The Science of Birds - The Osprey

Episode Date: April 7, 2025

In this episode—which is Number 114—host Ivan Phillipsen dives into the world of the Osprey (Pandion haliaetus)—a bird that’s all about fish. With a global distribution and a singular place in the avian family tree, the Osprey is both biologically unique and instantly recognizable. Ivan explores this raptor’s physical traits, from its distinctive wing shape to its powerful, semi-zygodactyl feet designed for grabbing slippery prey.Listeners will also learn about the Osprey’s evolutionary history, its cosmopolitan range, and the adaptations that allow it to thrive on a diet of pretty much just fish. The episode touches on the Osprey’s conservation story—one of dramatic decline and hopeful recovery—underscoring how this bird serves as a vital indicator of aquatic ecosystem health.Whether you’ve seen an Osprey hover over a lake or are just discovering this raptor for the first time, this episode offers a deep, fascinating look at one of the most iconic birds on the planet.Links of InterestOsprey in Scotland diving in slow-motion [VIDEO]Bald Eagle steals fish from Osprey [VIDEO]~~ Leave me a review using Podchaser ~~Link to this episode on the Science of Birds website Support 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 exploration of bird biology for lifelong learners. This episode, which is number 114, is all about the Osprey. This bird's scientific name is Pandian Halliitis. It's a distinct handsome raptor and it's found across most of the world and it has many fans among bird lovers. If I had to pick just one word to associate with the Osprey, that word would be fish. This bird is

all about catching and eating fish. It's not surprising then that some other common names in English for this species include fish hawk, fishing hawk, and river hawk. But I say, why stop there? How about aqua hawk or river raptor, stream eagle or H2O spray? H2 Osprey. I don't know. Yeah, and just where did the name Osprey come from anyway? Well, stick around and we'll answer that in a little bit. Something I had to double check when I sat down to create this episode was the correct word to describe more than one osprey. In other words, what's the plural form of osprey? The answer is ospreys. So just like one might say, look at all those chickens.

We should say, look at all those ospreys. But part of my dumb little brain wants me to say, look at all those ospreys. Maybe because it seems to have the word prey tucked in there, and prey is the same in both singular and plural form. And with birds, some of them have names like grouse, scop, and quail, which can work both ways. So, yeah, in case you didn't know, the plural of osprey is ospreys. These birds are revered in both folklore and modern culture. For example, there's the Boeing V-22 Osprey. an American military aircraft that looks like what would happen if a helicopter and an airplane

made a baby together. And then there's the company Osprey that makes backpacks and travel gear. We name sports teams after Ospreys. There's a book publishing company in the UK called Osprey, and so on. I suspect that a lot of you listening right now think that Ospreys, the birds, are really cool. And I agree. This is one of my favorite raptors, and I'm excited to finally be making this episode. First, we'll cover the physical traits of ospreys, their appearance and their sounds. Next, we'll dig into the species geographic distribution, habitats, migration patterns, and evolution. And of course, we'll take a look at what these birds eat and how they breed. Okay, we have a lot to talk about, so let's get into it.

The Osprey is such a widespread bird around the world, I'm betting that you already know what one looks like. But in the spirit of being thorough, let's go ahead and consider the body structure of the species. The basic shape is similar to that of a large hawk or an eagle. The Osprey is not technically a hawk or an eagle, and we'll get into why that is soon, but it's close enough if you're trying to picture what this bird looks like. Osprey wingspans range from 59 to 71 inches, or 150 to 180 centimeters. This bird is a bit larger than a red-tailed hawk, but significantly smaller than a bald eagle. Females are larger than males, which is typical in raptors.

Adult female Osprey can be up to 25% heavier than males. And as raptors go, the osprey has a kind of small head, and it has a medium-length tail, although some have described it as short, but I also saw some describing it as long, so let's compromise and call it medium. And these birds have exceptionally long wings. I think we all agree on that. The silhouette made by the wings has a different shape when an Osprey sores and when it glides. Soaring and gliding are similar but different modes of flight. Remember that when a bird is soaring, it stays in the air without flapping and without losing altitude. and sometimes even gaining height, like when the bird is riding a thermal or an updraft of wind.

Gliding, on the other hand, is more of a controlled fall. The bird is slowly losing altitude, but in a smooth forward motion. Anyway, when an osprey is soaring, its wings look really long and elegant. It can look like a large gull, especially when seen head on, because the wings are held in an uplifted bow posture, sort of like the drawing of a bird that a five-year-old kid might make, like a shallow letter M. But when an osprey glides, the wings take on an even more distinctive shape. The wings are bent, with the wrist jutting far forward.

The primary feathers of the hand angle sharply backward of the carpal joint. So if you're looking straight up at a gliding osprey, or straight down on it, I suppose, you see that the bent wings create, again, the shape of the letter M. but even more dramatically. So if you see a gliding raptor, it's probably an osprey if it looks like a flying M. Not to be confused with a flying V, which is a model of futuristic-looking electric guitar introduced by the company Gibson in 1958.

