The Cape ground squirrel Xerus inauris is unusual among social mammals as it exhibits a low reproductive skew, being a facultative plural breeder with not all females breeding within a group. We investigated pituitary function to assess whether there was reproductive inhibition at the level of the pituitary and potentially the hypothalamus in breeding and non-breeding female Cape ground squirrels. We did so during the summer and winter periods by measuring luteinizing hormone (LH) responses to single doses of 2 g exogenous gonadotropin-releasing hormone (GnRH) and physiological saline administered to 42 females from 11 colonies. Basal LH concentrations of females increased in response to the GnRH challenge. Basal plasma LH concentrations were greater during winter, when most oestrus events are observed. However, we found no differences in plasma LH concentrations between breeding and non-breeding females. We showed that the anterior pituitary of non-breeding female ground squirrels is no less sensitive to exogenously administered GnRH than that of breeding females. We therefore concluded that the pituitary is no more active in breeding than non-breeding females. The lack of differentiation in response to GnRH suggests that either non-breeding females have ovaries that are less sensitive to LH or that they refrain from sexual activity with males through an alternative mechanism of self-restraint.

6,7 and motivated the control of elephant numbers in some southern African parks. We are concerned that even recent plans to manage elephants continue to focus on controlling their numbers to reduce their effects, and do not address the forces that cause impact and lead to large local populations. Con- sideration of the causes of the elephant problem, as well as advances in conserva- tion sciences, allow us to present a fresh approach to managing the consequences that elephants have for vegetation and habitats. This approach avoids reducing numbers directly and addresses patterns of spatial use to reduce local impacts and limit regional numbers. It emphasizes the cause of the elephant problem and focuses on a systemic rather than a symptomatic treatment.

The multi-mammate mice Mastomys natalensis and M. coucha occur allopatrically through much of their ranges, suggesting some measure of ecological or competitive separation. In this study we examined pup growth and development to weaning in M. natalensis and M. coucha. Despite faster development by M. natalensis in the first week post partum, behavioural and physical development demonstrated no further differences. Therefore, it appears neither species exhibits a significant advantage in behavioural development at weaning. However, M. natalensis pups showed faster growth rates and heavier weaning mass than M. coucha pups. Differences in the growth and weaning masses of pups suggest a disparity in food intake, food quality, energy expenditure or energy assimilation rates that may be important in understanding social or ecological differences between these two cryptic rodents.

Aspects of renal physiology were examined to test the hypothesis that two cryptic species of the genus Mastomys (Mastomys natalensis and Mastomys coucha) are geographically separated by differences in aridity tolerance. Laboratory-bred females of each species were subjected to different levels of salinity in their water source (distilled water, 0.9% NaCl, and 1.5% NaCl; 10 conspecifics in each group) from weaning until sexual maturity. Individuals of the two species exhibited similar rates of water consumption and urine production. The salinity treatments caused sodium diuresis in both species, evident in increased urine volume, decreased osmolality and increased osmotic output. Urine concentration, kidney mass and kidney relative medullary area (RMA) did not differ between species. The results of our study do not support the hypothesis that differences in osmoregulatory ability separate these two cryptic species. Nor do they support the use of salt loading to elicit maximum urine concentrations in mammals.

Aspects of the physiology of the arid-occurring otomyine rodents of southern Africa (Parotomys brantsii, Parotomys littledalei and Otomys unisulcatus) were examined, including: (1) renal function; (2) thermal physiology. Parotomys littledalei exhibited a maximum predicted urine-concentrating ability similar to other arid-occurring rodents. Maximum concentrating abilities were moderate for O. unisulcatus and low for P brantsii. The extension of P littledalei into the driest regions, in which it occurs allopatrically, suggests the importance of renal function in determining the distributional limits of these species. The thermophysiology of these otomyine species demonstrated a mixed ability to cope with aridity. Typical of arid-occurring diurnal rodents, all became hyperthermic at high ambient temperatures. However, none exhibited several additional thermophysiological characteristics common to arid-occurring rodents. Thus, resting metabolic rate was not lower than expected for body size, while lower critical temperatures were relatively low and the thermal neutral zone was broad. Nevertheless, the upper limit of thermoneutrality of P littledalei was lower than that of P brantsii or O. unisulcatus. The failure of P littledalei to occur in hotter areas, in which P brantsii occurs, seems to be related to its thermal physiology. Whereas renal function or thermopbysiology may influence the and extension of P brantsii and P littledalei, the high vulnerability of its refuges to fire damage may limit the distribution of O. unisulcatus. Reviewing the thermophysiology of the Otomyinae from more mesic habitats, we argue that their thermophysiology is more closely related to refuge type than aridity. Compared to the apparently specialized physiological mechanisms used by omnivorous or granivorous desert rodents, our study suggests behavioural adaptations such as refuge type and food selection are more important to the survival of these herbivorous desert rodents.

