn error might intend to migrate southeast, but instead it flies southwest. The black pole warbler in North America is a classic example of mirror image misorientation. These birds normally breed in the boreal forests of Alaska and Canada and are programmed to head southeast toward the Atlantic Coast before jumping off for a long flight to South America.

However, some individuals catch a case of mirror image switcherooze and they head southwest instead. This is why individual blackpole warblers, a species we think of as an eastern warbler, show up so regularly as vagrants along the California coast. Back in the 1970s, researcher David DeSante actually scooped up some of these vagrants in California and put them in orientation cages.

This cage is a scientific contraption in the lab, and it's used to figure out which direction a bird has a strong instinct to travel in. DeSante confirmed that the internal compasses of those vagrant blackpole warblers in California were pointing them in a mirror image direction relative to where they were supposed to go. Just like there is the phenomenon of reverse migration shadows, ornithologists have been able to identify the shadows of mirror image misorientation.

For a given species, the mirror image misorientation shadow is the geographic region we would expect vagrants of that species to end up if the crossed wires in their little brains cause them to head east when they should head west, or vice versa. Okay, so we have reverse migration, and we have mirror image misorientation. These can explain a lot of vagrancy cases, but not all of them. One thing we need to keep in mind is, if the root of these programming errors is genetic or developmental, we should expect to find lots of variation.

If genes are responsible, there can be different combinations of genes, genes or mutations that lead to migratory behaviors that don't fit nicely into our models of reverse migration or mirror image misorientation. Mutations, or the unique developmental history of a young bird, can send it flying off in some crazy direction, something other than simply confusing north and south or east and west. So the internal compass of a bird can get messed up by internal forces like genetic mutations or gene expression errors or problems that occur in a bird's early development. But the compass can also go on the fritz because of external forces. This is particularly true for the magnetic compass. Out there in the world, there are these magnetic anomalies. One type of magnetic

anomaly is a natural irregularity in the Earth's magnetic field found in a specific geographic location. The underlying cause, literally, is the magnetic properties of rocks in the Earth's crust beneath that location. We're talking about things like large bodies of igneous rock buried beneath the surface or a big mass of iron-rich magma, things like that. The idea is that the planet's global magnetic field interacts with these magnetized materials in the crust, and they distort the field in that local area. Anomalies like this are found in places like Siberia, Sweden, New England, Central Africa, and many other places. In addition to these permanent local features, there can be temporary disturbances in the force. The classic example being the destruction of

Alderon by the first Death Star. But, of a Of course, that happened long ago in a galaxy far, far away. Much closer to home, there are things called geomagnetic storms. These are sudden disturbances in the Earth's magnetic field, typically caused by the sun getting all frisky and hyperactive. Solar flares or solar winds blasting outward from the sun can temporarily mess up the Earth's magnetic field. So magnetic anomalies, of one kind or another,

other can throw off a migrating bird's magnetic compass, at least temporarily. But that might be long enough to lead to vagrancy. Also, birds that are born and raised in areas with significant magnetic anomalies may have their navigation systems incorrectly calibrated from the get-go, leading them to set out in abnormal directions. This is the basis of the magnetic calibration hypothesis. It suggests that young birds use the local magnetic field around the place they hatched out of an egg as sort of a referenced point to prime their internal compass.

If this initial calibration is skewed by a local anomaly, it can permanently affect a bird's navigation ability, causing it to set out in an abnormal direction. And that can happen even if the rest of the bird's migratory programming is working just fine. There's another thing, which I guess we can call an external force, that can, at least hypothetically, screw up a bird's internal compasses. Some ornithologists have offered the hypothesis that tiny brain parasites found in many birds may be a reason some individuals get confused and end up as vagrants. These parasites create small, solid lumps inside the bird's brain that can grow to about one millimeter. Now that might sound tiny, but one millimeter is actually quite large for a foreign object growing in the brain of a bird.

