100,000 of them arrive here. Even half a million might fly away.

The nestlings look like small, stinky dinosaurs and are fed by their parents up until the moment they attempt their first flights. Although it happens that the parents can act disgracefully and throw their own children out of the nest, eat them or feed them to the remaining nestlings, they are also very fair parents. They don’t favor any one and they make sure that every one gets an even amount of food – says biologist Piotr Tryjanowski.

TVP WEEKLY: Do you agree with the statement that after the eagle, the stork is our second national bird?

I would even say that it’s the first. I know that in school we learn the rhyme “what’s your sign, the white eagle”, but when in comes to the recognizability of the species, people are better able to identify a stork. Ornithologists themselves often argue about whether we can differentiate eagles well, but with storks, no one has any doubt.

Even though no one has any doubts in this matter, all storks aren’t the same. Some are black, others are white. What are the differences, other than color, obviously?

I remember an anecdote from the 1970s. Ornithologists were collecting data on the locations of white and black storks, the feedback they received was that: “Mr. Doctor, we don’t have black or white storks, the ones here are only white-black storks.” In reality it’s not so straightforward, you have to take a good look to see that a white stork is more white and less black, since the tips of their wings are mainly black, while black storks have a lot of black on their coat, and only their stomach is white. The white stork is also somewhat bigger than a black one. Besides the differences in appearance, we are also dealing with a difference in habitat. The white stork is the one that lives near us, while the black one is a backwoods species. In short, it prefers to hide.

Spring is the time when storks appear near our homes and in meadows. How many of them fly into Poland each year?

We have over 50,000 pairs of breeding storks. So we can say that around 100,000 fly in and, taking into consideration that the average reproduction of a stork pair is two nestlings, around 200,000 fly away. When we have a good summer, as far as weather and no drought, a stork is capable of rearing even five nestlings, so there are decidedly more flying away. Unfortunately, due to the recent dry years, this fertility rate, like with humans, is falling.

So it’s true that every fourth stork is Polish?

It was like that 25 years ago. That’s what was said, there were even special posters. Now it’s not so simple. The reason is the fact that our stork population is shrinking, while the Spanish population is growing. Thus the lead position is shifting.

Is our stork under threat of becoming an endangered species?

Luckily, the total extinction of the stork is not a threat, at least for now, though there are countries like Denmark where there were a lot of storks, and now there aren’t any at all. The most important thing, like with any other species, is simply to leave them alone. Don’t knock down nests and if you’re remodeling a barn or other roof, replace it with an artificial nest and prepare a place for them to build it anew. It would be good to use water in the landscape to prevent dried-out places. But this is the economization of agriculture, which has had problems for a long time, but the more that we talk about this, then perhaps more information will reach those responsible for Polish agriculture.
An adult black stork (Ciconia nigra) with a black-headed gull (Chroicocephalus ridibundus). Photo: Marcin Karetta / Forum
In the introduction to the book Stork, An Unauthorized Biography, which you wrote together with Adam Zbyryt, the claim is made that the stork is an under-appreciated bird. Why do you believe this?

It’s not that we believe it, it’s that it’s plain to see. Academics, especially traditional ornithologists, love to study species about which nothing is known. It’s along the lines of “let’s find it, we’ll be discoverers.” The stork however is a long-ago discovered, even common species, that everyone knows and is easy to count. Already in the XIX century it was labeled as “easy.” Meanwhile, it’s not a totally known species. Studying it every year, we learn some new, heretofore undiscovered thing. So it’s also our opinion that it’s worth probing the mystery of even these more common bird species.

So what is the stork like?

Fantastic (laughter).

What are the good aspects of the stork that we should notice?

Yes, like I mentioned, this bird is recognized by everyone. People living in cities know what species this is even though it’s associated with the landscape of the Polish countryside. This stork egalitarianism, understood by everyone, is an ideal matter, especially in times when we need species of plants and animals for public education. Our great-grandmothers, grandmothers or grandfathers knew all of the plants and animals in the area. Now even professionals have trouble with this, and this is tied with the problem of educating society. Thus, the main virtue of the stork in socio-social education is precisely it’s universal recognizability.

Obviously, it also has research advantages. It’s relatively large, practically indifferent to the presence of humans and even likes it. The fact that this bird isn’t afraid of humans also allows for transmitters to be placed on them, little backpacks 1/3 the size of our smartphones, and from these knowledge can be drawn on their behavior and flights. I believe that this is the recipe for research success, made possible thanks to the observation of a well-known and common bird.

