Avian top predator and the landscape of fear: responses of mammalian mesopredators to risk imposed by the golden eagle
Résumé
Top predators may induce extensive cascading effects on lower trophic levels,
for example, through intraguild predation (IGP). The impacts of both mamma-
lian and avian top predators on species of the same class have been extensively
studied, but the effects of the latter upon mammalian mesopredators are not
yet as well known. We examined the impact of the predation risk imposed by a
large avian predator, the golden eagle (Aquila chrysaetos, L.), on its potential
mammalian mesopredator prey, the red fox (Vulpes vulpes, L.), and the pine
marten (Martes martes, L.). The study combined 23 years of countrywide data
from nesting records of eagles and wildlife track counts of mesopredators in
Finland, northern Europe. The predation risk of the golden eagle was modeled
as a function of territory density, density of fledglings produced, and distance
to nearest active eagle territory, with the expectation that a high predation risk
would reduce the abundances of smaller sized pine martens in particular. Red
foxes appeared not to suffer from eagle predation, being in fact most numerous
close to eagle nests and in areas with more eagle territories. This is likely due
to similar prey preferences of the two predators and the larger size of foxes
enabling them to escape eagle predation risk. Somewhat contrary to our predic-
tion, the abundance of pine martens increased from low to intermediate terri-
tory density and at close proximity to eagle nests, possibly because of similar
habitat preferences of martens and eagles. We found a slightly decreasing trend
of marten abundance at high territory density, which could indicate that the
response in marten populations is dependent on eagle density. However, more
research is needed to better establish whether mesopredators are intimidated or
predated by golden eagles, and whether such effects could in turn cascade to
lower trophic levels, benefitting herbivorous species.