Males of certain species of fairy-wrens (Aves: Maluridae) emit a unique voc
alization, the Type II vocalization, in response to the calls of potential
predators. We conducted field observations and playback experiments to iden
tify the contexts in which the Type II vocalization is emitted by splendid
fairy-wren (Malurus splendens) males, and to examine social and genetic fac
tors that influence its occurrence. In field observations and controlled pl
ayback experiments, Type II vocalizations were elicited most consistently b
y calls of the predatory gray butcherbird (Cracticus torquatus). Some vocal
izations from other avian species also elicited Type II vocalizations, and
the majority of these were vocalizations from avian predators. Splendid fai
ry-wrens are cooperative breeders, and males that responded with Type II vo
calizations to playbacks of butcherbird calls tended to be primary rather t
han secondary males, had larger cloacal protuberances, and were older than
those that did not respond. In addition, secondary males that were sons of
resident females were more likely than non-sons to respond with a Type II v
ocalization. In another playback experiment, females responded similarly to
the Type I song and Type II vocalizations of their mates. Although the Typ
e II vocalization is emitted primarily in response to predator calls, it is
inconsistent with an alarm call explanation. Patterns of reproductive succ
ess among Type II calling males suggest that it does not function as an hon
est signal of male quality. At present, the function of the vocalization re
mains anomalous, but indirect fitness benefits may play a role in its expla
nation.