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Everything begins in the nest. How does the stork’s look like? Do the birds live there alone?

If someone watched the story “Several Adventures of Ćwirek the Sparrow” they will remember that the main hero was the resident of the lower floors of a stork’s next. This isn’t just cinematic fiction. Truly, a stork’s nest can also be a home for sparrows, tree sparrows and starlings. They are huge structures, built by several generations, several meters tall and weighing up to 1.5 tons.

Storks situate their nests in various places. Flat surfaces that offer support or a foothold for falling sticks is a good place for them. The light slant of a roof isn’t a big problem. What’s important is that the roofing isn’t too slippery. In the past, thatched roofs were an ideal base for building nests. Currently in our country, the largest number of storks nest on power poles or free-standing ones with special platforms under the nest, prepared by humans.

In storks nests I’ve seen: underwear, boxers, shirts, bras, stockings, children’s pantyhose, aprons, work and garden gloves, socks, hats, shoelaces, belts, pieces of wire, pieces of colored glass and even old, Polish People’s Republic coins. The most interesting find was in the Czech town of Chomutov – a lot of bikini tops and bottoms, one-piece swimsuits, socks, underwear and towels were found there. Where did this odd assortment of junk come from? There is a popular bathing spot nearby. If beachgoers left something on the beach, it usually ended up in a stork’s nest. This isn’t the end of the surprises however. Also in the nest were found two full cases of… wine. No one knows how they ended up there.

Since there is a nest, nestlings have to show up there. What is stork reproduction like?

Every year it’s the same. The male flies in first, a week later, the female. It all starts with finding a favorable place, though it often happens that the stork returns to the same, tried-and-true location or nest built over generations. This is influenced by conditions and the reproductive success of previous years. Once the nest is ready, copulation takes place. Storks copulate a lot, and not only to fertilize the ovum. This is a strong signal that the storks are a pair and that their mutual relationship is strong.

Once the eggs have been laid, the female incubates them and nestlings hatch, looking like small, stinky dinosaurs and are fed by their parents up until the moment they attempt their first flights. It’s worth emphasizing that even though the parents can act disgracefully and throw their own children out of the nest, eat them or feed them to the remaining nestlings, they are also very fair parents. They don’t favor any one and they make sure that every one gets an even amount of food.

Before the departure to warm countries, assemblies take place. Young storks don’t know the route that their parents covered, they have to learn, practice flying, see who is behind who in the group, listen to elders. These assemblies are a kind of preparation for the hardest test of their lives, that is the migration to Africa, to that promised land.
While flying, they shape themselves as gliders. Photo: Krzysztof Chomicz
How many kilometers are they able to cover?

Maximally 11,000 kilometers during the seasonal migration, which lasts just a few weeks. That’s the record for a stork’s flight. They are able to conquer this many kilometers, since they have a sophisticated, cheap method of flight. They don’t flap their wings quickly, they don’t fly actively, they just shape themselves, as if into gliders. Obviously this has its limitations, since they can only fly on sunny days, when rising currents form over the ground. Similarly to us when traveling by car or plane, they also have to stop during such a flight. First of all to rest and not to fly at night, and secondly, to “tank up”, that is to feed themselves well before continuing the journey.

They are masters at utilizing energy, but also masters of fasting. They can go without food for as long as four weeks. They are able to make appropriate stores from what they eat, which in the case of birds is not so easy, since every extra gram is a greater load for the wings, kind of like a backpack is for the joints during our human wanderings on foot through the mountains.

Let’s talk for a moment precisely about this stockpiling of energy.

They very quickly and very precisely digest eaten food, they can even pull protein and calcium out of animal bones. In short, practically nothing goes to waste from their finds – not water, nor any energetic substances. All of this is quickly built into their organs without fattening them. If there is a surplus of food, the stork momentarily enlarges its stomach to fit these reserves. It’s also worth mentioning that the female and male digest in somewhat different ways. This results from the fact that they eat and look for food differently. She has to incubate the eggs, watch the nestlings, so she has less time to search for little delicacies, she prefers the larger, concrete ones. By this method of searching for food it’s possible, at first sight, to determine whether it’s a male or female. If it’s meandering around a field or meadow and collecting grasshoppers, it’s most certainly a Mr. Stork, and if it quickly returns to the nest with a larger catch, it’s a Mrs. Stork.

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And who digests more quickly and easily?

