Juvenile guanaco survival: management and conservation implications

Authors


Ronald J. Sarno, Laboratory of Genomic Diversity, FCRDC/NCI, Building 560, Room 11–84, Frederick, MD 21702–1201, USA (fax 301 846 1299; e-mail rjsarno@mail.ncifcrf.gov).

Summary

1. The Chilean National Forestry and Park Service is striving to implement a guanaco management programme of sustained-yield use. To achieve this, the rate, variation and causes of juvenile guanaco mortality must be understood thoroughly. Therefore, we monitored the survival of 409 radio-collared juvenile guanacos in Torres del Paine National Park, Chile, from 1991 to 1996.

2. The Kaplan–Meier product limit estimator of survival for staggered entry was calculated, and survival rates between juvenile males and females and among years were compared using the lifetest procedure in SAS. The Cox proportional hazards model was used to relate mortality rate to explanatory variables such as juvenile sex, birth weight, adult female aggression towards researchers during the capture and tagging of newborns, population density, and mean monthly winter snowfall.

3. Mean juvenile survival rate (Ŝ) was 0·38, but varied between 0·31 and 0·55. Survival rates between the sexes were not significantly different, although male survival was lower than that of females. Mortality rate was highest during the first 14 days after birth. Most deaths occurred between birth and 7 months of age.

4. The risk of mortality increased by almost 6% with every 1 cm increase in winter snowfall, whereas the risk of mortality decreased by almost 24% as adult female aggression increased towards researchers.

5. Current management objectives are aimed at the implementation of a rational harvest of guanacos on the Chilean side of the island of Tierra del Fuego. Our results provide improved and updated estimates of juvenile guanaco survival and will aid in the modelling of harvest rates of guanacos in southern Chile. Future proposed harvests from wild populations in southern Chile need to consider the rate and variation of this critical life-history parameter.

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