In this study we compare the reproductive ability of Mastomys natalensis, an agricultural rodent pest and that of the closely related species M. coucha, which has not been ascribed as a pest. We suggest that the ability of M. natalensis to plague, as well as dominate, resource-limited habitats, may in part be related to its differential breeding response to variation in diet quality. Thus, we examined the reproductive response of M. coucha and M. natalensis mothers to variation in dietary protein intake. Our results demonstrated that typical levels of reproduction extended over a narrower range of dietary protein content for M. coucha than M. natalensis females. Only M. natalensis females bred on 6% protein diets, while on 20% protein diets the reproductive output of M. coucha was lower than on diets containing 10- and 15% protein. M. natalensis responded to low protein diets by reducing litter size and litter mass but not individual pup mass. Thus, providing diet quality improves before parturition, conception under sub-optimal conditions may not compromise individual pup growth. Furthermore, the ability of M. natalensis to breed under conditions of low diet quality may advance their breeding season compared to species that cannot breed until diet quality improves, allowing M. natalensis to produce additional litters through the season, while more daughters could reproduce during the season of their birth, both factors that are known to contribute to the plaguing tendency of M. natalensis.

We review the options and technologies available to eradicate exotic mammals, especially rodents, from various habitats but in particular from islands. We also recommend possible measures against the house mouse population of Marion Island.

The sibling multimammate mice, Mastomys natalensis and M. coucha, occur throughout southern Africa, exhibiting limited sympatry. We examine body mass and growth characteristics of both species, from birth to 26 weeks of age. Gompertz growth curves were fitted to data for body mass and lengths of head and body, tail, hind foot, and ear. Males of both species exhibited greater asymptotic values, faster maximum growth rates, later age of maximum growth, and extended growth periods than females. However, neither species established body mass dimorphism before weaning, suggesting that differential maternal investment between sexes is not important in preweaning growth. Furthermore, M. natalensis exhibited significantly faster maximum growth rates to reach a greater predicted asymptotic mass than M. coucha. We discuss these results in relation to mating system and interspecific competition.

Temperatures were recorded in burrows of Brants’ whistling rat, Parotomys brantsii, and lodges of the surface-nesting Karoo bush rat, Otomys unisulcatus, in an attempt to relate within-refuge microclimate to known differences in the species’ thermophysiology. The two species were studied simultaneously at the same field site and, hence, under identical climatic conditions. The refuge microclimate of P. brantsii burrows was well buffered from ambient temperature variation, with a narrow average diel temperature range compared with the surface temperature. Maximum burrow temperature was independent of maximum ambient shade temperature. By comparison, the lodges of O. unisulcatus acted as poor buffers from ambient temperature fluctuations, exhibiting greater temperature range. Daily maximum temperature within the lodge was closely correlated with maximum ambient shade temperature. We argue that between-species differences in the thermophysiology of these and other otomyine rodents reflect differences in the thermal properties of their refuges, rather than differences in the degree to which the species in question are adapted to surface conditions in arid or mesic environments.

In Brants' whistling rat, Parotomys brantsii, single animals inhabit unusually complex burrow systems containing several nest chambers. We investigated burrow use and examined the effect of ectoparasites on choice of alternative nest chambers by radiotelemetrically monitoring the nocturnal sleeping locations of individual whistling rats, before and after treating them to remove ectoparasites. Prior to treatment, animals used several different nest chambers within a single burrow, moving from one chamber to another every 1.6 d on average, and most individuals also slept in more than one burrow. Anti-parasite treatment reduced the rate at which animals switched from one nest chamber to another within a burrow. Screening of a separate sample of animals for ectoparasites revealed that they were infested with fleas, mainly Xenopsylla eridos. We suggest that by switching periodically from one nest chamber to another, whistling rats reduce the rate at which ectoparasites, especially fleas, accumulate.

