SAVI'S WARBLER (Locustella luscinioides)

 

Locustelle luscinioide

Savis_Warbler.jpgSo now things get a little tricky - here we have a bird that sounds more like an insect than some insects do !

Savi's Warbler is a summer resident from the end of March until the end of September (although some birds seem to leave as early as the end of July). It favours wetland areas with mature reed beds and so occurs only spasmodically across Switzerland. Good populations can be found in the wetlands on the south eastern shores of Lac Neuchâtel where I made my recordings.

Not an easy bird to see deep in the reeds, it is also well disguised by its song which is a rapid, mechanical buzzing noise just like that of a grasshopper.

It will sit at mid-level up a reed stalk making this sound with its beak open, slowly turning its head from side to side to project the sound around. This effect can be heard in the recording, when the open beak was pointing directly at the microphone the sound becomes very loud, so I am guessing that the throat, mouth and beak shape act as a sort of avian megaphone to amplify and project the call:

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The rattling of the dry reeds, gulls and coots can all be heard in the background.

The sounds are made much too rapidly to show a video of the sonogram - it is just a big blur ! But I will include here some still pictures of the analysis of the sound:

 

Savis_Warbler_anal1.jpg

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This graph shows three sequences of singing, 0 - 10 secs, 21 - 37 secs and 42 secs to the end. It has two parts:

The upper (blue) part shows the intensity of the sound in the recording against time in seconds; the further the blue area extends from the centre line the louder is the sound entering the microphone. You can see how the blue area gets wider and narrower as the bird turns its head towards and away from my microphone. The lower (grey) part shows the sound frequency against time; the dominant frequency is around 4 Khz.

To better understand what is going on here I have taken a "slice" of the analysis at 52 seconds (the red circle) and magnified it in the graph below:

Savis_Warbler_anal2.jpg

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This graph shows what was happening from 52.0 seconds to 52.2 seconds in the recording - i.e. the total time shown across the bottom axis is only one-fifth of a second. During that brief snatch in time, if we count the blue "beats", we can tell that the bird made about 20 separate "clicks" - this is about 100 per second, or 6,000 in a minute. In the recording you just listened to, the longest call sequence lasted 34 seconds so the bird must have made about 3,400 separate clicks just in that sample alone. Extrapolating that to 12 hours of singing per day for a 2-month breeding season just makes my head hurt !

There is something else interesting going on in this diagram however.

You can see that in each one-tenth of a second there are two "beats" of sound, the first being a bit shorter in duration and less intense, the second being a bit louder and longer. Next, if you look at the frequency diagram below each beat the first sound seems to have a wider range of frequencies in it - 3 Khz to about 6.5 Khz, whilst the second is from about 3.2 Khz to 5 Khz. So it seems as though there are two separate things going on here.

Now humans have one "voice box" - the larynx, situated above the point where the two bronchii (the tubes that connect our lungs to our mouth) meet, and we push air from our lungs over membranes in the larynx to make human speech. But birds have two voice boxes in a complex structure called the syrinx, and this is situated just below where the two bronchii meet and so can receive two independent air flows. Not only that, but the two parts of the syrinx have independent sets of muscles and nervous connections to the brain. Hence two independent voice boxes, This "two-voice theory" accounts for a lot of the complexity in bird song. It has also been shown that the two syrinxes can play different roles in the final sound that comes out.

So, what I think is happening in our diagram is that the Savi's Warbler is first producing a sound from the right syrinx and then from the left, and by working them in alternation it can produce these incredibly rapid vibrating sounds.

But of course producing the sound is only one half of communication in birds - hearing and interpreting it is the other half. We know that birds have much better hearing acuity than humans, being able to discern both frequencies and speeds much better than we can. So whilst to our pathetic human ears this bird is simply making a buzzing sound, the chances are very high that another Savi's Warbler is hearing much more detail. If we slow down that area around 50 secs above by a factor of 10 (which lowers the pitch by the same amount) it may be that another Savi's Warbler may be hearing something like this:

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But here we can still only take a guess.

So why "Savi's Warbler" and not "buzzing bird" ?  Well it is a member of the warbler family and is named after an Italian geologist and ornithologist, Paolo Savi, who first described the bird in 1824 !

 

 

 

 

 

MARSH WARBLER (Acrocephalus palustris)

Rousserolle verderolle

Acrocephalus_palustris_Marek_Szczepanek.jpgI love this crazy bird ! It is a migrant species nesting in Switzerland and present from May until September. It is found in a large arc to the north of the country along the line of the River Aar and the rivers that drain north from the alps eventually into the Rhine, but throughout this arc occurs only spasmodically, the main range in Europe is to the east of us.

The song is a wild frantic chorus of extremely complex notes and phrases and the literature tells us that it is made up of a large amount of mimicry of other species. However since any individual probably spends more time in its African wintering grounds than in Europe breeding, not many of the model species that it mimics are recognisable to us. It apparently has the largest repertoire of any of the Acrocephalus warblers in Europe. I recorded this bird alongside the Saane River which you can hear in the background:

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But as you can hear the song is delivered with an effort and a wild urgency that few other species can deliver. It sounds completely random but there are features within the song that seem to recur, for example these rapid repetitions that sound as though the bird is tripping over itself seem to occur regularly:

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I am also reliably informed that the slurred rather nasal "tschay" notes in the middle of this sequence are also diagnostic:

The alarm call that I have recorded starts with a rather short "chack" note and then progresses into a churring scolding noise, but whilst this bird did this when I approached too close it then moved into full song, presumably to drive me away ! :

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But it is the ability to imitate other species that is remarkable in this bird. A study from Belgium of 30 different individuals showed that 80% of the song phrases were definitely imitated (the remaining 20% were unknown), and that 80% consisted of an average of 76 different song types in each bird: 45 derived from the wintering grounds in Africa and 31 from other European species. It would seem that young birds begin to learn their song whilst in Europe, but then continue to do so for a further 6-7 months as they migrate across the equator and take up their winter quarters in eastern Africa, picking up song phrases from other species as they go. Once the learning phase is finished the songs learned then become fixed (Dowsett-LeMaire 1979).