Females digest nearly 80 percent of the food they eat, while males a little over 70 percent, which leads to them to produce more spit-outs, so the remains of food. In the case of males, the efficiency of digestion influences the change in body mass, which means that the greater the efficiency, the quicker the body mass grows. In females this effect is the opposite, thus: the greater the efficiency in digestion, the lesser the growth in weight. Why does this happen? We don’t know, but most likely females have some kind of internal mechanism that allows for the control of body mass. It could be tied to the greater burden of egg production and later parenting care. I think that many women would be jealous of this process in lady storks (laughter).

So what’s with the frog? Do storks really not eat them?

They eat them, though these days they have increasingly fewer opportunities to do so. Watering holes, ox-bows and lakes are drying out, so there are less frogs. I would however put modern storks into the category of mice-eaters. The vole is the basis of their nutrition. In turn, in Spain storks have taken a liking to an invasive variety of crawfish, the Louisiana crawfish. By eating it, they mature a little faster, so I would compare this to fast food. More so than frogs, storks prefer to eat fish, carrion or insects. One experiment also showed that in the case of an abundance of prey, storks choose vertebrates more often than insects or earthworms.

Do we know why?

It’s most likely because vertebrates provide more energy and protein than invertebrates of the same mass. To paint a picture: a meal consisting of a mole provides as much energy (measured in kilojoules, kJ) as 90 earthworms and 235 field crickets. Perhaps someone managed to see a white stork with a hunted-down grass snake? This is also highly caloric prey, even more so than the plump mole, since it’s equivalent to 100 earthworms and over 261 crickets. The logic is simple – if you eat only potatoes every day, and one time you also get a chicken, you aren’t going to take a long time to think about what to start with. We used to count how many grasshoppers a stork is able to hunt down over the course of five minutes. The record-holder hunted as many as 90, and the average was 30.
Storks hunt better with the assistance of cows. Photo: Marek Maruszak / Forum
We talked about how storks are birds that aren’t afraid of humans, but they also don’t shun the company of cows. Where does this friendship come from?

The cow is a natural lawn mower. It shortens grass and thanks to this it’s easier for storks to get to food. With their assistance they catch a lot more food than when they do it alone. Based on a study that we did, it turns out that if storks feed alone, then around 1:45pm, a noticeable drop in effectiveness in catching prey takes place, then it slowly grows until the evening but it never reaches the level achieved by storks hunting in the company of cows. Besides this, they are attracted not only to the company of cows, but to what they “produce”, so excrement. Cow patties are bait for many types of insects, such as beetles, and on the other hand are useful material for building nests. Dried manure mixed with straw acts like a hydrophilic sponge, which collects water accumulated after rain or downpours.

Is it true that storks can be unfaithful?

These birds most often match in pairs with individuals of a similar age, but, as in life, they don’t always stay with them forever. Among storks, changes in partners and therefore in nests, happens most often when the previous brood ends in failure. This usually has to do with the youngest couples, most often up to nine years old, so up to the time that they achieve their peak reproductive capabilities.

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Why do the younger birds divorce more often?   

The answer is quite simple. They usually occupy worse, less nutritionally abundant territories, so if some young “married woman” manages to find a better partner (along with a more nutritionally abundant terrain), she gladly takes up the offer. The size of the brood depends on the female, not the male, so the number of eggs laid, thus they are the ones that more eagerly make the decision to divorce and move to a different nest. Is this change beneficial? It turns out that not always. Loyalty and staying with the same partner often causes that the success of the brood in the following year is much greater than in the case of changing partners. A curiosity is that a stork that has not yet finished caring for one brood never leaves with another partner.

Is it true that the molting process, the replacement of feathers, occurs in the time of arrival from, then return to, warmer countries?

Yes, though this concerns stork youth. We can joke that at precisely this time young storks change their wardrobe. With all birds, similarly like with humans, since we don’t have the same hair on our heads after all, a replacement of feathers takes place. All material things, including elements in our bodies like hair, skin and feathers in birds, become damaged and have to be rebuilt, fixed and replaced. The stork is not an exception in this respect. Before a replacement takes place though, young individuals undergo a process of growth. It is incredibly interesting in the case of these birds. When we look at a person, the growth of fingernails or hair is totally different than the rest of the body. In the case of storks, feathers, legs and beaks behave differently. The first ones only grow and change shape. The older the bird the rounder it becomes.

I understand that this change occurs for some reason.

Indeed. It occurs so that the stork can fly more efficiently, to be like an aerodynamic machine, a helicopter. It’s about the feathers making the least resistance. The black feathers in the wings, which serve in flight, are called first or second class ailerons. In connection with them wearing down quickly, birds regularly replace them – we call this process molting. In the case of white storks, it happens in hatcheries, so during the period when they reside in our country and raise their young.

