Table of Contents
Waterbird Diversity in Wetlands: Thol Bird Sanctuary’s Birds, Trends & Conservation
Last Updated: August 31, 2025
Introduction
Waterbird Diversity in Wetlands is a direct indicator of habitat quality, food availability and hydrological regime. Thol Bird Sanctuary supports hundreds of species and large seasonal flocks; changes in water, sediment and benthic life quickly show up in bird counts. This post uses verbatim thesis excerpts (with page numbers) from the Ph.D. of M. H. Bhadrecha (2018), explains findings in plain language, and gives clear, copy-paste management points for WordPress.
“Thol wetland being fresh water ecosystem is dominated by birds. Almost 92 different species of waterfowl falling across 14 different families have been recorded. It is also a potential Ramsar site as it supports more than 20,000 waterfowl. 15 bird species which are reported here are identified as rare, vulnerable, threatened or endangered globally. The flagship species of Thol are Sarus Crane (Grus antigone) and Osprey (Pandion haliaetus). It is an important place for pre-breeding congregation and for nesting of the Sarus Crane.” (p. 28)
Note: Thol hosts high waterbird diversity and supports large migratory aggregations — making it regionally significant.
“The foraging habits, roosting habits along with the richness and abundance of water fowls in a wetland is influenced by the availability of water (GEER Foundation, 2002, Sasikumar K., 2014).” (p. 28)
Note: Water regime directly controls food supply and bird use—shallow foraging areas vs deep pools determine which species feed and when.
“Table 3.4: Estimated Population Census of Waterfowl at Thol Bird Sanctuary … Grand Total 18372 17991 25165 31380 51255 27180 61438 (Source: Office of the DCF, Wildlife Division, Sanand).” (p. 29)
Note: Bird census numbers show large inter-annual variation and major seasonal influxes; totals can exceed 50,000 in peak years.
“Tourists visits … 84% tourists came for picnic/recreation, 14% came for bird watching and only 2% came for photography/filming (Sasikumar K., 2014). This pattern undermines the real significance of Thol Wildlife Sanctuary among the tourists, especially as an important Bird destination site.” (p. 4)
Note: Visitor behavior matters — recreation-heavy use increases disturbance and reduces the sanctuary’s value to birds.
“The abundance and distribution of wildlife in a habitat depends on distribution and extent of water-bodies.” (p. 2)
Note: Hydrology — timing, depth and extent of water — is the master variable controlling waterbird diversity in wetlands.
In-depth analysis — what the thesis data show and why it matters
Waterbird Diversity in Wetlands is shaped by four linked elements: hydrology, food base (benthic & planktonic productivity), habitat structure, and anthropogenic disturbance. Bhadrecha’s thesis documents how these elements combine at Thol to produce large but variable bird populations.
Hydrology is decisive. The thesis describes Thol’s water inputs (catchment runoff and Narmada canal releases) and seasonal storage rules (maintain between ~3–6 feet for bird interest). Water level changes break the wetland into variable shallow and deep patches. Shallow zones (1–10 cm depth) are ideal for many shorebirds and waders; deeper pools sustain diving ducks and some piscivores. When irrigation releases or monsoon pulses alter these depths, the foraging habitat shifts rapidly. The thesis quotes: “The abundance and distribution of wildlife in a habitat depends on distribution and extent of water-bodies.” (p. 2). In plain language: when water moves, birds move.
Food base: The thesis connects benthic macroinvertebrate composition and primary productivity to bird food availability. Where benthic diversity and biomass are high, foraging birds (eg. waders, storks) find more prey. Conversely, sedimentation, eutrophication or trace-metal contamination degrades benthic communities, favoring pollution-tolerant taxa that may be lower in biomass or nutritional value. Bhadrecha notes seasonal productivity swings — summer peaks in GPP and monsoon troughs — and links these to benthic and bird responses. The clear implication: waterbird diversity tracks aquatic productivity and benthic health.
Habitat structure matters beyond water depth. Emergent vegetation (e.g., Nelumbo lucifera) creates refuge, nesting substrate and shade. The thesis documents prolific lotus growth at certain locations and observes its mixed effects — shelter and food-web support on one hand, shading that reduces phytoplankton in some spots on the other (pp. 93–95). For nesting species like Sarus Crane, the right mix of shallow marshes and elevated dry islands is crucial. The thesis explicitly highlights Thol’s importance for pre-breeding congregation and nesting of the Sarus Crane (p. 28), meaning management must protect nesting habitats from trampling, grazing and disturbance.
Anthropogenic pressures are multiple. The thesis lists tourism, grazing, oil wells, agricultural runoff and plastic litter as key human pressures (pp. 3–6). Each affects birds differently: oil contamination can impair prey and directly harm waterfowl; grazing and trampling destroy nesting and foraging substrates; high visitor picnic activity increases disturbance, reducing bird presence during daylight hours. Bhadrecha’s tourism data show the vast majority of visitors come for recreation, not birdwatching (p. 4), indicating a mismatch between site use and site value. The consequence is predictable: reduced effective habitat for birds despite legal protection.