Moving on to look at the bird's head. It's got a classic raptor profile with a strongly curved bill with a hook at the tip. In adults, the bill is typically dull blackish. with a bluish-gray sear. Remember that the sear, C-E, is the fleshy covering at the base of the upper mandible, the area around the nostrils. The large eyes of an osprey are a piercing yellow color in an adult bird, but youngsters in the first year of their life typically have orangeish red eyes. Looking at the opposite end of the body, we have the feet. The legs and feet are white.

but there's a lot more to say about the osprey's foot. This is a beautifully well-adapted fish-catching apparatus. First of all, wow, the talons on this bird are serious. They're black, slender, exceptionally long, and wickedly hooked. And the talons are also rounded when you look at them in cross-section. Other raptors typically have grooved talons. The large talons of an osprey are nearly uniform in the. size. In many other raptors, we see more variation in talon size among the toes. For example,

hawks and eagles in the family excipitrity have significantly larger talons on digits one and two compared to three and four. Digit one is the toe that faces backward, sort of like a thumb. Digit two is the forward-facing toe on the inside, closest to the bird's midline. You can think of digit two as sort of like your index finger. So ospreys have extra long, curvy talons, man, they're all more or less the same size, the talons, that is. But one of the ospreys superpowers is its ability to rotate the fourth toe, digit four backward. Normally, this toe faces forward and it's the one on the outward edge, like your pinky finger. The normal foot position for an osprey, like when it's perched on a tree branch, is to have three toes forward

and one toe facing backward. In birds, we call this toe arrangement an isodactyl. That's what you see on a typical songbird or a typical raptor. But remember that one of the alternative toe arrangements seen in some other birds is called zygadactyl. A zygadactyl foot has two toes facing forward and two facing backward. We see this with woodpeckers, owl, and cuckus. So when an osprey is diving, rocketing downward to catch a fish, it rotates digit four around so that it faces backwards. So a diving osprey has zygodactyl feet, temporarily two toes face forward and two face backward. We can say that the feet of this bird, therefore, are semi-zygadactyl. Among raptors, only owls share this special ability, of being able to

switch between anisadactyl and zygadactyl arrangements. We'll talk a little bit more about ospre feet when we get into how these birds hunt for fish. But let's move on now to look at the plumage color and pattern on the osprey. Adult ospreys have dark brown upper parts and mostly white underparts. The breast is white, often with brown speckling or a darker necklace, especially in females. The head is white with a dark stripe through the eye. And that black mask on an otherwise white head is a distinct and striking feature. Then, of course, the yellow eyes really pop because they're surrounded by black feathers. Under the wings, if you're looking up at an osprey, you'll see it has dark patches at the wrists.

Those are called carpal patches, and they really stand out. So they're a good field mark for this bird. Also, the flight feathers are barred when seen from below. males tend to be slimmer with less breast marking while females show more dark feathers on the chest and neck. Some regional differences exist in plumage. For example, Caribbean birds are whiter and North American ones are darker bodied with paler breasts compared to those in Europe. We'll talk some more about regional differences in a few minutes. Juvenile birds look a little bit different.

They have a buffy wash on the nape and breast. and the dark feathers on their backs are edged with white. So the feathers on the back of a juvenile osprey look sort of scaly. Now let's check out the sounds that ospreys make, their vocalizations. These are all simple whistling or screaming sounds. The pitch of these calls is usually a little lower in females. And that might be simply because a female has a larger body. Ornithologists have identified five basic call types for ospreys.

First, there's the alarm call. It's given when a potential predator is spotted at a distance. Young ospreys that are almost at the fledging age also give alarm calls in response to humans near the nest. This call, the alarm call, is a series of short, clear notes. Then we have the solicitation or food-begging call. Only the female makes this sound. You hear it a lot in Osprey breeding colonies. The food-begging call is triggered by the presence of the male near the nest,

and it reaches a fever pitch when the male is coming in carrying a fish in his talons. That's when the female is like, Oh, would you look at that? That is my man. My man's got a fish. Give me that fish, baby. give me that fish. Yeah, that's what she's like. But sometimes a female osprey makes the food begging call when her mate is just sitting there perched near the nest doing nothing. Ornithologists

suspect the female in this case might be signaling to her mate to get off his lazy butt and go fishing already. Next we have the guard call. This one is made by both sexes. It's a succession of slow whistled notes that fall rapidly in pitch. Some say it sounds like a whistling kettle taken rapidly off a stove. Ospreys make the guard call when there's an intruding osprey that gets too close to their nest within, let's say, 300 to 1,000 feet, or 0.1 to 0.3 kilometers. The defending ospreys on their home turf often show some behaviors at the same time they make the guard call. They might fly around, land on perches, or chase the intruder. If the guard call and these display behaviors don't spook the intruding osprey into leaving,

the home team gets even more ramped up and they bring out the big guns. They start using the excited call and the screaming call. These sounds have more of a wavering pitch. Now, I wish I had a perfect audio recording for each of the five calls to play for you, so that you can hear some examples. But unfortunately, I just couldn't track them all down. But I do have a nice recording made by my friend Bruce. In it, you're going to hear three individual ospreys recorded in Florida.

