Impact of urban noise on nesting success in urban-dwelling songbirds.

Thesis Abstract

Urban environments impose acoustic landscapes that can disrupt avian communication and breeding outcomes, yet the degree to which anthropogenic noise affects nesting success in urban-dwelling songbirds remains equivocal across taxa and habitats. This study addresses the problem by examining how ambient urban noise levels influence nest initiation, attendance, incubation success, and fledging outcomes, with attention to species-specific vocal ecology and behavioral plasticity. The aim is to quantify relationships between noise exposure and nesting metrics, and to identify thresholds where noise begins to impair reproductive success. The specific objectives are (1) to quantify spatial and temporal variation in ambient noise at nesting sites of two prevalent urban songbird species, the resident American robin (Turdus migratorius) and the house sparrow (Passer domesticus); (2) to evaluate associations between noise metrics and nest initiation date, clutch size, parental incubation attentiveness, feeding rates, fledging success, and nest failure; (3) to assess whether vocal adaptation or masking susceptibility mediates the noise-nesting relationship; (4) to compare urban core versus peri-urban nest outcomes to infer habitat-specific noise effects; and (5) to integrate results within the framework of the noise–signal–fitness theory and the acoustic niche hypothesis. The methodology adopts a mixed-methods field design conducted over two breeding seasons (April–July) across 40 nesting territories in a metropolitan landscape. The population comprises nesting pairs of Turdus migratorius and Passer domesticus. A stratified random sampling approach selects 40 active nests, ensuring representation from high, medium, and low noise zones, with an estimated total sample of 120–160 nest monitoring events per species across seasons. Data collection employs calibrated sound level meters to record continuous ambient noise (Leq, Lmax) at nest sites, paired with standardized nest checks to document initiation date, clutch size, hatching and fledging dates, and parental attentiveness through focal sampling and video monitoring. Acoustic analyses utilize signal-to-noise ratio (SNR) measurements, frequency masking analyses, and quantification of vocalization rate and repertoire adjustments. Parental behavior is examined via ethograms and feeding rate calculations derived from 15-minute focal observations, supplemented by nest fate outcomes (success, failure, predation proxies). Validity and reliability are ensured through inter-observer calibration, instrument calibration prior to each field session, and routine data quality checks. Data analysis proceeds with generalized linear mixed models (GLMMs) to test associations between noise metrics and nesting outcomes, controlling for habitat type, weather variables, and species. Structural equation modeling (SEM) will explore mediation pathways whereby noise influences vocal behavior, which in turn affects incubation and provisioning, culminating in fledging success. Hierarchical Bayesian models may be applied to estimate nest-level effects and account for repeated measures. Theoretically, the study engages the noise–signal–fitness framework and the acoustic niche hypothesis, drawing on optimality and sender–receiver theory to interpret masking, redirection of vocal effort, and potential compensatory behaviors. Expected findings include a negative relationship between higher ambient noise exposure and incubation stability, reduced parental provisioning rates, increased clutch loss, and lower fledging success in high-noise zones, with species-specific differences reflecting vocal ecology and plasticity. The study anticipates identifying noise thresholds beyond which nesting success declines markedly, and evidence for vocal adjustments mitigating but not fully offsetting noise costs. The contribution to knowledge lies in providing robust, site-specific quantifications of urban noise effects on breeding success in two common urban songbirds, integrating fine-scale acoustic measurements with behavioral ecology and reproductive outcomes, thereby informing urban planning and biodiversity-friendly design. Practical implications include recommendations for noise management around critical nesting habitats, timing of urban development activities to minimize disturbance during peak breeding periods, and the potential to guide citizen science initiatives for monitoring urban avifauna. The study concludes that while some species exhibit adaptive vocal and behavioral responses, persistent elevated noise levels compromise nesting success, underscoring the need for integrated urban–ecological strategies to sustain urban songbird populations.