The alarm vocalizations of the whistling rats Parotomys brantsii and P. littledalei were investigated at the Goegap Nature Reserve in the Northern Cape, South Africa, where they occur sympatrically. Parotomys brantsii's call is a single note vocalization, characterized by an upward frequency sweep and high frequency plateau with a dominant frequency of 10.0 +/- 0.3 kHz and duration of 164 +/- 11 ms. The alarm whistle of P. littledalei has three overlapping components and is both shorter (53 5 ms) and lower in dominant frequency (7.7 +/- 0.1 kHz) than that of P. brantsii. The frequency bandwidth of P. littledalei calls (10.2 +/- 0.7 kHz) is significantly higher than that of P. brantsii (6.8 +/- 0.4 kHz). These significant distinctions are attributed to habitat preferences of the two species. Our data support the acoustic adaptation hypothesis in that P. littledalei, which inhabits a more closed habitat, has calls which are lower in frequency than P. brantsii calls, but contrary to the hypothesis, P. brantsii calls do not show greater frequency modulation than those of P. littledalei. Despite these differences, the alarm calls of the two species are both high-pitched, and may have converged in structure to be difficult for predators to locate.

It is predicted that differences in mammalian alarm call systems may be explained relative to the complexity of their habitat, with species inhabiting three-dimensional habitats classifying predator types (externally referential), and those living in two-dimensional environments indicating the level of risk (urgency-based). We tested this prediction in a two-dimensional environment for a small African rodent, Brants' whistling rat, Parotomys brantsii. Colony members were presented with predator models of a raptor and puff adder, as well as a human observer, to investigate their alarm call repertoire. Alarm calls consisted of simple, single-note vocalizations, often repeated in non-rhythmic bouts. Virtually no variation was detected in the structure of alarm whistles between the calls elicited by the two model predators and humans, indicating that P. brantsii did not identify different predator types by means of vocalizations. However, note duration was dependent on the reaction of the caller: when the caller bolted towards safety, the whistle was significantly shorter than when it remained stationary. A snake and far-off human elicited relatively long-duration calls and the caller would remain above ground, signifying a low-risk situation. High-risk encounters with a nearby raptor or human provoked short calls before the whistling rat bolted underground. We conclude that P. brantsii's alarm call repertoire represents a graded 'urgency-based' system, indicating perceived threat level rather than predator type. Our study supports the prediction that mammalian alarm call systems in two-dimensional environments primarily provide information indicating the level of risk and not predator type.

The function of variation in single call duration and alarm calling bouts was investigated in Brants' whistling rat, Parotomys branisii, by means of playback experiments and video analyses of the vigilance displayed. Short calls are produced in hi.-h-risk situations, and long calls in low-risk encounters, but these calls apparently do not communicate this variance in risk to conspecifics. Both short and long single calls induced heightened vigilance in receivers, but rats did not respond differentially to the two call types, and it was concluded that P. brantsii alarm calls are not functionally referential. Multiple calls maintained a state of increased alertness in receivers for a longer period than single calls, even after the bouts had ended, but long bouts (duration: 64 s) did not lead to longer periods of vigilance than short bouts (29 s). Thus the tonic communication hypothesis is only partially supported by our study.

The hypothesis that Brants' whistling rat Parotomys brantsii is a central place forager, whose foraging decisions are modified by (a) predation risk, (b) time of day, and (c) food choice, was tested. Field observations showed that whistling rats followed central place foraging rules for a single-prey loader and much or their food material was brought back to burrow entrances to feed on, with larger food items being carried back greater distances than small ones. Small food items were consumed in situ more often than large ones, suggesting that predation risk may also play a role in their foraging behaviour. Larger food items were preferentially stored at burrow entrances or carried underground, whilst smaller items tended to be consumed immediately. Individuals foraged more actively in the afternoon than in the morning and, although there was no tendency for individuals to eat more food at this time, far more food was stored or taken underground during the afternoon. Different foraging strategies were used for different plant species with some species preferentially eaten, and others stored or taken below ground more frequently. This study shows that the foraging behaviour of Brants' whistling rats is complex., and whilst they may follow simple central place foraging strategies, other factors such as the time of day and food plant species also influence their foraging behaviour.

