environmental acoustics

In penguin species, mates or parents and chicks recognise each other in the hubbub of the colony using mainly acoustic cues, via the display call. From their ability to recognise a particular call in the continuous background noise, it is assumed that they use peculiar strategies of coding/decoding. We have studied these strategies by playing-back modified display calls to two species of penguins. One, the adelie penguin (AP), has a nest which serves as a meeting point, and the other, the king penguin (KP), has no nest site and consequently it has no possibility to use visual landmarks. Both species exhibit signals that are highly redundant in the temporal and frequency domains and have sharp amplitude changes which confer to the call a maximal locatability. As in most other birds, the AP can discriminate a signal at the same intensity as the noise, but the KP is able to identify an individual call when its level is well below the level of the noise generated by other calls (cocktail party effect). According to the theory, two processes facilitate the detection of a signal embedded in the noise: the frequency-band analysis and the temporal analysis of amplitude or frequency modulations. Our experiments demonstrate that the vocal signature of the AP corresponds to the first process and that of the KP to the second. The differences in the strategies of coding-decoding are discussed with respect to the territorial habits and the environmental constraints of both species.

In most anuran species males advertise calls to attract females. In a natural environment these calls can be masked by the natural background noise. We investigated in the cricket frog the threshold at which females are no longer able to locate a male call, when the call was embedded in noise. We used artificial white noise and a natural frog chorus as background noise and embedded male calls at a different call/noise ratio in the noise. In phonotaxis experiments we played the noise versus the call embedded in noise. We tested females 9om a population living in an open grassland. Females responded to masked calls even when the call and the noise were of the same loudness. We will discuss the results in relation to other studies.

Despite the complexity and variability, the entity of sounds in particular time and space characterises the environment. Japanese people have an idea that the riverside environment provides important sound resources for comfort and relaxation, and attempt to include it in the local area planning. However, what is the riverain sound environment in bioacoustic senses? The Tone River, which covers a large area of mountains and plains in north and east of Tokyo, has historically been altered in many ways such as flood control and other human activities. In 1993-94, the sound environment survey was carried out from the lower reach of artificially constructed river banks, along the middle reach amidst the plain of agricultural activities to the upper reach of natural mountain forest tributaries. The present paper focuses upon the analysis methods to characterise the varieties of sound environment along the river. From identification of natural sound sources and examination of recorded samples using wave form, power spectrum and sonogram methods, I attempted to relate the sound source composition and their acoustic features to the land utilisation and structure of environment. It appears that the present method may provide a useful method to understand the structure of sound environment.

The king penguin breeds without a nest in colonies of several thousand birds. To beg for food, the chick must recognise the parents in a noisy environment, without using visual and olfactory, only vocal, cues. The parental call has to be distinguished from among the calls of other parents and chicks and the display calls of mating pairs. This recognition process is made more difficult not only by these interfering noises but also by propagation problems due to the parent-chick distance and to the mass screen of birds which together impose a particularly difficult problem of acoustic communication. To study this recognition process, we have quantified some of the problems which the chick must solve. Firstly we described the main characteristics of parental calls. Secondly we measured the ambient noise of the colony in the feeding area. Thirdly, in this area, we studied the propagation of adult calls to analyse the degradation of the signal at different distances, quantifying the effect of the mass body screen by comparison with propagation in an open area. Then, we conducted experiments with chicks, establishing mean and maximum distances of detection of the parental call and testing their ability to detect parental calls in a "jamming'' situation, i.e. among extraneous adult calls. At last, we tested chicks to determine which are the main acoustic parameters involved in the recognition process of the parental call. Our results demonstrate that the noise in the colony is almost continuous, that it has a high sound pressure level and that the spectrum is occupied by numerous birds at a time. There is total masking effect in terms of frequency and amplitude, increasing the difficulty the chick has in detecting its parents. Nevertheless, the chick can compensate for this effect, since it is able to detect an information-carrying signal whose intensity is below that of a background noise with similar temporal and spectral characteristics. This process of perception against a background noise (i.e. the "cocktail-party'' effect) is linked to a coding-decoding of the parental call closely adapted to these particular environmental constraints.

