Acoustic analysis of cattle (Bos taurus) mother-offspring contact calls from a source-filter theory perspective

Cattle vocalisations have been proposed as potential indicators of animal welfare. However, very few studies have investigated the acoustic structure and information encoded in these vocalisations using advanced analysis techniques. Vocalisations play key roles in a wide range of communication contexts; e.g. for individual recognition and to help coordinate social behaviours. Two factors have greatly assisted our progress in developing an understanding of animal vocal communication. Firstly, more rigorous call analysis methods allow us to describe the variation in the vocal parameters in unprecedented detail. Secondly, the adoption of the "source-filter theory" of call production links the acoustic structure of vocalisations to the morphology and physiology of calling animals. Using these approaches, it is possible to quantify the potential for each acoustic component to carry information. In this study, we examined naturally occurring contact calls produced by crossbred beef cows and their calves-under free-ranging-conditions. Our main aims were-to identify vocal parameters, which can be used to characterise cow and calf contact calls, and to describe variation in these parameters under relatively undisturbed conditions. Additionally, we aimed to provide information for future studies on potential acoustic indicators of animal welfare in cattle. We identified two different types of cow contact calls associated with different behavioural contexts, and with differing acoustic structures. Low frequency calls (LFCs) were produced by cows when they were in close proximity to their calves, in the first three or four weeks postpartum, and they were made with the mouth closed or only partially open (fundamental frequency (F0) = 81.17 +/- 0.98 Hz). By contrast, high frequency calls (HFCs) were produced by cows when they were separated from their calves (e.g. not in visual contact) and preceded nursing (F0 = 152.8 +/- 3.10 Hz). Calf calls were produced when separated from their mothers and preceded suckling (F0 = 142.8 +/- 1.80 Hz). A detailed analysis of cow LFCs and HFCs, and of calf calls, showed that all three types of calls are individually distinctive. We also show that calf calls encode age, but not sex. Although it has previously been suggested that cattle contact calls are individually distinctive, to our knowledge, our study is the first to use the most rigorous, modern methods to analyse their calls. This study represents an important advance in our knowledge cattle contact vocalisations, which is essential for future work on cattle communication and welfare. (C) 2014 Elsevier B.V. All rights reserved.