Volume 129, Issue 3, March 2011
Index of content:
- BIOACOUSTICS 
129(2011); http://dx.doi.org/10.1121/1.3544370View Description Hide Description
Putative audio recordings of the Ivory-billed Woodpecker (Campephilus principalis) are presented along with discussions of the videos from which they were extracted and the observations that were made when these data were obtained. On two occasions, high-pitched calls were heard coming from the direction of a bird that was identified in the field as an Ivory-billed Woodpecker. These calls seem to match the description of an alarm call that was reported in the 1930s. One of the videos captured a series of the high-pitched calls, which sound similar to the Blue Jay (Cyanocitta cristata) bell call but do not match published sonograms of that call. A putative double knock, which is characteristic of the Ivory-billed Woodpecker, was captured in another video a little over a minute before a large bird with characteristics consistent with an Ivory-billed Woodpecker flew into view. Since it is extremely difficult to observe this critically endangered species, information on audio clues could have an impact on its conservation.
Sources of acoustic variation: Implications for production specificity and call categorization in chacma baboon (Papio ursinus) grunts129(2011); http://dx.doi.org/10.1121/1.3531944View Description Hide Description
Elucidating the information content of vocal signals is fundamental to the understanding of animal communication. Acoustically distinct calls produced in specific contexts allow listeners to predict future events and choose adequate responses. However, the vocal repertoires of most terrestrial mammals consist of a limited number of call types that vary within and between categories. These “graded signaling systems” are thought to be rich in information, at the cost of increasing uncertainty regarding call categorization. In this study, patterns of acoustic variation in grunts of wild chacma baboons (Papio ursinus) were assessed in relation to different contexts, callers’ arousal, the presence of listeners, and individual identity. Although overall production specificity was low, and sensitive to the number of contexts under consideration, grunts given in three contexts could be statistically distinguished from each other. Contextual differences remained when controlling for caller arousal, suggesting that these differences cannot be explained by variation in arousal. No audience effect was detected, but individual identity was found to have an influence on acoustic structure. Overall, these results support the view that, in comparison to other signaling systems associated with hazardous conditions, lower production specificity might evolve under relaxed circumstances where unambiguous signaling is less important.
Two-dimensional simulation of linear wave propagation in a suspension of polymeric microcapsules used as ultrasound contrast agents129(2011); http://dx.doi.org/10.1121/1.3543966View Description Hide Description
A generation of tissue-specific stable ultrasound contrast agent (UCA) composed of a polymeric capsule with a perfluorocarbone liquid core has become available. Despite promising uses in clinical practice, the acoustical behavior of such UCA suspensions remains unclear. A simulation code (2-D finite-difference time domain,FDTD) already validated for homogeneous particles [Galaz Haiat, Berti, Taulier, Amman and Urbach, (2010). J. Acoust. Soc. Am.127, 148–154] is used to model the ultrasound propagation in such UCA suspensions at 50 MHz to investigate the sensitivity of the ultrasonic parameters to physical parameters of UCA. The FDTD simulation code is validated by comparison with results obtained using a shell scatterer model. The attenuation coefficient (respectively, the sound velocity) increases (respectively, decreases) from 4.1 to 58.4 dB/cm (respectively, 1495 to 1428 m/s) when the concentration varies between 1.37 and 79.4 mg/ml, while the backscattered intensity increases non-linearly, showing that a concentration of around 30 mg/ml is sufficient to obtain optimal backscattering intensity. The acoustical parameters vary significantly as a function of the membrane thickness, longitudinal and transverse velocity, indicating that mode conversions in the membrane play an important role in the ultrasonic propagation. The results may be used to help manufacturers to conceive optimal liquid-filled UCA suspensions.