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Therthangal Spoonbill Colony Returned to 12 Active Nests After Complete Breeding Failure

Flock of Eurasian spoonbills at Vedanthangal Bird Sanctuary, Tamil Nadu, India
Research: Reproduction & development · Conservation: Population & status

A Eurasian Spoonbill (Platalea leucorodia) colony at Therthangal Bird Sanctuary in Tamil Nadu returned to 12 active nests in 2025–2026 after a complete breeding failure two seasons earlier. Six breeding seasons were monitored between 2019–2020 and 2025–2026; 2020–2021 was not surveyed because of COVID-19 restrictions. The sequence shows the establishment of a regular breeding site together with substantial year-to-year variation rather than a simple steady increase.

Nest numbers rose, collapsed and returned

Monthly surveys from September to February revealed a consistent breeding calendar. Courtship began from the second week of September, nest building was concentrated in October and active nesting peaked in November. Hatching occurred mainly in December, while fledging extended through January and February. Peak abundance reached 42 spoonbills in 2022–2023.

Active nests numbered three in 2019–2020, six in 2021–2022 and 12 in 2022–2023. No breeding was recorded in 2023–2024, after which eight active nests were recorded in 2024–2025 and 12 again in 2025–2026. Across the six monitored seasons, annual peak bird abundance and nest numbers did not show a clear one-directional trend. The pattern is therefore better described as an emerging colony with pronounced annual fluctuations than as continuous population growth.

Hatching success varied, but the failure year remains unexplained

Across seasons with breeding, the researchers recorded 41 nests. Clutches contained two to five eggs, with three eggs the most common clutch size. Colony-level hatching success ranged from 68.4% in 2021–2022 to 85.7% in 2024–2025. The complete failure in 2023–2024 stands out, but the study did not measure hydrology, prey availability, disturbance or predator pressure closely enough to identify a single cause.

Most nests were built in Acacia nilotica. The invasive Neltuma juliflora was first used as a nesting tree in 2022–2023 and accounted for a smaller share of nests in later seasons. The authors emphasise maintaining seasonal water conditions, retaining suitable nesting trees and limiting disturbance during breeding. Repeated nesting after the failure year supports Therthangal as a regular breeding site for Eurasian Spoonbills in southeastern India, while also showing how strongly colony performance can vary between years.

Sources and image credit

  1. Byju, H., Maitreyi, H., & Raveendran, N. (2026). Temporal Dynamics and Establishment of Breeding Colony of Eurasian Spoonbill (Platalea leucorodia) at Therthangal Bird Sanctuary, Tamil Nadu, India. AgroEnvironmental Sustainability, 4(3), 295–302.Primary open-access research article published 15 September 2026 under CC BY 4.0; full text checked. Six breeding seasons were monitored from 2019–2020 to 2025–2026, excluding 2020–2021. Peak active nests were 3, 6, 12, 0, 8 and 12 across the monitored seasons; there was no significant temporal trend. Courtship began in September, nesting peaked in November, hatching occurred mainly in December and fledging extended into January–February. Colony-level hatching success in breeding years ranged from 68.4% to 85.7%.

Image: Many Eurasian Spoonbills (Platalea leucorodia) at Vedanthangal Bird Sanctuary, Tamil Nadu, India, photographed 14 January 2012. Photo: VasuVR. Source: Wikimedia Commons. CC BY-SA 3.0. Representative colony image from Tamil Nadu; not birds from the Therthangal study. · CC BY-SA 3.0 · Source

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