Between May and August, gaps in the plumage of their wings appear – we can observe them most often when birds fly between the nest and local meadows. New feathers soon grow in their place, and thanks to them, by the end of August, when storks set off on their long journey, they have a refreshed and fully-functional flight apparatus. Young individuals in their second and third year of life (in the fourth they are treated as adults, though some are capable of reproduction even a year earlier) begin the replacement of their flight feathers a month earlier than mature birds, so in April. The replacement process of these important feathers takes place in a wilder way among younger birds than older ones, since in the course of a year they replace up to 10 flight feathers, while older ones – half as many.
Over the course of five minutes the record-holder can hunt as many as 90 grasshoppers. Photo: Krzysztof Chomicz
And what about the beak and legs? Do they also evolve in some way? Why do they have a red color?

This is due to red pigments called carotenoids, which give them such an intense hue. Birds aren’t capable of producing them on their own, so they supply their bodies with it through food. Black legs and beaks in nestlings and very young individuals become red. This is like a stork ID card, a sign of its age and gender maturity. This red pigment shows that the individual is not only an adult, but that they can also commence brooding. It’s also a sign of a functional immune system.

Quite similar to humans, if our skin or fingernails change color and hair starts to fall out, this often indicates that something in our body is starting to fail. Precisely a red beak and legs signal health in a stork. While we can treat ourselves and take vitamin supplements, you aren’t likely to meet a sick stork. Natures works in a way that before we notice it, some predator will get to it and kill it. When, in the fall we see a bird with a dark beak and legs, it’s a sign that we’re dealing with a young individual from the current year.
Storks spend a large portion of time in our country in hot months, in the sun. How do they deal with this excessive heat and sun exposure?

In a very peculiar way. Like all birds, they don’t sweat, since they don’t have sweat glands, but they feel warmth and the glare of the sun, and as you rightly noticed, they have to deal with it somehow. Naturally, white feathers help with this, reflecting rays, but not all parts of a stork are white, look at the aforementioned legs. What does it do with them. It whitens them. This is the very nice name for the process that consists of dirtying the legs with urine and excrement. An overheated stork shoots a stream of liquid excrement (during heatwaves it is very watery) on one of its legs, and as it dries it cools the body, which, thanks to this, efficiently draws away heat. Besides this, it helps, like with a human at the beach, to wade into water, but they also pant, or arrange their feathers so that they don’t retain heat. Young individuals in the nest can’t wade into water, so their parents bring water in their beaks to pour over them to cool them. It’s worth noting that covering the legs with urine and excrement is very durable. Getting rid of this covering is quite a challenge – even while hunting in water.

Since we’ve disproved the frog-eating stork myth to a certain degree, what should be do with the stork bearing children? 

This is a very interesting “cultural legend”. To a certain degree it has even been studied by academics, who came to conclusions supported by statistical analysis that where there are more storks, there are more children. The legend that storks bring children is not only popular in Poland, but even reached America. In any case, there is a certain explanation. Let’s look, stork assemblies took place in August, so during harvests. At that time, people celebrated the end of work, nights were warm, long, they sat on sheafs and observed these stork groupings, and, since blood is thicker than water, intimate encounters happened here (laughter). From August to April, when storks returned again, these 9 months went by and in this way the saying came to pass, “the stork flies, children will arrive”. People connected the dots and this is how the legend persisted and in a certain sense, it’s true (laughter).

– In conversation with Marta Kawczyńska

TVP WEEKLY. Editorial team and jornalists

–Translated by Nicholas Siekierski
Piotr Tryjanowski, Adam Zbyryt „Stork. An unauthorized biography”
Professor, postdoc, dr h.c. Piotr Tryjanowski (b. 1970) is a biologist and director of the Zoology Department of the University of Natural Sciences in Poznań. A researcher of fauna in the agricultural landscape, but above all the interaction of animals and people. He worked on projects of the Intergovernmental Panel on Climate Change (IPCC) and the International Union for the Conservation of Nature (IUCN). He has published 17 books and over 300 academic articles in the best international publications. Among others, he is the co-author of the books “Ecology of birds in the agricultural landscape” and “Therapeutic ornithology” and about a dozen works on the agricultural landscape, but also on how contact with nature influences the functioning of the brain. In free moments he loves to observe birds, to drink good Moravian wines, eat cheese and delight in the baa-ing of sheep.
Main photo: A white stork (Ciconia ciconia) on a nest in the Kępa Skorecka village. Photo: Piotr Rybarczyk / Forum
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