Spatial organization and monogamy in the mara Dolichotis patagonum

Maras, Dolichotis patagonum , were observed and radio-tracked in Argentina. They travelled as monogamous pairs that bred either alone at solitary burrows or communally at settlements where up to 29 pairs shared warrens.
Members of a mara settlement grazed within 2.5 km of the communal warrens, using intensively about 1 ha per day, within drifting daily ranges of 11 ha, seasonal ranges of 98 ha and annual ranges of 193 ha.
Their home ranges drifted continuously. Consequently, the long-term movements of neighbouring pairs overlapped substantially, but at any given moment they were territorially spaced.
Monogamous, drifting territoriality is explained by the patchy dispersion of food, the need to minimize interference competition, and a cycle of grazing and fallowing in the use of food plants.
Two hypotheses explaining the adaptive significance of settlements are evaluated: one relates to resource availability (through the indirect effect of ground water and sheep dung on vegetation); and the other relates to predation (through the protective influence of human dwellings). The size of sheep flocks grazing at outstations during January provide a measure of the resource richness of patches where maras graze, and the richness of these patches in the dry season appear to limit the number of maras breeding at each settlement during the following wet season.
Maras face extremes of resource dispersion between the wet and dry seasons: in the former, sparsely dispersed grazing and interference competition favour spacing out and territoriality; in the latter, clumping of resources facilitates pairs congregating in herds around outstations and dry lagoons. Superimposed upon the ecological factors favouring spacing out during the wet season are the sociological factors that cause the maras to den communally. The resulting compromise is a social system unique among mammals.     

Diet of the mara (Dolichotis patagonum), food availability and effects of an extended drought in Northern Patagonia (Mendoza,Argentina)

The mara is a near threatened Caviomorph, endemic to Argentina. Studies on feeding ecology allow assessment of the dietary adaptability of maras to habitat changes. The mara diet and food availability on two sampling sites, belonging to distinct landscapes of Northern Patagonia, were estimated using microhistological analysis and point-quadrat transects, over four seasons, and besides during an extended drought. Significant differences were detected by Kruskall-Wallis ANOVA, feeding selection by the χ² test, and dietary preferences by Bailey's confidence interval. Grasses dominated food availability, with Panicum and Poa as major species, followed by shrubs and scarce forbs. Plant cover and forbs increased in spring and summer. The drought caused a strong decrease in plant cover and proportion of grasses. Maras ate all grass species, most forbs and several shrubs. Grasses dominated the diet, with Poa and Panicum being the major species, supplemented by the shrubs Lycium and Prosopis. Maras ate more grasses and forbs in spring and summer, and shrubs in autumn and winter. More shrubs and forbs, and less grasses, were eaten during the drought. Plant categories were used selectively only in autumn and winter, and in the drought period, with preference for shrubs and avoidance of grasses. Bromus, Poa, Plantago and Prosopis were preferred, and Panicum avoided. The mara qualified as a grazer but shifted to a mixed feeder during the drought. Dolichotis patagonum shared habitats with several big and medium-sized herbivores and showed the highest dietary similarities with plain vizcachas, brown hares and horses. Protective measures for natural habitats are needed, given that increasing impacts on food resources and habitat quality could be threats to the survival of maras and other wild vertebrates in Northern Patagonia.     

Communal breeding: clever defense against cheats

High levels of conspecific brood parasitism are found in a communally breeding bird, with implications for the evolutionary links between brood parasitism and communal breeding. It also uncovers a novel egg recognition mechanism hosts use to foil brood parasites.     

Trophic interactions between two medium-sized mammals: the case of the native Dolichotis patagonum and the exotic Lepus europaeus in a hyper-arid ecosystem

As medium-sized herbivores, the exotic Lepus europaeus (European hare) and the native Dolichotis patagonum (mara) have been considered ecological equivalents. These species coexist in Ischigualasto Provincial Park, a hyper-arid ecosystem with scarce food resources. Our objective was to evaluate diet composition, relationship between diets and food availability, and trophic relationships between both herbivores. Collection of feces and vegetation sampling were made in the Mesquite woodland community. Diet composition was analyzed by microhistological analysis of feces. In both seasons, shrub species represented the most abundant cover type in the area, and annual forbs and grasses appeared in the wet season. Herbivores showed similar dietary ecology: shrubs were the main food items along the year, showing a higher plasticity compared to their diets in other ecosystems, where they selected mostly grasses. The mara selected shrubs such as Atriplex sp. and Prosopis torquata, whereas the European hare selected Cyclolepis genistoides, Atriplex sp., and Bulnesia retama. During the wet season, both herbivores supplemented their diets with grasses and annual forbs. In the dry season, there was increased consumption of cacti, such as Tephrocactus sp. The mara and the European hare are likely close ecological equivalents, in terms of dietary similarity, and they showed strong dietary overlap across the dry season (over 60 %). Thus, we can assume the existence of a potential trophic competition between mara and European hare, especially during the season when food resources are scarce. These results can be important for the management of drylands in South America, where populations of threatened herbivorous species, such as the mara, coexist with exotic animals, sharing spatial and trophic resources even in protected areas.     