These parasitic lumps can physically damage the brain or block the flow of blood in the brain. And that might mess with a bird's internal compass, causing it to fly in a very specific but completely wrong direction during migration. Because some bird species are infected by these brain parasites more than others, this hypothesis could explain why certain. species get lost more often. While being led off course by a parasite would usually be a dead end for the individual bird because it often dies or fails to find a mate, this relationship could still have major ecological effects. From the parasites' perspective, this could be a dispersal strategy to hitch a ride to new areas and infect new groups of birds. And this might explain why some parasite types are spread across multiple continents,

even when the birds that they infect usually do not travel that far. So infected vagrant birds act sort of like shuttles or airliners for brain parasites, linking different environments together. If there's any truth to this hypothesis, a possible upshot for the birds is that by hijacking the brain, parasites might inadvertently allow bird poppocket, to expand into new territories. In the rare cases, that is, where the birds manage to survive and breed in their new location. What are some other things from the external environment

that could lead a bird into being a vagrant? Weather and wind play significant roles in causing vagrancy. This is probably what most of us intuitively think of as the cause of a bird getting off course, like literally being blown off course by the wind. Maybe the most important way this happens is through wind drift, where strong winds physically push migrating birds off their intended flight paths. While birds flying over land can often hunker down and wait for better weather, the ones that are crossing large bodies of water like the ocean may have no choice but to fly with the wind. And that can lead to some serious disdemeanor. displacement. Large-scale weather systems like hurricanes or typhoons also contribute to vagrancy.

For instance, anticyclones, which are large areas of high pressure, can create persistent winds that sweep birds away from where they're supposed to be. And in the North Atlantic, birds moving along the coast are often caught in cold fronts and cyclones, or low-pressure systems which can drift them rapidly across the ocean toward distant continents. As an example, there was the situation with Hurricane Edalia back in August of 2023. In the wake of this powerful storm, birders were delighted to find vagrant American flamingos scattered all across the eastern U.S., not just in Florida where the storm hit, but across at least eight states. There were flamingos as far north as Pennsylvania, Ohio, and Wisconsin.

Which is kind of crazy because the normal range of the American flamingo, is basically the Caribbean, like Cuba and the island of Hispaniola, as well as some small areas in Mexico and the coast of South America. In other words, Ohio ain't got no flamingos, bro. Not on the regular anyway. I mean, if it did, we could call it Flamingo Ohio, right? Anyone? Flamingo, Ohio?

Anyway, another related term is overshooting. Overshooting, which typically happens during spring migration when strong tailwinds carry birds way further north than their intended breeding grounds. Overshooting is frequently observed in adult birds, particularly inexperienced younger adults or unmated males. For example, birds like the Alpine Swift and Eurasian Hupu often appear in northwest Europe in the spring because warm southerly winds pushed them to overshoot their normal breeding areas in the Mediterranean region. Many birds that get pushed too far by tailwinds end up seeking refuge in vagrant traps. So there's another term for us, vagrant trap.

This is an isolated patch of good habitat, like a coastal island, an oasis in the desert, or apparently a big fancy fountain on the Las Vegas strip. Vagrant traps like these concentrate exhausted birds from the surrounding area. Some individuals that overshoot may have insisted. instead experienced an internal error where they simply failed to turn off their migratory instinct when they reached their usual breeding grounds. And another possibility is that birds that can't find a mate or any high-quality territory may continue moving along their original trajectory in an attempt to find better breeding opportunities further afield, sometimes much further. Yet another

external force that might cause vagrancy in birds is the event. availability, or the lack thereof, of food. If food is scarce in a particular season, this can push certain bird species beyond the bounds of their normal ranges, as they look for greener pastures, so to speak. This is the case for eruptive species. These are birds like finches and owls from boreal regions that occasionally move en masse far to the south in search of food. The arrival of such birds in unusual places is called an eruption, spelled I-R-R-R-U-P-T-I-O-N. This happens with birds like snowy owls, northern hawk owls, pine ciskins, pine gross beaks, and so on. Individuals in such species will move much further south than they normally do when their food

resources at home are in short supply in a given season. So they can end up as vagrants. And this can happen for desert-dwelling birds as well. They end up in unexpected places in years when food in the desert is scarce. And finally, I should mention one more external force that sometimes leads to vagrancy. This one is anthropogenic, meaning it has to do with humans. Birds can get ship assistance if they become physically exhausted by high winds over the ocean and they end up landing on a vessel to get some rest. The ship might then carry the little stowaway to a new destination. In September 1988, for example, there was a white-crowned sparrow that landed on the Queen Elizabeth 2, the QE2, as the ship was heading out from New York. The little sparrow stayed on the ship

