Olfactory eavesdropping: The odor of feathers is detectable to mammalian predators and competitors

The role of olfactory eavesdropping in interactions between mammalian predator and
prey species is well established. Bird plumage can be odorous and consequently nest
predators could use odor to identify and locate avian prey, and nest competitors could
use odor to assess occupancy of nest cavities by birds. However, despite extensive
research on avian nest predation and competition, the costs of olfactory eavesdropping
on plumage odor by nest predators or competitors remain largely unknown. We
used two experiments to investigate whether feather odor is detected by marsupial
species which are competitors for nest hollows and predators of eggs and nestlings of
crimson rosellas, Platycercus elegans. In the first experiment, odor presentation at nest
boxes utilized by ringtail possums (Pseudocheirus peregrinus) and rosellas showed that
the latency of possums to enter the nest was shorter when crimson rosella odor was
present compared to the controls. In the second experiment, carried out away from
nest hollows, brushtail possums (Trichosurus vulpecula) discriminated odors of two
predators (dingo, Canis lupus dingo, and cat, Felis catus) from crimson rosella and control
odors; however, they did not discriminate between crimson rosella odor and a
control. We show that marsupials may use feather odor cues to assess nest hollow
status, information which could aid their detection of avian prey or their vigilance at
nest hollows (for which they compete with parrots). To our knowledge, our study is
the first to show that wild mammalian predators and competitors of birds respond to
plumage odor at nests and suggest that odor signaling may have hitherto unrecognized
costs for birds.