EURASIAN PYGMY OWL (Glaucidium passerinum)

Chevêchette d'Europe

 

The main breeding range of the Pygmy owl is in boreal forests from Norway across Russia and Siberia to the Pacific coast of the Eurasian continent. In the Alps and the Jura mountains of Switzerland occur a small population of what is thought to be a relict of the last ice-age, they hung on here when the ice retreated. They are found in the western Jura, pre-Alps and Alps in forests between 1000m - 2000m.

 

This is an unusual owl because it is diurnal - active during the day. In fact its ability to see in the dark is said to be comparable to that of humans (Voous and Cameron 1988). And it lives up (or down !) to its name "pygmy" as it is barely the size of a starling, and hunts small birds like tits (mésange), and small mammals like voles along the forest edge. But being so small it is vulnerable to larger predators itself and takes great care to use its cryptic coloration to blend in with the background and so can be very difficult to see.

 

Despite its size it is a ferocious hunter and will take prey opportunistically, hiding excess prey items in "larders" - store places in the crown of tall conifers where it will return and retrieve the food when needed. This helps it through periods of scarcity and is presumably one of the strategies that helps it survive the harsh winters of its breeding range. Like many owls it is a hole nester but this little guy uses holes made by woodpeckers, usually Great Spotted or Three-toed Woodpeckers.

Its voice is a very distinctive but monotonous series of "poop" notes all at one frequency:

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Despite being a soft note it carries for quite some distance, I was about 300m from that last recording when it was made. Closer up it is really quite powerful:

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In the first recording the calls came at intervals of 2.05 secs, in the second recording the two bouts were at intervals of one call every 1.7 secs. The first recording also had calls at a frequency of 1.32 Khz and the second was a bit higher at 1.41 Khz. The literature (Voous and Cameron 2008; Cramp et al) tells me that females call at a slightly higher pitch and more rapidly than males, but whether the differences in my recordings are of sufficient difference I cannot say and needs more investigation. Cramp et al state that the pitch difference can be up to a third higher which is much more than I recorded. So maybe my difference is simply a reflection of excitement level?

 

 

 

Here is a sonogram of the second recording, from it you can see that each note lasts for about 0.3 secs and is accompanied by a harmonic at twice the frequency (= 2.8 Khz):

This species also has a set of notes on a rising scale, the so-called "scale-song", this is used mostly at the height of territorial disputes but I have yet to experience this.

You can read more about the day and location where I made these recordings here.

 

 

TAWNY OWL (Strix aluco)

Chouette hulotte

 

The Tawny Owl is found throughout the Western Palearctic region with a separate east Asia population. About a dozen sub-species have been described across this range with two colour morphs - a brown one (which is mostly in western Europe) and a grey one, the latter more common in colder areas and mountainous regions.

In Switzerland it is found in all forest/ woodland types up to about 1200m, but is more patchy in distribution as you get higher. This is the archetypical woodland owl, reasonably common throughout Europe. It is sedentary and pairs will occupy territories over a number of years.

In English the call is usually verbalised as "too-whit, too-whu" which most children know even if they have never heard one  - but this is wrong and mixes two kinds of call - and may have its origins in the song for winter which closes Shakepseare's play "Love's Labour's Lost":

When icicles hang by the wall

And Dick the shepherd blows his nail

And Tom bears logs into the hall

And milk comes frozen home in pail,

When blood is nipp'd and ways be foul,

Then nightly sings the staring owl, Tu-whit;

Tu-who, a merry note,

While greasy Joan doth keel the pot.

When all aloud the wind doth blow

And coughing drowns the parson's saw

And birds sit brooding in the snow

And Marian's nose looks red and raw,

When roasted crabs hiss in the bowl,

Then nightly sings the staring owl, Tu-whit;

Tu-who, a merry note,

While greasy Joan doth keel the pot.

 

 

The "tu-whu" part of Shakespeare's description is probably the common advertising call, which is a low-frequency series of notes best verbalised as "hooo-huhuhohoooo" with that final "hooo" prolonged and resonant and tremulous. It is a strong sound and in the quiet of the night can carry a long way, this bird was about 400m away when I recorded it with my parabola:

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The following is a recording made from about 50m, it is a long piece but gives a true reflection of the timing and the silence between calls.Closer up you can appreciate better the qualities of the sound, the first note rises and falls, this bird had a very brief second note leading to the third which is more prolonged and tremulous with almost a rasping quality to it:

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There are other noises in that last piece, rustling sounds are the feet of a small herd of Chamois in the dry leaves, they were slowly moving away from my approach, around 1.38 - 1.44, then again at 2.06 are some clear calls from overhead that sound rather like a Coot flying about.

