Data from: Nest association between two predators as a behavioral response to the low density of rodents

Many birds nest in association with aggressive birds of other species to
benefit from their protection against predators. We hypothesized that the
protective effect also could extend to foraging resources, whereby the
resultant resource enriched habitats near a nest of aggressive raptors
could be an alternative cause of associations between nesting bird species
with non-overlapping foraging niches. In the Arctic, the Rough-legged Hawk
(Buteo lagopus) and the Peregrine Falcon (Falco peregrinus) are 2 raptor
species with non-overlapping food resources that have been reported to
nest sometimes in close proximity. Since nesting Peregrine Falcons are
very aggressive, they may protect the small rodent prey near their nests
from predation, and Rough-legged Hawks could use these hot spots as a
nesting territory. In 2 regions in low Arctic Russia we found that (1) the
nesting territories of Peregrine Falcons were indeed enriched with small
rodents as compared to control areas, (2) the probability of nest
association between the 2 raptors increased when rodent abundance was
generally low in the region where hawks did not use alternative prey, and
(3) hawk reproductive success increased when nesting close to Peregrine
Falcons. These results suggest that implications of aggressive nest site
defense in birds in certain cases may involve more mechanisms than
previously explored. A key ecological process in tundra, rodent population
cycles, may explain the occurrence and adaptive significance of a specific
behavior pattern, the nesting association between 2 raptor species.