Habitat type and density influence vocal signal design in satin bowerbirds

This study provided a thorough test of the acoustic adaptation hypothesis using a within-species comparison of call structure involving a wide range of habitat types, an objective measure of habitat density and direct measures of habitat-related attenuation. The structure of the bower advertisement call of the satin bowerbird was measured in 16 populations from throughout the species' range and related to the habitat type and density at each site. Transmission of white noise, pure tones and different bowerbird dialects was measured in five of six habitat types inhabited by satin bowerbirds. Bowerbird advertisement call structure converged in similar habitats but diverged among different habitats; this pattern was apparent at both continent-wide and local geographical scales. Bowerbirds' call structures differed with changes in habitat density, consistent with the acoustic adaptation hypothesis. Lower frequencies and less frequency modulation were utilized in denser habitats such as rainforest and higher frequencies and more frequency modulation were used in the more open eucalypt-dominated habitats. The white noise and pure tone transmission measurements indicated that different habitats varied in their sound transmission properties in a manner consistent with the observed variation in satin bowerbird vocalizations. There was no effect of geographical proximity of recording locations, nor was there the predicted inverse relationship between frequency and body size. These findings indicate that the transmission qualities of different habitats have had a major influence on variation in vocal phenotypes in this species. In addition, previously published molecular data for this species suggest that there is no effect of genetic relatedness on call similarity among satin bowerbird populations.

Design for sampling - preliminary exploration

A modern mineral processing plant represents a substantial investment. During the design process, there is often a period when costs (or revenues) must be compensated for by cuts in capital expenditure. In many cases, sampling and measurement equipment provides a soft target for such 'savings'. This process is almost analgous to reducing the capital investment in a corner store by not including a cash register. The consequences will be quite similar - a serious lack of sound performance data and plenty of opportunities for theft - deliberate or inadvertent. This paper makes the case that investment in sampling and measurement equipment is more cost-effective during the design phase. Further, a strong measurement culture will have many benefits including the ability to take advantage of small gains. In almost any business, there are many more opportunities to make small gains than to make large, step changes. In short, if a project cannot justify the cost of accurate and reliable measurement of its performance, it probably should not be a project at all.