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Industrial Basin Loss Halved Nesting Habitat for Black-winged Stilts

A pair of black-winged stilts in shallow water
Conservation · Threats

More than half of the nesting habitat used by black-winged stilts (Himantopus himantopus) disappeared as settling basins were progressively filled in at an industrial wastewater-treatment site in central Italy. A 16-year monitoring series found that the numbers of breeding pairs, adults and chicks all declined as the available wet area contracted.

The study followed stilts at the Huntsman-Tioxide plant, later renamed Venator, beside the Padule di Scarlino wetland in Tuscany. Observers surveyed a roughly three-kilometre route once each breeding season in mid-June from 2009 to 2024, recording breeding pairs, adults and chicks in seven basins.

All seven basins were active in 2009 and provided 23.6 hectares of suitable wet habitat. Progressive infilling left four basins and 10.7 hectares from 2017 onwards—a reduction of more than 50 per cent. Counts changed from 12 breeding pairs, 49 adults and 18 chicks in 2009 to three pairs, six adults and two chicks in 2024. Statistical analyses showed significant year-by-year declines across all three measures.

Because fewer birds were compressed into a much smaller area, density remained stable or increased slightly, although the density trends were not statistically significant. The researchers describe this as a possible crowding effect. The median number of chicks also fell significantly between the first four-year period, 2009–2012, and 2017–2020.

Industrial ponds can offer shallow water, relatively stable levels and protection from terrestrial predators and disturbance. The authors nevertheless warn that infilling can turn such sites into ecological traps — habitats that attract birds because they appear suitable but may impose longer-term survival or reproductive costs. Possible accumulation of toxic substances must also be considered when assessing their long-term value. They argue that the conservation costs and benefits of artificial wetlands should be evaluated together.

Sources and image credit

  1. Giovacchini, P., Baronti, F., Fattorini, C., Radi, G., & Battisti, C. (2026). Black-winged Stilt Himantopus himantopus breeding in an industrial plant: long-term trend (2009–2024) following progressive burial of settling water basins. Rivista Italiana di Ornitologia, 96(1), 88–94.

Image: A pair of black-winged stilts in shallow water. Photo: Ryzhkov Sergey / Wikimedia Commons; cropped to 16:9. Representative image for this story; not presented as an animal or scene from the reported study or event. · CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ · Source

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