Aquatic Warbler

The Aquatic Warbler Memorandum of Understanding (MOU) was concluded in Minsk, Belarus, under the auspices of the Convention on Migratory Species (CMS) and became effective on 30 April 2003. It aims to safeguard the Aquatic Warbler Acrocephalus paludicola that is the rarest migratory songbird of Europe, and the only globally threatened passerine bird found in mainland Europe.

Once widespread and numerous in fen mires and wet meadows throughout Europe, the Aquatic Warbler has disappeared from most of its former range. Nowadays, its world population of only 9,000-14,000 vocalising males is confined to fewer than 40 regularly occupied breeding sites in only five countries, covering together only less than 400 km2 (area of occupancy) with four sites supporting over 80% of the global population.

The Aquatic Warbler regularly breeds in Belarus, Lithuania, Poland and Ukraine (irregularly in Germany and Hungary; populations in West Siberia and Latvia are probably extinct), with major populations in Belarus, Ukraine and Poland. The breeding distribution is fragmented because of habitat constraints. The species became extinct in Western Europe during the 20th century and has declined dramatically in central Europe. It formerly bred in France, Belgium, Netherlands, former West Germany, former Czechoslovakia, former Yugoslavia, Austria and Italy.

A small geographically and probably genetically isolated subpopulation of the Aquatic Warbler exists in Germany/northwest Poland (so-called Pomeranian population), but is actually threatened by extinction (34 males in 2012). Another small satellite population in West Siberia (Russia) was latest confirmed in 2000 and is probably extinct in the meanwhile.

The Aquatic Warbler migrates up to 12,000 km from Eastern Europe to sub-Saharan Africa. The migration strategy of the Aquatic Warbler requires the availability of many suitable autumn stop-over sites, the loss of which can be a potential bottleneck for the species. On migration, the Aquatic Warbler is regularly being recorded in 11 countries mainly in the west and southwest of Europe as well as in Morocco. The species winters in West Africa south of the Sahara. There are four confirmed Aquatic Warbler wintering sites. The most well studied wintering site is situated in the Senegal delta within and north of the Djoudj National Park (Senegal). Here, a major part of the global population is wintering. Recent searches for more wintering sites resulted in 2 small sites discovered in southern Mauritania and one bigger site discovered in the Inner Niger Delta in Mali in February 2011.

This MOU reflects the common concern over the dramatic decline of this bird species and the Signatory States’ determination to reverse the current trend. The MOU applies to 22 countries where the Aquatic Warbler breeds, rests on migration or winters. The MOU area includes Belarus, Belgium, Bulgaria, France, Germany, Hungary, Latvia, Lithuania, Luxembourg, Mali, Mauritania, Morocco, the Netherlands, Poland, Portugal, the Russian Federation, Senegal, Slovakia, Spain, Switzerland, Ukraine and the United Kingdom. CMS and BirdLife International, which also was involved in the MOU’s development, have also signed the MOU as collaborating organizations.



The Second Meeting of Signatory States (Biebrza National Park, Poland, 2010) agreed to extend the geographical coverage of the agreement till the current scale and also adopted a new International Species Action Plan for the Aquatic Warbler, prepared by CMS’s partner BirdLife International on behalf of the European Union. During the Meeting France and Mali signed the agreement, with Luxembourg joining them shortly after. During the CMS COP10 in 2011 Switzerland also became a signatory of the Memorandum.

The MOU calls for cooperation among national authorities to promote the conservation of the species. It requires the strict protection of the species and the maintenance and restoration of its habitat.

The Action Plan

A detailed Action Plan is annexed to the MOU. It summarizes the distribution, biology and conservation status of the Aquatic Warbler, and describes precise actions to be taken by relevant countries. The main objective of the Action Plan is to maintain the Aquatic Warbler throughout its range and, in the medium to long term, promote the expansion of the breeding population to other suitable areas. Priority conservation actions to be taken by the Signatories can be summarized as follows: legislative measures to ensure the species’ and habitat protection, conservation of all existing sites, increase of the area of suitable habitat at existing sites and restoration of additional sites, monitoring and research, and the establishment of a public awareness strategy.


