Male Hyrax Research Articles

Social context mediates testosterone's effect on snort acoustics in male hyrax songs

Testosterone affects physical and motivational states, both of which may strongly influence vocalization structure and acoustics. The loud complex calls (i.e., songs) of male rock hyraxes (Procavia capensis) are used as honest signals for advertising physical and social states. The snort, a low frequency, noisy element of the song, encodes information on the singer's age and social rank via harshness, as measured by jitter (i.e., acoustic frequency stability) and duration; suggesting that the snort concomitantly advertises both vocal stability and aggression. Our past findings revealed that testosterone levels are related to both vocal elements and social status of male hyraxes, suggesting that hormonal mechanisms mediate the motivation for aggressive and courtship behaviors. Here we examined whether long-term androgen levels are related to snort acoustics and song structure by comparing levels of testosterone in hair with acoustic and structural parameters. We found that songs performed by individuals with higher testosterone levels include more singing bouts and longer, smoother snorts, but only in those songs induced by external triggers. It is possible that hyraxes with higher levels of testosterone possess the ability to perform higher-quality singing, but only invest in situations of high social arousal and potential benefit. Surprisingly, in spontaneous songs, hyraxes with high testosterone were found to snort more harshly than low-testosterone males. The context dependent effects of high testosterone on snort acoustics suggest that the aggressive emotional arousal associated with testosterone is naturally reflected in the jittery hyrax snort, but that it can be masked by high-quality performance.

The progression pattern of male hyrax songs and the role of climactic ending

The study of animal vocal signals can either focus on the properties of distinct vocal elements or address the signal as a whole. Although some attention has been given to the continuous progression patterns of bird songs, such patterns in mammalian vocalisations have been largely overlooked. We examined temporal changes in structural and acoustic parameters in male rock hyrax songs. We found a gradual increase in call frequency and amplitude towards the song ending, as well as an abrupt increase in bout syntactic complexity, peaking in the last quintile of a song. In musical terms, such a pattern can be described as a crescendo (amplitude increase) with a terminal climax. In Western music, crescendos are used to maintain attention and direct the listeners towards a memorable highpoint of the musical piece. This structure may have an analogous function in animal communication, recruiting audience attention towards the climactic and potentially most informative part of the signal. Our playback experiments revealed that hyrax males tend to reply more to songs with a climactic ending, indicating that this progression pattern is important for hyrax communication. We suggest that animal vocal communication research can benefit from adding musical concepts to the analysis toolbox.

A mixed strategy of counter-singing behavior in male rock hyrax vocal competitions

Maynard-Smith’s game-theoretical framework suggests that conflicts should be resolved through an exchange of agonistic displays which can be as effective as physical attack in securing contested resources. Hence, participants use signaling tactics that are governed by game-theoretical competition rules to maximize their benefit from the interaction. In rock hyraxes, males initiate singing in response to conspecific male songs, possibly to self-advertise and to facilitate comparison of performance by receivers. We hypothesized that hyrax counter-singing strategy can be explained by resident-intruder model and its outcome is determined by the identity and ability of the participants. Natural hyrax singing events and playback-induced events were classified according to the participants’ residence status—resident or bachelor (i.e., non-resident). As predicted by the resident-intruder model, resident listeners tended to reply to conspecific males at high rates (≈40 %), while bachelors showed low reply rates (17 %) to resident initiators. Unexpectedly, the lowest-ranking bachelors showed a tendency to reply to the highest-ranking residents. One possible explanation for this counter-intuitive behavior might be that weaker individuals exploit a situation in which it is unremunerated for a stronger opponent to retaliate (i.e., Napoleon strategy) and seize a self-advertisement opportunity in front of a large audience attending to the high-ranking males’ signal. Overall, we show that male hyraxes employ different counter-singing tactics depending on the residence and rank differences between the participants. This choice of competition tactics can be based on opponents’ individual recognition or/and on direct decoding of opponents’ traits encoded in the song. In nature, conflicts are usually resolved through signaling rather than by actual fighting. Rock hyrax males often participate in vocal competitions, possibly to reduce the need for physical confrontations. During our study on the dynamics of male hyrax vocal competition, we discovered that hyraxes employ mixed counter-singing strategy dependent on the residence status and social rank differences between the participants. A paradoxical “Napoleon-complex” tactic was observed in interactions between males, when low ranking bachelors were found to interact and challenge the highest-ranking residents. On the other hand, residents were found to interact with opponents regardless of residency and/or rank. On top of the cognitive abilities required to individually recognize an opponent and possibly decode its vocal signals, our results suggest that male hyraxes compare own individual traits to those of the opponent in a mutual signal assessment interaction.

Harsh vocal elements affect counter-singing dynamics in male rock hyrax

Morton’s motivation-structural (MS) rules suggest that the acoustic structure of a signal can reflect the caller’s motivation and internal state. In many species, low-frequency and noisy (harsh) sounds have been found to comply with MS rules, accompanying agonistic interactions and functioning as a badge of aggression and dominance. Male rock hyraxes (Procavia capensis) often produce long and complex advertisement calls (songs) both spontaneously and in counter-singing sessions with other males. Hyrax songs include a vocal element, which is a harsh sound produced only by mature, dominant males. We predicted that the number of snort elements in the song would affect the dynamics of male hyrax counter-singing. We performed 3 series of playback experiments of natural and artificially manipulated songs on a wild hyrax population. We found that the probability of initiating counter-singing by nearby males increased together with the number of snorts in the stimulus song. Furthermore, the receivers replied to the synthetic snort-only vocal sequences at an equal rate as to their origin song as long as the snort elements maintained their original position within the signal. Our findings suggest that the snort component is one of the main information transfer channels in male hyrax singing and can elicit conspecific singing even when isolated from other vocal elements. In addition, the position of snort elements (their temporal pattern and rhythm) bears a possible significance in keeping the overall signal meaningful. Finally, our findings support previous claims that harsh sounds constitute one of the key components in vocal communication.

