Publications

Abstract

Formants, or resonance frequencies of the upper vocal tract, are an essential part of acoustic communication. Articulatory gestures—such as jaw, tongue, lip, and soft palate movements—shape formant structure in human vocalizations, but little is known about how nonhuman mammals use those gestures to modify formant frequencies. Here, we report a case study with an adult male harbor seal trained to produce an arbitrary vocalization composed of multiple repetitions of the sound wa. We analyzed jaw movements frame-by-frame and matched them to the tracked formant modulation in the corresponding vocalizations. We found that the jaw opening angle was strongly correlated with the first (F1) and, to a lesser degree, with the second formant (F2). F2 variation was better explained by the jaw angle opening when the seal was lying on his back rather than on the belly, which might derive from soft tissue displacement due to gravity. These results show that harbor seals share some common articulatory traits with humans, where the F1 depends more on the jaw position than F2. We propose further in vivo investigations of seals to further test the role of the tongue on formant modulation in mammalian sound production.

Abstract

Chicks can convey information about their needs with calls. But it is still unknown if there are any universal need indicators in chick vocalizations. Previous studies have shown that in some species vocal activity and/or temporal-frequency variables of calls are related to the chick state, whereas other studies did not confirm it. Here, we tested experimentally whether vocal activity and temporal-frequency variables of calls change with cooling. We studied 10 human-raised
Siberian crane (Grus leucogeranus) chicks at 3–15 days of age. We found that the cooled chicks produced calls higher in fundamental
frequency and power variables, longer in duration and at a higher calling rate than in the control chicks. However, we did not find
significant changes in level of entropy and occurrence of non-linear phenomena in chick calls recorded during the experimental cooling. We suggest that the level of vocal activity is a universal indicator of need for warmth in precocial and semi-precocial birds (e.g. cranes), but not in altricial ones. We also assume that coding of needs via temporal-frequency variables of calls is typical in species whose adults could not confuse their chicks with other chicks. Siberian cranes stay on separate territories during their breeding season, so parents do not need to check individuality of their offspring in the home area. In this case, all call characteristics are available for other purposes and serve to communicate chicks’ vital needs.

Abstract

Vocal individuality provides a method of personalization for multiple avian species. However, expression of individual vocal features depends on necessity of recognition. Here we focused on chick vocalizations of demoiselle, Siberian and red-crowned cranes that differ by their body size, developmental rates and some ecological traits. Cranes are territorial during summer, but gather in
large flocks during autumn and winter. Nevertheless, parents keep feeding their chicks, even on winter grounds, despite the potential of confusing their own and alien
chicks. Here we aimed to compare expression of individuality and sex in calls of three crane species between solitary and gregarious periods of a chick’s life, and between species. We found significant individual patterns of
acoustic variables in the calls of all three species both before and after fledging. However, only red-crowned crane chicks increased expression of individuality significantly after the fledging. Also, we found that chicks of all three species significantly increased occurrence of nonlinear phenomena, i.e., irregular oscillations of soundproducing membranes (biphonations, sidebands, and deterministic chaos), in their calls after fledging. Non-linear phenomena can be a way of increasing the potential for
individual recognition as well as avoiding habituation of parents to their chicks’ calls. The older chicks are, the less
their parents feed them, and chicks benefit from keeping the permanent attention.