The sonogram below gives two calls extracted from that last piece. I have focused just on the lower frequencies, the main energy is around 800 Hz but there are many harmonics above that, in the sonogram in addition to the base call you can also see the first harmonic at 1600Hz. Note how the first note rises from about 750 Hz to 850 Hz before falling back again, the third note is also not constant and the vibrato effect is clearly seen:

 

 

I have read that individual birds can be recognised by the pitch and degree of vibrato in their calls. Books often describe this as the male song, but in fact both sexes can make this call.

The "tu-whit" part of Shakespeare's description is probably a rendition of a more explosive call that sounds like "kewick". Birds use it to locate each other, and females will use it to respond to a male song, so it is often referred to as a female song,  but again both birds are capable of making this sound. Here is a recording from a noisy location which required heavy filtering:

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In addition to the above there are also a host of variations around these two most common calls. I cannot really comment and clearly need to find myself a breeding pair and spend a few nights in the forest !

 

 

 

TENGMALM'S OWL  (Aegolius funereus)

Chouette de Tengmalm

 

This owl is found throughout the boreal forest zone and is typical of that habitat (boreal means "northern", and these forests are found between 50 deg and 60 deg latitude in a region which has short, moist, warm summers and long, cold, dry winters; 65% of such forests are found in Siberia and the rest in Scandinavia, Canada and Alaska). In North America this bird is called the Boreal Owl (for obvious reasons). The European name Tengmalm comes from  Swedish medical doctor and scientist Peter Gustav Tengmalm (1754-1803) who discovered the species in Sweden and its original scientific name was Strix tengmalmi which has now changed but that original vernacular name stayed with it.

The population in Switzerland is part of an isolated branch of that zone where boreal conditions are imitated by altitude. It is found in the sub-alpine forests of the Jura and Alps between 1000m - 2000m. Like the Pygmy Owl they use old woodpecker nest holes, but being almost twice the size of that bird it is the old holes of Black Woodpeckers which Tengmalm's chooses. But even though it is bigger than a Pygmy Owl this is still a small owl, weighing between 100g and 160g only (females are larger than males).  Its main diet is small mammals, mainly voles although small birds are also taken sometimes.

It hunts using sound as its main cue and to help this it has evolved very special ear structures, the ear-slots occupy almost the full length of the skull and the right ear slot is 6.5mm higher than the left and differently shaped. The difference we hear between our two ears is important in locating sounds, so this effect is enhanced in Tengmalm's Owl and by processing in the brain it is thought to make it a very accurate locating system (Norberg 1978). It also has internal ear structures that make it more sensitive to low frequency sounds like a small mammal rustling on the ground and it is said to be able to dive through shallow snow and catch voles which are tunnelling beneath based entirely on sound localisation (Voous and Cameron 1988). Such adaptations help it to hunt in those long dark winters.

Various sounds have been recorded for this species but most seem to be variants of the basic advertising call which is a series of rather hollow and rapidly repeated "poop" notes:

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[NOTE: these recordings were made in June using an unattended overnight recorder (a Sony PCM M10); you will hear cow bells from a nearby alpage, and also rustling sounds of nocturnal mammals and insects near the microphones]

That last recording had some unusually long call phrases in it ranging from 8 - 32 calls in each phrase, but the rhythm is very regular at around 5 notes per second. In fact in two sample of 10 calls from these recordings the average was 5.1, and 5.03 calls per second - remarkably consistent. At 1m25s in that last recording you could hear a slight change in intensity before it took off and then resumed calling further away at 1m32s.

In that last sequence the pitch was very constant at about 700 Hz.


Here is another piece with shorter calling sequences of between 5-7 notes in each phrase, which seems more typical, also hear how each phrase rises slightly from 700Hz to 800Hz:

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And see this on the sonogram:

All these recordings were made during the hours of darkness, but they will call at dawn or soon after as the light is breaking. Here is one during the dawn chorus it starts with the "chack-chack" alarm call of a Ring Ouzel which may have seen the owl, with Song Thrush, MistleThrush, Blackbird and Robin among the background singers.

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I was very happy to have found a location where this rather unusual bird can be found.

 

 

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