Male hyraxes increase song complexity and duration in the presence of alert individuals

The goal of vocal communication is the efficient delivery of signals to a target audience. Long and complex vocalizations are especially challenging because they are subject to environmental interference and may incur significant costs for the signaler. One of the various ways of increasing the efficiency of signal delivery is enhancement of communicational efforts only when potential audience is perceived nearby in an attempt to maximize the benefit over the cost of signaling (audience effect). Another way is signaling subsequently to events that intensify individual alertness in order to ensure audience attentiveness and sensitivity to the transmitted information. Rock hyraxes (Procavia capensis) are social mammals that use complex acoustic signals to communicate. Adult male hyraxes produce elaborate vocalizations (known as songs) that serve as honest advertisements of their quality. By combining analysis of male hyrax songs recorded in the field over a period of 11 years and playback experiments, we found that songs performed during and following attention-grabbing events (agonistic interactions, alarm calls, predator presence, and songs performed as a reply to conspecific singing) have an increased structural and syntactic complexity in comparison to spontaneous singing. Male hyraxes demonstrate a cognitive ability to optimize their advertising efforts in response to multiple types of events. This signaling strategy exploits the effective communication window created by attention-grabbing events and by the presence of an alert audience to delivers structurally and syntactically enhanced signal. To our knowledge, this is the first report of syntactic complexity of vocal signaling being altered following various triggers that change conspecifics mental state in terrestrial mammals.

Disseminated Tuberculosis in Hyrax (Procavia capensis) Caused by Mycobacterium africanum

Tuberculosis due to Mycobacterium africanum was diagnosed in an adult female hyrax (Procavia capensis). Pathologic examination revealed disseminated tuberculous lesions. The same pathologic changes were also found in a male hyrax that died a year later. Both animals were imported from the United Arab Emirates and were held in captivity at the Zagreb Zoo in Croatia. The source of infection remains unknown. The acid-fast bacteria isolated from the lungs of the female hyrax were identifyed by polymerase chain reaction as Mycobacterium tuberculosis complex and Geno Type MTBC test confirmed the strain to be M. africanum I.

Tuberculosis in imported hyrax ( Procavia capensis) caused by an ususual variant belonging to the Mycobacterium tuberculosis complex

Tuberculosis was diagnosed in an adult female hyrax ( Procavia capensis) imported from South Africa and held in a captive colony at the Perth Zoo. An organism similar to Mycobacterium microti was isolated from the lung of this animal and the lung of an adult male hyrax in the colony. The organism was not pathogenic to rabbits or guinea pigs. Protein profiles and RFLP patterns using the probes IS6110 and pTBN12 showed both hyrax isolates were identical. These isolates were similar to a M. tuberculosis complex strain isolated from dassies (hyrax) in the late 1950s in South Africa and to M. microti, but appeared to be more closely related to the “dassie bacillus”. It is likely that at least once of the hyrax was infected at the time of collection in South Africa. The finding of tuberculosis in these imported animals highlights concern over the lack of suitable tests for the detection of tuberculosis in unusual animal species such as these, and the problems that can arise as a result of the importation of infected animals.

Application of Ovine Luteinizing Hormone (LH) Radioimmunoassay in the Quantitation of LH in Different Mammalian Species

A sensitive double antibody radioimmunoassay has been developed for measuring luteinizing hormone (LH) in various African mammalian species, using rabbit anti-ovine LH serum (GDN 15) and radioiodinated rat LH or ovine LH. Serum and pituitary homogenates from some African mammals (hyrax, reedbuck, sable, impala, tsessebe, thar, spring-hare, ground squirrel and cheetah, as well as the domestic sheep, cow and horse and laboratory rat and hamster) produced displacement curves parallel to that of the ovine LH standards. The specificity of the assay was examined in detail for one species, the rock hyrax. Radioimmunoassay and bioassay estimates of LH in hyrax pituitaries containing widely differing quantities of pituitary hormones were similar. In sexually active male hyrax mean plasma LH was 12.1 ng/ml and pituitary LH 194 microgram/gland, but in sexually quiescent hyrax mean plasma LH was 2.4 ng/ml and mean pituitary LH 76 microgram/gland. Intravenous injection of 10 microgram of luteinizing hormone releasing hormone increased mean LH levels in hyrax from 0.9 ng/ml to 23.2 ng/ml by 30 min. Conversely, im injection of 250 microgram testosterone induced a fall in LH levels in male hyrax from 1.7 ng/ml to 0.7 ng/ml 6 h after administration. Although the specificity of the assay for quantitating plasma LH in other species was not categorically established, there was a good correlation between plasma LH concentration and reproductive state in the bontebok, impala, spring-hare, thar, cheetah, domestic horse and laboratory rat, suggesting the potential use of the antiserum in quantitating LH in a variety of mammalian species.

Hypothalamic, pituitary and gonadal hormone production in relation to nutrition in the male hyrax (Procavia capensis).

Hypothalamic, pituitary and gonadal hormone production in relation to nutrition in the male hyrax (Procavia capensis).