Translocation cancelled in Poland due to unprecedented drought and cold Spring

The 2025 season has brought one of the most challenging years on record for the Aquatic Warbler population in Poland, particularly in the Biebrza Valley — a key site for the species. Extreme drought, described by residents and experts as the worst since the establishment of Biebrza National Park, has severely affected breeding conditions. This climatic stress was compounded by an unusually cold spring, with May temperatures averaging 2°C below the long-term norm, according to the Institute of Meteorology and Water Management – National Research Institute. The combined impact of drought and cold significantly disrupted both habitat quality and food availability, particularly insect populations essential for feeding chicks. Compounding the problem, large areas of the Biebrza Valley were mowed during the winter, further affecting vegetation growth in spring.

Breeding Delay and Low Nest Numbers

Nest searching for the Aquatic Warbler translocation began on May 19 — a schedule consistent with previous years — yet by June 9, only eight nests had been found, two of which had already failed. No chicks had hatched by that date. In contrast, the 2024 season had already reached peak hatching by late May, with 28 nests and 130 chicks found by early June. Of those, 46 chicks from 10 nests were successfully selected for translocation to the Pomeranian region.

Due to the logistical challenge of transporting chicks over the 8-hour distance to Western Pomerania, translocation can only occur when there is a sufficient group of chicks of similar age and good health. Given the poor breeding results, the team had initially considered reducing the target number of translocated chicks from 50 to 25. However, this was conditional on their quality and condition. Due to the logistical challenge of transporting chicks over the 8-hour distance to Western Pomerania, translocation can only occur when there is a sufficient group of chicks of similar age and good health. Given the poor breeding results, the team had initially considered reducing the target number of translocated chicks from 50 to 25. However, this was conditional on their quality and condition.

Difficult Decision for the Sake of the Species

fter careful evaluation and collective discussion among the Polish OTOP team, the decision was made to cancel the 2025 translocation. Naturalists concluded that the current breeding conditions would not allow for the safe or effective translocation of chicks. To successfully move 25 chicks, around 70 viable eggs would be needed, implying the discovery of around 18 nests. This goal was not reached.. Additionally, the average clutch size seemed to be much smaller than in 2024.

Additionally, the environmental stress likely to affect chick health could significantly reduce survival rates during migration and lower the probability of return next season — ultimately nullifying the intended support to the fragile Pomeranian population.

Looking Ahead: Climate Adaptation and Planning

Despite the droughts, Aquatic Warblers were present in the Biebrza National Park. Photo by Klaus Nigge.

The Polish team remains committed to the conservation of the Aquatic Warbler. Efforts are underway to prepare for future challenges linked to climate change, including solutions to secure chick availability even in adverse conditions. With hopes for more favourable weather and improved habitat quality in the coming year, the team aims to resume translocation efforts in 2026, armed with stronger adaptive strategies and ecological insight.