The interspecific relationships of black rhinoceros (Diceros bicornis) in Hluhluwe-iMfolozi Park

<p>As habitat loss, predators (human and non-human) and disease epidemics threaten species worldwide, protected sanctuaries have become vital to species conservation. Hluhluwe-iMfolozi Park (HiP) in South Africa is at the centre of one of the world’s greatest conservation success stories. The formal proclamation of HiP in 1895 prevented the extinction of the south-central black rhino (Diceros bicornis minor) population. In recent times HiP has been a strategic source population for the D. b. minor range expansion program, facilitating an 18-fold population increase across southern Africa. However, HiP’s own black rhino population appears to be in decline. Evidence for decline is most often attributed to overpopulation and poor habitat quality that is driving apparently significant increases in the average home range sizes, poor growth rates (i.e., low calf recruitment) and poor body condition of black rhino. Other factors such as non-human calf predation and parasitism have also been raised as potential causes of decline but remain untested. HiP does have some of the highest densities of lion (Panthera leo) and spotted hyena (Crocuta crocuta). HiP’s black rhino population also suffers from remarkably severe chronic haemorrhaging lesions caused by a filarial parasite (Stephanofilaria dinniki). Empirical evidence if or indeed why the HiP black rhino population might be in decline is lacking. Investigating this population’s true status and any potential causes of an apparent decline is urgently needed. This thesis therefore aimed to test three hypotheses for poor performance that included: (1) investigations of the average black rhino home range size, (2) confirmation of black rhino calf predation and (3) the relationship between filarial lesions and black rhino body condition. I inserted horn-implant VHF radio transmitters into 14 adult (i.e., >5 years) female black rhino in HiP and regularly monitored them on-foot over a three-year period. I found that average home range estimates (9.77 km2) were not significantly dissimilar to estimates using a similar technique obtained forty years prior (i.e., 7.5 km²). I also established the first confirmed link between predation attempts and tail amputation during a lion attack on a black rhino calf. Black rhino body condition, while significantly inversely and temporally correlated to lesion severity, did not appear to be driven by lesion severity itself and highlights the need for further research. An additional research focus for my thesis developed while in the field. I regularly witnessed red-billed oxpeckers (Buphagus erythrorynchus) feeding at black rhino filarial lesions while also alarm calling to alert them to my presence. Studies have found it difficult to empirically show how oxpecker-host interactions have net positive benefits that make it a mutualism. Thus, two chapters were designed to determine if red-billed oxpeckers were predominately mutualistic or parasitic when visiting black rhino. Determining this depended on whether I could identify net positive benefits or net costs to black rhino. Oxpeckers provide rhino with two possible benefits i.e., benefit 1 is cleaning ectoparasites and benefit 2 is increasing vigilance, and one cost i.e., lesion parasitism. More than 50 hours of behavioural observations established that oxpeckers favoured haemorrhaging filarial lesions over sites of tick attachment on black rhino. Moreover, black rhino appeared to be completely tolerant of oxpeckers that fed at lesions. To test whether oxpeckers increased rhino’s anti-predator vigilance, I conducted 84 human approach trials towards black rhino both with and without oxpeckers present. Results showed that rhino were immediately responsive to oxpecker alarm calls and benefitted from more than a two-fold increase in human detection rate and detection distance. Rhino predominately orientated to face towards their sensory blind spot (i.e., downwind) after an oxpecker alarm call. The traditional name (Askari wa kifaru) of the red-billed oxpecker, which translates as the rhino’s guard, appears to be validated. However, future research will need to confirm whether black rhino’s tolerance of parasitic oxpeckers is directly related to vigilance benefits. In summary, black rhino managers in HiP can be confident that the average home range sizes have not increased significantly. Further, predation of calves might be a greater problem than previously realised and requires further investigation. Monitoring changes in the filarial lesion severity of black rhino might be a useful tool for detecting impending changes in a rhino’s condition. Finally, black rhino are clearly eavesdropping and benefitting from oxpecker alarm calls – a co-evolution that has implications for conserving oxpecker populations as well.</p>

The interspecific relationships of black rhinoceros (Diceros bicornis) in Hluhluwe-iMfolozi Park