for five days, crossing the entire Atlantic, and I imagine it idled away the time by playing the slot machines and hanging out in the nightclub. Then, when the QE2 arrived at the port in Southampton in the UK, the bird took off and went ashore, going down in the history books as a vagrant. So far, we've been talking primarily about migratory bird species. We've considered ways in which an individual migrant can end up as a vagrant. Through some internal compass error, the effects of magnetic anomalies, pesky brain parasites, wind and storms, or escape, scarcity of food. But many, if not most, birds do not make their long migratory journeys alone.

They tend to fly with other birds. They migrate in flocks with members of their own species, perhaps with their own parents or other close relatives. What's cool about flocking behavior during migration is that it might be a great way to mitigate, to correct for any compass errors that afflict individual birds. Even if your brain is full of parasites or you were born with your innate compass wires crossed, you might still be okay if you just stick with your flockmates. Maybe don't trust your own navigational programming

if it's telling you to go the opposite direction from the 100 other birds in your flock. Trust your buddies instead and just follow them. So migrating in a flock or family group might allow for navigational error checking. The birds crowdsource their plan for their roots. A flock may act sort of like a self-correcting hive mind. But there's a potential twist here,

because some species do not have any innate programming. Their migratory roots are not strictly hardwired by instinct. These are species that ornithologists call obligate social navigators. Young birds in these species have to learn their specific paths by following more experienced members of their flock. This is the case for a lot of waterfowl, birds like geese, but also cranes. Because these birds typically travel in family groups, it's generally rare for juveniles to become lost or appear as vagrants, because they're guided by adults who already know the way. This is lovely when it all works and everything is going smoothly.

However, a social context for vagrancy can emerge when an individual becomes separated from its own kind, and it finds itself alone and away from its familiar surroundings and companions. Because these birds are still strongly attracted to being part of a group, a solitary individual might choose to hook up with a flock of an entirely different species. This process is known as group entrainment. Not group entertainment, like going to the movies or something, but group entrainment. The Lost Bird follows the new flock to a destination that is normal for that group, but way outside its own species regular range.

An example of this social learning, this group entrainment, leading to vagrancy, is when a rare barnacle goose is found in the northeastern U.S. or eastern Canada. This usually occurs because the vagrant bird had goofed up and joined a flock of migrating Canada geese. The barnacle goose was entrained to follow the Canada geese to their wintering grounds. This is sort of like that one time when I was seven years old and I was at Disneyland with my parents. I got separated from them and then I was wandering around with my giant Mickey Mouse-shaped lollipop. I eventually found a nice Korean couple that reminded me of my mom and dead. Well, close enough anyway. So I got all entrained and just tagged along with them. In fact, I followed

them all the way home. And let me tell you, I was quite the celebrity in South Korea. Because that place is way outside of my normal range. So I was basically a vagrant there. No, not a true story. But what if? Stranger things have happened, I'm sure. Let's shift gears to talk about the consequences of vagrancy in birds. Hopefully you now have a better understanding of how these events happen, the underlying causes. A bird gets off course and becomes a vagrant, ravenous birders converge from far and wide to gawk at it,

and then the birders pack up and go home. But then what? What happens to the poor, lonely vagrant bird once the paparazzi has left it alone? Well, sadly, it is true that many a vagrant is doomed to die. often sooner rather than later. Because that bird likely finds itself in an environment that it's not well adapted for. Even if it finds enough food and shelter to live for a few months, it may succumb when the season turns and conditions get worse. And since many vagrants represent the only

member of their species for hundreds, if not thousands of miles, in every direction, there's no hope of finding a mate and raising a family in this new strange land. I mean, think of that stellar sea eagle in North America. After its wanderings through the U.S., it was seen repeatedly in eastern Canada, including through 2024 and early 2025. As far as I know, it appears that this eagle has settled in, at least loosely, in that region. And it's great to think that it may still be alive and doing okay, but it probably isn't going to find a mate, no matter how long it lives. Let's look at all of this through the lenses of ecology and evolution. Individual vagrancy events like what happened with the stellar sea eagle can be considered

