Common Tern

Its breeding was first confirmed on the seashore in 1983, when nine pairs nested in the Sečovlje salt pans. In the same year, we started mapping censuses of nesting birds in the Sečovlje salt pans. This paper presents the breeding distribution, status and threat status of the Common Tern in the Sečovlje salt pans in the period 1983-2019.

In 1991, the number of breeding pairs in the Sečovlje salt pans increased, which is consistent with data from other Mediterranean sites, especially salt pans, where this species breeds. Since 1991, the breeding population of Common Terns has been fairly stable or has been increasing moderately, with several dozen pairs regularly nesting here. The breeding success of the Common Tern in the Sečovlje salt pans is poor in all seasons, mainly due to heavy rainfall and predation. Long dry periods without precipitation have a positive effect on the hatching and fledging success of Common Tern chicks. Adequate water management and control of access to nesting sites can prevent disturbance by visitors and, to some extent, predation by terrestrial predators such as fox and marten. In Slovenia, the Common Tern used to nest along major watercourses, but today it nests only locally on artificial nesting sites, including the Sečovlje Salt Pans. Its survival therefore depends on active management of this area, otherwise it will disappear as a nesting species. However, expected climate change, with accelerated sea level rise and consequent increased flooding of low-lying coastal areas, is making its existence and survival in the Sečovlje salt pans even more difficult. The common tern nests in Slovenia in coastal and coastal landscapes. It has nested in the Sečovlje salt pans since 1983, while in Škocjan Bay it started nesting in 2007 after the bay was renovated. Nine pairs nested in the Sečovlje salt pans in 1983. The number of nesting pairs has increased over the years. In 1991, the number of nesting pairs in the Sečovlje salt pans increased significantly, which is consistent with data from other Mediterranean sites, especially salt pans, where this species breeds. This trend is also due to the small artificial islands created in industrial and other salt marshes. Since 1991, the breeding population of Common Terns has been fairly stable or has been increasing moderately (TRIM: p < 0.01), with between 30 and 70 pairs regularly breeding here. Breeding success of Common Terns in the Sečovlje Salt Pans is low (0 to 1.1 fledged chicks/pair), mainly due to high rainfall and consequently high water levels and predators.

The Common Tern is not considered a threatened species in Europe, although in some countries populations have declined significantly due to habitat degradation, human disturbance and other factors. It is a species in need of active protection and management, including in our country.

The Common Tern in the Sečovlje Salt Pans is threatened most by weather events with flooding (40%), predators (35%), salt production (10%), maintenance works (10%) and visitation and recreational activities (5%).

The Sečovlje Salt Pans are a national site of high natural, cultural, economic and aesthetic value, where biodiversity can be maintained and managed in a sustainable way. The breeding population of Common Terns in the Sečovlje Salt Pans is quite stable, despite the difficulties and challenges faced by this species. In the second half of the 21st century, climate change is expected to accelerate sea level rise and consequently increase the frequency of flooding of low-lying coastal areas. This could have important consequences for organisms associated with these areas, including shorebirds that feed, nest or overwinter in these habitats during migration.

Analyses of the breeding patterns of some breeding birds (Kentig Plover, Little and Common Tern and Black-winged Stilt) in the Sečovlje Saline Landscape Park have shown that the breeding dynamics of these birds in recent years clearly point to the coming climate change.

*It is considered a qualifying species in favourable conservation status in the Sečovlje salt pans.