<p>As habitat loss, predators (human and non-human) and disease epidemics threaten species worldwide, protected sanctuaries have become vital to species conservation. Hluhluwe-iMfolozi Park (HiP) in South Africa is at the centre of one of the world’s greatest conservation success stories. The formal proclamation of HiP in 1895 prevented the extinction of the south-central black rhino (Diceros bicornis minor) population. In recent times HiP has been a strategic source population for the D. b. minor range expansion program, facilitating an 18-fold population increase across southern Africa. However, HiP’s own black rhino population appears to be in decline. Evidence for decline is most often attributed to overpopulation and poor habitat quality that is driving apparently significant increases in the average home range sizes, poor growth rates (i.e., low calf recruitment) and poor body condition of black rhino. Other factors such as non-human calf predation and parasitism have also been raised as potential causes of decline but remain untested. HiP does have some of the highest densities of lion (Panthera leo) and spotted hyena (Crocuta crocuta). HiP’s black rhino population also suffers from remarkably severe chronic haemorrhaging lesions caused by a filarial parasite (Stephanofilaria dinniki). Empirical evidence if or indeed why the HiP black rhino population might be in decline is lacking. Investigating this population’s true status and any potential causes of an apparent decline is urgently needed. This thesis therefore aimed to test three hypotheses for poor performance that included: (1) investigations of the average black rhino home range size, (2) confirmation of black rhino calf predation and (3) the relationship between filarial lesions and black rhino body condition. I inserted horn-implant VHF radio transmitters into 14 adult (i.e., >5 years) female black rhino in HiP and regularly monitored them on-foot over a three-year period. I found that average home range estimates (9.77 km2) were not significantly dissimilar to estimates using a similar technique obtained forty years prior (i.e., 7.5 km²). I also established the first confirmed link between predation attempts and tail amputation during a lion attack on a black rhino calf. Black rhino body condition, while significantly inversely and temporally correlated to lesion severity, did not appear to be driven by lesion severity itself and highlights the need for further research. An additional research focus for my thesis developed while in the field. I regularly witnessed red-billed oxpeckers (Buphagus erythrorynchus) feeding at black rhino filarial lesions while also alarm calling to alert them to my presence. Studies have found it difficult to empirically show how oxpecker-host interactions have net positive benefits that make it a mutualism. Thus, two chapters were designed to determine if red-billed oxpeckers were predominately mutualistic or parasitic when visiting black rhino. Determining this depended on whether I could identify net positive benefits or net costs to black rhino. Oxpeckers provide rhino with two possible benefits i.e., benefit 1 is cleaning ectoparasites and benefit 2 is increasing vigilance, and one cost i.e., lesion parasitism. More than 50 hours of behavioural observations established that oxpeckers favoured haemorrhaging filarial lesions over sites of tick attachment on black rhino. Moreover, black rhino appeared to be completely tolerant of oxpeckers that fed at lesions. To test whether oxpeckers increased rhino’s anti-predator vigilance, I conducted 84 human approach trials towards black rhino both with and without oxpeckers present. Results showed that rhino were immediately responsive to oxpecker alarm calls and benefitted from more than a two-fold increase in human detection rate and detection distance. Rhino predominately orientated to face towards their sensory blind spot (i.e., downwind) after an oxpecker alarm call. The traditional name (Askari wa kifaru) of the red-billed oxpecker, which translates as the rhino’s guard, appears to be validated. However, future research will need to confirm whether black rhino’s tolerance of parasitic oxpeckers is directly related to vigilance benefits. In summary, black rhino managers in HiP can be confident that the average home range sizes have not increased significantly. Further, predation of calves might be a greater problem than previously realised and requires further investigation. Monitoring changes in the filarial lesion severity of black rhino might be a useful tool for detecting impending changes in a rhino’s condition. Finally, black rhino are clearly eavesdropping and benefitting from oxpecker alarm calls – a co-evolution that has implications for conserving oxpecker populations as well.</p>

Discrimination of Acoustic Stimuli and Maintenance of Graded Alarm Call Structure in Captive Meerkats

Animals living in human care for several generations face the risk of losing natural behaviors, which can lead to reduced animal welfare. The goal of this study is to demonstrate that meerkats (Suricata suricatta) living in zoos can assess potential danger and respond naturally based on acoustic signals only. This includes that the graded information of urgency in alarm calls as well as a response to those alarm calls is retained in captivity. To test the response to acoustic signals with different threat potential, meerkats were played calls of various animals differing in size and threat (e.g., robin, raven, buzzard, jackal) while their behavior was observed. The emitted alarm calls were recorded and examined for their graded structure on the one hand and played back to them on the other hand by means of a playback experiment to see whether the animals react to their own alarm calls even in the absence of danger. A fuzzy clustering algorithm was used to analyze and classify the alarm calls. Subsequently, the features that best described the graded structure were isolated using the LASSO algorithm and compared to features already known from wild meerkats. The results show that the graded structure is maintained in captivity and can be described by features such as noise and duration. The animals respond to new threats and can distinguish animal calls that are dangerous to them from those that are not, indicating the preservation of natural cooperative behavior. In addition, the playback experiments show that the meerkats respond to their own alarm calls with vigilance and escape behavior. The findings can be used to draw conclusions about the intensity of alertness in captive meerkats and to adapt husbandry conditions to appropriate welfare.