Two of them were flying around overhead, while the third one, the one that sounds the loudest, was perched in a large snag, a dead tree. Now it's time to talk about the family of the Osprey, as well as the origin of its common and scientific names. Remember when I said that the Osprey is not a hawk or eagle? Well, one of the really cool things about the Osprey, Pandyan-Haleides, is that this species belongs to its own family. It is not in the hawk and eagle family, exibatrity.

No, the Osprey family is Pandyonidy, and it has just one species. When a taxonomic family has just one species like this, we would say this is a monotypic family. monotypic meaning just one type right monotypic the family pandionity has just one species and therefore it has just one genus as well pandian remember the hierarchy of taxonomic levels it goes domain kingdom phylum class order family genus and species when one of these levels is monotypic it contains just one of whatever the next level down is in other words the next subordinate taxonomic level. So when we say monotypic family, that's supposed to mean that there's just one genus within that family, because genus is the next level below family.

So if we just imagine there were actually five bird species, all belonging to the genus Pandian, and Pandian was the only genus in the family Pandionidae, we should still say that this is a monotypic family because it has just one genus. But it seems that when birders talk about monotypic families, what they mean is a family with just one species. Of the approximately 250 bird families in the world, the number that fit this criterion is somewhere between 30 and 40. It depends on which bird taxonomy you're using. Well, of those 30 to 40 bird species that belong to a monotypic family, our friend Pandyan Halli Edis is quite possibly the most famous of all, the one recognized by the most people around the world. And the Osprey certainly has the largest geographic distribution.

Anyway, that was a bit of a tangent, but I hope it made sense. Now let's consider the names of the Osprey. Where did the English name Osprey come from? Well, this one has kind of a convoluted history. It starts with a guy named Pliny the Elder. Have you heard of him? Pliny was a Roman guy, his real full name being Gaius Plinius Secondus. Then he was an author, a naturalist, and a naval commander who lived in the first century C.E. He's best known for his massive encyclopedia called the Naturalis Historia. This set of 37 books attempted to catalog all known knowledge of the natural world at the time, at least from the Roman perspective. It covered everything from astronomy and geography to zoology, botany, mineralogy, medicine, and art. Pliny the Elder didn't always get things right,

however. He compiled a lot of his info from second or third-hand sources like travelers, soldiers, and earlier writers. So some tall tales made their way into the Naturalis Historia, like the idea that barnacle geese are born, not by hatching out of eggs, but by emerging out of barnacles, or even growing out of driftwood. Pliny also included some fantastical humanoid creatures in his books. For example, there are the Blemie, a race of people who don't have heads. Instead, their faces are in their chests. And I'm not joking, there really is a bunch of crazy stuff like that in these books. Well, Pliny wrote about birds in his naturalis Historia, too. One of them he named the

Osafrega. That translates as bone breaker, which is pretty hardcore. It seems the bird Pliny was referring to was the species we know today as the bearded vulture, or Lamergeyer. That old world vulture has a specialized diet. It breaks open the bones of dead animals to eat the marrow inside.

So it is a bone breaker. So here you've got a bird Pliny the elder is calling the Osafraga. Hundreds of years after Pliny's time, some French scholars in medieval times took the word Osapraga and they mistakenly thought it referred to the Osprey. They called it the Osferi. That word eventually made its way into the English language. First as Hossbre, then Osprey and Asprey. And finally, we ended up, of course, with Osprey. So the Os in Osprey originally comes from the Latin word for bone.

And the full name has its origin in a case of mistaken identity. Kind of silly, but it stuck, and here we are. Also, I think it's time to bring back the name Pliny. And if we did, we would always have to use it in the form of Pliny the somethinger. Pliny the elder, Pliny the uglier, Pliny the dumpster, Pliny the birder. The possibilities are endless. So, if you're pregnant and you haven't chosen a name for your baby, I'm just saying. Now, how about the scientific name, Pandian Halliades?

Pandian was the name of a couple different mythical Greek kings of the city Athens. Apparently, it was King Pandian the second they had in mind when they came up with the Osprey genus. That king had a child named Nysus, who was, for some reason, transformed in to a hawk. And that myth was the inspiration for the Osprey. But in that case, doesn't it seem like Nysus would have been a better name? But how about the second part, the specific epithet of the scientific name? Halleitis. This one is pretty straightforward. It comes from the Greek and it means sea eagle. Halleitis, spelled slightly differently, is also the genus name of some large actual eagles, including the white-tailed eagle, Stellars Sea Eagle, and the Bald Eagle.

