Maternal expenditure in the polygynous and monomorphic guanaco: suckling behavior, reproductive effort, yearly variation, and influence on juvenile survival

Abstract

We investigated patterns of maternal expenditure and its influence on juvenile survival in the polygynous monomorphic guanaco (Lama guanicoe) in southern Chile from 1990 to 1994. Birth weight and growth rate (until age 1) of males and females were similar. Suckling rates of males and females were not significantly different, although mothers of males rejected suckling attempts more often than mothers of females during fall and winter. Mothers with sons terminated suckling bouts in equal proportion as did mothers with daughters. Our estimated level of reproductive effort for guanacos falls within the range of species exhibiting no sex-biased maternal expenditure on offspring. Mean yearly birth weight was negatively correlated with population density. Mean suckling time throughout the year differed among cohorts, as did the mean number of suckling attempts and rejected suckling attempts per hour throughout the year. Juvenile survival was estimated until age 1. Of the model with five covariates including juvenile sex, birth weight, adult female aggression toward taggers, mean suckling time, and population density, only mean suckling time and population density were significantly related to survival. The risk ratio for mean suckling time indicates that the risk of mortality increases as suckling time increases, whereas the risk ratio for population density indicates that the risk of mortality decreases as population density increases. Under some conditions increasing population density may be correlated with lower offspring birth weight, yet enhanced juvenile survival. This effect on survival was possibly associated with the number of predators on the study area from year to year.

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

“…In applications where one needs to know sex and age structure, this problem can be minimized, if not overcome, if surveys are conducted towards the end of the birth season when chulengos are abundant. In addition, with training and experience, sexes can be identified even at moderate distance by morphological characteristics (testes/vulva, penis/mammary gland, and body shape) and behavioral cues, as demonstrated by field studies with a more acceptable 3 to 5% unclassified animals Fritz 1991, Fritz andFranklin 1994;Ortega and Franklin 1995;Sarno and Franklin 1999;Young and Franklin 2004b). Methodological improvements by guanaco researchers and managers need to be made to substantially increase the reliability of field identification of guanaco sexes and social groups.…”

“…Guanacos are sexually monomorphic and aggregate in social groups during the breeding season (Sarno and Franklin 1999) and winter (Franklin 1983). The spatial distribution of individuals is strongly influenced by a mating system of resource defense polygyny, a territorial system wherein males compete for access to resources required by females (Franklin 1983;Young and Franklin 2004a).…”

Did Humans Cause the Late Pleistocene-Early Holocene Mammalian Extinctions in South America in a Context of Shrinking Open Areas?

“…The other survivors are some eurytopic species such as large carnivores (Panthera onca, Puma concolor). The guanaco is a special case because it is one of the most frequently cited taxa in archeological sites, but once again we could fi nd an explanation in its lifehistory traits: the age of maturity in females is one year, the gestation period is 335 days, the reproductive rate is one offspring a year, the lactation period is six to 12 weeks and the parental care lasts one year, and the population density is 2.13 individual km 2 −1 (Sarno and Franklin, 1999;Nowak and Paradiso, 1983;Montes et al, 2000). Consequently, guanaco does not appear to be a species easy to extinguish.…”

The difference between killing and eating: ecological shortcomings of puma energetic models

“…We estimated the monthly weights of 1-year (chulengos) and 2-year guanacos using linear growth estimates, a birth weight of 12.7 kg, and 1-yr and 2-yr weights of 42 kg and 100 kg, respectively (Sarno and Franklin 1999). Guanacos .2 years of age were estimated to weigh 120 kg (Raedeke 1979).…”