Older males tend to have a competitive advantage over younger males in sexual selection. Therefore, it is expected that signals used in sexual selection change with age. Although song repertoire size in songbirds is often mentioned as an age-related trait, many species, including the banded wren (Thryothorus pleurostictus), do not increase their repertoires after the first year. Here, we show that banded wrens reproduce the trill notes in their songs with less variability between them (i.e. more consistently) when they grow older. In a playback experiment, we also show that banded wrens discriminate between younger and older birds based on structural aspects of their song. In a second experiment, banded wrens also respond differentially to natural songs versus songs with artificially enhanced consistency. We argue that consistency in trill note reproduction may be achieved through practice. Sexual selection in the form of male-male competition may therefore operate on a phenotypic trait, the expression of which is enhanced by practice.

Although the genetic and ecological effects of population declines in endangered species have been well studied, little is known of the social consequences. Changes in signaling behavior may result in disrupted communication and affect both reproductive and conflict-resolution activities. The North Island Kōkako (Callaeas wilsoni) is an endangered, duetting (i.e., alternating, coordinated singing by mated pairs) songbird endemic to New Zealand temperate rain forests. Scattered populations (approximately 1500 individuals in 13 surviving and 11 translocated populations) in isolated conservation areas of different sizes have been rescued from extirpation and are currently recovering. We examined key song attributes of the Kōkako to assess whether population size or growth rate are related to song complexity, the reduction of which may compromise effective communication. We analyzed song repertoire size and phrase-type sharing (i.e., Jaccard index of similarity), vocal performance (singing rates, song switching rates, and diversity of phrase types), and song syntactical characteristics (i.e., unpredictability in sequences of phrase types) in surviving and translocated populations (populations of approximately 19-250 territorial individuals). Population size was positively correlated with a population's song repertoire, song diversity, and switching of song phrase types and negatively correlated with shared phrase types and variation in syntactical structure of songs. Population growth rate correlated positively with pair repertoire size, population repertoire size, and singing rates during song bouts. As for solo-singing species in fragmented landscapes, songs in the fragmented populations of Kōkako appear to be undergoing microevolution as occurs in island colonization events. Our results suggest that vocal changes in small populations could affect population establishment and growth, particularly in multiple-source translocations. We believe measurement of vocal behavior could be used as a supplement to periodic population censuses to allow more frequent monitoring of population size.

Summary1. Translocation of individuals from healthy source populations to newly colonize or recolonize suitable habitat is a vital tool for the conservation of a species. Demographic, genetic and landscape factors, but also acoustic signals and cultural factors, will all affect translocation success. 2. We investigated variation in song, and response to song, of the endangered North Island k okako Callaeas wilsoni (Bonaparte 1850) in New Zealand in two translocated populations and their source population. 3. We found significant vocal variation between the source population and both translocated populations, the latter of which had reduced repertoire sizes and increased repertoire sharing, as well as structurally different song elements of higher frequency and shorter duration. 4. Despite the song divergence and clear variability in the nature and level of response among populations, we did not find any evidence for discrimination against nonlocal song in our reciprocal playback experiments. 5. Synthesis and applications. Vocal divergence and reduced variability in translocated populations suggest founder effects or reduced social interaction rates. The variation could be viewed as cultural erosion and may undermine translocation success. Persistence of response to playback, despite vocal divergence, suggested that social restrictions on gene flow require at least a few decades of separation after translocation. The decision to translocate individuals of threatened species is becoming a more common tool for species conservation world-wide. We argue that it is important to take vocal variation into account during such management decisions as it may affect success of establishment and persistence of translocated populations.

Context Animal translocations are an important conservation tool; however, post-release dispersal can hinder successful population establishment. Playback of conspecific song attracts dispersing individuals in some species, although its application following animal translocation has yet to be rigorously investigated. Aims To determine whether conspecific song can be used as an ‘acoustic anchor’, we adopted an experimental approach during the translocation of 60 North Island robins (Petroica longipes). Methods At one of two release locations, we broadcast song at natural rates from four speakers (4 h per morning), for 9 days following release; we set the second release location as a control where identical conditions were established but no playback occurred. To assess the impact of playback, we monitored speaker and control locations, surveyed tracks around the release areas, and radio-tracked robins over nine playback days and an additional 9 days. Key results Most robins left both immediate release areas; however, our results showed that (1) more robins (6 birds on 14 of the 18 days), in particular females (3 birds), approached the playback location than the ‘flagged’ control location (3 male birds on 5 of the 18 days), (2) individual robins returned to the playback location repeatedly, unlike those at the control site, and (3) robins also visited the playback location longer after playback than they did silent control locations. In contrast, radio-telemetry data from five robins suggested that general dispersal was not influenced by playback. Two radio-tracked females moved over long distances (some to >3 km from their release location), whereas two radio-tracked males remained relatively close to the release sites. Conclusions We demonstrated a short-term attraction effect of playback over a period of several weeks for some birds, particularly females. In contrast, we detected fewer birds over a shorter period at the silent control release site, where no females were detected. However, long-term monitoring at both sites suggested that the effect of playback on reducing post-release dispersal was transitory. Implications The lack of a clear and lasting effect of acoustic anchoring on dispersal in the present study has provided information on the limited utility of song playback as a conservation management tool for this species. Consideration of the species’ ecology and suitability for ‘acoustic anchoring’ must be made before playback is employed as a conservation measure to reduce excess post-translocation dispersal.

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