Now, we've established that the Osprey isn't an eagle, and it isn't a hawk. But the avian family that's most closely related to the Osprey is indeed Excipitrity, the family of the Eagles and Hawks. This leads us a little. into the topic of evolution. Because the most recent common ancestor of the osprey, hawks, and eagles appears to have lived about 50 million years ago. 5-0. Paleontologists haven't discovered any fossils of that very ancient ancestor yet, but analysis of genetic data from living birds gives us that estimated divergence time of roughly 50 million years ago. That's when the

Osprey lineage split and went off on its own tangent of evolutionary history. Evidence from genetic data also points to the geographic origin of the Osprey, and that origin is somewhere in the Americas, most likely here in North America. From here, ospreys may have spread down the east coast of Asia before they colonized the Australasian region. That's hard to say Australasian region. Later, Ospreys radiated out from Indonesia and Oceania to settle in the rest of Asia and in Europe. Today, the species has four geographically distinct populations. One of them is widespread across the Americas. But there's a second distinct population in the Caribbean. A third is found across Europe and Asia, and the fourth population is restricted to Australia, New Guinea, and

some other islands in the southwestern Pacific Ocean. Genetic analyses suggest that these four groups have diverged from each other over the last 1.16 million years. And these groups are different enough that we treat them now as subspecies. And some ornithologists have argued that one or two of these subspecies should be elevated to full species status. I think there is still some debate around this idea. In any case, there are some consistent differences in the appearances of the subspecies. For example, the Caribbean Osprey, Pandyan-Haleetus Ridgway Eye, has a very pale head and breast, and the Australasian subspecies, Pandian-Haleidus Christatus, sports a dark breastband and a pale head.

When it comes to the distribution of the osprey, well, I've already pointed out that it's found across most of the planet. This bird is, therefore, a cosmopolitan raptor. In fact, this is probably the raptor species with the largest range. The Peregrine Falcon is a close contender, however. And interestingly, these two raptors, the Osprey and the Peregrine Falcon, are both conspicuously absent from New Zealand. And the Osprey is also not found on the island of Madagascar. This seems kind of mysterious to me, because it doesn't seem like New Zealand or Madagascar are too far away from their nearest continents to ever be colonized by Ospreys. But it is what it is. Mysterious or not?

In any case, the osprey is found on every continent, every single one of them, except for the continent that no self-respecting bird, cosmopolitan, or otherwise, would ever willingly set its feet upon. Yes, the name of that continent is Antarctica. The fish in its coastal waters are under no threat from ospreys. Penguins, yes, and some seabirds, but not ospreys. Ospreys are tough, adaptable birds. They live in many environments, but the challenges of Antarctica are just, apparently, too much. But what is the typical habitat for an osprey?

Where do they like to live? Ospreys are found in a wide variety of habitats, including lakes, rivers, boreal forests, mountain valleys, temperate and subtropical coastlines, and even salt-flat lagoons in the desert. Despite this diversity, Osprey habitats share several key features. Maybe the most important is an abundant and accessible supply of fish within a reasonable flying distance from the nest,

like less than 6 to 12 miles or 10 to 20 kilometers. Shallow waters generally provide the easiest access to fish. Another key feature is the availability of nesting sites. Ospreys need open nest sites that are safe from predators, particularly mammals. And these sites are typically elevated, such as at the tops of trees, on large rocks located over water, or on cliffs. And the third key feature of Osprey habitat is a sufficiently long ice-free season. This allows there to be enough time to raise a family through the spring and summer before snow and ice return in the autumn. And when the chilly weather

does return, many ospreys that breed in the temperate latitudes, well, they clear out. They migrate south to find fish in warmer climates. This is true for ospreys that breed in most of northern North America and Eurasia, and their migratory journeys can be thousands of miles. For example, ospreys that breed in the northeastern United States, such as those in Maine or New York, typically migrate south along the U.S. East Coast, cross over Florida, and then fly across the Caribbean Sea before reaching their wintering grounds in northern South America. They spend the non-breeding season in places like Colombia, Venezuela, and Brazil. And that's an epic one-way journey of about 4,000 to 5,000 miles, or 6,400 to 8,000 kilometers.

So this bird migrates farther than almost every other raptor. Most North American ospreys are migratory, and most of them have left the continent by November. But there are some non-migratory osprey populations, too. The best examples are the Caribbean subspecies and the Australasian subspecies. Those guys occupy the same habitats all year. And that kind of makes sense because they live in relatively warm or even tropical environments. So no need to clear out in winter. Among birds in general, most migrants make one or more stopovers to refuel with food.

