Sexual Dimorphism of Acoustic Signals in the Oriental White Stork: Non-invasive Identification of Sex in Birds

Abstract

Identification of the sex of birds is important for captive breeding of endangered species. In the oriental white stork (Ciconia boyciana), an endangered species, both sexes produce an acoustic signal called "clatter" by rattling their mandibles together to generate sounds. We examined the structure of male and female clatter to determine whether clatter is sexually dimorphic. The acoustic structure of the clatter of the two sexes proved to be dimorphic with respect to the fundamental frequency; female clatter had higher fundamental frequencies. The fundamental frequency correlated significantly and positively with bill length, suggesting that bill morphology contributes to the sexual dimorphism of clatter. Sexing can be done by acoustic signals without capturing birds, and thus is useful as a non-invasive sexing method for ecological and conservation studies of birds.

Gender identification using acoustic analysis in birds without external sexual dimorphism

“…11) were nonoverlapping between sexes: they were <670 Hz in males and >703 Hz in females, that is, they were always lower in males than in females, allowing 100 % reliable sexing. In addition, the dominant frequency is negatively correlated with the bill length of the storks (Eda-Fujiwara et al 2004).…”

“…Such species are usual in many taxa: among geese, cranes, rails, raptors, owls, parrots, doves, auks, shearwaters and some passerines (e.g. Clapperton 1983;Cavanagh and Ritchison 1987;Carlson and Trost 1992;Ballintijn and ten Cate 1997;Smith and Jones 1997;Venuto et al 2001;Eda-Fujiwara et al 2004;Volodin et al 2005aVolodin et al , 2009Klenova et al 2012). Sexing monomorphic birds represents a problem in both captive and wildlife management, e.g., in forming pairs for breeding and estimating sex ratios during censuses.…”

THE TECHNIQUE OF NONINVASIVE DISTANT SEXING FOR FOUR MONOMORPHICDENDROCYGNAWHISTLING DUCK SPECIES BY THEIR LOUD WHISTLES

“…For example, both sexes in Leach's Storm-Petrel Oceanodroma leucorhoa and Y elkouan Shearwater Puffin us yelkouan can be sexed with 100% accuracy by measuring the maximum fundamental frequency alone (Taoka et al 1989;Bourgeous et al 2007). Male and female Whooping Crane Grus americana can be sexed with 99% accuracy by guard calls (Carlson & Trost 1992), and male and female Oriental White Stork Ciconia boyciana with 100% accuracy by clatter calls (Eda-Fujiwara et al 2004). Collared Dove Streptopelia decaocto and Orange-bellied Fruit Dove Ptilinopus iozonus can be sexed with up to 100% accuracy by their coo vocalizations (Ballintijn & ten Cate 1997;Baptista & Gaunt 1997).…”

Vocal cooperation between the sexes in Little Spotted Kiwi Apteryx owenii

“…That inter‐sexual call frequency differences are not a result of size dimorphism is in contrast to many other bird species (Eda‐Fujiwara et al . , Seddon & Sorenson , Martin et al . ).…”