Understanding the interactions between shorebirds and their prey with emphasis on their foraging behaviour in selected stop over sites

Abstract

Shorebirds are critical indicators of coastal ecosystem health, yet their populations are declining globally due to habitat degradation, resource depletion, and environmental pollution. This thesis synthesizes a decade of research (2010–2023) on the population dynamics, foraging ecology, habitat use, contaminant exposure, and novel behavioural adaptations of migratory shorebirds along the west coast of India. Long-term monitoring revealed significant population declines of near threatened Eurasian Curlew and Bar-tailed Godwit, and their shifts in habitat use from traditional mudflats to sand beaches and mangroves. Foraging observations and dietary analyses, including droppings assessments, demonstrated species-specific prey preferences, with Bar-tailed Godwits predominantly consuming polychaetes and medium-sized crabs in mangroves, while Eurasian Curlews exhibited a preference for Cosmonotus crabs and small fishes on sand beaches. Prey capture rates varied across habitats, with mangroves supporting higher foraging success, although a marked decline in capture efficiency over time underscored the impacts of habitat degradation. The pandemic-induced reduction in human disturbances temporarily improved foraging conditions, further highlighting anthropogenic pressures on shorebird populations. Long-term changes in environmental variables led to significant decline in zooplankton abundance, indicating severe habitat degradation and reduced prey base for higher trophic levels. Distinct foraging behaviours were documented, including the continuous stitching movement of Bar-tailed Godwits in two distinct modes, straight-line and zigzag, optimizing prey capture while minimizing energy expenditure in resource-scarce environments. Additionally, foot trembling behaviour was observed across multiple shorebird species, including both visual and tactile foragers, indicating a functional response to habitat constraints. Adaptive prey transport mechanisms, facilitating small prey profitability wereidentified, enhancing capture efficiency in degraded mudflats. Additionally, the study documented a concerning shift in shorebird recruitment patterns, with increased over-summering in agroecosystems coinciding with declining juvenile abundance in coastal habitats. Comprehensive assessments of microplastic contamination revealed high levels of polyethylene, polypropylene, and polystyrene in water, sediment, macroinvertebrate prey, and shorebird droppings, establishing trophic transfer pathways. Heavy metal analyses detected elevated concentrations of zinc, copper, cobalt, chromium, lead, and cadmium in droppings, further raising concerns about pollutant bioaccumulation. The prevalence of microfibers and polymer-specific ingestion patterns among shorebirds emphasized the urgent need for targeted conservation measures. By integrating ecological monitoring with contamination assessments, this thesis provides a comprehensive framework for understanding the complex interactions shaping shorebird populations. The findings underscore the need for immediate conservation interventions, including habitat restoration, pollution mitigation, and adaptive management strategies to safeguard migratory shorebirds in rapidly changing coastal ecosystems in India