Many of the signals used for communication by animals are capable of transmission over long distances, that is, several times the usual spacing between individuals. From this observation it follows that a number of signallers and receivers are within communication range of each other and have the potential to interact. Such a grouping of several signallers and receivers is referred to as a communication network. They are thought to be common in all signalling modalities. The concept of communication networks has important implications for the evolution of signalling systems and the perceptual abilities of receivers. Studying communication networks presents a number of challenges, not least of which is how the signals of the individuals in a network can be simultaneously monitored without affecting the animals' behaviour. I describe a passive monitoring system for acoustic signals. This acoustic location system (ALS) uses the differences in arrival time of the same sound at several microphones to calculate its site of production and simultaneously record the signals of interest. This technique and its potential are explained using examples of male song birds (great tits Parus major) defending territories. In particular, the timing of singing interactions between neighbouring territory holders and their use of song variants will be related to location with respect to each other and shared territory boundaries. Preliminary indications are that timing and song variation are used to "address'' an otherwise widely broadcast signal to a particular member of the communication network.

Emperor Penguins Aptendodytes forsteri are able to add a sequence of syllables into their song. The proportion of songs having an additional sequence varies through the breeding season. The proportion of songs having an additional sequence increases because the percentage of one-sequence songs decreases and the percentage of three-sequence songs increases. Short songs were more inclined to be lengthened by an additional sequence: at the minimal percentage of one-sequence songs is more quickly attained than the maximal percentage of three-sequence songs; b) the proportion of lengthened one-sequence songs is three times higher than the proportion of lengthened two-sequence songs; e) twenty-one birds singing short and long variants have been recorded: 20 of them sang short variants whose duration was shorter than the mean measured for the population. The sound pressure level varies through the breeding season. Conclusion: Redundancy by an additional sequence found in songs of emperor penguins may be the result of the increase of the ambient noise level of the colony.

Whales living within seismically active regions are subject to intense disturbances
from strong sounds produced by earthquakes that can kill or injure individuals.
Nishimura & Clark (1993) relate the possible effects of underwater earthquake noise
levels in marine mammals, adducing that T-phase source signal level (10- to 30- Hz
range) can exceed 200 dB re: 1 µPa at 1 m, for a magnitude 4-5 earthquake, sounds
audible to fin whales which produce low frequency sounds of 16-20/25-44 Hz over
0.5-1s, typically of 183 dB re: 1 µPa at 1 m. Here we present the response of a fin
whale to a 5.5 Richter scale earthquake that took place on 22 February 2005, in
the Gulf of California. The whale covered 13 km in 26 min (mean speed = 30.2 km/
h). We deduce that the sound heard by this whale might have triggered the costly
energy expenditure of high speed swimming as a seismic-escape response. These
observations support the hypothesis of Richardson et al. (1995) that cetaceans may
flee from loud sounds before they are injured, when exposed to noise in excess of 140
dB re: 1 µPa 1 m.

We examined the extent to which acoustic noise in urban environments influences song characteristics and singing behaviour of Northern Cardinals Cardinalis cardinalis and American Robins Turdus migratorius. We predicted that, in response to loud noise, birds would improve signal transmission by (1) increasing singing rate and (2) adjusting song characteristics such as pitch and length. From May – July 2006, 42 cardinals and 53 robins were recorded in forests located within four acoustic environments in central Ohio: rural, residential, commercial, and highway. Following each recording, we measured ambient noise level and recorded information describing location, weather, habitat, and conspecific presence within 75 m. As predicted, frequency range was positively correlated with noise level for both species, but neither song length nor rate was related to noise level for either species. These data support the idea that anthropogenic noise influences avian singing behaviour and acts as a selective force in urban areas.