GREAT REED WARBLER (Acrocephalus arundinaceus)
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:
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 !