The MOU provides an intergovernmental framework for governments, scientists and other groups to monitor and coordinate ongoing conservation efforts. Progress in MOU and Action Plan implementation is described in the Secretariat’s Overview Report provided at regular MOU Signatory meetings.

Governments and conservation groups throughout the species’ range are working actively to conserve the Aquatic Warbler and its breeding and migratory habitats. Several large-scale projects have been successfully implemented or are underway in key Aquatic Warbler flyway countries in order to secure breeding and stop-over sites. Additionally, CMS has worked with BirdLife International to establish a jointly-funded MOU coordinator. Working out of Belarus, the MOU coordinator supports partner organizations all over the species range with the development, fundraising and implementation of conservation projects aimed at this species, working in close cooperation with the CMS Secretariat, the Royal Society for the Protection of Birds (RSPB), and the International Aquatic Warbler Conservation Team (AWCT). The coordinator oversees the publication of the Aquatic Warbler Flyway Newsletter, and maintains the website ( and Arc GIS data base for the species.

In January of 2007, the BirdLife International Aquatic Warbler Conservation Team discovered a key site within the Aquatic Warbler’s wintering grounds in West Africa, which were completely unknown until then. According to first estimates, the Djoudj National Park in Northwest Senegal and its surroundings are believed to harbour a major part of the world population. Later on three more sites were discovered, they are located in southern Mauritania and in the Niger River delta in Mali Much of the Aquatic Warbler’s presumed historic wintering habitat has been converted into farmland and sugarcane plantations. Drought conditions caused by climate change could put increasing pressure on the Aquatic Warbler’s remaining habitat.

The discovery of the wintering sites contributes to implementing the MOU and Action Plan. In 2010, signatories included Mauritania and Mali into the geographical scope of the MOU. This would allow Senegal, Mauritania and Mali to coordinate their conservation efforts. Additionally, the discoveries create an extra incentive for European conservation efforts to be extended into Africa to truly encompass the bird’s full migratory range.


Map prepared by Uladzimir Malashevich.


Titresort descending Statut Status date CMS Party number Region
Belarus MOU Signatory 2003 084 Europe
Belgium MOU Signatory 2005 035 Europe
Bulgaria MOU Signatory 2003 061 Europe
France MOU Signatory 2010 032 Europe
Germany MOU Signatory 2003 016 Europe
Hungary MOU Signatory 2003 001 Europe
Latvia MOU Signatory 2003 060 Europe
Lithuania MOU Signatory 2003 079 Europe
Luxembourg MOU Signatory 2010 001 Europe
Mali MOU Signatory 2010 024 Africa
Mauritania Range State 054 Africa
Morocco Range State 042 Africa
Netherlands Range State 001 Europe
Poland MOU Signatory 2004 049 Europe
Portugal Range State 001 Europe
Russian Federation Range State AM Europe
Senegal MOU Signatory 2003 027 Africa
Slovakia Range State 045 Europe
Spain MOU Signatory 2003 017 Europe
Switzerland MOU Signatory 2011 046 Europe


Instrument nameMemorandum of Understanding concerning Conservation Measures for the Aquatic Warbler (Acrocephalus paludicola)
TypeArticle IV(4)
DepositaryCMS Secretariat
SignatureSigned by 16 States and 2 Co-operating Organizations (for details please scroll to 'others' and 'MoU Signatory')
In effectImmediately following the signature by the fifth State; open for signature indefinitely, will become effective for each subsequent Range State on the date of signature
Website URL
OtherSigned also by Co-operating Organizations: CMS Secretariat and BirdLife International on 30 April 2003. First Meeting of the Signatories MoS1), 25-27 June 2006, Griewen, Germany Second Meeting of the Signatories (MoS2), 13-15 May 2010, Biebrza National Park, Poland

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