So most birds treat foraging and migration as temporally separated activities, not things that they do simultaneously. Ospreys, however, do things a little differently. They've got a trick that allows them to fuel their journey continuously by hunting along the way. It's called the Fly and Forage Strategy. An osprey on a 5,000-mile migration journey can just swoop down to a lake or wherever, snatch up a fat fish, then keep on flying. No need to stop over for any length of time.

The Osprey carries the fish in its talons like a fifth grader carrying a lunchbox on the way to the bus stop. Do kids still use lunchboxes? Is that still a thing? Man, lunchboxes were a serious business when I was like eight years old. They always had a theme, some cartoon or a movie. I had a metal lunchbox that was based on the return of the Jedi, Star Wars and whatnot, you know, circa 1983.

And I had another one that was all about Indiana Jones. Those lunchboxes were dope, man. I think I might have had a My Little Pony lunchbox at one point. Maybe. I have a vague memory of that. Probably a traumatic memory that I've been repressing. Who knows? But yeah, Ospreys will sometimes carry fish a long way from where they caught them.

It's a grab-and-go lunch for the road. The Osprey has one of the most well-known comeback stories in bird conservation. Between the 1700s and the early 20th century, these birds were often persecuted. They were killed because, I guess, people saw them as competition for fish. For example, ospreys were driven to extinction in England by 1847 because of persecution and egg collecting. Similarly, they were extirpated in Southern California by, the 1920s. But then there were major population declines from the 1950s to the 70s. Osprey numbers dropped dramatically in areas like the U.S. Atlantic Coast, Chesapeake Bay, and the Great Lakes.

In some places, over 90% of breeding pears disappeared. The main cause was DDT, a pesticide that was sprayed widely to control mosquitoes and agricultural pests. The problem was DDT passed through the food chain to reach haust sprays, other raptors, and other animals, and it caused some major damage. This process of accumulation through the food chain starts with DDT being sprayed in agricultural areas. The pesticide then gets washed into aquatic ecosystems, like rivers and lakes, through runoff. There, it gets absorbed by tiny plankton, and then it gets more and more concentrated as it moves up the food chain.

Small fish eat the plankton, and larger fish eat those small fish. Ospreys, being top predators that eat lots of large fish, can end up with high concentrations of DDT and its byproduct DDE in their bodies. Eggs laid by these contaminated birds have unnaturally thin shells. So when an adult osprey tries to incubate such fragile eggs, they break. This phenomenon led to widespread nest failures and population declines for ospreys. This crisis, which hit other bird species just as hard, helped to reveal how harmful DDT was. And, thankfully, that led to the pesticide being banned in the U.S. in 1972. After the ban, ospreys started to rebound.

nesting success improved and people began putting up nest platforms, which ospreys readily accepted. These platforms became super important in the recovery process, especially where trees had been cut down or shorelines had been developed. And reintroduction programs helped bring the birds back to parts of the U.S., Great Britain, and Europe where they had vanished. Today, osprey numbers are strong across much of the species range. Estimates of the worldwide breeding population range from 100,000 to 1.2 million. In North America, many populations are growing steadily, at about 2% per year from 1966 to 2019. So the species is now listed in the least concern category by the IUCN. And that reflects the Osprey's vast range and its globally stable population.

And yet, not everything is perfect. For example, in Chesapeake Bay on the east coast of the U.S., Osprey nest success has dropped again. This is possibly because of a decline in the local population of Menhaden, a key food fish for ospreys. And scientists aren't quite sure yet what's causing that decline, like why the menhaden are declining. But other threats to ospreys, in general, include, fishing line entanglement, dependence on all those man-made nest sites that need upkeep, and water quality issues. Because ospreys are top predators in many aquatic ecosystems, they can tell us something about the overall health of those systems. So the osprey is an

indicator species. If water quality sucks, or the plankton and fish aren't healthy, the local osprey population is probably going to suffer. And hey, speaking of fish, it's time to talk some more about what and how ospreys eat. 99% of an osprey's diet is fish. This species is what biologists call an obligate piscivore, or some say piscivore. Some other raptors like bald eagles, well, they like to eat fish too. There are also fish owls, fishing owls, and the six species. species of fish eagles. Fish eagles are all in the genus Icteophaga, and that literally means

fish eating. But none of those raptors are as specialized in their paciferous diet as the osprey. A wide variety of fish are taken. For example, over 80 species of fish have been recorded in the diets of North American ospreys. And in Florida, as a more specific example, the dominant prey include gizzard shad, threadfin shad, sunfish, speckled trout, mullet, and crappy. And yes, if you didn't know, there really is a fish species

with the unfortunate common name, Crappy. But I guess some people say croppy, using a euphemistic pronunciation shift to make the word sound less vulgar. You know, like saying pisivore, because saying pisivore makes you nervous. Anyway, as another,