This study examines interspecific differences in the architecture and field characteristics of the burrow systems of Brants' whistling rat, Parotomys brantsii, and Littledale's whistling rat, Parotomys littledalei. The two rodents are endemic to the arid west region of southern Africa. Both build complex burrow systems with numerous nest chambers and associated interconnecting tunnels, as well as a number of entrances. Burrow systems of P. littledalei are restricted to areas of good plant cover, whilst many P. brantsii burrows are situated in open locations with only limited plant cover. Further, the burrows of P. brantsii cover a much larger area than those of P. littledalei, with many more entrances. As P. brantsii feed predominantly within the boundaries of their burrows and not in the open veld, their burrow systems effectively serve as a predator refuge, into which this diurnal rodent can quickly run in the event of danger. Thus, by building large multi-holed burrow systems, P. brantsii have become independent of the protection offered by bush cover and can exist within relatively open areas within their distributional range. On the other hand, the reduced number of entrances to P. littledalei burrow systems may largely restrict this species to areas with adequate cover, including coastal and riverine bush, with which it is often associated.

This study examines aspects of the nesting behaviour of Brants' whistling rat Parotomys brantsii, a medium-sized rodent indigenous to southern Africa. In the semi-arid regions in which it occurs P. brantsii breeds opportunistically, modifying its breeding period in relation to rainfall. Within a winter rainfall area, females produced up to four litters of three to four young during the winter-spring period following a gestation period of c. 38 days, with females showing a post-partum oestrus. The behaviour of females was modified by the birth of their pups, after which they spent extended periods underground,. interspersed with bouts of food-collecting activity. With the emergence of pups above-ground, females increased their vigilant activity. At 5 weeks pups had developed all the important behavioural characteristics of adults, such as creating their own overnight food stores, collecting nesting material and defending st warren area against conspecifics. This was also the age at which the young dispersed from their natal nest area as well as the time at which females could reach sexual maturity, despite physical immaturity. The high reproductive output of female P. brantsii, as well as the rapid ontogeny of their young, compared to other otomyine rodent species, may represent an adaptation for maximizing reproductive potential in the semi-arid areas they inhabit.

Brants' whistling rat Parotomys brantsii is a gregarious rodent that undergoes marked population fluctuations every few years. Previous studies have variously described them as solitary or social. In this field study, based on direct observations, the social structure and breeding system of a population that almost quadrupled over 7 months was investigated. At the onset of the breeding season, the animals were solitary, each occupying a separate warren. By the end of the breeding season, there was multiple occupancy of some warrens. Each individual maintained a discrete territory within the warren, and exhibited no apparent social behaviour. Outside the breeding season the behaviour of males and females did not differ and both remained at their resident warrens. During the breeding season male P. brantsii visited more neighbouring warrens than did the females, and their visits were to unoccupied warrens or to those occupied by females. Females tended to remain within their own warren. Both sexes avoided warrens occupied by males and few male–male interactions were observed. Females were solicited at their warrens by males, who were frequently chased away. There was, however, evidence that reproductively receptive females were more tolerant of males, who may guard females following mating. This breeding system, based on competitive mate searching by males, and not overt aggression between males, parallels the scramble competition polygyny described for a number of other species, including North American ground squirrels.

In this article we examine the gut morphology of the only three arid-occurring otomyine rodents; Brants' whistling rat, Parotomys brantsii, Littledale's whistling rat, Parotomys littledalei and the Karoo bush rat, Otomys unisulcatus and relate this to the semi-arid environment in which they are endemic. All three otomyine rodents display a gastro-intestinal system well suited to a wholly herbivorous diet, with a well-developed caecum and relatively long large intestine. Despite the broad similarity in the gross gastro-intestinal anatomy between the species examined in this study and their mesic-occurring otomyine counterparts, the results suggest an elongation of the large intestine, with a concurrent reduction in the size of the small intestine in the arid-occurring species. We argue that this trend may be related to water conservation and is supported by the distribution of the three species, with P. littledalei, which occurs in the most arid areas of the three, having the longest large intestine.