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Behavioral Ecology Vol. 10 No. 1: 41-47
© 1999 International Society for Behavioral Ecology

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

Ronald J. Sarno and William L. Franklin

Department of Animal Ecology and Program in Ecology and Evolutionary Biology, 124 Science II, Iowa State University, Ames, IA 50011-3221, USA

Address correspondence to R. J. Sarno, Laboratory of Genomic Diversity, FCRDC/NCI, Building 560, Room 11-12, Frederick, MD 21702-1201, USA. E-mail: rjsarno{at}mail.ncifcrf.gov.

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.

Key words: Chile, guanaco, Lama guanicoe, maternal expenditure, survival.


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