Comparative Foraging Strategies in Urban-Dwelling Songbirds Across Cities

Thesis Abstract

Urbanization alters resource landscapes and predator–prey dynamics, potentially reshaping foraging strategies in passerine communities that exploit anthropogenic habitats; despite extensive studies in isolated locales, cross-city comparisons remain scarce, limiting generalizable understanding of how urban structure, food subsidy regimes, and noise regimes influence foraging behavior and efficiency. This study aims to compare foraging strategies of urban-dwelling songbirds across three metropolitan contexts differing in green space configuration, human activity intensity, and food subsidy patterns, with objectives to (i) quantify intercity variation in foraging microhabitat use and prey selection, (ii) assess the influence of urban resource heterogeneity on foraging efficiency and vigilance, (iii) evaluate interspecific differences in behavioral plasticity linked to urban features, and (iv) test the applicability of optimal foraging theory and the patch-use model in predicting realized foraging effort across cities. The research adopts a comparative cross-sectional design focusing on three common urban songbird assemblages the American robin (Turdus migratorius), the house sparrow (Passer domesticus), and the great tit (Parus major). Fieldwork was conducted in six representative urban neighborhoods per city, spanning three cities with contrasting urban morphologies—dense high-rise cores, medium-density mixed-use districts, and peri-urban parks—over a 12-month period to capture seasonal variation. A sample of 540 focal foraging events (90 per species per city) was recorded using standardized focal-animal sampling and instantaneous scan sampling to capture foraging bout duration, prey type and size class, substrate, handling time, search time, and vigilance bouts. Complementary video recordings (n=180) were analyzed for microhabitat structure and prey availability indices. Data collection instruments included calibrated ethograms, a standardized habitat characterization checklist, and a portable microclimate logger to account for ambient temperature and noise levels as confounding variables. Validity and reliability were ensured through inter-observer calibration (Cohen’s kappa > 0.80) and pilot testing of instruments in each city. Statistical analyses employed mixed-effects modeling to account for nested data structure (foraging events within individuals within species within city), with fixed effects including city, habitat type, prey availability, noise level, and human activity index, and random effects for individual identity and site. Multivariate analyses used redundancy analysis (RDA) to relate foraging strategy profiles to environmental gradients, while generalized linear models tested hypotheses on foraging efficiency (energy intake rate per unit time) and vigilance costs. Model selection followed information-theoretic criteria (AICc). The study anticipates that urban foraging strategies will exhibit significant intercity variation shaped by resource mosaics and disturbance regimes; specifically, sites with abundant anthropogenic subsidies are expected to show reduced handling times but elevated vigilance, while structurally heterogeneous green spaces will promote diversified prey use and higher foraging flexibility. Theoretical integration centers on optimal foraging theory and the patch-use model, with expectations of nuanced deviations due to urban-specific constraints such as interference competition and temporal resource predictability. Anticipated findings include clear species-specific differences in plasticity Passer domesticus may exhibit the greatest tolerance to altered prey spectra and microhabitat shifts, Turdus migratorius may rely more on opportunistic foraging in fruiting and invertebrate-rich patches, and Parus major may show heightened sensitivity to predation risk signaling in denser urban cores. The study contributes to knowledge by offering a cross-urban synthesis of foraging ecology in songbirds, elucidating how urban form and human-mediated resource flows shape behavioral strategies and ecological efficiency, and by testing the cross-context validity of foraging models in dynamic urban ecosystems. Practical implications include informing urban biodiversity planning, green-space design, and city-wide measures aiming to sustain insectivorous and omnivorous songbird populations. The conclusion posits that while city-level context strongly modulates foraging behavior, core adaptive strategies persist across urban gradients, with plastic foraging enabling resilience to resource variability; recommendations emphasize preserving habitat heterogeneity, mitigating noise pollution, and fostering diverse, patchy food resources to support efficient foraging and population stability across urban landscapes.