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Heilige ibissen in Nederland
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A risk analysis of the sacred ibis in the Netherlands

Photo: Jan van der Winden

To gain insight into the likelihood of the sacred ibis (Threskiornis aethiopicus) establishing a population in the Netherlands, Bureau Waardenburg was commissioned by Team Invasieve Exoten of the Ministry of Agriculture, Nature and Food Quality, to carry out a risk analysis. The report consisted of a scientific analysis into the potential ecological, economic and safety issues posed by the species, and possible solutions.

Sacred ibises are native to sub-Saharan Africa and Iraq (the species is extinct from Egypt). In the Netherlands, the species has existed as an escaped species since the 1990s. Since 2002, the species has bred in three areas of the Netherlands, including the Natura 2000 area of Botshol. The species occurs as an escape in several other European countries and has established populations in France (where it numbers several thousands) and Italy (where it has only recently established).

Photo: Ralph Smits

French example indicative for the Dutch situation

The species is an opportunistic forager and consequently takes a wide range of food items, including the nestlings of terns and cormorants. Sacred ibises can be found in a range of habitats and competes for nest sites with both herons and spoonbills. The ecological impacts of such predation and competition have been documented in both native and established populations. Furthermore, attempts to eradicate the established populations in France have proved unsuccessful. The risk analysis concluded that the small numbers currently present in the Netherlands have the potential to establish larger populations if no measures are taken.

Between 2000 and 2007, numbers in the Netherlands increased to around 15 pairs. Left unchecked, numbers could be expected to reach 60 pairs by 2025. Since 2008, however, containment measures have been carried. This, along with a number of severe winters has reduced the number of free flying birds in the Netherlands to around four birds in 2010.

Report outcome and measures recommended 

To assess the potential risk posed by the sacred ibis in the Netherlands, the report (A risk analysis of the sacred ibis in the Netherlands) employed two different methods: the Bomford and the Invasive Species Environmental Impact Assessment (ISEIA) methods. These methods categorised the sacred ibis as a serious threat and a moderate threat, respectively. The risk analysis provides recommendations for controlling the risk posed by the sacred ibis in the Netherlands and distinguishes preventative measures, elimination and management.

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