Examination of pair-duet stability to promote long-term monitoring of the endangered red-crowned crane (Grus japonensis)

Acoustic-based monitoring has proved useful for many birds and seems promising for the endangered red-crowned crane. However, its validity in crane conservation is unclear in the absence of knowledge concerning the long-term stability of pair-specific duets. The red-crowned crane is monogamous and long-lived, with stable pair bonding both within and between years. Pair mates perform loud duets-a succession of male and female calls emitted with definite temporal coordination. We examined the stability of duets for five captive pairs over five years (2003-2007) on the basis of analysis of the syllables within the duets. MANOVA showed that the effect of pair identity on syllable characteristics was always stronger than the effect of the year of recording. Cross-validation of duets from 2004, 2005, 2006, and 2007 with discriminant analysis (DFA) functions derived, respectively, from pooled samples from 2003, 2003-2004, 2003-2005, and 2003-2006 resulted in comparably high percentages of correct classification into pairs. The pairs could be reliably identified by their duets and pair-specific differences in syllable characteristics were stable with time. These data suggest acoustic monitoring is a feasible alternative to more invasive methods of identification.