So think about that amazing learning and copying process and have another listen to this crazy bird: here is another sequence that you can try and memorise !!

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REED WARBLER (Acrocephalus scirpaceus)

Rousserolle effarvatte

 

A summer visitor to Switzerland the Reed Warbler is found almost exclusively in reed beds at low altitude (normally below 600m), this means its distribution is somewhat limited since such habitat is now rare in this country.

Also the Reed Warbler is a rather shy bird, difficult to see in the dense reeds where it often stays low down, and even when seen it is just a bland brown thing with few real distinguishing characteristics. However when it sings the paler throat becomes prominent and the song is very distinctive - a rapid chattering of rather coarse sounding, guttural noises, the syllables of each phrase are repeated a variable number of times, usually 3-4 times each but can be up to 6 or 8 repetitions, usually with a slight change in pitch from one phrase to the next, giving the impression of a mechanical instrument "krek-krek-krek, chee-chee-chee-chee, kerr-kerr-kerr" etc separated by the occasional screech or whistle, it gives the impression of a very industrious bird working hard at its song:

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The speed of delivery and the repetitive nature of the phrases are apparent if we look at just 5 secs of the sonogram:

The song is mostly delivered from a hidden place in the reeds, although the literature tells us that they do have favoured song posts (specific favoured spots to sing from). Individuals will also include mimicry of other species in their songs but this is often hard to pick out amongst the general cacophony of noise from this bird. Here is another sample from a different bird:

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As yet I do not have any recordings of the calls.

 

 

 

GREAT REED WARBLER (Acrocephalus arundinaceus)

Rousserolle turdoïde

 

I confess this species is one of my favorites in the reed beds around the bigger lakes and rivers of Switzerland. It is hard to explain why - a mixture of the nature of its song and complexity of its life I think.

In Switzerland numbers have been in decline for the last 30+ years as marsh lands and reed beds suffer from drainage and land works. The Great Reed Warbler is found all across the continent from the Atlantic coast of Europe to Japan and the far East. Across this vast range are about 5 different races and all migrate south into the tropics during the northern winter. They are present in western Europe from mid-April to mid-September, and as the name implies they are reed bed specialists eating a wide variety of insects, but they are sturdy birds so will also take the young fish, lizards and (as you can see on the right !) frogs. On the breeding ground they are partially polygamous making things even more complicated.

But you always know when they sing that they are around. Their song can carry up to 1 km, it is delivered usually from the top of a reed stem, and consists of a series of low-pitched, harsh, almost frog-like croaking and grating sounds, often alternating in pitch and each repeated 4-5 times in each song phrase. The phrase itself is sung in a very deliberate and steady manner - "kraa-kraa-kraa, kree-kree-kree-kree, krok-krok-krok" etc, here is a fairly lengthy sequence of a marsh scene with a Great Reed Warbler as the focal species:

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You can detect the steady rhythm and deliberate nature of the song, however you can also hear that whilst there is a steady rhythm there is also great variability in the pattern. It is worthwhile dissecting this a little to understand better what is going on. Let's look first at 3 phrases, the gap between them has been shortened in this sonogram:

You can see that each phrase has a similar structure, let's look at the first one in more detail, see if you can spot the 4 parts to it:

The following is a still image of that sonogram and I have labelled the four parts. Part 1 is an opening of slow frog-like croaks, part 2 is made up five higher pitched shrieks, part 3 is very brief - a quick hiccup lasting  about a tenth of a second, part 4 is then another five sounds which again are croaks but more like grasshopper-type stridulations. Watch the single phrase sonogram and see the 4 parts.

 

 

 

Now, let's look at a still of the sequence of three phrases again you can see the four parts in each phrase:

 

 

 

Compare again to the sonogram:

 

But now see that although each of the parts is present they often differ in subtle ways:

Phrase 1: part 1 is the "frog croak": part 2 the "shriek": part 3 the "hiccup": part 4 the "grasshopper" (just as before)

Phrase 2: part 1 is the "frog croak": part 2 the "grasshopper": part 3 a longer "hiccup": part 4 is now a double "shriek"

Phrase 3: part 1 is the "frog croak" (but only twice this time): part 2 a "shriek": part 3 a new hiccup: part 4 a "shriek" similar to part 2 in phrase 1

 

Phew, its complicated !! Try and have the sonogram playing on your screen whilst also following the still photo that might make it easier.

Each of the "parts" I have referred to here are also known as syllables to bird researchers. A Great Reed Warbler may have many dozens of such syllables in its repertoire, and Catchpole (in Catchpole and Slater 1995) found that the more syllables a male Great Reed Warbler could fit into a single phrase the greater its chance of attracting and mating with a female - thus contributing to success in its polygynous world !

 

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