Selective alarm call mimicry in the sexual display of the male superb lyrebird (Menura novaehollandiae)

Despite much research on mimicry, little is known about the ecology of dynamic mimetic signals involving mimicry of multiple species. Some of the most conspicuous examples of phenotypically plastic mimicry are produced by oscine passerines, where vocal production learning enables some species to mimic multiple models and flexibly adjust what they mimic and when. While singing from a perch, male superb lyrebirds (Menura novaehollandiae) accurately imitate multiple songs and calls of over 20 species of bird. However, at key moments within their multimodal displays performed on display arenas on the forest floor, males mimic a small number of mobbing-alarm calls creating the acoustic illusion of a mixed-species mobbing flock (‘D-song’). Using observations from camera footage and a field-based playback experiment, we tested six hypotheses for alarm call model selection within D-song. Mimicked species were remarkably invariant, with 79% of D-song made up of imitations of just three different bird species. Males did not mimic the most common species in their general environment, but neither did they mimic rare species. Instead, males imitated the mobbing-alarm calls of heterospecific birds that foraged on or near the forest floor. Indeed, males primarily mimicked the alarm calls of heterospecific species that foraged alongside lyrebirds and were likely to appear together in experimentally-induced, terrestrial mobbing flocks. These findings support the hypothesis that males mimic a cue of a terrestrial predatory threat to lyrebirds, most likely to exploit the antipredator behaviour of female lyrebirds. Our study illustrates the importance of investigating the drivers of model selection in dynamic multi-model mimicry

Asymmetric Response of Costa Rican White-Breasted Wood-Wrens (Henicorhina leucosticta) to Vocalizations from Allopatric Populations.

Divergence in song between allopatric populations can contribute to premating reproductive isolation in territorial birds. Song divergence is typically measured by quantifying divergence in vocal traits using audio recordings, but field playback experiments provide a more direct way to behaviorally measure song divergence between allopatric populations. The White-breasted Wood-Wren (Henicorhina leucosticta; hereafter "WBWW") is an abundant Neotropical species with four mitochondrial clades (in Central America, the Darién, the Chocó and the Amazon) that are deeply divergent (~5-16% sequence divergence). We assessed the possibility that the WBWW as currently defined may represent multiple biological species by conducting both statistical analysis of vocal characters and field playback experiments within three clades (Central America, Chocó and Amazon). Our analysis of vocal traits revealed that Central American songs overlapped in acoustic space with Chocó songs, indicating vocal similarity between these two populations, but that Central American songs were largely divergent from Amazonian songs. Playback experiments in the Caribbean lowlands of Costa Rica revealed that Central American WBWWs typically responded aggressively to songs from the Chocó population but did not respond to playback of songs from the Amazonian population, echoing the results of the vocal trait analysis. This marked difference in behavioral response demonstrates that the songs of Central American and Amazonian WBWWs (but not Central American and Chocó WBWWs) have diverged sufficiently that Central American WBWWs no longer recognize song from Amazonian WBWWs as a signal to elicit territorial defense. This suggests that significant premating reproductive isolation has evolved between these two populations, at least from the perspective of the Central American population, and is consistent with the possibility that Central American and Amazonian populations represent distinct biological species. We conclude by advocating for the further use of field playback experiments to assess premating reproductive isolation (and species limits) between allopatric songbird populations, a situation where behavioral systematics can answer questions that phylogenetic systematics cannot

Summary of subspecies and their clades based on [21].

<p>Birds from western Colombia are presumed to be within the Chocó clade pending further evidence.</p

Percent of individuals approaching the speaker in each experiment.

<p>Responses to the Amazon experiment are on the left and responses to the Chocó experiment are on the right. Note that sympatric trials serve as positive controls (wrens approached the speaker in all sympatric trials).</p

Summary of vocal traits for three populations of WBWWs.

<p>Vocal trait values are presented as mean +/- standard deviation.</p

Spectrograms showing representative song phrases from White-breasted Wood-Wren populations.

<p>(A) Central American (Costa Rica, ML3922); (B) Amazon (ML46962); and (C) Chocó (XC17276).</p

Range map of the White-breasted Wood-Wren.

<p>This map illustrates the distributions of four deeply divergent mitochondrial clades (A = Central American, B = Darién, C = Chocó, D = Amazon; the precise distribution of the Darién clade is unknown and marked in dashed lines). The location of La Selva Biological Station in the Caribbean lowlands of Costa Rica, where fieldwork for this study was completed, is marked by a star. Map from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144949#pone.0144949.ref023" target="_blank">23</a>].</p

Behavioral response to playback experiments.

<p>Responses to the Amazon experiment are on the left and responses to the Chocó experiment are on the right. Latency to approach (A), closest approach to speaker (B), total number of songs (C) and latency to vocalize (D). Boxplots illustrate median (horizontal black bar), first and third quartiles (boxes), and minimum and maximum values (points and dotted lines). Raw data are plotted as points in front of the boxplots, with points offset slightly to better display values. Sympatric treatments elicited aggressive responses (fast approaches, close approaches, many songs, low latency to vocalize) in both experiments. Allopatric treatments elicited asymmetric responses: individuals typically responded aggressively to playback of Chocó songs but not to playback of Amazonian songs.</p