Hiroko Yamada

Spontaneous vocal differentiation of coo-calls for tools and food in Japanese monkeys.

Vocal production and its usage in nonhuman primates may share common features with primitive human language. We trained two Japanese monkeys to use a rake-shaped tool to retrieve distant food. After the training, the monkeys spontaneously began vocalizing coo-calls in the tool-using context. We then trained one of the monkeys to vocalize to request food or the tool. Three independent acoustic parameters were measured and each parameter was independently analyzed across conditions using a multiple comparison test. We found that the monkey spontaneously differentiated their coo-calls to ask for either food or tool during the course of this training. This process might involve a change from emotional vocalizations into intentionally controlled ones by associating them with consciously planned tool use. We thus established a novel hypothesis about the origin of voluntary vocal control that could be approached from neurophysiological procedures.

Developmental learning of complex syntactical song in the Bengalese finch

We developed a neural network model for studying neural mechanisms underlying complex syntactical songs of the Bengalese finch, which result from interactions between sensori-motor nuclei, the nucleus HVC (HVC) and the nucleus interfacialis (NIf). Results of simulations are tested by comparison with the song development of real young birds learning the same songs from their fathers. The model shows that complex syntactical songs can be reproduced from the simple interaction between the deterministic dynamics of a recurrent neural network and random noise. Features of the learning process in the simulations show similar trends to those observed in empirical data on the song development of real birds. These observations suggest that the temporal note sequences of songs take the form of a dynamical process involving recurrent connections in the network of the HVC, as opposed to feedforward activities, the mechanism proposed in the previous model.

Decreased Fecal Corticosterone Levels Due to Domestication: A Comparison Between the White-Backed Munia (Lonchura striata) and Its Domesticated Strain, the Bengalese Finch (Lonchura striata var. domestica) With a Suggestion for Complex Song Evolution

The Bengalese finch (BF; Lonchura striata var. domestica) is a domesticated strain of the white-backed munia (WBM; Lonchura striata). Environmental stresses activate the hypothalamic-pituitary-adrenal (HPA) axis and release corticosterone (CORT). We hypothesized that domesticated songbirds have reduced CORT levels because of reduced levels of environmental stresses (compared to wild conditions) and reductions in the role of CORT, which is necessary for survival in the wild. However, no study has examined the effects of domestication on songbird CORT levels. To explore the domestication effects, we compared CORT levels between domesticated BFs and their wild ancestors WBMs. We also compared CORT levels between bought and aviary-raised BFs, and between wild-caught and captive-raised WBMs to examine the influence of being raised. However, blood collection causes stress, which affects endocrine dynamics and makes continuous sampling difficult in small birds. Therefore, we used a non-invasive method to measure fecal CORT. Parallelism between diluted fecal extracts and a CORT standard, extraction efficiency, and ACTH challenge demonstrated the effectiveness of this method. This study demonstrates that BFs have lower fecal CORT than do WBMs, regardless of whether the WBMs were wild-caught or captive-raised. In addition, BFs sing more complex songs than WBMs. Considerable evidence suggests that song complexity is related to CORT levels. Previously, we found that the corticosteroid receptors were expressed in song-control areas of the BF brain. Based on these results, we hypothesize that reduced CORT levels through domestication might be one factor allowing for the development of more complex songs in BFs.

Complex song development and stress hormone levels in the Bengalese finch

Models of birdsong are useful in the study of developmental and evolutional mechanisms of vocal learning behaviour. Knowledge of these mechanisms is important for understanding the evolutionary adaptation strategies of organisms. The Bengalese finch sings a complex song believed to have evolved by domestication because the song of its wild ancestor, the white-backed munia, was very simple. There is evidence that the song complexity is used as an indicator of male quality during mate selection. Because songbirds learn their song as juveniles, development of the song system is affected by developmental stress. Therefore, song traits may reflect developmental conditions and that may be honest sexually selected signals. We compared the level of the stress hormone corticosterone between Bengalese finches and white-backed munias. Results showed that Bengalese finches had lower circulating corticosterone levels than white-backed munias. Relaxation from natural selection pressures and the addition of artificial selection due to domestication may have decreased the corticosterone levels and allowed for the evolution of the complex song in the Bengalese finch. Two subtypes of corticosterone receptors, the glucocorticoid receptor and mineralocorticoid receptor, showed expression in song nuclei of the Bengalese finch brain. Thus, these results suggest the possibility that song development is regulated by corticosterone via binding to the corticoid receptors. Song-nuclei-related expression of corticoid receptors might have had an increasing developmental condition-dependent influence on song traits. Thus, our results suggest that decreased stress hormone levels secondary to domestication might account for one reason why songs became complex in Bengalese finches.

Detection and characterization of whale signals using seafloor cabled seismic networks offshore Japan

Ocean ambient noises against seismic signals are well studied using archived waveforms recorded on three-component seismometers and hydrophones connected to a seafloor cabled seismic network off Kushiro, Hokkaido, Japan basically facing the Pacific Ocean. The system was deployed to install in late July 1999 by Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Outstanding “noises” at frequency bands of 15-30 Hz are recorded on all components of both seismometers and hydrophones, which are directly recognized as fin whale calls in comparison with in-situ visual surveys carried in September to October 2009. It is extremely conspicuous that a seasonal variation of the fin whale calls has been revealed in ambient noise spectrograms of continuous longterm waveform records from 2009 to 2013. High-intensity signals associated with the fin whale calls appear commonly in the periods from September to February over cold winter at high latitudes. The remarkable seasonal pattern should be corresponded to their annual living behavior and might be related to climate changes in the Pacific Ocean.