example, research on ospreys in the Willamette River, here in my home state of Oregon, found that 90% of their diet is composed of just two fish species, large-scale sucker and northern pike minnow. The typical fish prey for ospreys, in general, fall within a length of roughly 6 to 14 inches, which is 15 to 36 centimeters. And the typical weight of each fish is about 0.3 to 0.7 pounds, or 0.13 to 0.32 kilograms. Now I said that 99% of an ospreys diet is fish. So you might be wondering about the remaining 1%. What are the other things that ospreys sometimes eat? Well, first of all, it's very rare for an osprey to eat anything other than fish. But that said, these birds have been observed eating things like snakes, amphibians, crustaceans, small mammals, and even

carrion. But again, this is rare. We'll talk about the hunting or foraging method of ospreys in a moment. But first, let's look at their unique physical adaptations that are related to catching fish. First, ospreys have keen eyesight that's well adapted for detecting fish below the water's surface from a height of 30 to 130 feet or 10 to 40 meters. They can even adjust the angle of their dive to compensate for the refraction of light as it passes from air to water. This is similar to what kingfishers do. You remember that? I talked about that in episode 102, which was all about the common kingfisher. Earlier in this episode, we discussed the ability of an osprey to rotate one of its toes so that two digits face forward and two face

backward. This semi-zygidactylie ability transforms the bird's feet into highly effective fish traps. And remember that the talons are long, slender, and deeply curved, and they're rounded in cross-section. The shape of the talons is ideal for hooking into the flesh of a fish. The skin on the toes and feet of the osprey are also adapted for gripping fish. The pads on the soles of the feet are covered in sharp, spine-like projections called spicules. These act like barbs or sandpaper, giving them extra traction on a slippery fish. So you can think of the feet of an osprey, sort of like the textured latex gloves used by fishermen or gardeners. When an osprey hits the water in pursuit of fish, it risks becoming waterlogged and drowning. Raptors in

general are not known for their swimming skills. So another adaptation of the osprey is that its plumage is dense and oily. This prevents the plumage from becoming waterlogged. It allows the osprey to dive relatively deep and to resume flight more easily. Those other fish-loving raptors I mentioned earlier, well, those guys mostly snatch fish right at the water's surface. They don't really dive into the water the way an Osprey does. Getting back into the air from the water requires powerful wing strokes. The bones in an Osprey's wings appear to be adapted for this purpose. Special features include a prominent deltoid process on the humorous, that's the upper arm, and a relatively long manus. The deltoid process serves as a lever and an attachment site for

important flight muscles. And the manis is basically the bird's hand. A powerful wing stroke not only helps an Osprey take off from the water after a dive, it also allows the bird to hover. And hovering is part of the actual dive sequence. So let's go ahead and get into that. Ospreys typically hunt by flying 30 to 130 feet above the water or 10 to 40 meters, as I said. They're flying over the water, flapping or gliding. But when it spots a fish, an osprey may hover for a few moments before taking the plunge. And that's what these birds do. Their foraging technique is called plunge diving. Other birds that hunt this way include gannets and boobies, brown pelicans, and many kingfishers. But the osprey is the only raptor that is a true plunge diver. So after locking onto a fish with its eyes, with laser focus,

and maybe hovering for a few beats, the osprey goes for it. It rockets downward. It throws its legs forward in front of its head. The feet are brought close together. The toes splay and swivel into their zygodactal arrangement, and the hooked claws form a murderous fish trap. At the last moment, the osprey throws its wings backward, and the feet are what hit the water first. If all goes according to plan, the bird now has a fish locked in its talons. Ospreys catch fish in only the top three feet or one meter below the surface. They don't make super deep dives. If the captured fish is big and strong, it might make things hard for the osprey and the two struggle

against each other for a while. With or without a fish, the osprey eventually uses its long, powerful wings to take off from the water. The success rates of dives like this vary among regions and among studies, but the rough average is about 25%. So about one quarter of all dives end with a fish being carried away and eaten. I'll put a link in the show notes to a beautiful video clip from a BBC documentary. It shows the dive of an osprey in slow motion, and it really shows how the bird struggles in the water with the fish before getting back into the air. Having successful, caught a fish, an osprey will typically maneuver the fish in its feet to face forward,

taking advantage of the fish's streamlined shape to reduce aerodynamic drag. So you'll almost always see the fish with its head facing forward when it's being carried by an osprey. This is kind of morbid, but since I imagine it sometimes takes a while before the fish dies, its last moments must be pretty surreal. I mean, it was just swimming around, enjoying its day when, bam, it's suddenly caught by this feathered beast from the heavens. And now, just moments later, the fish is flying through the air, far above the water. That must be a crazy experience. But yeah, poor fish.

