The Ornithological Reserve, proclaimed as early as 1983, is one of the most ornithologically valuable areas in Croatia and is a fundamental phenomenon for conservation of the entire Nature Park. With an area of 8.83 km2, it occupies the northwestern part of Lake Vrana to the very border of the Nature Park.
This small wetland area is the rest of the former ten-fold greater Vrana’s mud, swamp that is almost completely dried during 18th century by amelioration canals and digging Prosika canal on lake’s southeastern coast to the sea. It was brought to the brink of survival, together with it the living world that depended upon it. However, today’s Ornithological reserve is characterized by a wealth of wildlife, especially ornithofauna (bird life). 102 bird species use the Reserve at the nesting season, when the tall reed represents an ideal shelter for their nests and young birds, and water and land are abundant with food. In the winter 87 species of wintering birds hide on Vransko Lake from harsh northern cold, and on sunny winter days on the lake’s open water can be seen up to 100,000 birds enjoying the mild climate and abundance of food. During the autumn and spring migration at Vransko Lake stop over 140 species of migratory birds to feed and rest.
Often some birds appear to Vransko Lake as wintering, migratory or nesting birds, so the total number of species is not equal to the sum of wintering, migratory and nesting birds. From more than 260 bird species that live in the Reserve, nest, winter or use it as a resting and feeding area during migrations, 136 species belongs to the critically endangered, endangered, vulnerable or species at the low-risk on the national (129), the European (95) or even global level (9). In addition, reed beds and flooded meadows of Ornithological reserve, as part of wetland ecosystems, are among the most threatened habitats in Croatia.
Inside the Reserve inhabited important populations of 13 bird species whose local population from Vransko Lake are important for the stability of the entire population on national, European, global level, or even important for survival of the entire species! These are:
Purple Heron Ardea purpurea is a species at the risk in Europe and Croatia. Nesting population on Vransko Lake is the only one in the Croatian coastal part and makes over 10% of the Croatian population.
The Great Bittern Botaurus Stellaris is a species at the risk in Europe, and endangered (EN) in Croatia. Since the Vransko Lake is one of the only three breeding sites of this kind in the Croatian coastal area, it is important despite the fact that the Great bitterns probably nest here irregularly. If in the near future comes to Lake’s hydrological stabilization and prevention of burning reed bed, Great Bitterns nesting population will stabilize and grow.
Great Egret Egretta alba is an endangered species in Croatia, regardless of the nesting irregularity on the lake this population is important because it is the only one at the coastal area.
Marsh Harrier Circus aeruginosus is an endangered species in Croatia with only two breeding sites at the coastal area: Vransko Lake and the downstream of river Neretva. Therefore, this population is important regardless of paucity.
Corncrake Crex crex is a risk species at global, European and Croatian level. Unfortunately, the nesting population extinct at the Vransko Lake, but it’s still present as migratory bird. With the lake’s hydrological stabilization, the Park expansion and the replacement of intensive agriculture with extensive cattle breeding could be created conditions for returning of the nesting population.
Little Crake Porzana parva is most likely endangered nesting bird in Croatia with a population of less than 100 pairs. Therefore, it is important Vrana’s population, especially because it’s the only one at the coastal area together with Neretva’s population.
Spotted Crake Porzana porzana is even rarer and less frequently nesting bird then little crake in Croatia with a total population of probably less than 50 pairs. Nesting population on Vransko Lake was discovered only in 2003 by the method of sound night bait.
The Euroasian coot Fulica atra is widespread nesting bird, but the Mediterranean wintering population is under great pressure of hunting and therefore is considered to be low-risk. Therefore, the number of wintering population of the Vransko Lake is important for the stability of the total Mediterranean wintering population.
Moustached warbler Acrocephalus melanopogon is critically endangered nesting species in Croatia and any potential nesting of this species is of great importance. Furthermore, numerous wintering population is also important for the stability of this species.
Pygmy Cormorant Phalacrocorax pygmaeus: critically endangered species in Croatia whose only stable nesting in Croatia is Vransko Lake. Therefore, protecting this area is of crucial importance for the survival of the species in our country.
The squacco heron Ardeola ralloides is species at risk, and in Croatia is endangered. At the lake is regularly present at the nesting season, but there are indications that occasionally nest here. Population from Vransko Lake is important since nowhere else nest at the entire Croatian coastal area, especially in the case of the lake’s hydrological stabilization that would result with the stabilization of the squacco heron population.
Because of the small area, ornithological reserve of Vransko Lake is exposed to the pressure of various negative influences eg. the impact of intensive agriculture in the reserve and surrounding areas (habitat destruction, pesticides, fertilizers which increase production and accelerate lake’s eutrophication), hunting and poaching (due to a small protected area birds come out and get hurt in the nearby area), tourism and sport fishing (a lot of users in a small area constantly harass birds) etc. The best feeding areas of the most important endangered species of Vransko Lake are located outside the boundaries of the ornithological reserve and even the Nature Park: purple herons and pygmy cormorants feed on the flood plain area and canals outside the Park and Reserve. Their range of movement is often up to several kilometers.
In addition, in this area, especially at flooded fields, temporarily or permanently reside full range of waders (Charadiiformes), herons (Ardeidae), ducks (Anatidae), birds of prey (Falconiformes) and passerines (Passeriformes) and even this area meets the criteria of protection.