Impact of Urban Noise on Songbird Repertoire Diversity and Breeding Success

Thesis Abstract

Urban environments impose acoustic landscapes that can alter avian communication and reproductive outcomes, yet the mechanisms linking anthropogenic noise to songbird repertoire diversity and breeding success remain incompletely understood. This study addresses the problem by examining how varying levels of urban noise influence the complexity of song repertoires and subsequent reproductive metrics in common North American songbirds. The aim is to quantify the relationship between ambient noise, song repertoire richness and diversity, and breeding phenology and success, while testing mediation by territorial defense and mate attraction. Specific objectives include (1) characterizing urban noise profiles across a gradient of sites with differing levels of anthropogenic disturbance; (2) documenting song repertoire size, repertoire diversity (Shannon and Hill numbers), and vocal plasticity in male individuals of a focal species, the American Robin (Turdus migratorius), using 2–3 minute standardized dawn recordings per individual; (3) evaluating breeding success indicators ( clutch size, hatching success, fledgling survival) in relation to noise exposure and song metrics; (4) testing theoretical predictions from the Lombard effect and the acoustic adaptation hypothesis, and (5) identifying potential mediation by territorial aggression and mate choice as inferred from behavioral observations and playback experiments. The research adopts a longitudinal field design conducted over two breeding seasons in an urban-rural gradient within a mid-latitude metropolitan area. Population comprises adult male robins (n ? 120) across 12 study sites, with targeted sampling to include at least 10 individuals per site. Data collection combines passive acoustic monitoring (automatic recorders deployed for 14 days per site), high-fidelity vocal analyses, and standardized ecological and behavioral observations. Repertoire analyses employ automated syllable segmentation followed by manual validation, with repertoire size and diversity computed from 1,000–1,500 high-quality song bouts per individual; noise exposure is quantified using calibrated sound level meters (LAeq,24h and percentile metrics) and spectral analysis of ambient noise profiles. Breeding data include clutch initiation dates, clutch size, egg viability, and fledgling survival tracked through weekly nest checks. Analytical approaches include generalized linear mixed models to assess associations between noise metrics, repertoire attributes, and reproductive outcomes while accounting for random effects of site and year; structural equation modeling to test mediation pathways through territorial aggression and mate choice; and multivariate analyses (perMANOVA and canonical correspondence analysis) to explore the joint influence of noise and habitat variables on song structure. Temporal autocorrelation and potential confounders such as food availability, temperature, and predation risk will be controlled. The study expects to find that higher urban noise correlates with reduced repertoire diversity and lower breeding success, mediated by diminished male efficiency in territory defense and diminished mate attraction efficacy, consistent with the Lombard effect and acoustic masking theories, but with potential species-specific resilience in certain urban microhabitats. Anticipated findings include a threshold effect where noise above 65 dB LAeq,24h corresponds to measurable declines in repertoire richness and a 15–25% reduction in fledgling survival, moderated by habitat complexity and food resource availability. The contribution to knowledge lies in elucidating the causal chain linking anthropogenic acoustic environments to avian communication strategies and reproductive fitness, integrating quantitative vocal ecology with reproductive ecology and behavioral mediation. The study will advance understanding of urban ecological traps for songbirds and inform urban planning and noise management strategies aimed at preserving avian communicative functions and population viability. The main conclusions are expected to emphasize the importance of mitigating chronic noise exposure in urban cores and promoting noise-buffering habitat features; recommendations include prioritizing green corridors with low ambient noise, implementing quiet hours in peak breeding periods, and integrating acoustic considerations into urban design to sustain songbird biodiversity and reproductive success.