I guess circle of life and all that. Anyway, ospreys can sometimes reduce their search times looking for fish by observing other ospreys that have been successful. They're like, hey, Sally, check out that guy. he caught a fish. Let's see if we can retrace his steps to find the school of fish that he found. And seriously, I'm not joking. This is a real behavior we see in ospreys. Well, some of them anyway. This kind of information transfer among ospreys doesn't seem to be universal. But still, it's pretty cool. Now, just because you're an osprey that caught a fish doesn't mean you get to actually eat that fish. Because sometimes you have to deal with pirates. The bald eagle is famous for

acting as a kleptoparasite on ospreys. An eagle waits for an osprey to do all the hard work. Then the eagle swoops in like a pirate. It lunges at the osprey. The much larger, more powerful raptor can intimidate the osprey into dropping its lunch, which is then scooped up by the eagle. I'll put a link in the show notes to another video that shows this kleptoparasitic behavior in eagles. All right, now it's time to talk about the breeding biology of the osprey. Ospreys are monogamous. They form pair bonds that often last for the lifetime of the birds. Although not all pairs stay together every year, particularly if breeding is unsuccessful,

most osprey pairs reunite at the same nest site each breeding season. This fidelity, both to each other and to the nest site, reinforces the bond between mates and helps them be more successful in raising brood after brood year after year. The pairs form and are reinforced through courtship behaviors, usually in the vicinity of the nest. One of the most outstanding features of Osprey courtship is the aerial display known as the Sky Dance. During this performance, the male ascends above the nest in a slow, undulating flight. He dangles his legs below him, and sometimes he carries a fish or a sea.

stick. Meanwhile, he makes a loud, high-pitched screaming call. Another important aspect of Osprey courtship is courtship feeding. This is where the male brings fish to the female before she starts to lay eggs. And if the pair actually breed, she's going to depend on him for an extended time. This courtship feeding behavior serves multiple functions. It reinforces the pair bond, nourishes the female during egg formation, and provides a signal about the male's ability to provide fish for a future brood. Research in British Columbia has shown that the frequency of courtship feeding is positively correlated with both the likelihood of egg laying and later chick provisioning.

So it seems a female can assess a male's fishing skills early on if he's really good at courtship feeding. And if he's a good provider like that, she wants to give that guy on lock. He's a keeper. Now, how about territoriality? Ospreys are generally solitary outside of the breeding season, but their behavior becomes more socially complex during the nesting period. In some regions, they form loose breeding colonies, with several nests clustered together. Within these colonies, groups of ospreys can sometimes

be seen soaring together. Ospreys in densely packed colonies seem to suppress overt aggression. They recognize and tolerate familiar neighbors while remaining defensive toward unfamiliar intruders. This allows them to nest in high densities with minimal conflict. I guess this is kind of how I live. I live in the heart of a busy neighborhood in Portland in a cluster of apartments and condos. In order to minimize conflict, I have to suppress my natural tendency to be overtly aggressive. I tolerate my familiar neighbors, just barely. When it comes to nesting, Ospreys combine their instinctive engineering skills with an opportunistic attitude.

Males typically select the nest site, and they gather most of the building materials. A male might gather sticks off the ground, but he will also break them off of trees while in mid-flight. I've seen this in action, and it's pretty amazing. The male delivers sticks to the female at the nest site, and she arranges them. Nest construction begins even before full pair bonding and continues throughout the breeding season, especially after hatching or nest failure. Nests are bulky structures built from large sticks and padded with softer materials like grass, moss, seaweed, and bark. And ospreys frequently incorporate human-made materials into their nests,

things like plastic bags, nylon mesh bait bags, baling twine, beach toys, and even dry, ride cow manure. One nest was even found to have the desiccated, sort of mummified body of a great blue heron in it. Yikes. That was probably a tactic the ospreys used to scare away any potential nest invaders. Because, as everyone knows, the scariest mummies of all are great blue heron mummies. So like I said earlier, ospreys tend to use the same nest site over and over year after year. Over time, nests can become enormous, reaching 10 to 14 feet deep or 3 to 4 meters and up to 6 feet across. Under natural historical conditions, ospreys nested in tree tops or on cliff edges. But they're opportunistic, so they'll also nest among

large boulders on the coast, in mangroves, and even on the ground on islands where there are no terrestrial predators. I've also seen ospreys nesting among the spines of massive cardone cactuses in Baja California. Now, as we've already touched on, these birds have adapted to using artificial nest sites in response to widespread habitat loss. Today, many ospreys use man-made structures such as utility poles, radio towers, channel markers, and especially erected nesting platforms. And as we were talking about earlier, those artificial platforms have become critical to the recovery and conservation of ospreys. In some places, 90 to 95% of nesting pairs use these artificial supports. Such is the state of things. So we've got a nest, now it's time for

eggs. A typical osprey clutch contains one to four eggs, with three being the most common. eggs are laid sequentially, and they're incubated primarily by the female, with some assistance from the male now and then. The incubation period lasts 36 to 42 days. The first egg is often significantly larger than the others, which may contribute to an early size advantage for the chick that hatches first. So yeah, Osprey chicks usually hatch asynchronously, meaning there can be a gap of up to four or five days between the first and last hatching. This creates a size hierarchy within the brood. In times when fish are scarce, older chicks may dominate feedings and out-compete their younger siblings.

