The role of male-male aggressive signals in reproductive isolation between two hybridizing warblers

Bird-song has been extensively studied for its role in pre-mating reproductive isolation between species. Sometimes song fails to effectively isolate a species and hybrids are produced, giving an opportunity to investigate the mechanisms of how song might act as a reproductive barrier. The ways in which two hybridizing species respond to and recognize each other’s songs can influence the dynamics of the hybrid zone, both via female mate choice and male-male competition. In many species the same song functions for both female mate choice and male-male competition. However, some species, such as the Parulidae Warblers, sing songs with specific functions, where one song is thought to function for female mate choice and the other for male-male competition. My main research goal was to determine how a song thought to function in the context of male-male competition might influence hybridization dynamics between two species. I used Blue-winged Warblers (Vermivora cyanoptera) and Golden-winged Warblers (Vermivora chrysoptera) as my model system because they are closely related species that hybridize frequently and produce fertile offspring, yet tend to mate assortatively and hold overlapping territories. They sing two different categories of song; Type-I song (thought to function for female mate choice) and Type-II song (specialized songs thought to function primarily in male-male territorial disputes). My results demonstrate that patterns of hybridization are associated with differences in both Type-II song structure and the ability to discriminate between conspecific and heterospecific Type-II songs, suggesting that Type-II song can facilitate a breakdown in reproductive isolation between BWWA and GWWA.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

Multilevel Bayesian analysis of monk parakeet contact calls shows dialects between European cities

Geographic differences in vocalizations provide strong evidence for animal culture, with patterns likely arising from generations of social learning and transmission. Most studies on the evolution of avian vocal variation have predominantly focused on fixed repertoire, territorial song in passerine birds. The study of vocal communication in open-ended learners and in contexts where vocalizations serve other functions is therefore necessary for a more comprehensive understanding of vocal dialect evolution. Parrots are open-ended vocal production learners that use vocalizations for social contact and coordination. Geographic variation in parrot vocalizations typically take the form of either distinct regional variations known as dialects or graded variation based on geographic distance known as clinal variation. In this study, we recorded monk parakeets (Myiopsitta monachus) across multiple spatial scales (i.e., parks and cities) in their European invasive range. We then compared calls using a multilevel Bayesian model and sensitivity analysis, with this novel approach allowing us to explicitly compare vocalizations at multiple spatial scales. We found support for founder effects and/or cultural drift at the city level, consistent with passive cultural processes leading to large-scale dialect differences. We did not find a strong signal for dialect or clinal differences between parks within cities, suggesting that birds did not actively converge on a group level signal, as expected under the group membership hypothesis. We demonstrate the robustness of our findings and offer an explanation that unifies the results of prior monk parakeet vocalization studies.publishe

callsync : An R package for alignment and analysis of multi‐microphone animal recordings

Abstract To better understand how vocalisations are used during interactions of multiple individuals, studies are increasingly deploying on‐board devices with a microphone on each animal. The resulting recordings are extremely challenging to analyse, since microphone clocks drift non‐linearly and record the vocalisations of non‐focal individuals as well as noise. Here we address this issue with callsync, an R package designed to align recordings, detect and assign vocalisations to the caller, trace the fundamental frequency, filter out noise and perform basic analysis on the resulting clips. We present a case study where the pipeline is used on a dataset of six captive cockatiels ( Nymphicus hollandicus ) wearing backpack microphones. Recordings initially had a drift of ~2 min, but were aligned to within ~2 s with our package. Using callsync, we detected and assigned 2101 calls across three multi‐hour recording sessions. Two had loud beep markers in the background designed to help the manual alignment process. One contained no obvious markers, in order to demonstrate that markers were not necessary to obtain optimal alignment. We then used a function that traces the fundamental frequency and applied spectrographic cross correlation to show a possible analytical pipeline where vocal similarity is visually assessed. The callsync package can be used to go from raw recordings to a clean dataset of features. The package is designed to be modular and allows users to replace functions as they wish. We also discuss the challenges that might be faced in each step and how the available literature can provide alternatives for each step.publishe