Wildlife Hormones and Behavioral Ecology
Information encoding in rock hyrax harsh vocalization
Male rock hyrax produce loud complex calls. Only calls of mature or dominant males include low-pitched, harsh elements, we term snorts. In the past, we found that snorts are related to male weight, social status, and androgen levels. We hypothesize that long and stable snorts are difficult to produce. Therefore, snort length and stability should provide reliable information on the singer’s quality. In the current study, we used "jitter" and "shimmer" to describe periodicity and amplitude deviations (i.e., roughness), and link social status, weight, and the ability to produce longer, smoother snorts.
We found that in wild hyrax songs, snort length was associated with weight but not with social status. Heavier males had longer, more stable snorts, which may show higher levels of vocal control. Higher ranked individuals produced harsher snorts, possibly indicating aggressiveness. Surprisingly, this was seen only in spontaneous calls. These calls may represent the individual’s true ability to persistently advertise itself, while induced calls may show the maximal potential. Playback experiments in the field showed that longer or harsher snorts included in songs decreased conspecifics’ answer rate. Snorts may therefore communicate complex messages including information on both weight and dominance in a single vocal component, by balancing length and harshness.