Sadly, this sometimes leads to the starvation of the youngest chicks. Parental care is a joint effort with distinct roles. The male primarily provides food, often feeding himself first before delivering fish to the female and chicks. The female breaks the fish into small pieces and distributes it among the begging chicks, typically starting with the most vigorous beggar. And who is the most vigorous beggar? That's right, it's usually the largest, oldest chick. As the chicks mature, parents gradually adjust their provisioning strategies.

At first, they bring dead or incapacitated fish. Later, they deliver live fish, encouraging the chicks to develop some basic skills in fish manipulation. Fledging occurs around 50 to 55 days after hatching. But young ospreys might remain near the nest and continue to depend on their parents for some time. But as far as I know, there isn't much scientific evidence that parent ospreys teach their offspring how to dive and catch fish. So the young birds probably rely on instinct and practice to feed themselves. This idea is supported by situations where ospreys have been raised by humans. because once released into the wild, those captive-raised birds have learned to fish on their own.

Reproductive success in Ospreys depends heavily on food availability and nest site security. Ample fish resources and stable nesting platforms significantly increase the chances of fledging healthy chicks. And those healthy chicks, if they're lucky, they can live up to about 25 years in the wild, although a more typical lifespan might be closer to seven to ten years. With each passing year, experienced bonded pairs are more likely to succeed in raising their young, as long as the conditions of their environments around the nest remain favorable. Earlier I described the Osprey as an indicator species for aquatic ecosystem health. The argument for this idea rests on

several key factors. First, ospreys are, as we know, obligate piscivores. This specialized diet directly links their well-being to the health and abundance of fish populations in their foraging areas. As top predators in aquatic food webs, ospreys are particularly susceptible to the bioaccumulation of environmental contaminants, such as DDT and mercury. Another reason the osprey can serve as an indicator species is because these birds are relatively easy for scientists to study and monitor. They have conspicuous nesting habits, for example, often on these artificial platforms, and they're in open areas. Changes in osprey population size or their reproductive success, and the presence of contaminants in their eggs or blood, can therefore provide valuable insights into

the overall health of the local aquatic ecosystem. Finally, the broad distribution of the osprey across various aquatic habitats also makes this a potentially useful indicator species for monitoring contaminant levels in rivers, lakes, reservoirs, and estuaries worldwide. So we should celebrate the osprey. This is an amazing bird for many reasons. It's found around the world. It belongs to a monotypic family that's been evolving independently

from other raptors for 50 million years. It's a highly specialized fish-killing machine. It's elegant and beautiful. And it can teach us a lot about the interconnectedness of the natural world. That, my friends, does it for our episode on Pandian Haleidis. I hope you enjoyed it and that you learned something new here today. For well-known birds like the Osprey, I sometimes worry that my listeners already know everything there is to know about it. So I try to dig deep to find some factoids that are

relatively obscure. Things I think might excite you to learn. I try anyway. And those of you who try and succeed at supporting this podcast as members of my Patreon community, well, I owe you an enormous thank you. Your support is what keeps me going. You keep the fire lit. My newest Patreon supporters are John Gettys, June Lee, Aaron Donahoe Bellman, Alana, Yvonne Wright, Claire Wing, Margaret Hurley, and Cedric. I thank each of you for believing in what I'm doing here and for helping to make educational material like this freely available to everyone. If you have some interest in supporting this podcast as well, you can check out my Patreon page at patreon.com slash science of birds. a support the show link in the show notes. And just a reminder that if you decide to become a

supporter, you'll want to sign up on a desktop computer or an Android mobile device. Because if you sign up using the Patreon app on an iPhone, Apple is going to charge us and steal our money. You can also shoot me an email if you have something you'd like to share with me. Maybe your thoughts about the podcast, your favorite euphemistic pronunciation, or which kind of mummy you prefer to decorate your house with in order to deter would-beenvaders. Whatever the case, you can reach me at Ivan at Scienceof-Birds.com. This is episode 114. You can check out the show notes for this episode, along with some photos of Ospreys that I

handpicked for you on the Science of Birds website, which again, scienceofbirds.com. I'm Ivan Philipson, and True Fact About Me, you know how 99% of an Ospreys diet is fish? Well, 99% of my diet is popcorn and peanut butter and jelly sandwiches. True fact. Thanks for listening and I'll catch you in the next episode. Cheers.