Comparative Vocalization Ecology Across Ant-Symbiotic Birds and Relatives

Thesis Abstract

Cross-species variation in vocal signaling among ant-symbiotic birds and their relatives is examined to elucidate how mutualistic associations shape vocal communication, social coordination, and information transfer in noisy tropical habitats where ant-guarded interactions and brood parasitism may constrain acoustic signaling. The study addresses the problem that traditional avian vocal ecology has underexplored the extent to which mutualistic ant associations modulate repertoire size, call structure, and context-specific usage, potentially affecting mate attraction, territory defense, and offspring provisioning. The aim is to quantify interspecific and intraspecific variation in vocalization ecology across ant-symbiotic birds and closely related non-symbiotic relatives, linking vocal traits to ecological and social factors. Specific objectives are (1) to characterize vocal repertoires (size, note types, and syllable combinations) across four ant-symbiotic species and three non-symbiotic relatives using standardized field recordings; (2) to assess the influence of ant-guarded nesting and foraging contexts on vocal tempo, amplitude, and call-structure using controlled playback experiments; (3) to evaluate correlations between vocal features and social variables such as group size, cooperative breeding, and nest defense intensity; (4) to test competing hypotheses derived from the Acoustic Adaptation and Information Theory frameworks regarding signal reliability and efficiency in ant-rich environments; and (5) to develop a comparative model predicting vocal flexibility as a function of ecological constraints. Methodologically, the research adopts a mixed-methods design combining quantitative acoustic analysis with qualitative behavioral observations. The population comprises eight sympatric species within a Neotropical frugivorous passerine assemblage known for varying degrees of ant association, sampled across three habitat types (primary forest, secondary forest, and agroforestry canopy) in two regions. A target sample of 240 individuals (30–40 per species, balanced by sex where detectable) will be recorded using high-fidelity omnidirectional microphones and 24-bit digital recorders. Data collection instruments include standardized field notebooks, automated acoustic analysis software (Raven Pro, Luscinia, and PAMGuard) for spectral, temporal, and harmonic measurements, and observational scan sampling for social context coding. Measurement variables include repertoire size, syllable diversity, duration, fundamental frequency, maximum amplitude, inter-note intervals, context-specific usage (mating, aggression, alarm, provisioning), and response latency to playbacks. Validity and reliability are ensured through intercoder agreement for behavioral coding (Cohen’s kappa > 0.80) and calibration of acoustic measurements across recording sessions. Data analysis employs a sequence of methods (i) multivariate analysis of variance (MANOVA) to compare vocal repertoires across species and ecological contexts; (ii) generalized linear mixed models (GLMMs) with species and site as random effects to test associations between vocal traits and ecological variables (ant presence, nesting height, habitat type); (iii) spectral-temporal analysis and linear mixed models to quantify context-driven variation in call structure; (iv) playback experiment results analyzed with repeated-measures ANOVA and nonparametric tests where appropriate to assess vocal responsiveness and discrimination; (v) phylogenetically informed analyses (PGLS) to account for shared ancestry. A conceptual model integrating Acoustic Adaptation Theory, Information Theory, and Social Complexity Theory will be tested to explain patterns in signal reliability, energetic cost, and social function. Expected findings anticipate greater repertoire specialization and higher call temporal precision in ant-symbiotic species, particularly during nest defense and provisioning contexts, with reduced repertoire diversity but heightened call intensity in noisy ant-guarded environments. We expect positive associations between cooperative breeding and vocal flexibility, and between ant density at nesting sites and increased emphasis on amplitude modulation and alarm-type vocalizations. The study will contribute to knowledge by revealing how mutualistic interactions with ants influence avian vocal ecology, highlighting signal design under multi-taceted ecological constraints, and informing broader theories of animal communication in resource-competitive, architecturally complex habitats. The study will advance methodological approaches in comparative vocal ecology by integrating standardized cross-species sampling, rigorous playback experiments, and phylogenetically controlled analyses. Implications include refining predictions about how ecological mutualisms shape communication systems, contributing to conservation strategies for ant-symbiotic birds by recognizing species-specific communication needs, and guiding future research on the evolutionary trajectories of vocal signaling in environments with strong interspecific interactions.