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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