Diurnal birds of prey (ord. Falconiformes)
Fens of resurgences area are of particular importance for the staging, wintering and reproduction of harriers (gen. Circus). The harriers are medium size birds of prey with slender bodies, long narrow wings and tail, characterized by a marked sexual dimorphism: adult males have the plumagealmost entirely gray in color and females mainly brown flecked with apparent rump of white.
They have a very distinctive and very elegant fly with wing beats alternated to glides with "V" wings; they frequent open areas with low shrubs and trees.
The Montaguís harrier (Circus pygargus) is a regular migrant, it is present from April to August-September in different environments of Friuli plain and locally it plays. Until about fifteen years ago, the Stella resurgences represents the most popular station of the region for the reproduction of the species. In particular, in the 80s of last century, fens housed a breeding population of at least fifteen pairs. Subsequently there has been a progressive depletion of the species in almost all known breeding sites of the region and currently, the Montaguís harrier is still present with a population in the whole areadoes not exceed 3-4 breeding pairs, which often fail to complete the reproductive cycle.
Since October the Montaguís harrier go to Africa for wintering and it is replaced by hen harrier (Circus cyaneus), regular migrant and wintering in the region. The first subjects, coming mainly from central and northern Italy, can be observed from the beginning of October until the end of March, with sporadic observations in April. The wintering population may vary considerably from year to year and the species is generally more frequent during the coldest winters. The fens of resurgences area represent an excellent environment for the location of the dormitories.
Periodic censuses carried out in these sites by the end of October to the end of March, showed that the highest concentrations are found during the month of January with 15-20 subjects surveyed. Outside the overnight sites, the species can be observed in all suitable open areas, especially those of the plains and lagoon belt.
It also notes the pallid harrier (Circus macrourus), uncommon in the region and reported only during the migratory movements, which are known to very few observations for the area examined.
The marsh harrier (Circus aeruginosus) is present throughout the year even if not on a regular basis. In the region it especially frequents the lagoon environment and coastal lowlands, with the exception of the migration period, especially in the spring (March-May), when it can be observed in transit in most open areas. The crowded areas for nesting are almost always characterized by the presence of reeds (Phragmites australis).
About ten years ago the marsh harrier showed a gradual colonization of suitable breeding sites in inland wetlands of the plains. This trend has occurred even in humid environments suitable in the area of resurgences with a couple who has played for about five years.
The black kite (Milvus migrans) is a regular migrant and until a few years ago also a regular nester with some pairs in the resurgences area within the SCI boundaries. This bird is easily recognizable in the air for the characteristic slightly forked tail. The first reports in resurgences area are generally the last decade of March; during the post-reproductive migration it can be observed until the end of September.
The nests are usually built on old oaks in the past strips of plain wood or, more rarely, on isolated trees along towpaths.
It is a greedy opportunist who, in addition to capture live animals, often feeds on carrion and waste. To search for the food it attends different types of environment including fish farms and landfill of waste.
Recent surveys carried out to identify breeding pairs of this species showed a local depletion during the breeding season without identifying the causes that have caused it.
The honey buzzard (Pernis apivorus) is a regular migrant and localized nester. The first subjects are reported in the last days of March, even though such major steps in our region are during the month of May. Substantial movements are also recorded in late August-early September, with individuals' stays until the end of the month. The pairs that reproduce in the resurgences environment are mainly located within the last stretches of lowland woods during the breeding season and are not easily identifiable because of the confidential and secretive habits; even their nests, which are usually built on old trees, are often difficult to locate. In recent years it has been noticed an increase in the number of pairs that breed on site.
This species feeds mainly social Hymenoptera (larvae, adults, parts of the nests of bumblebees, wasps, bees, etc.). Often, you can surprise isolated individuals while they are digging holes in the ground for prey on the nests of these insects.
The Eurasian hobby (Falco subbuteo) is a migratory hawk that comes in the region in April-May and depart for the wintering areas in September; as breeding it is localized mainly in the plain areas, rarely in the hills and highlands.
During the spawning it attends environments characterized by the presence of open spaces interspersed with wooded areas, tall isolated trees; it can also nest in the poplar planting using old nests of crows.
Reproduction is rather late, probably the depositions not occur until the second half of June. Even in August can be found nests containing not-flying young individuals, in this period is easier to locate nesting pairs because the behavior of adults is less bashful.
It feeds mainly of small birds captures in flight, particularly swallows and swifts, and large insects; it has been observed occasionally catching of bats.
Among the other diurnal birds of prey of the area is also remembered the osprey (Pandion haliaetus), reported during the migration and nesting species such as the common buzzard (Buteo buteo), the Eurasian sparrowhawk (Accipiter nisus) in expansion in recent decades throughout the plain, and between the hawks, the common kestrel (Falco tinnunculus), more common in cultivated fields.