Comparative Foraging Strategies in Urban-Dwelling Birds and Toads

Thesis Abstract

Urban environments impose novel foraging challenges and opportunities for sympatric vertebrate taxa with distinct ecologies. This study investigates comparative foraging strategies in urban-dwelling birds (primarily Passeriformes and urban adapters such as pigeons and crows) and toads (Bufo/Batrachyla spp.) to illuminate how urban structuring of resources, noise, light, and predation risk shape foraging decisions, microhabitat use, and temporal activity. Aims are to (1) quantify and compare foraging efficiency, prey selection, and patch-use patterns between birds and toads across urban gradients; (2) identify behavioural plasticity mechanisms enabling coexistence in degraded habitats; and (3) evaluate the applicability of optimal foraging theory and risk-avoidance frameworks to cross-taxon urban foraging in situ. Specific objectives include (a) estimating diet breadth and prey size distribution through stable isotope analysis and direct stomach content checks for birds and stomach flushing for toads; (b) assessing foraging efficiency and prey encounter rates via focal animal sampling and automated RFID-based foraging event logs; (c) examining the influence of anthropogenic factors (traffic density, presence of green corridors, artificial lighting) on foraging patch selection using generalized linear mixed models (GLMMs); (d) testing the applicability of optimal patch use and marginal value theorem across taxa with model selection via AIC; and (e) exploring temporal shifts in activity using 24-hour data from camera traps and acoustic monitors. The study adopts a comparative cross-sectional design across three urban centers with distinct habitat mosaics, selecting 120 birds (40 individuals each of three species with high urban tolerance) and 180 toads (60 individuals per species) sampled over two breeding seasons to capture seasonal variability. Data collection instruments include motion-activated cameras, acoustic recorders, RFID feeding loggers, pitfall and soil moisture sensors, manual foraging observations, diet analyses (fecal DNA metabarcoding for birds; gut content and isotopic signatures for toads), and environmental covariate measurements (noise levels, light pollution, vegetation structure). Validity and reliability are ensured through pilot testing of observation protocols, triangulation of diet data (metabarcoding, stable isotopes, direct observation), and inter-observer reliability checks yielding intraclass correlation coefficients above 0.85. Data analysis encompasses descriptive statistics to profile foraging metrics; GLMMs to evaluate fixed effects of urban variables while accounting for random effects of site and individual; regression analyses to link prey encounter rates with foraging success; non-parametric tests for temporal activity comparisons; and model-based inference comparing across taxa using standardized effect sizes. The theoretical framework integrates Optimal Foraging Theory (OFT) and Risk Allocation Theory to interpret patch choice, prey profitability, and predator-avoidance trade-offs, with supplementary application of Niche Theory to understand coexistence patterns in shared landscapes. Anticipated findings include (i) birds exhibiting higher prey discriminability and larger prey patch profitability in green corridors, while toads show elevated foraging under moist microhabitats with reduced ambient noise; (ii) temporal partitioning of foraging windows aligning with human activity cycles, reducing interspecific competition; (iii) greater behavioural plasticity in birds manifesting flexible search patterns and microhabitat switching in response to artificial lighting and noise; and (iv) convergence in risk-sensitive foraging strategies under high disturbance, albeit via different modalities (avian vigilance vs. toad concealment). The study will contribute to knowledge by integrating cross-taxa urban foraging paradigms, validating or refining OFT and risk-based models in anthropogenic landscapes, and offering insight into how urban structure modulates foraging ecology and coexistence. Practical implications include informing urban biodiversity planning, green infrastructure design, and management of urban pest dynamics through an understanding of species-specific foraging responses. The main conclusion is that urban foraging strategies are heavily contingent on species-specific ecology and habitat context, with shared pressures from disturbance promoting convergent risk-sensitive behaviors, while divergent foraging tactics reflect taxon-specific morphology and life history. Recommendations emphasize enhancing habitat heterogeneity, reducing abrupt light and noise disturbances during peak foraging periods, and incorporating multi-species monitoring to guide urban conservation strategies.