Justification of Red List Category
The population is believed to continue to decline at a moderately rapid rate following a major decline caused by habitat destruction during the second half of the 19th century. The species therefore qualifies as Vulnerable. Targeted surveys with a consistent methodology have improved the estimates of the population size and with that monitoring of trends, however declines continue even in areas receiving extensive conservation efforts; outside the core range rapid declines continue and further national extinctions are likely.
The global population is estimated at 11,000-16,000 singing males (M. Flade in litt. 2012), equivalent to 22,000-32,000 mature individuals or 33,000-48,000 individuals in total. The European population is estimated at 9,000-13,800 calling or lekking males, which equates to 18,000-27,600 mature individuals or 27,000-41,400 individuals (BirdLife International 2015).
The majority of Aquatic Warblers now breed in Europe, where data collated for the European Red List of Birds (BirdLife International 2015) estimated that populations are continuing to decrease by 30-49% in 13.2 years (three generations). Outside Europe remaining populations are small and considered at high risk of extinction.
This species breeds across a highly fragmented range at fewer than 50 regular breeding sites in the following countries, with numbers given of singing males reported for the European Red List of Birds (BirdLife International 2015) or subsequent updates (BirdLife International 2008, J. Krogulec in litt. 2016): Poland, 2,700 - 3,100 (year: 2012); Belarus, 2,968 - 5,548 (2013); Ukraine, 3,400-3780 (year 2014 [Poluda 2015]); Germany, 0-10 (years 2005 - 2009), Lithuania, 106- 138 (2014 - 2015) and European Russia, 4-5 (2004-2008). The west Siberian population in European Russia is thought likely to have disappeared, with the last confirmed record in 2000 (J. Krogulec in litt. 2016). In Hungary, the population collapsed in the period 2002 - 2007, and zero calling males were estimated in 2011 - 2012 (BirdLife International 2015, Végvári and Flade 2012). Within Europe declines are continuing, if at a slower rate than previously in the central European strongholds in eastern Poland and Ukraine, but in Belarus the population declined by 47-55% between 2000-2011 (BirdLife International 2015) and the Pomeranian population of northwest Poland and northeast Germany has declined to critical levels.
Post-nuptial migration initially occurs in a westerly and south-westerly direction with birds passing both north and south of the Alps (Jiguet et al. 2011, Salewski et al. 2013) and it has been recorded from all European countries except Malta and Cyprus. The initial key stopover sites appear to be in west and southwest France (Jiguet et al. 2011, Latraube and Le Nevé 2014, Marquet et al. 2014) and the northern Iberian Peninsula (Salewski et al. 2013). The species winters in the Sahelian belt of sub-Saharan West Africa (Schäffer et al. 2006, Walther et al. 2007). Wetlands along the lower Senegal River, especially those within and to the north of Djoudj National Park are significant wintering areas (Bargain et al. 2008, Flade 2008, U. Malashevich in litt. 2012), as are wetlands in south-west Mauritania and the inner Niger Delta in Mali (U. Malashevich in litt. 2012, Schäffer et al. 2006, Walther et al. 2007).
It breeds in large open lowland sedge fen mires and similarly structured marshy habitats with a water depth of 1-10 cm (BirdLife International 2008, Aquatic Warbler Conservation Team 1999). In strongly euthrophic habitat the species is more or less dependent on human management to maintain open habitat, while in poorer areas water table variation may be sufficient to maintain suitability; however the species avoids very poor mires (BirdLife International 2008). Targeted agri-environment schemes can maintain suitable breeding habitat for the species in central Europe, especially where conservation action has already taken place (BirdLife International 2008). The highest densities of singing males were found where vegetation was between 60-90cm high and densities increased with percentage ground cover by water (Kloskowski et al. 2015). On migration the species uses low stands of sedges and reeds, seemingly the latter for resting and the former for feeding (Bargain 2002). The sites where it is found during migration are mostly coastal marshes, lagoons and estuaries, but there are also regular records at sites along large rivers (de By 1990). It winters in the grassy saline Scirpus, Eleocharis and Oryza marshes of the Senegal and Niger deltas (Flade et al. 2011).
The most important threats are loss of breeding habitat owing to drainage for agriculture and peat extraction, damming of floodplains, unfavourable water management and the canalisation of rivers. Habitat degradation is widespread where traditional fen management has ceased allowing succession to unsuitable overgrown reedbed, scrub or woodland (Aquatic Warbler Conservation Team 1999, BirdLife International 2008). Any changes that alter the hydrological regime of breeding sites result in reduced breeding success and population declines (BirdLife International 2008). Uncontrolled fires in spring and summer pose a direct threat to birds and nests, and can burn out the upper peat layer of fens (Aquatic Warbler Conservation Team 1999, BirdLife International 2008), although in certain locations controlled burning on frozen ground in winter may increase the density of singing males in following seasons (Grzywaczewski et al. 2014). Similarly, grazing at too high an intensity, cutting too early or too frequently may cause significant local reductions in breeding success (BirdLife International 2008). In the wintering grounds, agricultural cultivation and irrigation (creation of rice and sugar cane plantations), drought, wetland drainage, intensive grazing, succession to scrub, desertification and salinisation of irrigated soils are all potential threats (Aquatic Warbler Conservation Team 1999, M. Flade and L. Lachmann in litt. 2007).
Conservation Actions Underway
CMS Appendix I and II. EU Birds Directive Annex I. It is legally protected in all countries of its breeding range except Ukraine and Russia (U. Malashevich in litt. 2012). All key breeding sites in Belarus, Germany, Hungary and Poland are located within protected areas (Aquatic Warbler Conservation Team 1999, U. Malashevich in litt. 2012). In Ukraine, 85% of breeding habitat is within protected areas (Poluda 2015). Habitat is actively managed in Poland, Belarus, Ukraine, Lithuania, Hungary and Germany. All breeding range states but Russia have monitoring programmes (Aquatic Warbler Conservation Team 1999, M. Flade and L. Lachmann in litt. 2007). A study to identify the wintering range of the species was conducted in 2007 (Flade 2008). Studies on halting succession have been conducted in Belarus, Poland and Ukraine (M. Kalyakin in litt. 1999). A European action plan was published in 1996 and updated in 1998, 2003, 2008 and 2015 (Flade and Lachmann 2008, BirdLife International 2008). The species was put into agenda of the Conference of Parties for the CMS in November 2011, where a special resolution on African-Eurasian landbirds was adopted, which applies to Aquatic Warbler (U. Malashevich in litt. 2011).
12-13 cm. Small, heavily streaked, buff-and-black warbler. Strong black streaking on mantle bordered by pale tramlines. Pale coronal stripe with black border. Pale lores. Streaked back, rump and uppertail-coverts. Finely streaked breast. Similar spp. Sedge Warbler A. schoenobaenus generally browner and less streaked. Lacks strongly streaked mantle and pale tramlines, pale coronal stripe and streaks on breast. Song more complex and varied with mimicry and distinctive sweet notes. Voice Series of simple trills and short whistles, given from vegetation or short song flight. Does not mimic extensively. Low tuk or dry churr call.
Text account compilers
Ekstrom, J., Peet, N., Martin, R, Derhé, M., Khwaja, N., Symes, A., Ashpole, J, Capper, D.
Malashevich, U., Lachmann, L., Kalyakin, M., Flade, M., Krogulec, J., Burfield, I.
BirdLife International (2021) Species factsheet: Acrocephalus paludicola. Downloaded from http://www.birdlife.org on 25/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/10/2021.