non-adaptive and not part of the species' normal behavior. When vagrants die without returning home or reproducing, they really do seem to be evolutionary dead ends. They aren't going to contribute anything to the gene pool of their home population or their species. But what about those rare occasions where either, A, a vagrant does make its way back home, or B, a vagrant isn't alone in its newfound territory, if there are some other members of its species to breed with? In such cases, vagrants can act as pioneers or vanguards that discover and colonize newly evasive. or ecologically suitable habitats. The ones that survive can be the founders of new populations far beyond their species' ancestral range. For example, the northward expansion of tropical

kingbirds into North America has been happening in conjunction with multiple instances of long-distance vagrancy. These birds have shown up as far north as British Columbia, Eastern Canada, and New England. Those vagrant tropical kingbirds ended up in places that, last time I checked, are decidedly untropical. But the tendency of these kingbirds to fly beyond the normal bounds of the species range might be what's helping the species expand northward. Vagrancy can also lead to the discovery of new viable migration strategies. If a vagrant bird survives its journey, then returns home to its breeding grounds and then successfully reproduces, it may transmit info about this new migratory route to its offspring,

either genetically or through cultural learning. Exploratory behavior or wandering is somewhat common in seabirds. It allows individuals to identify and potentially colonize new breeding sites or new foraging areas. So a tendency to become vagrants is just sort of hardwired into them because they naturally wander. Even though vagrancy is more common in migratory species and in wanderers like seabirds, species that we think of as sedentary can still end up producing some vagrants. Remember that a sedentary species is one that does not migrate long distances. It stays put more or less in the same geographic area year-round.

Some ornithologists think there might be an evolutionary advantage for a species that produces at least some vagrants every year, because again, vagrants might act as pioneers that discover new habitats. And if they do, they can potentially increase the long-term prospects for their species. So that might explain why we see vagrants even in sedentary species, because there's an evolutionary advantage to having a few crazy, adventurers in your population, even if the rest of you play it safe and just stick close to home. This brings us to the idea of pseudo-vagrancy. The term describes small but viable populations that perform regular annual migrations to wintering grounds far from where their species usually

goes. Unlike a lost individual, a pseudo-vagrant follows a novel and idiosyncratic migratum. strategy. It returns to the same non-breeding spot year after year and has strong migratory connectivity, proving that it's following a specific route rather than just being lost. A classic example of this is Richards Pippet. This species breeds in northeastern Asia, as in Siberia. It normally spends the winter in southern and southeast Asia. But for decades, Richard's Pippets have been showing up during the winter in Europe, Western Europe. They were treated with all the usual fanfare of being vagrants. People thought they were just Siberian birds that had lost their way. And maybe at first they were. However, tracking data from recent research on Richard's Pippets in Europe

has confirmed them as pseudo-vagance, representing a viable population that has successfully established a new westward migration route between Siberia and Western Europe. So this has enormous ecological and evolutionary implications. Pseudo-vagrants are not dead ends. They're individuals that have successfully survived and returned to their breeding grounds to pass their new migration route onto their offspring, either genetically or through social learning. The first Richards Pippets that showed up in Europe really were vagrants, but they helped establish a new wintering area, and they paved the way for the pseudo-vagrants we see there today. So we've been watching this ecological, evolutionary change

happen in real time over several decades. At some point, I imagine, we'll just stop calling Richard Pippets in Europe pseudo-vagrants. We'll all just accept the fact that it's normal for this species to spend the winter there. The last major consequence I want to talk about is long-term evolutionary change, including the development of new species. Think about all the little islands out there, scattered across the world's oceans. Many of them are incredibly isolated and have never been connected to the mainland. They emerged from the boiling sea as barren, lifeless volcanoes,

or perhaps a bit more gradually if they were coral atolls. And yet, today, many of those isolated islands have birds flapping around all over them. What gives? Well, we can probably thank the phenomenon of vagrancy. Long ago, like millions of years ago, a small flock of birds got way off course and was lucky enough to find salvation on an oceanic island. The flock survived, reproduced, and generations of their offspring adapted and evolved. They became new species. They may have even radiated and diversified into multiple new species.

