Abstract:
Mannar is a rapidly industrialising island, yet with tremendous waterbird diversity. Our study site is the
shallow, mangrove-dominated ‘Keeri Lagoon’, located in the immediate vicinity of a recent
construction facility. The study aimed at investigating how dietary niche partitioning drives the
community architecture of waterbirds, to understand the functional diversity and health of this
threatened, still understudied ecosystem. Sampling was carried out within the bird migratory season,
from December 2025 to March 2026 (18 visits, rarefaction curve flattened), at five point-count stations
observed from 06:30h to 09:30h and from 15:30h to 18:30h. The wetland supported a rich waterbird
community with 38 species (Shannon-Wiener H'=2.37). Eleven feeding guilds comprising different
combinations of seven dietary preferences (e.g., aquatic invertebrates, plants, seeds) were identified
within the community. All statistical analyses were conducted using R. Berger-Parker Index (d) showed
a highly skewed community structure, with a hyper-dominance of the Brown-headed Gull
(Chroicocephalus brunnicephalus, d=0.34). Rank-abundance modeling supported this observation,
producing a steep decay curve. Chi-square testing revealed a significant departure from a random
equitable resource usage distribution (χ2>7000, p<0.001), with a profound effect strength (Cramér’s
V=0.50). A sensitivity analysis was carried out by repeating the test, excluding the hyper-dominant
population. Yet, the highly non-random functional structure remained with moderate changes (χ2>4000,
p<0.001, Cramér’s V=0.50, d=0.19), confirming the significance was not due to them. The results
pointed to a specialised functional pathway involving aquatic invertebrates and fish (>47% of bird
species), indicating that the energy flow of the ecosystem was funneled through a narrow niche, despite
the high baseline taxonomic and functional diversity. The extreme trophic polarisation towards
predatory guilds suggested a high-energy, top-down (trophic cascade) dynamic for community
architecture. This signaled the sustained availability of aquatic prey species, indicating a healthy
ecosystem and potential nutrient cycling via guano, highlighting the need for its proper management
amidst local constructions. The implementation of long-term monitoring programmes is recommended
hereby to ensure ecologically sound development in the region.