Population data show large interannual variability. Table 3.4’s annual census numbers (e.g., Grand Totals ranging from ~18,000 to >61,000 across sampled years) reveal that Thol can host huge immigrant waves in favorable years. That variability is typical of wetlands on migratory flyways, where regional rainfall, cropping cycles, and upstream water management drive resource availability. The thesis cites Thol’s potential Ramsar value and records of rare and threatened species — 15 species are globally listed as rare/ vulnerable/ threatened (p. 28) — emphasizing conservation urgency.
Seasonality: Bird guilds change with season. In winter, dabbling ducks, geese and shorebirds dominate; monsoon sees dispersal and breeding in resident species; summer concentrates species in remaining permanent pools. The thesis’ seasonal analyses tie these patterns to benthic macroinvertebrate trends and to primary productivity: monsoon dilution leads to lowered GPP and benthic density, reducing available prey, while summer concentrations and elevated GPP in sheltered pools can temporarily increase prey biomass, attracting certain species. Managers must therefore match protective measures to seasonal windows: protect shallow foraging flats in winter, nesting islands in pre-breeding periods, and permanent pools in summer.
Threat linkage and actionable inference: the thesis repeatedly links water regime and benthic health to bird outcomes — e.g., declines in shallow foraging area due to sedimentation or bundh damage reduce shorebird numbers; oil-stained ditches near wells threaten both benthos and higher trophic levels. Hence, managing water levels, controlling sediment inputs, limiting shoreline disturbance, and addressing point-source contamination are direct measures to sustain waterbird diversity in wetlands.
Monitoring recommendations implicit in the thesis are robust: integrate bird counts with benthic surveys, water quality (WQI), sediment trace metal testing, and GPP/P-R monitoring on the same seasonal cadence. This triangulated approach gives managers early warning and attribution capacity — if bird numbers drop, is that due to reduced prey (benthic decline), poor water quality (toxicity), or disturbance (tourism/grazing)? The thesis shows that combined datasets increase confidence in diagnosis and guide effective interventions.
Finally, community and visitor management are central. The thesis’ data on visitor intent (84% picnic/recreation) indicate the need for outreach, visitor zoning, and creation of designated birdwatching platforms to redirect recreational pressure. Protecting nesting seasons with restricted access and training local stewards to patrol sensitive areas are low-cost, high-impact measures that the thesis supports implicitly through its mapping of pressures and bird responses.
Management actions
- Protect and restore shallow foraging flats (1–10 cm depth) during winter.
- Maintain designated water levels (3–6 ft) during key migration/nesting windows where feasible.
- Integrate seasonal bird censuses with benthic, water quality and sediment tests.
- Restrict picnic access near nesting and foraging areas; build raised birdwatching platforms.
- Map and remediate contamination risks near ONGC wells to protect prey base.
- Use local stewards for disturbance control and community outreach on bird-friendly behavior.
- Create an annual bird-health report tied to monitoring metrics (GPP, WQI, sediment, benthic indices).
FAQs
Q: Which species are Thol’s flagship birds?
A: Sarus Crane (Grus antigone) and Osprey (Pandion haliaetus) are listed in the thesis as flagship species (p. 28).
Q: When are bird numbers highest?
A: Census data show large peaks in certain years; overall, winter months see large migrant influxes (see Table 3.4, p. 29).
Q: Do visitors harm bird populations?
A: Yes — when visitors concentrate in nesting/foraging zones and behave like picnickers rather than birdwatchers, disturbance reduces bird use (p. 4).
Author Bio
Researcher: Dr. M. H. Bhadrecha — Ph.D., Department of Zoology, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara (2018). Research Guide: Prof. P. C. Mankodi.
Source & Citations
Thesis Title: Ecosystem Assessment of Thol Bird Sanctuary with Special Reference to Benthic Macroinvertebrate Community — click to open the full thesis.
Researcher: Dr. M. H. Bhadrecha
Guide (Supervisor): Prof. P. C. Mankodi
University: The Maharaja Sayajirao University of Baroda, Vadodara — click to visit.
Year of Compilation: 2018
Excerpt Page Numbers Used: pp. 2, 3–5, 28–31, 39, 54, 90–95, Table 3.4 (pp. 28–29), Table 5.11 (p.100)
Disclaimer: Some sentences have been lightly edited for SEO and readability. For the full, original research, please refer to the complete thesis PDF linked in the section above.
Which management step would you start with to protect waterbird diversity in wetlands — water-level rules, visitor zoning, or prey-base restoration? Comment and share.
Discover more from Professor Of Zoology
Subscribe to get the latest posts sent to your email.