出口 智広

Abstract The constraints imposed by morphology on acoustic signals have received little attention in non-vocal sound communications. Storks (family Ciconiidae) are ‘voiceless’ birds, as they have lost syringeal muscles and gained bill sounds for acoustic communication. In the bill-clattering displays performed for courtship or agonistic interactions with conspecifics, many species rapidly strike the mandibles against each other in succession to produce percussive ‘machine-gun-like rattles’. By looking into among-species variations in the temporal structures of bill-clattering sounds, we asked whether the evolution of rhythms is influenced by morphological traits. Specifically, based on the simple physics of the bill as a third-class lever, we predicted that longer bills would serve as a velocity multiplier. Our phylogenetic comparative analyses confirmed this idea, revealing that longer-billed species are characterized by faster bill-clattering. Interestingly, this relationship is opposed to commonly accepted and previously observed size-relationships in acoustic communication, where species with bigger bodies or bills tend to produce slower sound signals. The findings here point the way towards future research on whether sonation (mechanical sounds) can convey the attributes of signallers, particularly given the long bills of species such as storks. We propose that simple biomechanics could highlight new avenues in studying the evolution of percussive sounds.

Abstract Long-lived territorial bird populations often consist of a few territorial breeding adults and many nonbreeding individuals. Some populations are threatened by anthropogenic activities, because of human conflicts for high-quality breeding habitat. Therefore, habitat restoration projects have been widely implemented to improve avian population status. In conjunction with habitat restoration, conservation translocations have been increasingly implemented. Adequate nonbreeder survival can be a key factor in the success of these attempts because nonbreeding birds may represent reservoirs for the replacement of breeders. The maintenance of breeding pair numbers is also influenced by the transition rate of nonbreeders to breeders. The reintroduction of Oriental Stork (Ciconia boyciana), a long-lived, territorial, endangered species, was initiated in Japan in 2005 using captive birds in hopes of increasing the population’s use of restored habitat. Our objective of this study was to elucidate the factors determining reintroduced stork survival and recruitment to the breeding populations. We estimated the survival rate and breeding participation rate by sex, age, generation, wild-born or not, haplotypes, and breeding status in storks reintroduced during 2005–2022 using Bayesian hierarchical models. There was no significant difference in survival rate between nonbreeders and breeders. However, the survival rate was lower in wild-born birds than released birds, which may be related to the longer-distance natal dispersal of new generations. Accelerated habitat restoration around breeding areas and preventive measures for collision with human-built structures should be implemented for the sustained growth of reintroduced populations. A low survival rate was also detected for a specific mitochondrial DNA (mtDNA) haplotype that accounts for the majority of the reintroduced population. This phenomenon might be explained by mtDNA-encoded mutations. Moreover, captive breeding and release history might contribute to an increase in the proportion of this haplotype in the wild.