Data from: Mortality and lamb body mass growth in free-ranging domestic sheep – environmental impacts including lethal and non-lethal impacts of predators

The management and recovery of large predator populations in areas where
human persecution has driven them to ecological extinction requires a
solid understanding of the effects of both predation and food limitation
on prey populations. We used 11 yr of data on reported losses among 17.3
million free-ranging sheep Ovis aries in the Norwegian farming industry to
elucidate the relative roles of climate, vegetation characteristics, sheep
densities, lamb body mass and densities of predators and alternative prey
on the number of lambs and ewes lost on summer pastures. We first examined
whether predator densities predicted autumn lamb body mass through
possible impacts of predators on body growth (non-lethal effects) but
found no evidence for such effects in our study system. This might be due
to weak anti-predator behavioral responses in domesticated sheep. However,
autumn lamb body mass was predicted by both sheep density and winter and
spring weather conditions, probably through food availability. Losses of
both lambs and ewes were positively and strongly related to the density of
Eurasian lynx Lynx lynx, wolverine Gulo gulo and brown bear Ursus arctos.
In addition, food availability and spring weather conditions were
associated to losses of lambs, while precipitation in May predicted losses
of ewes. There was little evidence for interaction effects of predator
species on losses, suggesting that most of the effects of the predators
were additive to each other. Given the strong effect of predator densities
on sheep losses, we conclude that changing livestock husbandry practices
towards a system that actively protects sheep and/or active management of
predator densities may be necessary to reduce sheep losses where predators
are recolonizing.