Sources of Variation in a Two-Step Monitoring Protocol for Species Clustered in Conspicuous Points: Dolichotis patagonum as a Case Study

In species showing distributions attached to particular features of the landscape or conspicuous signs, counts are commonly made by making focal observations where animals concentrate. However, to obtain density estimates for a given area, independent searching for signs and occupancy rates of suitable sites is needed. In both cases, it is important to estimate detection probability and other possible sources of variation to avoid confounding effects on measurements of abundance variation. Our objective was to assess possible bias and sources of variation in a two-step protocol in which random designs were applied to search for signs while continuously recording video cameras were used to perform abundance counts where animals are concentrated, using mara (Dolichotis patagonum) as a case study. The protocol was successfully applied to maras within the Península Valdés protected area, given that the protocol was logistically suitable, allowed warrens to be found, the associated adults to be counted, and the detection probability to be estimated. Variability was documented in both components of the two-step protocol. These sources of variation should be taken into account when applying this protocol. Warren detectability was approximately 80% with little variation. Factors related to false positive detection were more important than imperfect detection. The detectability for individuals was approximately 90% using the entire day of observations. The shortest sampling period with a similar detection capacity than a day was approximately 10 hours, and during this period, the visiting dynamic did not show trends. For individual mara, the detection capacity of the camera was not significantly different from the observer during fieldwork. The presence of the camera did not affect the visiting behavior of adults to the warren. Application of this protocol will allow monitoring of the near-threatened mara providing a minimum local population size and a baseline for measuring long-term trends.     

Communal singing in the cooperatively breeding subdesert mesite Monias benschi: evidence of numerical assessment?

It has long been suggested that competing groups of social animals assess one another on the basis of communal vocalisations, but so far this has only been demonstrated in mammals. We investigated this idea in the subdesert mesite, a group-living bird that produces communal songs during aggressive territorial interactions with other groups. Where groups compete as units, differences in group size might outweigh inter-individual differences in determining the outcome of contests. Given this species' variable social system, we predicted that the composition of groups would also influence their resource holding potential. Playback experiments showed that the number of simulated intruders significantly influenced the strength of response by defending groups hearing the stimulus: groups were less likely to approach but gave more protracted and more communal vocal responses as the number of vocalising intruders increased. We found that the likelihood of a group approaching playback increased as the ratio between the number of males in the defending group and the number of males in the intruding group increased. Furthermore, the ratio of adult males to females in the defending group significantly affected the probability of approach, with the probability increasing as groups became more male-biased. This finding supports the idea that the social structure of groups may be important in determining the outcome of contests between groups. Overall this study provides some indication in birds of relative numerical assessment based on vocal cues.     

Estrogens and progesterone during gestation in Dolichotis patagona

During pregnancy, a progesterone-binding plasma protein is present and is similar in several respects to the binding protein reported in other hystricomorphs. These findings establish estradiol-17 beta as the predominant estrogen of pregnancy and that progesterone rises during pregnancy and does not decline until after parturition. Gestation length is 96 days. This study establishes similarities between the mara and its closest relative, the guinea pig.     

Communal nursing in the domestic cat,Felis catus

Communal nursing in the domestic cat has been observed in group living conditions. (In high density conditions, cats have social lives.) In our laboratory, when females were kept in the same cage, they delivered kittens nearly simultaneously, and started to nurse their kittens communally. This process, which was videotaped, was shown to be begun by the mother’s retrieving kittens. They seemed to have no ability to discriminate their own kittens from those of others, as our test of recognition of kittens showed. Communal nursing resulted in high mortality of kittens, the release of mothers from caring for kittens, and incomplete reproductive division of labour. Abortion was often observed in group-living cats in captivity. High mortality and low birthrate are helpful in controlling population. All members of the group were very familiar to each other, so that they formed a ‘pseudo’-kin group.     

The Communal Way of Life in the Splendid Wren,Malurus splendens

Splendid Wrens were studied over 7 breeding seasons in Western Australia. A colourbanded population (54 adults and 160 nestlings) of these small dimorphic passerines occupied a saturated habitat and dispersed little. Annual mortality of ♀♀ was 57% compared to ♂♂ at 29%; this high rate of turnover of ♀♀ reduces the chances of inbreeding. 2/3 of the territorial groups contained one or more helpers; groups with helpers did not produce more young than those without, but the helping role ensured priority of opportunity to inherit their own group-territory or to succeed to a neighbouring one, wheresoever breeding vacancies occurred. Helpers reduced the stress on breeding ♀♀ in many ways.