Vigilance Patterns of Territorial Guanacos (Lama guanicoe): The Role of Reproductive Interests and Predation Risk

Abstract

We conducted focal observations of territorial guanacos, a highly polygynous and social mammal, to compare time budgets between sexes and test the hypothesis that the differences in reproductive interests are associated with differential group size effects on male and female time allocation patterns. In addition, we used group instantaneous sampling to test the hypothesis that grouping improves detection capacity through increased collective vigilance. We fit GLM to assess how group size and group composition (i.e., presence or absence of calves) affected individual time allocation of males and females, and collective vigilance. As expected from differences in reproductive interests, males in family groups devoted more time to scan the surroundings and less to feeding activities compared to females. Both sexes benefited from grouping by reducing the time invested in vigilance and increased foraging effort, according to predation risk theory, but the factors affecting time allocation differed between males and females. Group size effects were significant when females were at less than five body‐lengths from their nearest neighbour, suggesting that grouping benefits arise when females are close to each other. Female time budgets were also affected by season, topography and vegetation structure. In contrast to our expectation, males reduced the time invested in vigilance as the number of females in the group increased, supporting the predation risk theory rather the intrasexual competition hypothesis. The presence of calves was associated with an increase in male individual vigilance; and vegetation type also affected the intensity of the group size effect over male time allocation. In closed habitats, collective vigilance increased with the number of adults but decreased with the number of calves present. Although male and female guanacos differed in their time allocation patterns, our results support the hypothesis that both sexes perceive significant antipredator benefits of group living.

Guanaco abundance and monitoring in Southern Patagonia: distance sampling reveals substantially greater numbers than previously reported

“…In northern areas, densities are also highly variable (1.0 to 13.9 ind/ km 2 ; Puig et al 1997), and extreme values over 40 ind/km 2 have been calculated (Puig et al 2008). The same pattern can be found in central Patagonia where densities ranged between 0.6 and 8.8 ind/km 2 (e.g., Saba and Battro 1987;Baldi et al 1997;Marino and Baldi 2008). Variability in higher latitudes outside Santa Cruz, including Tierra del Fuego, varied in a narrower range (0.3 to 4.7 ind/km 2 ; Raedeke 1982;Bonino and Fernández 1994;Ortega and Franklin 1995;Montes et al 2000).…”

Indirect measures of reproductive effort in a resource-defense polygynous ungulate: territorial defense by male guanacos

“…Alternatively, it is intriguing that territorial males showed high levels of vigilance effort regardless of predation pressure or the number of females in their groups. A previous study on guanaco vigilance patterns in a low-density population exposed to puma predation showed that territorial males reduced their vigilance effort as the number of females in their harems increased (Marino and Baldi 2008), as would be expected under the anti-predatory vigilance hypothesis. As Raedeke (1979) previously suggested, at a low population density, territorial defense may be suspended since it may not be necessary.…”

“…Other variables that were not directly related to former predictions were addressed to account for their possible influence on individual behavior. Previous studies among guanacos have shown that habitat structure might affect individual vigilance (Marino and Baldi 2008). Thus, vegetation physiognomy in a radius of approximately 50 m around the group was described and classified into two types: open grasslands, composed mainly of grasses and forbs, and shrublands, with at least 20% of shrub cover.…”

Reporte de la presencia de guanacos (Lama guanicoe cacsilensis) en las lomas de Marcona y alrededores (Ica-Perú) durante la estación seca

“…Este territorio limitaría al norte con la pampa Media Luna (límite sur de la RNSF), por el sur con Miramar (lomas de Marcona), por el oeste con las playas La Chorrera y El Conchal, y por el este el límite es poco definido. En comparación a otros grupos de guanacos sedentarios (L. guanicoe guanicoe) que habitan ambientes secos, el tamaño del territorio familiar registrado en el área de estudio (2,73 Km 2 ) estuvo dentro del rango mínimo de tamaño territorial reportado para grupos familiares en la costa de Chubut, Argentina, que fue de 2 -9 Km 2 (Marino & Baldi, 2008), pero por debajo del rango de 13 -51 Km 2 reportado para guanacos en el Chaco boliviano (Cuellar et al, 2014). Durante los 3 meses de observación del guanaco solitario, sólo se le observó en 2 sectores muy reducidos y ubicados inmediatamente al norte y al sur del territorio familiar.…”

“…El método de avistamiento de guanacos fue el de observación directa con el uso de binoculares (Bushnell 12X 50mm) y Monoculares (Carl Zeiss 25-60X 80mm) vía desplazamiento terrestre, a pie o en camioneta. El sexo de los animales se determinó mediante observación directa de los órganos genitales (Franklin, 1983), mientras que el estrato etario (cría, juvenil o adulto) se calculó en base al tamaño relativo de los individuos (Marino & Baldi, 2008). También se consideraron como evidencias indirectas de la presencia de guanacos las huellas, los senderos, los restos óseos, los dormideros, los revolcaderos y los estercoleros; que para este último se indicó su estado de utilización, como abandonado o en uso, en base el estado de las heces.…”