The islands were created from spoil excavated during the deepening of the waterway from Świnoujście to Szczecin. Scientists from the Museum and Institute of Zoology of the Polish Academy of Sciences, the West Pomeranian Nature Society and the University of Szczecin have studied their impact on birds for five years. Their findings have been published in the journal Estuaries and Coasts.

The two islands developed differently. On the first, W22, known as Brysna to the scientists, deposition of spoil was stopped after some time and the island was left as a habitat for birds. The second, W28, known as Śmięcka, is still used to deposit sediment extracted during maintenance of the waterway.

That difference proved crucial.

“Initially, both islands had vast, almost vegetation-free areas of sand and silt. Shallow pools and muddy shores formed. These conditions are particularly valuable for birds that build nests directly on the ground and need open spaces,” said study first author Dominik Marchowski, PhD, a professor at the Museum and Institute of Zoology of the Polish Academy of Sciences.

Such habitats are becoming increasingly scarce. Natural sandbanks are disappearing because of river regulation, while beaches are heavily used by people.

“So if there is an open space, a lot of sand, undeveloped and muddy places, this group of birds immediately appears,” Marchowski said.

That is what happened on the Szczecin Lagoon. In the first year of monitoring, 2021, scientists recorded seven breeding species on the two islands. Four years later, there were 35.

One of the most striking examples is the pied avocet. The species had previously nested in Poland only occasionally, usually in single pairs and for short periods. The new islands provided it with a stable breeding habitat. Scientists counted 14 pairs in 2021 and 85 in 2025.

The black-winged stilt also appeared, while in 2024 researchers confirmed the first breeding of the Caspian tern in Poland. The world’s largest tern had previously been observed in the country only during migration, but now returns to breed every year.

Other rare species have also reached significant numbers, including the little tern, ringed plover, shelduck and redshank.

The importance of the islands is disproportionate to their size. Together, they cover only about 3.7 square kilometres, yet they host a significant share of regional populations and, for some species, a substantial proportion of Poland’s breeding population.

For the avocet, black-winged stilt and Caspian tern, the islands account for 94-100% of breeding pairs in Pomerania and roughly 40% to almost 100% of the national population.

“Such places, if properly planned and maintained, can be a kind of incubator for the development of populations of rare species,” Marchowski said.

The islands offer favourable conditions because of their sandy, sparsely vegetated terrain and their isolation from predatory mammals. Human pressure is also low, as mooring and staying on the islands without permission is prohibited.

“This isolation is important because foxes, raccoon dogs, raccoons and American minks can cause huge losses in colonies of birds nesting on the ground,” Marchowski said.

But the very lack of new sediment that helped create Brysna’s habitat has now become a problem.

With deposition stopped, the island has gradually become overgrown. Reeds and willow thickets appeared, followed by small trees. In 2021, tall vegetation covered less than 1% of the island. The figure rose to 2.5% in 2022, 6.5% in 2023 and about 12% in 2024. By June 2025, it had reached 23%. Including grasses and lower vegetation, half of the island was covered by plants.

This does not mean that bird numbers decline as vegetation spreads. Instead, the island begins to favour different species. The number of breeding pairs of passerine birds has increased significantly, with sedge warblers, reed buntings and chiffchaffs also appearing.

From a conservation perspective, however, this is not an equivalent trade-off. Birds that depend on reeds and shrubs have many other suitable habitats, while species such as avocets, little terns and ringed plovers need open, sparsely vegetated ground that is becoming increasingly scarce.

Scientists’ simulations show that without human intervention, tall vegetation could cover almost all of the available space within the next few years. For birds dependent on open habitats, that would mean losing their nesting grounds.

“In 2025, there were still breeding avocets on Brysna. This year, we did not have them there anymore, precisely because they lacked suitable pioneer habitats free of vegetation,” Marchowski said.

Conditions remain more favourable on the second island, Śmięcka, where continued deposition of dredged material creates new sandy and muddy areas free of vegetation.

According to this year’s data, more than 8,000 pairs of black-headed gulls and about 800 pairs of common terns nested there. Scientists also recorded 65 pairs of avocets.

For Marchowski, the experience of the Szczecin Lagoon shows how material dredged from shipping channels could be used to create new habitats. Such sediment is often simply deposited in designated areas of the seabed, but it could instead be used to build islands that benefit wildlife.

“It combines major port infrastructure projects with turning what is essentially a byproduct into something that benefits nature. Similar solutions are used in the Netherlands, for instance, where artificial islands are designed to provide habitats not only for birds but also for fish and amphibians,” Marchowski said.

Creating an island, however, is only the beginning. The research shows that without further intervention, the open habitats that attract rare breeding birds can disappear within just a few seasons.

The authors say this could be countered through measures such as mowing, partial removal of vegetation or periodically exposing the substrate. The islands also need to be monitored for the appearance of predators.

PAP - Science in Poland, Katarzyna Czechowicz (PAP)

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