Singing Travelers / Perfect Diver Magazine 19 issue

Singing Travelers

Planet earth

Text and photos WOJCIECH JAROSZ

This time, I am going to invite you to the world of small and rarely noticed on a daily basis birds (this does not apply, of course, to ornithologists and 'birdwatchers'). We have visited this world several times with Perfect Diver (getting to know the bearded reedlings, PD No. 13, and the wagtails, PD No. 17) and we return to it to learn about the next species of bird, which we may be able to hear or even see while preparing for the next dive in inland waters.

Sedge warblers (Acrocephalus schoenobaenus) are birds of the Acrocephalidae family, i.e. a group of passerine birds that have taken a liking to the environment ofwet open areas with high and compact vegetation, forming primarily reed beds and sedges. As places of their existence, including breeding, these birds prefer the covered with vegetation shores of water reservoirs, both flowing and stagnant water. Their preferences are therefore similar, to some extent, to those who love sports and water and aquatic activities. We, humans, rarely purposely get ourselves into reeds, but we take a bath, dive, sail or just walk right next to it. That's when we have a chance to meet these feathery inhabitants of the rushes.

Most often we will hear them, as their songs and voices are an inherent element of the waterside natural surroundings. There will be time to write about the scratchy and loud singing of the great reed warbler (A. arundinaceus), probably in one of the next editions of PD (if the Editor-in-Chief finds this topic interesting for the Readers of the Magazine), so now let's focus on the sedge warbler and its singing. As is most common in birds, males sing. They do it in order to persuade the females to set up a nest together. In the case of birds of this species, it has been observed that the nicer and more diverse the male singing, the greater the chances to arise interest of a representative of the slightly less beautiful sex (this is not a mistake, after all, in birds the males are usually prettier). The variety of singing of male sedge warblers consists in folding into one song a variety of syllables and phrases that can be a copy of the singing of various birds belonging to other species. It is the richness of the repertoire that is to be the decisive factor in the success in seducing the lady sedge warbler. Birders explain these observations differently. One of the suggestions is that the male imitates in his singing mainly birds from the neighbourhood. If so, it means that he recognized the area well, and this may translate into a deeper knowledge of places where there is more food, and even which places will be the best in terms of setting up a nest there.

The subject probably requires further research, because the studies that were carried out, for example, on sedge warbler's cousins – marsh warblers, indicate the fact that they imitate the singing of a huge number of species (over 200!), of which a slightly larger part concerns species found not in the breeding area, but on wintering grounds in distant Africa. Perhaps what is more important is the more creative juxtaposition of overheard phrases and song fragments compared to the rivals? Is it not the same as with us, people? After all, the poet uses the same words as each of us, and only in their selection and order of compilation lies the secret of the difference between Mickiewicz's Polish alexandrine and the call of the potato seller from the local market. Of course, the greater supply of words makes it easier for the poet to effectively express their intentions, so perhaps this is also the point of birds? I apologize to the experts of poetry and language science for gross simplifications and far-reaching ignorance, but such examples can sometimes activate our curiosity and imagination without requiring in-depth knowledge of the field they concern. Coming back to the birds and to the Africa mentioned a few sentences earlier. It is there, more precisely in the sub-Saharan part, that European sedge warblers overwinter. When they raise their young, and sometimes it is done twice during the season, they prepare for a long flight. And what preparations these are! Well, these birds simply begin to eat without moderation. The goal is to quickly double the body weight and turn from a 10-gram bird to a 20-gram ball of feathers with a solid fat reserve.

This is all because sedge warblers do not like to stop on their way. In fact, they only make one stop in southern Europe, where they replenish their supplies, and then in one jump (4,000 km!) They move to the tropical regions of the Black Continent. Sedge warblers have adopted a strategy of quickly covering long distances, hence the need to accumulate the so-called migratory fat, which enables long-term active flight.

While flying non-stop, they probably use different navigation systems at the same time. Researchers report that birds can use many complementary ways of orienting themselves in space. Not so long ago, it was even established how birds 'see' the Earth's magnetic field, thanks to which they flawlessly reach their destination – that is due to the presence of a photoreceptor protein from the group of the so-called cryptochromes. Hitting the same nest box or reed clump after traveling many thousands of kilometers seems surprising, but the navigation of migrating birds is indeed excellent. Birds also support themselves with astronavigation and a precise biological clock, thanks to which they perfectly interpret the position of our Daily Star in the sky. In addition, birds are great observers and they remember and recognize specific places without errors, both during their stay in the breeding grounds and during their migrations. We still do not know everything about bird orientation, and although science is making great progress, also in the field of ecology and ethology of birds, still some water in the rivers will flow before we know all the bird secrets. I hope we will have the opportunity to do so, because the rate of extinction of insufficiently known species of organisms has not slowed down recently... So far, sedge warblers, fortunately, are still doing well, as their numbers are increasing. However, they require the protection of habitats, which is generally true for most species of birds and not only, from Europe and the whole world.

So how to distinguish a sedge warbler from other birds inhabiting similar biotopes? Certainly, the characteristic eyebrow will be a clue here (I refer to the photos), but although it is not extremely skittish, it will not always sit at such a distance that you can look at it comfortably (that's why we take binoculars for birds). However, we should not have a problem hearing the males sing. To flawlessly assess that the heard sing is emitted by the sound-forming apparatus (anatomically called the larynx) of the sedge warbler, it is good to support yourself the first or second time with a bit of help (recordings on the Internet) or an application for recognizing bird voices. An excellent tool was created by specialists from the Cornell Lab of Ornithology – an application for mobile devices to download in places from where we usually download applications. I recommend it because it works – I checked it many times in the field.

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