The alarm vocalizations of Brants' whistling rat, Parotomys Brantsii

Le Roux, Aliza (2001-12)

Thesis (MSc)--Stellenbosch University, 2001.

Thesis

ENGLISH ABSTRACT: The alarm calls of a colonial rodent, Brants' whistling rat (Parotomys brantsii), were investigated at Goegap Nature Reserve in the Northern Cape, South Africa. At this site P. brantsii occurs in sympatry with the congeneric P. littledalei, and the alarm calls in response to humans was compared between the two species. Parotomys brantsii's typical call in reaction to a human is a simple whistle, characterized by an initial upward frequency sweep and high frequency plateau, whereas the alarm whistle of P. littledalei has three overlapping components. Parotomys littledalei's calls are significantly shorter and lower in dominant frequency than those of P. brantsii, and have a significantly wider frequency bandwidth. These distinctions were attributed to species discrimination and habitat preferences. The acoustic adaptation hypothesis is supported in part, as P. littledalei, which inhabits a closed habitat in comparison with P. brantsii, has calls which are lower in frequency than P. brantsii calls, but contrary to the hypothesis, P. brantsii calls show less frequency modulation than those of P. littledalei. The high pitch of both species' vocalizations may be a convergent feature making the callers difficult for predators to locate. The alarm call repertoire of P. brantsii was investigated by presenting members of the P. brantsii colony with models of some typical predators, a raptor and puff adder, as well as a human observer. Virtually no variation was detected in the structure of alarm whistles elicited by different predators, indicating that P. brantsii did not identify different predator types by means of vocalizations, even though behavioural responses showed that P. brantsii do distinguish between different predators and non-predators. Note duration varied in conjunction with the physical reaction of the caller. When the caller bolted towards safety, the whistle was significantly shorter than when it remained aboveground. During an encounter with a snake or far-off human the caller would utter relatively long duration calls, signifying a low-risk situation, while highrisk situations such as a nearby human or raptor provoked short calls, emitted just before the whistling rat bolted underground. I regard P. brantsii's alarm call repertoire as a graded "urgency-based" system, indicating threat level perceived rather than predator type. This system is widespread among ground squirrels and is usually associated with animals inhabiting a two-dimensional environment. Playback experiments were conducted to determine the meaning of alarm calls to conspecifics, focusing specifically on the effect of variation in single call duration and function of alarm-calling bouts. All alarm calls induced heightened vigilance in receivers, but the behavioural response did not differ between short and long single calls. Multiple calls lead to significantly longer periods of high vigilance than single calls even after calling bouts have ended, showing that one of the functions of multiple calls is to maintain high vigilance in conspecifics for relatively long periods. The non-iconic nature of their alarm calls and the undiscriminating response of receivers to different calls emphasizes the importance of contextual clues in the communication system of animals living in an open habitat like that of P. brantsii.

AFRIKAANSE OPSOMMING: Die alarm-roepgeluide van 'n koloniale knaagdier, Brants se fluitrot (Parotomys brantsii), is ondersoek by Goegap Natuurreservaat in the Noordkaap, Suid-Afrika, waar hulle simpatries voorkom met die naverwante P. littledalei. Die species se alarmroepe in reaksie op mense is met mekaar vergelyk. Die tipiese alarmroep van P. brantsii is 'n eenvoudige fluit, gekenmerk deur 'n aanvanklike skerp frekwensiestyging en hoë-frekwensie plato. Parotomys littledalei se fluitroep het drie komponente wat mekaar gedeeltelike oordek. Parotomys littledalei se roepgeluide is beduidend korter en laer in heersende toonhoogte as dié van P. brantsii, en hul frekwensie-wydte is ook beduidend wyer. Hierdie verskille word toegeskryf aan species-verskille en habitat-voorkeure. Die akoestiese aanpassingshipotese word gedeeltelik deur die studie ondersteun, aangesien P. littledalei, wat 'n geslote habitat verkies in vergelyking met P. brantsii, alarmroepe het met 'n laer dominante toonhoogte as P. brantsii. In teenstelling met die hipotese, toon P. brantsii se fluitgeluide minder frekwensie-modulasie as P. littledalei se geluide. Die hoë toonhoogte van beide species se alarmroepe kan 'n konvergente verskynsel wees wat dit vir roofdiere moeilik maak om fluitende individue te lokaliseer. Die alarm-repertoire van P. brantsii is ondersoek deur individue bloot te stel aan 'n menslike waarnemer en modelle van tipiese predatore, naamlik 'n jakkalsvoël en pofadder. Daar was omtrent geen variasie in die klank-struktuur van alarmroepe in reaksie op verskillende roofdiere nie. Dit wys daarop dat P. brantsii nie roofdiere deur middel van roepgeluide klassifiseer nie, hoewel gedragsresponse getoon het dat individue wel tussen roofdiere kan onderskei. Die duur van alarmroepe varieer na gelang van die gedrag van die fluitende individue - 'n fluitrot wat vlug, se roep is beduidend korter as die geluid van een wat bogronds bly. 'n Pofadder en 'n veraf mens ontlok lankdurende geluide, wat dui op 'n lae-risiko situasie, terwyl rotte op vlug slaan in reaksie op 'n hoë-risiko situasie, soos met 'n nabygeleë mens of jakkalsvoël, wanneer kort alarmroepe geuiter word. Ek beskou P. brantsii se alarmrepertoire as 'n gegradeerde "nood-gebaseerde" stelsel, wat die mate van bedreiging aandui, eerder as die identiteit van die spesifieke roofdier. Hierdie sisteem is tipies van grondeekhorings en word gewoonlik verbind met diere wat 'n twee-dimensionele omgewing bewoon. Parotomys brantsii se reaksie op die terugspeel van die species se geluide is hierna ondersoek. Ek het gefokus op die effek van 'n verandering in die duur van alleenstaande fluitnote, asook hulle reaksie op fluitreekse. Alle alarmroepe het gelei tot hoër vlakke van waaksaamheid in luisterende individue, maar reaksies op kort en lang enkelnote het nie van mekaar verskil nie. Fluitreekse het beduidend langer periodes van hoë waaksaamheid veroorsaak as enkele geluide, en waaksaamheid het hoog gebly selfs nadat reekse geëindig het. Dit beteken dat fluitreekse onder andere die funksie vervul om waaksaamheid in kolonielede vir relatief lang tye te onderhou. Parotomys brantsii se eenvoudige alarm-repertoire en nie-onderskeidende reaksie op verskillene roepgeluide, beklemtoon die belangrikheid van aanvullende inligting uit die omgewing vir diere in 'n twee-dimensionele habitat wanneer die akoestiese kommunikasiestelse slegs 'n algemene waarskuwingsfunksie vervul.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52481
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