EURASIAN PYGMY OWL (Glaucidium passerinum) - Chevêchette d’Europe
Summary
A rather uncommon bird of forests between 1000-2000 meters altitude. It is a day-time hunter, small and the colouration makes it very hard to see. The call is distinctive however:
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 there occurs 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 mostly between 1000m - 2000m.
Artur Mikolajewski. Wikimedia
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) - although I have recorded them moving around very actively in dense forest in the dark. It lives up (or down !) to its name "pygmy" as it is barely the size of a starling, and hunts small birds like tits (mésanges), and small mammals such as voles along the forest edge. It is a fierce hunter though, and will tackle things as big as Mistle Thrush which are twice its body weight. But being so small it is vulnerable to larger predators, such as other owls, and takes great care to use its cryptic coloration to blend in with the background.
It 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 as it is mostly resident. 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 breeding season advertising and territorial call is a very distinctive but monotonous series of "poop" notes all at one frequency:
Despite being a soft note it carries for quite some distance, I was about 100m from that last recording when it was made. Closer up it is really quite powerful:
(That was a Jay that came in at the end, probably annoyed to find a predator in the same tree). 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 because of this I cannot say, and it 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):
Although this looks like a rather flat and uninteresting note, Galeotti et al (1993) were able to show that by measuring the exact frequency, duration and interval between the notes, they could identify individual birds with 85% accuracy. The owls themselves probably do much better!
This species also has a set of notes on a rising scale, the so-called "scale-call", 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.
UPDATE: JANUARY 2021
I learned last year that the “scale call” referred to above is used mostly in autumn (and is referred to as the “autumn song” by some). So at the end of 2020 I spent many dusk and dawn hours trying to understand this better, I also used some unattended recorders to see what variety of calls were being made. But I found it strange that these birds change their calls in autumn. It seems that they are strongly defending their territory, which may be an important task given the harsh winter months ahead of them and the need to defend a dwindling food supply. One need is to reduce competition and therefore drive out the offspring produced earlier in the year, forcing them to independence (Cramp etal). There is certainly a lot of excitement taking place, and I found the birds much more active than in the spring, moving around a lot and changing perch after almost every call.
The first thing I found was that the plain steady advertising song you heard above was now supplemented by brief intervening lower notes, “duh-duh”, delivered quite rapidly:
The same “poop” sound is there as before, but now anything up to 5 very brief intermediate notes, at a lower frequency, are inserted between each one. You can see these notes in the still photo of the sonogram and below is the sonogram movie:
Now, if you listen carefully to the sound above, at about the 10 second marker, you can hear in the background another song at a higher frequency. This is a second bird, possibly answering the hoot, using a “scale call”. Here are 4 samples of the scale call, recorded on different days and probably from different birds - I was doing this in the dark in various weather conditions, the last one in the rain!
The second cut in the above started with a distant scale call from a different bird.
As you can see the scale call very frequently starts with a single hoot, a note that sounds like those that make up the advertising call, at around 1.4kHz. The scale itself starts on the same frequency, but is a note that rises quickly and falls again, like an inverted U shape. Then as it rises up the scale it accelerates and the note becomes flatter, until finally, at the top of the scale it seems to have some modulations in it (depicted by the wavy line). This gives the scale call a very characteristic timbre (some authors describe it as like a bicycle tyre pump with your thumb over the end). Another aspect worthy of investigation is that the scale calls vary somewhat both in pitch and timing; so it is possible that this may be used to identify individual birds just as Galeotti etal (1993) found with the hoot.
One final call that I have recorded is what has been called by Magnus Robb (2015) as the “gyu” call and it is attributed to the female:
Robb (2015) presents them mostly as single calls, and whilst I did hear a small number of these, I mostly heard the sequences of 5-6 notes presented here, where the calls accelerate towards the end. Robb (2015) states that these repeated calls are a sign of excitement, sometimes used to alert the young to danger as they are leaving the nest. I am not in a position to comment on that, but in the same area where these calls were recorded I also heard several Tengmalm’s Owls, and Pygmy Owl remains have been found in the pellets of Tengmalm’s, so may be that could account for the excitement in my case! Here is a spectrogram of the “gyu” call.
But I don’t want to leave you with the impression that all is cut and dried and well-defined with this species. They prefer mature spruce forests which are dense to work in, (and in my case on steep limestone karst with potholes and crevices), they are elusive at the best of times, hard to census (Keller et al 2020) and I have only ever had glimpses of birds in flight. Couple that with the fact that in autumn they are most vocal in the first hour after dark and the last hour before dawn so you see rather little.
A typical sound scene is given below, just as darkness was falling, the first cut starts with a 27s sequence of “excitement” hoots, then at 30s there is what sounds like a completely bizarre “scale call”, but it jumps up and down, not a regular scale as my earlier examples, and it may be from the same bird or a different one (maybe a juvenile since it was so erratic?). I have removed about a minute silence then the second cut starts again with excitement hoots which, at 47s, are cut short by a “normal” scale call from a bird nearby, then at 1.13s there are two “gyu” calls followed immediately by excitement hoots from a bird much nearer the microphone, interrupted at 1.19s by another bizarre scale call from a distant bird. This all happened in the space of about 3 minutes, so unravelling how many individuals, of what gender and age there are out there is quite a challenge!
