Mortality and survival of semi-domesticated reindeer (Rangifer tarandus tarandus L.) calves in northern Finland

Abstract

During the period 1999 to 2004 the reindeer calf survival and mortality were studied in two reindeer-herding cooperatives and in five herding-groups in northern Finland, where in total 1725 calves were fitted with mortality indicating radio-transmitters fixed on expandable neck collars. The calves were weighed and marked at the age of 2-5 days in calving corrals and also during earmarking in June/July, when the age of calves was 2-8 weeks. The rate, timing and causes of mortality of calves were investigated. In 1999-2001 in Ivalo reindeer-herding cooperative 4.6% of radiocollared calves and in 2002-04 in Käsivarsi reindeer cooperative 5.2% was found dead. The average mortality of the calves radio-collared during calving time in May, and monitored to the end of October, was 6.7% in Ivalo and 9.0% in Käsivarsi. From July on, the average mortality rates varied between 1.8-5.7% among reindeer herding-groups. On average 54 and 42% of all radio-collared calves found dead in Ivalo and Käsivarsi cooperatives were attributed to predation, and golden eagle was the most significant cause of death in both cooperatives killing 0-3.5% of radio-collared calves in different study areas and years. Golden eagle predation accounted for 33-43% of all radio-collared calves found dead, 55-59% of the cases with identified cause of death and 80% of all identified predation. Most of the calves killed by golden eagle were found during July and August mainly in the open areas, as in highlands, bogs and clear-cut forest areas. The mean body weight of the calves radio-collared in May (weights adjusted on June 1 st ) and found dead during the summer was significantly (P<0.01) lighter than the mean weight of survivors both in Ivalo and Käsivarsi. Furthermore, the midsummer body weights of the calves (weights adjusted on July 1 st ) killed by all predators and by golden eagles were significantly (P<0.001) lower than the mean weight of surviving calves in both cooperatives. However, the weights did not differ between depredated calves and those calves that succumbed due to other causes than predation. The results of this study emphasize the relative importance of golden eagle as a mortality factor for reindeer calves in the northern part of the Finnish reindeer husbandry area.

Environmental variation as a driver of predator‐prey interactions

“…Still, the overall probability of being predated tended to decrease with increasing body weight. This result is consistent with previous studies showing a negative relationship between calf weight and predation probability (Nybakk et al 1999, Tveraa et al 2003, Nieminen et al 2011). …”

“…This interpretation is supported by previous studies showing that these predators tend to prey on the weaker and smaller individuals (Tjernberg 1983, Nybakk et al 1999, Nieminen et al 2011). More wolverine and eagle predation at the end of winter may therefore suggest that their inflicted calf mortality to some degree could be compensatory.…”

“…These predators use a broader variety of v www.esajournals.org habitats, and their predation pressure is therefore less related to the forested habitats (Watson 1997, Landa et al 1999, May 2007, Pagel et al 2010. It might even be skewed towards the tundra habitat in the case of the golden eagle (Nybakk et al 1999, Nieminen et al 2011. Finally, we examined whether nutritional status (measured by body mass and time into the winter season) influenced the foraging-predation risk trade-off decisions by testing whether habitat use patterns and predation rates changed through time and with body mass.…”

Attacked from two fronts: Interactive effects of anthropogenic and biotic disturbances generate complex movement patterns

“…Forest-dwelling reindeer might feel more protected from a predator flying above while hiding in the forest and move less to decrease the chances of being detected. Eagles usually attack and successfully kill ungulates in open areas (but see Kerley and Slaght 2013), and most predation events caused by eagles on reindeer occur in open areas (Nieminen, Norberg, and Maijala 2011). Ultimately, the response of reindeer to aircraft observed in this study may also depend on the occasional herding of the reindeer with helicopter performed by the herders in the study area, which may have made the animals less prone to acute responses to flights, as well as on the domestication process (Reimers, Røed, and Colman 2012).…”

“…This behavior may have originated as a response to a potential predator flying overhead. Golden eagles may indeed attack both adult females and calves (Nybakk, Kjelvik, and Kvam 1999;Nybakk et al 2002;Gustine et al 2006;Norberg et al 2006;Nieminen, Norberg, and Maijala 2011). Studies analyzing the antipredator response of reindeer to attacks by raptors are lacking in the literature, but attacks on other ungulates have been observed in some instances.…”