Global Aquatic Warbler population is still declining

Conference updates confirmed that the Aquatic Warbler’s situation remains critical. Recent assessments discussed in Vilnius suggest the global breeding population may have fallen to around 4,000–5,000 singing males in 2025—potentially a historic low and a warning sign of an approaching demographic bottleneck.  Because the situation is so severe, there have been discussions about reassessing the species’ IUCN Red List status, with some experts suggesting that the current classification may no longer reflect the scale and speed of the decline. 

Against this overall decline, Lithuania remains an important exception, showing growth in recent years—often highlighted at the conference as proof that targeted habitat management and sustained conservation effort can deliver results. At the same time, speakers reminded that Lithuania represents only a small share of the global population, meaning that recovery there alone cannot “carry” the species. 

The drivers behind the decline were described as both structural and increasingly climate-related. Across several range countries, breeding habitats are being lost or degraded through drainage, changes in land use, and progressive overgrowth by reeds and shrubs where management has weakened. Climate extremes are amplifying these pressures: participants pointed to how unstable water levels, cold springs, drought, and fire risk can rapidly reduce breeding success and habitat suitability—especially in large mire systems where hydrology cannot be actively managed. The discussions repeatedly returned to one adaptation message: sites with controllable water regimes tend to be more resilient, making water management an increasingly important tool under climate change. 

Habitat restoration remains the non-negotiable foundation

 A central takeaway was that long-term recovery cannot be achieved without extensive, high-quality fen mire habitat. Evidence shared at the conference reinforced that water management and late-mowing regimes are not “nice-to-have” measures—they are the backbone of any sustainable population recovery.  

New methods for habitat restoration

New methods for habitat restoration were also a very interesting—and highly debated—topic, driven by a shared reality: long-term management of large fen areas, especially without reliable subsidy support (a common situation outside the EU), is often not economically feasible with traditional approaches alone. That is why scalable solutions are urgently needed. 

Several experiments from Belarus were discussed.  

One trial tested a selective glyphosate application—targeting only taller vegetation (reeds and shrubs) with a specialised tractor-mounted device across 30 ha. After one year, reed stem density declined markedly. However, participants noted that this approach would likely face major barriers in many EU contexts due to environmental and health concerns: glyphosate residues can enter soil and water, may affect non-target organisms, and there is ongoing scientific and regulatory debate about potential impacts, including risks to wildlife and soil microbial communities. Belarusian colleagues added that, in this specific trial, they did not observe obvious negative environmental effects, but the discussion emphasised that such outcomes can be difficult to detect without longer-term monitoring and targeted ecotoxicological assessment. 

Another experiment focused on mechanically reducing reed regrowth by damaging fragile “winter buds” on rhizomes through high-pressure rolling, with strong reductions in reed stems in the following season and over several years, while open questions remain about potential effects on tussock structure. Prescribed burning, used preventively to reduce the risk of uncontrolled fires, was also highlighted—particularly in Zvaniec, where winter or early-spring burning was linked to improved breeding conditions. Overall, the message was clear: under climate change and hydrological disruption, success will depend on combining active water management with effective, locally suitable reed and shrub control—tailored to each country’s ecological and socio-economic context. 

We need integrated conservation: demography, genetics, and management together

Speakers repeatedly returned to the same point: effective conservation must connect the dots between habitat quality, breeding success, survival along the flyway, and genetic resilience. Population viability depends on improving survival and breeding outcomes while managing genetic risks and making management economically and practically sustainable.  

Connectivity and “stepping-stones” are becoming more urgent

New genomic insights highlighted a long-term decline in genetic diversity, with particularly worrying signals in small, isolated populations. In this context, restoring and maintaining habitat continuity—through a network of stepping-stone sites—was emphasized as a strategic priority to reduce fragmentation risk, support resilience under climate pressure, and strengthen connectivity between populations.  

Translocation is taking on a more central role

With the global population under increasing pressure, conference discussions suggested that conservation translocation is becoming more strategically important—not as a replacement for habitat work, but as a tool to prevent local extinctions and accelerate recovery where conditions are being restored. 

A key constraint raised was the growing difficulty of identifying reliable donor sites. In the current political context, cooperation with Belarus is not possible, while some Ukrainian sites still need time to recover. This leaves a limited number of potential source populations within the EU, with Biebrza often mentioned as the main remaining stronghold. Yet the conference also highlighted the risk of over-reliance on any single donor area—especially when climate-driven events (such as drought and fire) can sharply reduce breeding output in a bad year.  

Speakers emphasised that donor impacts must be assessed carefully: not only in terms of short-term numbers, but in relation to carrying capacity and long-term viability. Importantly, several participants argued that translocation decisions should be evaluated in a broader population context—weighing risks and benefits across the species’ range, rather than treating each site or country in isolation. That means considering both potential costs to donor populations and the conservation gains at recipient sites, using the best available demographic and habitat evidence. 

One particularly notable contribution from Lithuania was the presentation of a “rescue translocation” approach: using chicks that would likely not survive because of imminent threats such as intensive grazing or early mowing. This method is more complex and demanding, but early experience was presented as promising—suggesting it could become a standard translocation method in the future. 

At the same time, the conference was clear on one point: translocation cannot stand alone. Its long-term value depends on whether it is embedded in wider action—especially strong habitat policies, effective site management, and flyway-scale conservation that improves survival beyond the breeding grounds. 

Stopover sites in Nort West Africa are becoming a critical bottleneck

New tracking evidence shared at the conference sharpened the picture of where Aquatic Warblers depend most on wetlands outside the breeding season. Geolocator studies indicate that many birds winter in the Inner Niger Delta in Mali and wetlands across the western Sahel region, which—despite strong year-to-year fluctuations—still appear to offer substantial habitat at the population scale. The sharper risk lies further north: during spring migration, Aquatic Warblers rely on a small set of wetlands in Morocco, northern Algeria and southern Spain to refuel after crossing the Sahara. Many of these sites have been lost or degraded over the last 30–40 years due to land reclamation, expanding irrigated agriculture, freshwater extraction and persistent low precipitation. The conclusion was clear: protecting and restoring the remaining coastal wetlands in Morocco and Algeria must become a priority in international Aquatic Warbler conservation, because this spring stopover “stepping-stone” network may be approaching a bottleneck for the global population.  

Monitoring and data infrastructure are essential for smarter decisions

From field monitoring to genomic work, the conference reinforced the need for consistent, comparable data to guide adaptive management, improve models, reduce uncertainty, and respond faster to emerging risks.   

Explore the materials

All presentations, abstracts and video recordings are available online: https://aquaticwarbler.eu/2025/11/24/conference-materials-international-aquatic-warbler-conservation-conference/