Droughts and fires devastate Aquatic Warbler breeding habitats

“This spring was the driest ever recorded in Central Europe,” says Martin Flade, chairman of the Aquatic Warbler conservation team. In regions dependent on rainfall, drought has triggered large-scale fires. Poland’s Biebrza Valley experienced its worst drought since the park’s founding, according to Krzysztof Stasiak, member of the OTOP organisation, working with Aquatic Warbler conservation in Poland. This has caused the vegetation to dry out, creating perfect conditions for fires to start and spread to an area as large as 500 hectares, destroying the vegetation of around 185 hectares of Biebrza marshes. Reduced haymaking and increased eutrophication have led to overgrown vegetation, aiding the initiation of fires. Such was the case in Ukraine, where 30 to 90% of breeding areas burned this spring, with 75% of Aquatic Warbler habitats affected, according to Olga Yeremchenko from USPB, organisation responsible for Aquatic Warbler conservation in Ukraine. In contrast, areas along the Baltic Sea — such as Lithuania’s Nemunas Delta — fared better, as water levels there are more influenced by sea conditions and wind patterns than precipitation.

Insect decline threatens Warbler breeding success

The combination of droughts and unstable temperatures has also harmed insect populations, the Aquatic Warbler’s primary food source. Even though insect surveys are necessary to accurately compare population change, Krzysztof Stasiak says that so far he has barely observed any mosquitoes or horseflies. Adequate water levels and steady seasonal changes — a cold winter followed by a warming spring — are crucial for insect development. The lack of food in combination with abnormal weather patterns discourages the female birds from breeding, leading them to wait for an improvement in conditions or relocate. This causes the breeding cycle to be postponed further into summer and might affect whether the females decide to do a second round of breeding that season.

Integrated habitat management offers hope amid climate challenges

Habitats with artificial management systems show promise in counteracting the effects of a changing climate. In Zvaniec, Belarus, water levels remained rather stable despite droughts, thanks to water supply through a canal coming from Ukraine — a system developed during the LIFE MagniDucatusAcrola project — and controlled burning in winter over ice, which reduced fire risk in spring and preserved insect habitats.

Meanwhile, in Žuvintas, Lithuania, water levels dropped despite having a canal system — largely due to competing use by nearby aquaculture farms. During normal years, the farms consume 10% of the canal’s water, but this year usage spiked to 60%. Žymantas Morkvėnas, head of Baltic Environmental Forum Lithuania and responsible for Aquatic Warbler conservation in the country, suggests that the main solution is ensuring the canal is closed in early autumn to allow for better water storage.

Another important management methodology is maintaining the right amount of plant growth. Wintertime controlled burning reduces flammable biomass while protecting hibernating insects — though it depends on reliable frost, which is becoming less predictable. Mowing the vegetation remains a universal and essential practice, but it needs to be performed correctly to avoid disturbing the breeding of the Aquatic Warbler. For instance, according to Žymantas Morkvėnas, this should be done every two to three years, allowing for the regrowth of sedges — the key plant used for nesting by this endangered bird.

In general, preserving as many sites as possible is vital to creating a healthy breeding network for the Aquatic Warbler. In years of extreme weather, alternative habitats ensure the survival and continuity of the Aquatic Warbler population.

Meanwhile in Žuvintas, Lithuania, water levels dropped despite having a canal system—largely due to competing use by nearby aquaculture farms. During normal years, the farms consume 10% of canal water, but this year it spiked to 60%. Žymantas Morkvėnas, head of Baltic Environmental Forum Lithuania, responsible for Aquatic Warbler conservation in Lithuania, suggests the main solution is making sure the canal is closed in early autumn to allow for better water storage. Another important management methodology is the maintenance of the right amount of plant growth. Wintertime-controlled burning reduces flammable biomass while protecting hibernating insects—though it depends on reliable frost, which is becoming less predictable. Mowing the vegetation remains a universal and essential methodology, but it needs to be performed correctly to not disturb the breeding of the Aquatic Warbler. For instance, according to Žymantas Morkvėnas, this practice should be done every two to three years, allowing for the regrowth of sedges, the key plant used for nesting of the endangered bird.

In general, preserving as many sites as possible is vital to create a healthy breeding network for the aquatic warbler. In years of extreme weather, alternative habitats ensure the survival and continuity of the aquatic warbler population.