Take the Hawaiian honey creepers as a great example. This group of finches is thought to have originated from a single ancestral Eurasian species closely related to the rose finches and the family fringility. There was probably just one flock that landed on the Hawaiian Islands as vagrants five to seven million years ago. This small founding population diversified through adaptive radiation into as many as 60 species, with wildly different plumages, specialized bills, and distinct feeding strategies.

Vagrancy is one of those wonderful reminders that nature, is not tidy. Birds don't always follow the nice little arrows you see on maps in a field guide or app, the migratory pathways. Birds don't always stay within the boundaries we assign to specific ranges. Sometimes a bird ends up impossibly far from where it should be, and from our perspective, that can look like a mistake. Sometimes, perhaps even most of the time, it is a mistake, a tragic one even. But a big take-home message here today is that vagrancy isn't always a bad thing. Sometimes it's a result of exploration. Sometimes it's the raw material of biological change.

A wrong turn for one bird can, under the right circumstances, become the first step in a range expansion or the blazing of a new migration route. Vagrancy can even establish a new population, or in the grand sweep of time lead to the evolution. of an entire new lineage like the amazing Hawaiian honey creepers. Vagrants are rare and exciting for us birders. They get us scrambling across county and state lines with our binoculars and spotting scopes in the desperate hope of getting a glimpse. And adding a rare species to our list is thrilling for sure. But we should keep in mind that vagrancy reveals something deeper about

the living world. It shows us. us that evolution isn't just about stability, but also about chance, risk, and experimentation. So the next time you hear about a vagrant loon paddling around in a casino fountain in Vegas, or a red-footed booby hanging out in East Sussex in the U.K., or a common cuckoo chilling in Watsonville, California, all real-world examples, remember, you may not just be hearing about a sad, lost bird. Such situations might represent a mechanism by which birds colonize islands, expand or shift their ranges, respond to changing environments, and reshape the avian tree of life. Well, that does it for this here episode, which is 130.

I hope it helped you expand your knowledge about vagrant birds. Maybe the next time you chase a bird when you go twitching across the countryside or what, whatever, maybe you can share some of what you learned with your fellow birders out there. In any case, I hope you enjoyed the episode. And I'll tell you what I enjoy, guacamole. But more importantly, I enjoy the wonderful members of my Patreon community. Thanks so much to all my patrons for the generous support. You keep me going, big time.

A special hello and welcome to the newest members on Patreon. Three Pentacles, S, Annie, or maybe Ani, like the bird, Nicholas Smith and Sister Oak. I really appreciate your support. Thank you, thank you. As always, if you are interested in joining the community and offering support, you can check out my Patreon page at patreon.com slash science of birds, and there is a support-the-show link in your show notes and your podcast app.

You can also shoot me an email if you have something you'd like to share with me. My address is Ivan at Scienceofbirds.com. I'm always happy to receive friendly comments that you might have about the podcast, or maybe you'd like to tell me your craziest story about chasing a mega rarity, or to tell me about the kinds of wacky antics you've been forced into by an infestation of brain parasites. 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, Scienceof Birds.com. And I've got a couple more websites for you. Don't forget to check out bird merch, which is my online store, and that is at birdmerch.com. And if you'd like to go on an amazing birding adventure, please check out Wild Latitudes. Wild Latitudes is my ecotour business, and that is over at wildlatitudes.com.

I'm Ivan Philipson and true fact about me, one of the things I've been thinking a lot about in the last year or so is the mind-boggling, awe-inspiring scale of the universe. I mean, just in my lifetime in the last 50 years, scientists have greatly expanded our understanding of how old the universe is, as well as how big it is, at least the part we can observe, and how many galaxies are packed into it. A leading estimate now for the number of galaxies in the observable universe is around

two trillion galaxies. Two trillion! And what's even crazier is that each of those galaxies has hundreds of billions of stars in it, and each of those stars is probably orbited by at least a few planets. The scale of all this is way beyond human comprehension. And that, to me, is a wonderful, beautiful thing. thing. And with that, I wish you a lovely day and a lovely week ahead. Peace.