Eavesdropping on Referential Yellow Warbler Alarm Calls by Red-Winged Blackbirds Is Mediated by Brood Parasitism Risk

Referential alarm calls that denote specific types of dangers are common across diverse vertebrate lineages. Different alarm calls can indicate a variety of threats, which often require specific actions to evade. Thus, to benefit from the call, listeners of referential alarm calls must be able to decode the signaled threat and respond to it in an appropriate manner. Yellow warblers (Setophaga petechia) produce referential “seet” calls that signal to conspecifics the presence of nearby obligate brood parasitic brown-headed cowbirds (Molothrus ater), which lay their eggs in the nests of other species, including yellow warblers. Our previous playback experiments have found that red-winged blackbirds (Agelaius phoeniceus), a species also parasitized by brown-headed cowbirds, eavesdrop upon and respond strongly to yellow warbler seet calls during the incubation stage of breeding with aggression similar to responses to both cowbird chatters and predator calls. To assess whether red-winged blackbird responses to seet calls vary with their own risk of brood parasitism, we presented the same playbacks during the nestling stage of breeding (when the risk of brood parasitism is lower than during incubation). As predicted, we found that blackbirds mediated their aggression toward both cowbird chatter calls and the warblers’ anti-parasitic referential alarm calls in parallel with the low current risk of brood parasitism during the nestling stage. These results further support that red-winged blackbirds flexibly respond to yellow warbler antiparasitic referential calls as a frontline defense against brood parasitism at their own nests.

The cessation of contact calls does not provoke or modulate alarm behaviour in a social passerine

Vocalizations that signal predation risk such as alarm calls provide crucial information for the survival of group-living individuals. However, alarm calling may attract the predator’s attention and, to avoid this cost, animals can opt for alternative strategies to indicate danger, such as ‘adaptive silence’, which is the cessation of vocalizations. We investigate here whether abrupt contact call cessation would provoke alarm responses, or would reinforce the signal given by an alarm call. In an aviary setting, we conducted playback experiments with a group-living passerine, the Swinhoe’s white-eye, Zosterops simplex. We found that birds did not respond to a sudden call cessation, nor did they have a stronger response to alarm calls followed by silence than to alarm calls followed by contact calls. Confirming previous work investigating contact call rate, it appears that in this species contact calls encode information about social factors but not environmental conditions.

Vocalizations of European Honey Buzzards (Pernis apivorus) in Southern Africa

Contrary to some sources, the European Honey Buzzard is not silent in Africa. This study documents 51 records of the species vocalizing on the continent. Vocalizations were given by birds apparently encountered alone (n=30) and when accompanied by another European Honey Buzzard (n=22). Where age was known, 11 calling birds were adults and ten were juveniles. Where details were available, most calls were given by birds in flight (n=30), with 11 from perched birds and two from birds heard calling while both in flight and perched. In most cases the sex of the bird was not recorded (n=42) and young birds (first- and second-years) are difficult to sex with certainty; of the remainder, two were males and nine were females. Most calls were the typical flight call of the species (n=43), with apparent alarm calls (n=7) the next most frequent call type. Most calls were delivered in flight (n=31), 19 by single birds and 12 by two birds together in flight. The calling by two birds was associated with flight displays similar to those described on the breeding grounds and occurred especially in late summer (December onwards; 25/40 records). A relatively high proportion of calls occurred during interactions between two European Honey Buzzards (n=18). Calling associated with two birds together and accompanied by aerial displays has not been described in Africa before, and is suggestive of either early pairing of the adult birds prior to migration or breeding activity locally in Africa. Vocalizations between young birds though may be more social as opposed to sexual in nature. The large (5X) increase in records of European Honey Buzzards in South Africa in recent years likely increases the chances of conspecific interaction. It also raises the possibility of breeding, especially in more-temperate South Africa.