Predation by golden eagle Aquila chrysaetos on semi-domesticated reindeer Rangifer tarandus calves in northeastern Finnish Lapland

Abstract

Calf losses are an acute issue in Fennoscandian reindeer Rangifer t. tarandus management. We studied calf mortality in northeastern Finnish Lapland using 621 calves (304 in 1997 and 317 in 1998) marked with silent mortality transmitters and followed their survival during 2 July 1997 - 31 January 1998 and during 22 June 1998 - 31 January 1999. In total, we found 43 dead calves and investigated their causes of death. A Kaplan-Meier analysis indicated 91.5% survival during July–January in both study years. However, differences in the temporal distribution of survival between the two study years were found. A minimum of 53% of total mortality was attributed to predation, with golden eagle Aquila chrysaetos being the main predator. Mortality caused by golden eagle comprised 2.8 and 4.2% during the study periods in 1997/98 and 1998/99, respectively. Body weight of the calves at midsummer (all weights adjusted on 2 July) was a significant predictor for survival, whereas sex and pelt colour were not. We conclude that predation is a major source of calf mortality during July–January, and that golden eagle predation was prominent, especially during midsummer and in open alpine landscapes.