When it comes to the singing of birds, each of us will remember many kinds of feathered artists. A large number of scientific teams are also involved in songbirds and their acoustic manifestations in this field. But what about singing in other species? How about such ducks or grouse? We refer to their sound as signals that can be divided into vocal (produced by the vocal system) and non-vocal. An important property of these signals is the frequency that is responsible for the propagation of sound through space. The range of this variable is relatively wide, but in birds it very rarely falls below 20 Hz (so-called infrasound, which is used, for example, by whales, elephants or even tigers or rhinos).
It was the low-frequency signals that researchers from the Faculty of Forestry and Wood Technology studied in the capercaillie grouse. In the Czech Republic, Poland and Bavaria, the acoustic expression of captive grouse was recorded. During the courtship, the males use a song about four verses (clicks, trill, cork and whetting) courting the hens. It has been revealed that during the vocalisation they also emit a harmonically structured sound with a very low fundamental frequency (28.7 ± 1.2 Hz), which coincides with the whetting phase.
What is the purpose of such a signal to grouse? Its advantage is the wavelength, thanks to which the sound spreads over long distances and attracts more hens. The contribution of these signals to communication between cocks is also assumed: they can carry information about an individual's fitness. To some extent, they could even serve to distinguish individuals by voice. It is certainly interesting for hunters, zoologists and lovers of this species that the low-frequency sound coincides with the last phase of the mating call, i.e. with whetting, when the grouse is so-called deaf. The cause is probably the induced contraction of the muscles of the middle ear, which are responsible for the attenuation of various, mostly unpleasant or dangerous sounds. Thus, with temporary deafness, the grouse pays for an advantage in low-frequency communication. Most interesting of this discovery is that it was found in a relatively small bird, such as the grouse, compared to cassowaries, for which low-frequency signals are known.
Although the capercaillie is not a songbird, its love song is one of the most interesting and now better-known sounds in the animal world.
doc. Ing. Vlastimil Hart, Ph.D.
He has been a patriot of this faculty since the time of his studies at the Faculty of Forestry and Wood Sciences, CULS in Prague. During his studies, he worked for students and his alma mater and continues to do so as the head of the Department of Game Management and Wildlife Biology. At FLD, he established the tradition of Academic Trumpet Hunting and Lure Hunting Competitions and several student shooting competitions. He devotes himself to a large number of scientific works, such as the effects of solar activity on the Earth's magnetic field, which subsequently affects the behaviour of dogs.
Prepared by Lucie Hambálková